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SOHC.co.uk Forums => CB750 => Topic started by: El__burro on June 22, 2017, 11:54:51 PM

Title: re-jetting needed?
Post by: El__burro on June 22, 2017, 11:54:51 PM
good day,
I have been riding my cb750 k2 for over a month and today I went back to ride my Bmw r80/7 and
i have noticed a huge difference in maximum speed and overall performance.
my cb750 is definitely slower.
i have synced the carbs but not fully understood how to set the air mixture the same for all 4.
also I have replaced the standard air filter for K&H (like) stacks and gone to a 4-2 exhaust system but kept the stock jets..
would i see any difference in changing their size.
if yes, what size?
Thanks
el__burro


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Title: Re: re-jetting needed?
Post by: hairygit on June 23, 2017, 05:52:26 AM
Yes, increasing the jet size is necessary running stack or pod filters. As they are more free flowing than a stock filter set up the decreased resistance means it pulls less fuel through the jets, and gives a weaker mixture. Every bike will behave differently to given changes, so it's trial and error until it runs as best as it can with the filter/exhaust combination. What size jets are you currently running?

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Title: Re: re-jetting needed?
Post by: El__burro on June 23, 2017, 06:55:34 PM
The actual jet are 110.
Since i have both pods and 4-2 exhaust system, shall i go 4 up?
Where shall i buy them?
Thanks
el__burro (https://uploads.tapatalk-cdn.com/20170623/58c178d487187e31d34db3caa4233c5a.jpg)

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Title: Re: re-jetting needed?
Post by: El__burro on June 23, 2017, 07:22:32 PM
Actually I have just found this..
Shall i go +6 then?
el__burro (https://uploads.tapatalk-cdn.com/20170623/cf59c02f5d03e24bda04530006b5cf12.jpg)

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Title: Re: re-jetting needed?
Post by: hairygit on June 23, 2017, 08:01:58 PM
A U.K. K2 should have 115 as stock, so you're way too small at the moment!
Title: Re: re-jetting needed?
Post by: El__burro on June 23, 2017, 08:56:46 PM
The bike comes from Italy.
Should I go 4 or 6 up?
Thanks
el__burro

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Title: Re: re-jetting needed?
Post by: hairygit on June 23, 2017, 10:03:22 PM
Try 4, then you've still got the needles to give you play either side. How has it been riding up to now? Does it feel starved of oomph?

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Title: Re: re-jetting needed?
Post by: El__burro on June 23, 2017, 10:12:01 PM
It rides fine, I have tried to go very fast but as I said its much less responsive than my other bike. (Bmw r80)
Would reJetting make any difference?
el__burro

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Title: Re: re-jetting needed?
Post by: El__burro on June 25, 2017, 12:35:00 AM
Not sure what size to look for and where.  Any suggestions?
Thanks
el__burro

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Title: Re: re-jetting needed?
Post by: Bryanj on June 25, 2017, 01:28:18 AM
Sirius in canada do jet kits or individual jets
Title: Re: re-jetting needed?
Post by: El__burro on June 25, 2017, 10:10:36 AM
Woaw.. are you sirius.. in Canada?
🤣
What size should I go for?
Thanks
el__burro

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Title: Re: re-jetting needed?
Post by: Bryanj on June 25, 2017, 12:35:40 PM
Best card parts supplier I have found in 30+ years and no idea on jet size
Title: Re: re-jetting needed?
Post by: totty on June 25, 2017, 01:13:30 PM
Looks like you're going to have to do this by trial and error, so you probably need to order both +4 and +6. After finding best full throttle performance you'll them more than likely need to adjust needle height, then pilot adjuster and maybe even pilot jet. A lot of work on a four.
I don't know which jets this model uses, but I got my last jets from wemoto and I've also used allensperformance.
Title: Re: re-jetting needed?
Post by: philward on June 25, 2017, 08:42:44 PM
I've used Allens too - http://www.allensperformance.co.uk/carb-kit/keihin-jet-identification-chart/
Title: Re: re-jetting needed?
Post by: El__burro on June 25, 2017, 08:52:00 PM
Thanks Phil, I've been looking for jets on both wemoto and allens..
What jets would i need from the link above..?
Thanks a lot
el__burro

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Title: Re: re-jetting needed?
Post by: philward on June 25, 2017, 09:14:34 PM
I think its 6mm slot head m5 thread -
99-101-393-SIZE
https://www.catalyst-findit.co.uk/index.php?c=2f74fd408728adaf828b5b9373baedbb&w=900&nav=r&h=n&rpp=100&dest=listing&p=38
- this is based on me going to the garage to measure up spare set whilst under influence of a few pints whilst watching 'Chic' on Glastombury (after having 4 grandkids overnight!)
Seriously, I think that's correct but if you ring them to order, they should be able to confirm
Phil

Title: Re: re-jetting needed?
Post by: El__burro on June 26, 2017, 11:45:00 AM
thanks Phil.
i have just ordered the 122 (+5) size.
hopefully this will help.
i'll update this post once i receive and test ride.
Thanks a lot
el__burro


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Title: Re: re-jetting needed?
Post by: El__burro on June 29, 2017, 04:10:25 PM
After swapping the 110 jets with the 122 i have immediately noticed a worsening  in performance. Struggling in every gear until a few miles later it almost stopped running.
Carbs are popping tiny explosions..
Plugs Check, very dirty with carbon.
Any idea
el__burro

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Title: Re: re-jetting needed?
Post by: K2-K6 on June 29, 2017, 09:42:20 PM
That's showing way too rich,  as if the choke is on.  I'm not saying the choke is applied,  just that the plugs would look like that if you did use it.

Will it start when cold with no choke?

It just looks way out from that colour and needs to be run leaner.

Did you have a comparable plug colour on the old settings, if so what did it look like?
Title: Re: re-jetting needed?
Post by: hairygit on June 29, 2017, 10:33:18 PM
Popping through the carbs is often caused by air leaks, check that the clamps on the carb rubbers are going tight enough. As regards looking on the rich side, what setting are the needles at? Try dropping them a notch after thoroughly cleaning the plugs, or fitting new ones, then see how it is.

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Title: Re: re-jetting needed?
Post by: El__burro on June 29, 2017, 10:37:06 PM
Plug reading with 110 jets was almost perfect.
The only problem was poor top speed. Since (this morning) I swapped the jets it's been worse, niw it struggles even to start in 1st gear.
i have put the old jets and cleaned replaced the plugs but the problem i is still there.
The needles are in the second gap (stock position) if i remember well.
I guess (and hope) that a good carb clean will sort the problem.
Is 122 is too big or i need to look at other settings?
Thanks
el__burro

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Title: Re: re-jetting needed?
Post by: hairygit on June 30, 2017, 05:34:04 AM
Float levels may be worth checking again, and check float valves are shutting fuel off as they should. No way should it be running too rich on 110's unless it is flooding!

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Title: Re: re-jetting needed?
Post by: K2-K6 on June 30, 2017, 08:19:06 AM
There's something odd there as switching the jets back to 110 should get it back to where it was.

Are you confident that the ignition is advancing? Have you anything to check that?
Title: Re: re-jetting needed?
Post by: El__burro on June 30, 2017, 08:40:56 AM
I thought about checking the ignition, could swapping the jets could have caused it?
Shall I put the 122 and look at ignition timing then?
Float levels looks ok. (I have about 30ml of fuel in each carb)
Thanks
el__burro


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Title: Re: re-jetting needed?
Post by: K2-K6 on June 30, 2017, 09:44:39 AM
No, swapping the jets will not make a permanent change to the bike as if you swap them back as you've done it should be back to what you had before.

If it was in front of me I'd run it on the 110's as that gave reasonable plug colour and then look to see if anything else is a problem.

What the ignition does is to start at low revs with the static setting you adjust the system to in setting it up, as the revs rise the advance / retard mech brings the ignition point forward. If this doesn't happen properly the engine will struggle to gain rpm much over about 5000rpm and prevent making much power up there. You'd check this with a strobe to see if it moves and returns as you run the engine up and down revs.
You need to verify this to avoid chasing other things, if ignition checks out then you can work through carb issues more logically.

The two systems are not mechanically related,  they only come together in combined effect in the combustion chamber to make it run but each must obviously be ok to get the motor to respond well.
Title: Re: re-jetting needed?
Post by: Greebo on June 30, 2017, 10:06:26 AM
Plug reading with 110 jets was almost perfect.
The only problem was poor top speed. Since (this morning) I swapped the jets it's been worse, niw it struggles even to start in 1st gear.
i have put the old jets and cleaned replaced the plugs but the problem i is still there.
The needles are in the second gap (stock position) if i remember well.
I guess (and hope) that a good carb clean will sort the problem.
Is 122 is too big or i need to look at other settings?
Thanks
el__burro


I have 138 main jets & my needles are set on the bottom notch [5th] & it runs great & ticks over perfectly 

I have also tried / experimented with the ignition timing, set to stock & also tried it 10deg' advanced but the 2 settings did not seem to make any difference in the way the bike runs.

I think when you first changed the jets you must have disturbed something else in the carbs settings...I say this because when you put the stock jets back you say it had the same problem, obviously it did not have this issue before you started tinkering.
Title: Re: re-jetting needed?
Post by: neilg on June 30, 2017, 10:41:37 AM
Do you have any one near who runs a dyno? When I changed the carbs on my BMW a few years ago I tried all the usual methods with runs and plug chops up and down the local by-pass but couldn't get it right. In the end I found the only way to get it sorted was to take it to a specialist. He ran it up on the dyno and sorted everything right through the range from tick over to full throttle. The work also included setting the optimum ignition timing etc. I appreciate the cost might be a put off but he did in a few hours what was taking me an eternity in guess work messing with buying and swapping different jets only to find it still wasn't right.
Title: Re: re-jetting needed?
Post by: El__burro on June 30, 2017, 01:47:31 PM
I've started by removing the carbs as i wanted to give it a clean anyway, put the 122 jets and drop the needle by locking it on the top slot, (see pic)
Not sure if should be the way around.
Hopefully I'll receive a confirmation before mounting it all back and do a timing check.
Thanks
el__burro (https://uploads.tapatalk-cdn.com/20170630/5ee0515da4b6184cd3eb0440a030a8c5.jpg)

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Title: Re: re-jetting needed?
Post by: hairygit on June 30, 2017, 02:11:08 PM
Dropping the needle like you have makes it run weaker, which is what you need!
Title: Re: re-jetting needed?
Post by: El__burro on June 30, 2017, 02:28:24 PM
I have also realized that choke lever wasn't opening all the 4 shutters at the same level. Fixed this too.
Thanks
el__burro
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Title: Re: re-jetting needed?
Post by: K2-K6 on June 30, 2017, 03:19:39 PM
Will the choke lever lift those choke gates right up out of the inlet path? They should dissappear completely up into the carb body when not is use.
Title: Re: re-jetting needed?
Post by: Greebo on June 30, 2017, 03:46:46 PM
I've started by removing the carbs as i wante to give it a clean anyway, put the 122 jets and drop the needle by locking it on the top slot, (see pic)
Not sure if should be the way around.
Hopefully I'll receive a confirmation before mounting it all back and do a timing check.
Thanks
el__burro (https://uploads.tapatalk-cdn.com/20170630/5ee0515da4b6184cd3eb0440a030a8c5.jpg)

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I would have thought that dropping the needle would be defeating the object of having the larger jets for the more top end that you are trying to achieve, when increasing my jet size to 138 I also lifted the needles in stages, it only started running right when I got the needle clip on the 5th notch which increases the fuel to the Max, mine does run slightly rich but they do run better that way, not a good idea to run too weak 
Title: Re: re-jetting needed?
Post by: El__burro on June 30, 2017, 05:46:57 PM
Mine was very rich on the 2nd  (from bottom) so i went all the way up. Unfortunately i am struggling with setting the timing right. With strobo light doesn't pick any pulse on cylinder 1, ok on 4 and 2/3.


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Title: Re: re-jetting needed?
Post by: Bryanj on June 30, 2017, 05:50:21 PM
That suggests a weak spark on 1
Title: Re: re-jetting needed?
Post by: El__burro on June 30, 2017, 11:49:55 PM
After a short test ride it felt like starving on fuel so i lowered by one the clip on the needle.
Getting slightly better but still struggling.
Plug one gets quite carbon fouled but the rest look ok.
Thanks
 el__burro

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Title: Re: re-jetting needed?
Post by: Greebo on July 01, 2017, 10:00:56 AM
After a short test ride it felt like starving on fuel so i lowered by one the clip on the needle.
Getting slightly better but still struggling.
Plug one gets quite carbon fouled but the rest look ok.
Thanks
 el__burro

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"Being starved of fuel rings a bell",I had the same problem when we finished the build on my bike even with the larger jets, so we kept lifting the needle until it ran right, with my bike it would only run right with the needle in its highest position.
Title: Re: re-jetting needed?
Post by: El__burro on July 01, 2017, 10:06:28 AM
...the needle in the "highest position" did you put the clip at the bottom of the needle?
Thanks
 el__burro

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Title: Re: re-jetting needed?
Post by: Greebo on July 01, 2017, 10:45:35 AM
...the needle in the "highest position" did you put the clip at the bottom of the needle?
Thanks
 el__burro

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Yes on the last notch at the bottom... try it on the last notch & then if it runs much better check the plugs if they are too rich lean them off on the air adjuster screws, on your carbs to weaken the mixture the screw turns out anti clockwise
Title: Re: re-jetting needed?
Post by: El__burro on July 01, 2017, 11:01:15 AM
Thanks,
I hate having to adjust the needle (is there a quicker way than removing it all apart?) but hopefully it will be worth it.
Thanks a lot
el__burro
Title: Re: re-jetting needed?
Post by: Greebo on July 01, 2017, 11:26:15 AM
Thanks,
I hate having to adjust the needle (is there a quicker way than removing it all apart?) but hopefully it will be worth it.
Thanks a lot
el__burro

Yes its a pain in the arse on most carbs, but a much more awkward job on the PD carbs, yours are the earlier carbs so it should be a bit easier to do...hopefully
Title: Re: re-jetting needed?
Post by: El__burro on July 01, 2017, 05:26:11 PM
I have lowered the clip so the needle lets in more fuel, unscrewed the air fuel mix until the plugs were not wet, started the engine, in neutral.. low revs sounds ok, high revs struggles to go.
Then put first gear in to go but it's a struggle.
Not sure about my strobo light, I'll try timing with the static method.
Thanks
el__burro


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Title: Re: re-jetting needed?
Post by: Greebo on July 01, 2017, 06:38:22 PM
 it should be getting enough petrol through now, I suppose it could be electrical, but the timing would have to be a mile out to make a big difference. what about the coils ? have you checked them or the HT leads ?

what you described earlier was just how mine was on the first few runs after the build & we were not sure what is was at first, but on one run whilst opening the throttle it started the usual jerking & missing so I decided to pull out the choke whilst riding it, as soon as pulled the choke out it pulled away as it should, no missing or jerking, that's when I knew it was lacking fuel when on the throttle, adjusting the needles did the trick
Title: Re: re-jetting needed?
Post by: El__burro on July 02, 2017, 10:43:08 AM
I have static timed it, pulled the needle all the way up, checked the points gap, reser the bowls so they are even, cleaned the plugs, coils ok... still struggling.
I'll try pulling the choke on my next ride.
Thanks
el__burro
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Title: Re: re-jetting needed?
Post by: totty on July 02, 2017, 06:47:49 PM
"strobo light doesn't pick any pulse on cylinder 1
Plug one gets quite carbon fouled but the rest look ok."

I'd sort this first. Sounds like you've got a plug, cap, or lead problem.
After that get the main jets right for full throttle, leave the needles alone until the main is sorted. You will need a range of jets in order to find the correct one, you can't tell if you're got it near ideal or not in just one step, you have to see the effect of going a step or two either direction.

Title: Re: re-jetting needed?
Post by: El__burro on July 03, 2017, 03:13:04 PM
I have checked it all... spark plug, gap, still 1 and 4 very carbon dry.
Dropped the needle on the 3rd hoping to get better results but... no.
When i rev i have black smoke coming from exhaust 1-2.
Going crazy.
el__burro

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Title: Re: re-jetting needed?
Post by: totty on July 03, 2017, 04:06:17 PM
You've got a whole mix of symptoms going on, not surprised you're going crazy.

There's probably more than one problem, might be time to find a local specialist or a dyno tuner who's good at diagnostics.

Title: Re: re-jetting needed?
Post by: Greebo on July 03, 2017, 04:41:39 PM
You've got a whole mix of symptoms going on, not surprised you're going crazy.

There's probably more than one problem, might be time to find a local specialist or a dyno tuner who's good at diagnostics.

Yes I agree, not sure where you are located El_Burro...but  I have let you and everyone else on here know "Please Do Not Use Torquetune at Ollerton"
he made an absolute & complete bollocks of my carbs & another company had to sort them out, it cost me a not once but twice..
Thankfully now mine is running great, but it nearly drove me crazy at the time.
Title: Re: re-jetting needed?
Post by: El__burro on July 03, 2017, 10:37:20 PM
Getting close..
I realized that carb 4 (choke) slide wouldn't open probably causing most of the problems. Also testing the coils realised that some wire and cap connection were loose.
Anyway after a short ride i could feel the 3rd part of the throttle not pulling much power.
What next?
Thanks
el__burro



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Title: Re: re-jetting needed?
Post by: totty on July 04, 2017, 11:47:47 AM
Are you confident that you've found all issues and you're ready to go back to jetting, or do you want to check for more issues?

For jetting you'll need to start with the mains and either keep increasing until you've gone too rich then go back a step, or do plug chops, or a rolling road.

A full checkup would be along the lines of

Ignition:
Advancer not seized, and confirmed working by strobe
points not pitted
points gap and timing correct
condensers tested, or a visual check for points not sparking
primary and secondary resistance check for both coils
plug cap resistance check (plug or cap should be resistor type but not both)
consider new plugs

Carbs:
chokes open as already covered
all passages clear
all jets showing no signs of wear
float heights set and float valves tested
all throttle open evenly, fully and are static balanced
no inlet manifold leaks
clean airfilter(s)

I'd also do a compression test

To be honest last time I had a flat spot to deal with I replaced the entire ignition system with a Boyer kit, it saves a lot of time and effort if you don't have to focus on both fueling and ignition at the same time. Although in your case I'd try to go back to standard airbox and filter so you can run stock jetting.

Title: Re: re-jetting needed?
Post by: El__burro on July 04, 2017, 05:52:08 PM
A full checkup would be along the lines of

Ignition:
Advancer not seized, and confirmed working by strobe 👍
points not pitted 👍
points gap and timing correct👍
condensers tested, 👈 》trying to test but what's the best way?

visual check for points not sparking👈 》actually points 1/4 have a tiny blue spark when operating.

primary and secondary resistance check for both coils
plug cap resistance check (plug or cap should be resistor type but not both)👈》 that's next. I'm not sure about result on primary coil.
consider new plug 》Are this the right type? (pic)

Condensers?
Thanks
el__burro

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Title: Re: re-jetting needed?
Post by: totty on July 04, 2017, 07:21:34 PM
I don't recognise the first 3 plugs, the NGK ones are resistor plugs, you can tell by the R in the name.
You shouldn't mix resistor and none resistor plugs on the same coil. I think but I'm not certain that you shouldn't have both resistor plugs and caps. Check your caps by part number or resistance.
Title: Re: re-jetting needed?
Post by: El__burro on July 04, 2017, 10:45:07 PM
The plugs in grey (24..)
are the ones that came with the bike a while ago, i have used them until now. No problem.
The blue ones are new, couldn't use them as I have just learned (thanks to you) that the cap has a resistor too (VD05F 5KO)
Any good tips to test the condenser on the points. Or eventually a good shop.
Tried loading up and look for a spark (like in clymer pic)
but none of the 2 have it..
Thanks
el__burro
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Title: Re: re-jetting needed?
Post by: totty on July 05, 2017, 09:29:01 AM
I'm not sure how to test a condensor, looks like the test in the manual is to charge it and look for a spark on discharge, I've just googled it and come up with two answers that I'll paste below, but a spark at the points makes me think a condensor has failed.

By the way I don't think condensors can give the symptoms you've described, but failed ones will wear out the points quickly so it's worth sorting out while you're on.
While you've got the meter out I'd check those plug caps are all still 5Kohm as rated as they can fail, and also the coil primary and secondary resistance - I don't know the correct values but someone on here will and they might be in the manual.
Once everything tests OK I'd then use the strobe, or carefully check that all exhaust headers heat up from cold to too hot to touch quickly and evenly to confirm that it's firing on all cylinders. Ignition should then be all sorted.


Capacitor test instructions from google:

Choose your tool. Even cheap digital multimeters often have a capacitance setting "– ...
Shut off the power. ...
Discharge the capacitor carefully. ...
Disconnect the capacitor. ...
Set the multimeter to measure capacitance. ...
Activate REL mode if present. ...
Connect the leads to the capacitor's terminals. ...
Wait for the result.

OR

To test the capacitor with a multimeter, set the meter to read in the high ohms range, somewhere above 10k and 1m ohms. Touch the meter leads to the corresponding leads on the capacitor, red to positive and black to negative. The meter should start at zero and then moving slowly toward infinity.
Title: Re: re-jetting needed?
Post by: El__burro on July 05, 2017, 06:17:34 PM
Latest update.
After testing the resistors and deciding they are gone, i have ordereda set this morning.
Not sure about coils testing
Here is my finding
Primary coil 4.6 ohms
Secondary coil, plug to plug 14.8,
Plug to (any)pigtail wire 1  .
The same reading for both coils.
All of this whith the coils mounted on the frame.
Fail or..?
Thanks
el__burro

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Title: Re: re-jetting needed?
Post by: El__burro on July 07, 2017, 12:56:20 AM
Monologue update.
I received the new condensers from DSS (1 day after order, Impressive)
Put them on, all good, bike starts and revs properly.
Still i see a spark on both points, 1-4 also bridging on plate too.
Also noticed 3 of 4 coils leads arcing onto the frame too at the top connection
Not sure how serviceable are the leads to plugs but they should be better isolated.
Concerned about the bridging sparks on the points. Then workon the needle position again.
Getting there
Thanks
el__burro


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Title: Re: re-jetting needed?
Post by: hairygit on July 07, 2017, 06:08:06 AM
You need to sort the arcing of the coil leads to the frame as a matter of urgency, any arcing of HT leads will cause loss of power to spark plugs, as that will cause all sorts of problems, and will only get worse. Ashimoto done a great step by step of fitting new leads to coils, you'll find it in the "Aladddins cave" section. There is no point doing anything else before that!

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Title: Re: re-jetting needed?
Post by: Bryanj on July 07, 2017, 07:54:06 AM
Condensers REDUCE the sparking at the points they do not ELIMINATE it
Title: Re: re-jetting needed?
Post by: El__burro on July 07, 2017, 01:28:20 PM
Thanks, i have disvovered the Alladins cave, very interesting.
I could fix the ones i have or ..
what's your opinion on the replacement in the photo below.
Thanks
el__burro
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Title: Re: re-jetting needed?
Post by: Green1 on July 07, 2017, 07:13:50 PM
Nothing wrong with those coils I run them on the 550 and 750.
Mike runs then on his CR750 as well
Title: Re: re-jetting needed?
Post by: El__burro on July 07, 2017, 09:48:55 PM
PERFECT.

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Title: Re: re-jetting needed?
Post by: El__burro on August 02, 2017, 12:11:56 AM
Still running like sh*t.
when I rev it sounds great. The problem is the second part off the throttle, it feels like it is electrical. 2 of 4 plugs are quite carbon fooled. Needle is back on the last position so it lets in more fuel. What are the best spark plug I can fit with the resistor caps?
Thanks
el__burro
Title: Re: re-jetting needed?
Post by: Johnwebley on August 02, 2017, 11:13:41 AM
Still running like sh*t.
when I rev it sounds great. The problem is the second part off the throttle, it feels like it is electrical. 2 of 4 plugs are quite carbon fooled. Needle is back on the last position so it lets in more fuel. What are the best spark plug I can fit with the resistor caps?
Thanks
el__burro

  which 2 plugs are fouled?  are they a linked pair?  IE;  1-4 or 2-3 ,

 both those pairs use common coils,points etc.if the other plugs are cleaner,and on the same carb settings,you could have ignition
issues ,

 secondly ,if the needle has its clip at he lower groove,it lets in more petrol,so will run richer ,from maybe 1/3 to 2/3 throttle ,
but all 4 carbs should be set the same,and all 4 plugs should be about the same colour ,


 
Title: Re: re-jetting needed?
Post by: Greebo on August 02, 2017, 04:46:06 PM
Still running like sh*t.
when I rev it sounds great. The problem is the second part off the throttle, it feels like it is electrical. 2 of 4 plugs are quite carbon fooled. Needle is back on the last position so it lets in more fuel. What are the best spark plug I can fit with the resistor caps?
Thanks
el__burro

You have tried many suggestions now so I think its time to get it booked in for a Dyno  before it drives you potty.

I cant see it being the plugs or resistors unless they are old & shot. plugs I use are NGK DR8ES-L... Resistor caps Part Number 30700-GAR-000 30700-MW3-000
Title: Re: re-jetting needed?
Post by: El__burro on August 02, 2017, 04:48:37 PM
What's the cost for a dynodyno test and where in london.

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Title: Re: re-jetting needed?
Post by: Greebo on August 02, 2017, 06:46:46 PM
What's the cost for a dynodyno test and where in london.

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Sorry Mate no idea "of where in London" I'm in Yorkshire.
The cost depends on what needs doing but just a Dyno Run to find the issues is about £45 ish + parts + extra time etc.
do a search on google for your area
Title: Re: re-jetting needed?
Post by: El__burro on August 03, 2017, 05:20:29 PM
UPDATE
Plug 4 reads ok while the other 3 are fouled with carbon. all carbs needles are set up the same way and synced. After a 10 minutes ride i have notice that when i play with the fuel tap (on/res) it goes slightly better. It struggles at low rpm but when it reaches the second part of the throttle it pulls much more. Not sure if it is my imagination or there is a logic behind this. I have fitted the plugs DR8ES L and it goes "slightly" better.
Thanks
el__burro

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Title: Re: re-jetting needed?
Post by: El__burro on August 07, 2017, 06:31:16 PM
Again,i have synced the carbs with the same air mix screw turns, (1and 1/2) carbs sync almost perfect. Still plug 1,2 and 3 are quite black with carbon deposit, number 4 i think looks ok.
DO I set the other 3 carbs air mix  screw to a different setting?
Thanks
el__burro (https://uploads.tapatalk-cdn.com/20170807/5c79074f23f38687962d177b25e05124.jpg)

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Title: Re: re-jetting needed?
Post by: K2-K6 on August 07, 2017, 08:38:13 PM
It looks to me like you've got both resisted plugs and caps in use there at the same time ( correct me if wrong).Ordinarily it would be one or the other.

These engines are just not that fickle to get running well so it does seem that something odd is present to prevent a logical path through what's in front of you.

In answer to the idle air screws setting,  Honda setup instructions do allow for differences between each carb. They go through a routine of getting the lower speed  mixture the same for each one although they shouldn't in reality end up with any hugely odd set points as that would suggest some impairment of that particular circuit.
Title: Re: re-jetting needed?
Post by: El__burro on August 08, 2017, 12:12:11 AM
k2-k6 you are correct, i am heading to Halfords tomorrow to see if i can find either a set of plug caps or a set of plugs with no R.
Thanks
 el__burro

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Title: Re: re-jetting needed?
Post by: Johnwebley on August 08, 2017, 10:03:32 AM
k2-k6 you are correct, i am heading to Halfords tomorrow to see if i can find either a set of plug caps or a set of plugs with no R.
Thanks
 el__burro

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 can I suggest you try fleabay and/or amazon,both should be way cheaper than Halfords,
also more likely to be the correct items
Title: Re: re-jetting needed?
Post by: El__burro on August 11, 2017, 09:21:42 PM
After swapping the spark plugs for NGK D8EA I've seen a tiny improvement. Still Plug 4 is perfect  (almost too lean) while the other 3 still a bit carbon fouled (less than with previous plugs) but at least the same colour.
Needle clip is at the bottom but bike still struggles in the mid part of throttle.
In the meantime i have re adjusted the timing.
Thanks
el__burro
Title: Re: re-jetting needed?
Post by: Johnwebley on August 11, 2017, 10:43:21 PM
After swapping the spark plugs for NGK D8EA I've seen a tiny improvement. Still Plug 4 is perfect  (almost too lean) while the other 3 still a bit carbon fouled (less than with previous plugs) but at least the same colour.
Needle clip is at the bottom but bike still struggles in the mid part of throttle.
In the meantime i have re adjusted the timing.
Thanks
el__burro

  the needle clip at the bottom?   is that the lowest groove?  that would give a rich mid-range,,try fitting it either in the middle groove,or
second from the top ,

  that should clean up the middle range
Title: Re: re-jetting needed?
Post by: El__burro on August 11, 2017, 10:47:41 PM
After swapping the spark plugs for NGK D8EA I've seen a tiny improvement. Still Plug 4 is perfect  (almost too lean) while the other 3 still a bit carbon fouled (less than with previous plugs) but at least the same colour.
Needle clip is at the bottom but bike still struggles in the mid part of throttle.
In the meantime i have re adjusted the timing.
Thanks
el__burro

  the needle clip at the bottom?   is that the lowest groove?  that would give a rich mid-range,,try fitting it either in the middle groove,or
second from the top ,

  that should clean up the middle range
Will do tomorrow.
Thanks a lot
el__burro

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Title: Re: re-jetting needed?
Post by: sprinta on August 12, 2017, 08:26:45 AM
Are your air screws the solid type or the ones with holes in?
Title: Re: re-jetting needed?
Post by: JamesH on August 12, 2017, 04:25:07 PM
My advice would be fit a standard airbox, go back to stock 110 main jets, setup and re-sync the carbs and get the bike running properly on a baseline intake setup. Then if you really need to go back to pods at least you know you have a solid baseline. You're playing with too many unknown variables and a lack of experience to converge on a solution with your current approach. Just my opinion...
Title: Re: re-jetting needed?
Post by: El__burro on August 13, 2017, 01:33:27 AM
Replaced the needles with brand new ones, put the clip on 3rd gap, cleaned it all and.. it goes much better. Now it struggles a bit on the full throttle.
I didn't manage to check the plugs.
Any advice?
Thanks
el__burro

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Title: Re: re-jetting needed?
Post by: JamesH on August 13, 2017, 07:11:20 AM
Did you replace the needle seat? They're generally matched.
Title: Re: re-jetting needed?
Post by: Trigger on August 13, 2017, 07:42:30 AM
First question : why are you running it at full throttle ? Has this engine been rebuilt to any type of race spec ?
Honda spent a billion yen and thousands of Honda technician man hours to get this engine right so, why do people think they can get it running better with a few £'s.
As a wise man said once; If you want a faster bike, go out and buy a faster one.   
Title: Re: re-jetting needed?
Post by: Johnwebley on August 13, 2017, 11:22:52 AM
Replaced the needles with brand new ones, put the clip on 3rd gap, cleaned it all and.. it goes much better. Now it struggles a bit on the full throttle.
I didn't manage to check the plugs.
Any advice?
Thanks
el__burro

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  to check the plugs gives a good insight of whats happening,

 run the bike at constant 6,000rpm on half throttle ,then use the kill switch to stop and pull the plugs out ,check the colour,
 as for full throttle,you need to run at least 8,000rpm and full throttle under load ,then do the same,check the plug colours,

as Trigger asked,how many miles has the motor done since rebuild?
 maybe leave full speed testing till it has a few hundred miles on it
Title: Re: re-jetting needed?
Post by: El__burro on August 13, 2017, 11:38:49 AM
Engine has never been touched.
As i mentioned at the beginning I wanted the bike to be more responsive not faster.
I'm getting there..
I'll try my best to do a "plug chop" but it will be hard as i don't have a rev counter.
Thanks
el__burro
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