Post by: Erny on May 26, 2021, 12:10:10 AM
When accelerating using full trottle, bike accelerates but slower than I would expect (roar noise is increased of course), almost having feeling that opening full trottle is somehow "braking" engine revving fast. But closing trottle a bit (maybe 1/8 or 1/4) significanly increasing acceleration speed.
Based on my understanding how these carbs works, in such full trottle opening only main jet is in chanrge of A/F ratio, thus logically I would assume mixture is lean so I should replace main jets by bigger ones? I did not do plug test (yet) waiting for good weather occation...
Current bike and carb setup:
- bike is practically 100% stock, air filter element is aftermarket from cmsnl, replaced as new 2 years ago (up to 3.5k miles on it)
- carbs are 022A type, 38/100 jets, genuine Keihin.
- carbs are clean, setup according to HSM, otherwise than high spped (full trottle) running very smooth
Strange is that I did not observe this behaviour, maybe I just did not realise or this is "new" issue.
Any ideas?
If conclusion is to test bigger jets, how big then? 105? 110?
Note: normally I would expect changing main jets on otherwise stock setup will not bring any improvement and all works as it shoud
Post by: Bryanj on May 26, 2021, 12:16:41 AM
Post by: Erny on May 26, 2021, 08:01:35 AM
Post by: K2-K6 on May 26, 2021, 08:43:14 AM
You could try two notches to see what you get as if it cleans up all ok. If there's still some effect then it would suggest one jet size larger.
Post by: K2-K6 on May 26, 2021, 09:08:29 AM
Post by: Erny on May 26, 2021, 09:54:34 AM
Main jets change I can do with carbs on bike
But still wondering if this is not caused by something else as I have stock setup, I would expect default settings shall be fine (needle position, jets..)
Post by: K2-K6 on May 26, 2021, 10:31:08 AM
Main jets change I can do with carbs on bike"
it's certainly a pain if you have to change them. Suggested two steps as if you made one step and found improvement but not quite enough, then you'd have to do it all over again. Whereas jumping two steps answers the question of if it needs larger jets, if it's not successful then the next step is to consider a jet change.
They do different things, needle height versus main jet size. The larger jet is focused on fuel demand at full revs and full throttle, the needle position changes the points at which the jetting changes in volume on the way there.
Needle position and idle air screw are never absolute fixed position. They are there to compensate, in fine adjustment, for the jet sizes which are fixed. They need to be set for the environment and conditions in which you are running the engine and can quite happily be different from the manual which is always given as baseline setting from which to optimise.
Post by: deltarider on May 26, 2021, 10:34:46 AM
Post by: K2-K6 on May 26, 2021, 10:50:30 AM
You'd have to run it consistently in the "error"range for the plug colour to mean anything reliable for that error, which I doubt you could do.
Post by: Laverda Dave on May 26, 2021, 12:06:36 PM
Post by: deltarider on May 26, 2021, 02:52:20 PM
I would be tempted to go on a dyno. Might cost a bit more but at least you will have a full read out of what the engine is doing across the entire rev range and this will give you a chance to make small adjustments whilst you are there to potentially fix the problem.Yep, bike as it is now, definitely deserves it IMO. Oh and if you do, please make recordings. :)
Post by: Erny on May 26, 2021, 08:51:55 PM
Issue is present in wide range of RPMs, I confim it from ~3500 revs ->
Simply, when at whatever revs I'll open trottle fully, I feel engine does not accelate as good as if I close trottle a bit (approx 1/8-1/4).
After ride I pulled plugs (I installed them new, 55 miles before), all cyls are lean. See attached pics. Good news are are equally lean (I have never achieved that before!)
So, rising needle 1-2 notch looks to be next step..
Post by: Erny on May 26, 2021, 09:00:11 PM
Post by: philward on May 26, 2021, 09:18:02 PM
Short update after today's test ride (~50 miles)
Issue is present in wide range of RPMs, I confim it from ~3500 revs ->
Simply, when at whatever revs I'll open trottle fully, I feel engine does not accelate as good as if I close trottle a bit (approx 1/8-1/4).
After ride I pulled plugs (I installed them new, 55 miles before), all cyls are lean. See attached pics. Good news are are equally lean (I have never achieved that before!)
So, rising needle 1-2 notch looks to be next step..
Don't ride it too hard for too long with it running that lean Erny
Post by: K2-K6 on May 26, 2021, 10:07:41 PM
"Issue is present in wide range of RPMs, I confim it from ~3500 revs ->
Simply, when at whatever revs I'll open trottle fully, I feel engine does not accelate as good as if I close trottle a bit (approx 1/8-1/4)."
That makes it a different problem to initially described, in as much as it looks like it could take a one size up main jet if it's right across the rev range from about 3,500 upward, and worthwhile trying that first given this information and the plug colours.
You may find that if a jet change was too far, then in future you could either check with the larger jet plus needle drop, or it would persuade you to use original main jet plus lifted needles as they would be slightly different solutions.
At least you could assess it now with less work if you have any main jets to try just one size larger.
Post by: Erny on May 26, 2021, 10:49:10 PM
Ah ha
"Issue is present in wide range of RPMs, I confim it from ~3500 revs ->
Simply, when at whatever revs I'll open trottle fully, I feel engine does not accelate as good as if I close trottle a bit (approx 1/8-1/4)."
That makes it a different problem to initially described, in as much as it looks like it could take a one size up main jet if it's right across the rev range from about 3,500 upward, and worthwhile trying that first given this information and the plug colours.
You may find that if a jet change was too far, then in future you could either check with the larger jet plus needle drop, or it would persuade you to use original main jet plus lifted needles as they would be slightly different solutions.
At least you could assess it now with less work if you have any main jets to try just one size larger.
I'm trying to get bigger jets from friend (racing with CB550), but seems he has just 120 that sounds too much
Would you have some advice where to source bigger jets (proven source) in Europe?
One point to consider:
- my setup now is : Keihin pilot jets #38, Keihin MJ #100, Keihin needles (not sure 100%) but Keyster emulsification tubes (that looks from outside excatly the same as Keihin, but cannot confim ID as I have no mean to measure it properly)
Reason for replacing tubes was due to internal pitting/corrosion of original
tubes.
Just thinking - maybe Keyster tubes have bit smaller ID holes making mix leaner compare to stock? Was lazy to replace needles too, maybe mistake
To complete story - I got this carb set as refurbished from Gerben (NL), visually looks great, but I already found that emul. tubes were quite corroded inside, making mix too rich and impossible to tune carbs properly (I discussed this already here some time ago). Now, too lean but finally equal for all cyls.
Maybe, better would be now first to check orig. needles I have installed with Keyster if there is any difference in needles thickness (Keihin for 022A shall be 2.515mm). If keyster is less, that can explain lean mix. Will try to measure soon.
Other, but quite expensive option is to find NOS Honda needle kits. Maybe someone has some to sell? ;)
I attach photos of 022A Keihin tube I got in refurbed carbs - 022A tube it is one on the right side of picture with 2 tubes - you can see even what was level of corrosion/pitting before cleaning
Post by: deltarider on May 26, 2021, 10:50:29 PM
My gut feeling is somehow air intake is not correct. Also realise today's gas is not the same as in the 70s: with ethanol you can expect a leaner running. Like K2-K6 suggests, you could try a bigger MJ. But me personally, I'd first try - strange as it may sound - with the airscrews turned in half a turn.
Post by: K2-K6 on May 26, 2021, 11:00:55 PM
Doesn't look like they match the original.
120 MJ is a big jump and too far. Others on here are more familiar with supply of jets so may join to advise.
Post by: Erny on May 26, 2021, 11:10:49 PM
Keyster (new) tube is NOT on the picture (forgot to take comparison photo), but it looks EXACTLY as 022A, so all holes equal, OD, and other dimensions are the same.
I edited previous post - put text comment into pic to avoid confusion
Post by: Laverda Dave on May 27, 2021, 08:41:47 AM
When your 022A carbs are stock, there's only one notch left to raise the needles...
My gut feeling is somehow air intake is not correct. Also realise today's gas is not the same as in the 70s: with ethanol you can expect a leaner running. Like K2-K6 suggests, you could try a bigger MJ. But me personally, I'd first try - strange as it may sound - with the airscrews turned in half a turn.
That's a very good observation. Maybe try a thankful of super unleaded first and see how it performs. Less hassle than fiddling around with jets, tubes and needles. Personally I use Shell V-Power in the Jota, anything else and it feels flat and pinks if given full throttle quickly.
Post by: Erny on May 27, 2021, 09:47:27 AM
I still suspect too lean issue might come from tubes being too small ID (Keyster). Need to check that before hassling with MJ and/or needles
Post by: deltarider on May 27, 2021, 10:55:31 AM
Post by: K2-K6 on May 27, 2021, 11:37:55 AM
The overall experience from plugs and riding description are saying too lean, although not by much, which need to be addressed to bring it into more normal combustion performance.
The idle jets won't affect the upper ranges of rpm from adjustment of the air screw, but only if you changed their size. Once the idle jet reaches maximum flow it can't contribute more however the screw is set. The adjustment alters the slope of gain for idle jet flow and not the maximum.
Air screw further out will bring maximum flow at higher speed, in comparison to turned inwards when the idle circuit will reach maximum flow at lower rpm.
Worthwhile for some contingency protection while running is to raise the plug number by one to mitigate against plug tips going over temperature potentially causing pre-ignition, which you really don't want.
Post by: Laverda Dave on May 27, 2021, 12:16:36 PM
Octane in absolute terms is associated primarily with compression ratio and wouldn't change the mixture. It's mixed in with the causes of "pinking" with lean mixtures but the two reasons (too low octane induced, overheat conditions) need to be considered separately.
The overall experience from plugs and riding description are saying too lean, although not by much, which need to be addressed to bring it into more normal combustion performance.
The idle jets won't affect the upper ranges of rpm from adjustment of the air screw, but only if you changed their size. Once the idle jet reaches maximum flow it can't contribute more however the screw is set. The adjustment alters the slope of gain for idle jet flow and not the maximum.
Air screw further out will bring maximum flow at higher speed, in comparison to turned inwards when the idle circuit will reach maximum flow at lower rpm.
Worthwhile for some contingency protection while running is to raise the plug number by one to mitigate against plug tips going over temperature potentially causing pre-ignition, which you really don't want.
Thank Nigel. I have just learnt something new. Everyday is a school day :)
Post by: Erny on May 27, 2021, 08:39:01 PM
Replacing them will (to me) make mix even more lean.
Post by: K2-K6 on May 27, 2021, 08:48:46 PM
That for the needle itself.
Post by: Erny on May 27, 2021, 09:56:08 PM
According to Gerben (who did rebuild) now I shall have in carbs genuine Keihin needle (shall have 2.515mm according to HSM or bit less as it can be worn to some extend) in combination with new Keyster tubes.
Keyster needles I have available have 2.520mm so installing them into carbs will make mix even leaner.
Post by: K2-K6 on May 27, 2021, 10:50:28 PM
Possibly worth describing the problem as I understand it;- it's running almost perfectly as regards mixture for steady state (not accelerating) combustion.
With slide type carburettor this "perfect" mixture is reluctant to increase speed due to characteristic within the system in that as you start to open the throttle the immediate change is to reduce the vacuum in the carb throat, and force the mixture to move toward lean just at that point. This prevents the engine from gaining speed in this circumstance ordinarily.
The way this is compensated for is the manufacturer sets the mixture effectively too rich for technically ideal running to make sure it can cover this inherent error. It's one of their limitations on a road engine as it will always have to run richer than perfect to make sure you can easily accelerate it. We also get used to seeing plug colours that are effectively showing slightly rich and accepting those as normal, but they really show the error we have to run to describe them fully accurately.
It's this that CV type carbs and accelerator pump equipped slide carbs are designed to eliminate.
Back to this engine and carbs though, and you can judge where it is mixture wise from your riding description. As you open the throttle fully it makes it too lean to gain rpm but backing off a little just brings the vacuum and so the mixture back into competent range to get the increase.
You can see from this that it's running with just enough excess fuel to cover light to medium acceleration, but not fully wide open.
What it needs is just that final extra percentage to completely cover all throttle application.
It's very close but with that obvios error. Decision is how you make that final adjustment to get it just right.
Post by: Erny on June 20, 2021, 08:22:40 AM
Checked plugs for color, it looks to me still lean, especially plug no1 (plugs on the picture are sorted from left). Wondering if I should go one step more wirh jets (120?) or let it be.
Using Shell V-power racing petrol, as this one still has "just" 5% of bioshit (E5). Others are E10 here. Maybe plugs color can be explained also by petrol used? (https://uploads.tapatalk-cdn.com/20210620/f21eb4994f2b186f80ea0765b52c0b83.jpg)(https://uploads.tapatalk-cdn.com/20210620/88932d6a24366ee91f0983b2d7a93ffa.jpg)
Post by: fogrider on June 20, 2021, 09:54:38 AM
Watch your oil level !
Post by: Erny on June 21, 2021, 02:29:20 PM
Indeed some yes but not much. If you compare photos of plugs I posted before jets change, you can see they were really "white". The only change I did waa jets change from 100 to 115
Post by: K2-K6 on June 22, 2021, 07:12:23 PM
You can make an adjustment to the plug heat range though by going upward one number for NGK plugs. What this will do is shorten the heat pathway from the centre electrode to the plug outer material and so reduce the tip temperature, it should show as a darker colour when running and give more margin of safety to the conditions it's running in the combustion chamber.
Unless you've done anything differently than looking at the plugs after a run out they won't be showing that specific area of jetting to give you an accurate reading for the main jet size.
To do that, you'd have to get it fully warmed and then get it pulling hard in 3rd gear with the throttle full wide open, a long uphill or partly holding a little brake while you do it to make it fully loaded and working on the main jet calibration. 5 to 10 secs then cut clutch throttle and ignition, then check the plug colour to see what you've got (ordinarily called a plug chop) and assess the affect that main jet size is having.
If it pulls cleanly and runs without flat spot through full rev range it must be very close. You'd not expect that size engine with std intake to run a bigger main jet.
Post by: Erny on June 23, 2021, 06:51:26 AM
Your last sentence is still question in my mind - why on full stock bike (only exception is aftermarket air filter element from cmsnl) it runs fine (close to ideal) with 115 jets instead of 100
Post by: deltarider on June 23, 2021, 07:55:32 AM