re-jetting needed?

[philward]

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

[El__burro]

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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[El__burro]

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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[K2-K6]

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?

[hairygit]

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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[El__burro]

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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[hairygit]

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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[K2-K6]

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?

[El__burro]

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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[K2-K6]

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.

[Greebo]

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.

[neilg]

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.

[El__burro]

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

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[hairygit]

Dropping the needle like you have makes it run weaker, which is what you need!

[El__burro]

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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