adjusting idle : carb balance ?
#1
adjusting idle : carb balance ?
Idle is set around 1300 rpm.
The engine almost never stall.
The "rpm needle" isn't very stable : erratic between 1200/1400 rpm.
At neutral and snaping throttle quickly :
- The bike takes revs (5000 revs for example) and returns quickly to 2000 rpm then stay a little time at this revs and then return to idle
- at high temp, I often have a "pop" and engine does not take revs
- with pair system still working I can here exhaust popping while returning from high revs to idle
Have to setup pilot screws as well to richen/leanen a bit ? (pilot screws=mixture screws=idle screws ?)
This behaviour apart, the bike seems to run well.
I will do a carb balance this week end but what would you suggest to check/setup/mod at this time ?
Tuning pilot screws ? Disable Pair ? Shim needle ? Suppress manifold restrictors ?
In which order ?
I have a completely stock bike (airfilter/exhaust/jet settings/pair enabled)
Thanks a lot ;-)
The engine almost never stall.
The "rpm needle" isn't very stable : erratic between 1200/1400 rpm.
At neutral and snaping throttle quickly :
- The bike takes revs (5000 revs for example) and returns quickly to 2000 rpm then stay a little time at this revs and then return to idle
- at high temp, I often have a "pop" and engine does not take revs
- with pair system still working I can here exhaust popping while returning from high revs to idle
Have to setup pilot screws as well to richen/leanen a bit ? (pilot screws=mixture screws=idle screws ?)
This behaviour apart, the bike seems to run well.
I will do a carb balance this week end but what would you suggest to check/setup/mod at this time ?
Tuning pilot screws ? Disable Pair ? Shim needle ? Suppress manifold restrictors ?
In which order ?
I have a completely stock bike (airfilter/exhaust/jet settings/pair enabled)
Thanks a lot ;-)
#2
Guest
Posts: n/a
Re: adjusting idle, carb balance, etc
Well, if your carbs are out of sync, it's not going to idle well, so, since that doesn't take very long to do, I'd try that first. If that doesn't clear it up, it sounds like you might be a little bit lean at idle. You might try richening the mixture screws 1/2 turn (counter-clockwise). Remember to re-sync the carbs after any carb setting modification. (the RPM hanging up a bit after the throttle is "blipped" is a classic symptom of a lean idle circuit). "Popping" is usually from "lean-induced backfiring." Is it popping when riding at high revs and then cutting the throttle or is it popping when the bike is in neutral and returning to idle from high revs?
The following is taken from the Factory Pro site... the full write-up is here ( http://66.47.68.116/tech/carbtune,CV...m_engines.html ). It was written to accompany their jet kits, but it holds true for completely stock applications and is actually a great description of how to properly tune a CV carb.
From the Factory Pro site:
Fuel Screw setting (AKA mixture screws)
There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs have no caps, but use a special "D" shaped driver, usually supplied in the carb recal kit. We do have them available separately, too. 800 869-0497 to order -
Set for smoothest idle and 2nd gear, 4k rpm, steady state cruise operation. Set mixture screws at recommended settings, as a starting point. For smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8 throttle high rpm operation. (pj tuning information)
Pilot fuel mixture screw settings, float level (but, you've "fixed" the fuel level in Step 3 - which you have already done!) AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.
If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments. Alternative pilot jets are supplied when normally required.
Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause surging problems when the engine is operated at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem.
NOTE: A rich problem gets worse as the engine heats up.
If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
NOTE: A lean problem gets better as the engine heats up.
If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!
The following is taken from the Factory Pro site... the full write-up is here ( http://66.47.68.116/tech/carbtune,CV...m_engines.html ). It was written to accompany their jet kits, but it holds true for completely stock applications and is actually a great description of how to properly tune a CV carb.
From the Factory Pro site:
Fuel Screw setting (AKA mixture screws)
There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs have no caps, but use a special "D" shaped driver, usually supplied in the carb recal kit. We do have them available separately, too. 800 869-0497 to order -
Set for smoothest idle and 2nd gear, 4k rpm, steady state cruise operation. Set mixture screws at recommended settings, as a starting point. For smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8 throttle high rpm operation. (pj tuning information)
Pilot fuel mixture screw settings, float level (but, you've "fixed" the fuel level in Step 3 - which you have already done!) AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.
If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments. Alternative pilot jets are supplied when normally required.
Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause surging problems when the engine is operated at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem.
NOTE: A rich problem gets worse as the engine heats up.
If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
NOTE: A lean problem gets better as the engine heats up.
If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!
#3
Re: adjusting idle, carb balance, etc
Is it popping when riding at high revs and then cutting the throttle or is it popping when the bike is in neutral and returning to idle from high revs?
Seems that "hangs up" says "stay a little time" before dropping to idle ?
I may have misunderstood because you said:
the RPM hanging up a bit after the throttle is "blipped" is a classic symptom of a rich idle circuit
If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture.
#4
Guest
Posts: n/a
Re: adjusting idle, carb balance, etc
Oops... sorry...
Yes, when I said "hanging up" I did mean "stay a little time" before dropping to idle... this is a symptom of LEAN idle circuit... not rich idle circuit as I said in my post... had a momentary brain lapse there. I'll correct the previous post... Sorry for the confusion
It sounds like you may be a little bit lean, but as you know, PAIR can also cause some backfiring and since your idle is erratic, it sounds like your carbs could be out of balance. If it has been a while since they have been balanced I'd start with that and see how it runs. (Adjusting the mixture screws is a bit of a pain without a special tool... requires carb removal).
Yes, when I said "hanging up" I did mean "stay a little time" before dropping to idle... this is a symptom of LEAN idle circuit... not rich idle circuit as I said in my post... had a momentary brain lapse there. I'll correct the previous post... Sorry for the confusion
It sounds like you may be a little bit lean, but as you know, PAIR can also cause some backfiring and since your idle is erratic, it sounds like your carbs could be out of balance. If it has been a while since they have been balanced I'd start with that and see how it runs. (Adjusting the mixture screws is a bit of a pain without a special tool... requires carb removal).
#5
Re: adjusting idle, carb balance, etc
I check it again : blipping throttle at high temp (100°c) , the revs returns to idle with a step at 2000 while at cold/mid temp (50 to 75°c), it returns to idle really better.
Using a bit of choke at high temp, the engine stalls immediatly.
Sounds it is running rich isn't it ?
Would i have to adjust mixture screws even after I do the carbs balance ?
Any tips to adjust the mixture screw of 1/4 turn without the specific tool ?
Using a bit of choke at high temp, the engine stalls immediatly.
Sounds it is running rich isn't it ?
Would i have to adjust mixture screws even after I do the carbs balance ?
Any tips to adjust the mixture screw of 1/4 turn without the specific tool ?
#6
Guest
Posts: n/a
Re: adjusting idle : carb balance ?
can you smell gas in your exhaust when the bike is idling?
If I were you, I'd think about mixture screws after trying to sync the carbs. If they're far out of sync you'll be jetting based on carbs that are out of adjustment and trying to correct a sync problem with jetting... not a good idea.
#8
Re: adjusting idle : carb balance ?
Pair system disabled, carbs sync done.
No changes (carbs was pretty well sync'ed)
Blipping throttle at idle, returns to idle with a small step at 2000 rpm.
No changes (carbs was pretty well sync'ed)
Blipping throttle at idle, returns to idle with a small step at 2000 rpm.
#9
the failure to quickly return to idle can be cured(after all other tunining) by performing an'idle drop procedure" as described in the factory manual. I've used it and it works. you'll need a tachometer that will work on two cyclinders.
#10
Re: adjusting idle : carb balance ?
Withouth the tool it's near impossible to adjust the mixture on the bike. The dealer charged me $25 to do the idle-drop procedure detailed in the SH manual and it gave me a rock-solid idle. My bike didn't have the same symptoms but it's a good way to get the right setting. Good luck.
#11
#12
I have a dwell-tach that handles 2,4 & 8 cylinders. It is a Heathkit that I built twenty years ago. I suspect that there is a tach out there that can handle two cylinders and the 50rpm drop. This procedure is in most Honda factory manuals. The basic procedure is pretty much the same, but there are different start settings depending on your model. This should only be done after all tune up items and the TPS calibration. My '99 almost never 'coughs' and dies and when the throttle is closed it drops to idle speed staight away. I'm going to do a search for an appropriate tach online. I'll get back to you if I find anything.
#15
Re: adjusting idle : carb balance ?
Riding the bike with carbs sync'ed and pair sytem disabled, the idle is now less eratic and no more "pops" at exhaust during deceleration.
Just a little step at 2000 rpm returning idle after blipping throttle.
It goes worse as the engine temp increases.
I think my mixture screws are a little rich.
I'm too lazy to unmount all stuff, just to turn 1/4 in my mixture screws ...
Just a little step at 2000 rpm returning idle after blipping throttle.
It goes worse as the engine temp increases.
I think my mixture screws are a little rich.
I'm too lazy to unmount all stuff, just to turn 1/4 in my mixture screws ...
#16
I've just put in a Factory 1.0 jet kit, and played heck trying to get idle fixed. I found it was easy to miss the passage about "idle set to less than 1000 RPM", and that made a difference for some reason.
Right now, if I set idle to about 1000 and blip it, it doesn't hang up. If I adjust idle up to about 1200 and blip it, it hangs at 2000 before dipping back. And no amount of adjusting the pilot jet screws changes those symptoms.
Than again, I think temps are running a bit too high, indicating too lean...so maybe I still have other issues. <sigh>
Right now, if I set idle to about 1000 and blip it, it doesn't hang up. If I adjust idle up to about 1200 and blip it, it hangs at 2000 before dipping back. And no amount of adjusting the pilot jet screws changes those symptoms.
Than again, I think temps are running a bit too high, indicating too lean...so maybe I still have other issues. <sigh>
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