Help with idle problem!
02-19-2020, 05:49 PM
#1
apezman07
Squid
Thread Starter
Join Date: Dec 2019
Posts: 46
Help with idle problem!
The idle won't stay in one spot. It will hold at a certain rpm, then when I rev the bike, the idle will stick up high and then hold there for a while until slowly falling. I turn the idle adjuster and it will change the idle but doesn't help it hold at one rpm. The bike runs great while I'm riding and has tons of power; only having this issue at idle. If I adjust the idle screw down too far, the bike will stall as idle falls; if this happens then I have to add throttle while cranking the bike over for it to start.
Modifications to bike:
-2 into 1 exhaust
-PAIR valve deleted and block off plates installed
-TPS adjusted to somewhere around 500-600 ohms
-180 front jet, 185 rear jet
-dynojet adjustable needles set at lowest setting (closest to point of needle)
-all 3 lift holes in the slides are drilled out
-re routed carb breather lines so they point down
-I have 2 sets of slide springs, short and long. long ones are installed but the bike acts the same way with short springs installed
Mixture screws are 2.5 turns out on both carbs. Throttle cable is not sticking (not sure if butterflys and/or linkage isn't sticking). Airbox is factory. Fuel floats are non-adjustable.
The bike was doing the same thing BEFORE 2 into 1 exhaust was installed, tps adjusted, slide holes were drilled out, carb breather lines were re-routed, and regardless of what length slide springs are installed.
Also, am I correct in having the front jet leaner than the rear jet, and should I adjust the mixture screws differently or have them both at the same setting?
Modifications to bike:
-2 into 1 exhaust
-PAIR valve deleted and block off plates installed
-TPS adjusted to somewhere around 500-600 ohms
-180 front jet, 185 rear jet
-dynojet adjustable needles set at lowest setting (closest to point of needle)
-all 3 lift holes in the slides are drilled out
-re routed carb breather lines so they point down
-I have 2 sets of slide springs, short and long. long ones are installed but the bike acts the same way with short springs installed
Mixture screws are 2.5 turns out on both carbs. Throttle cable is not sticking (not sure if butterflys and/or linkage isn't sticking). Airbox is factory. Fuel floats are non-adjustable.
The bike was doing the same thing BEFORE 2 into 1 exhaust was installed, tps adjusted, slide holes were drilled out, carb breather lines were re-routed, and regardless of what length slide springs are installed.
Also, am I correct in having the front jet leaner than the rear jet, and should I adjust the mixture screws differently or have them both at the same setting?
02-19-2020, 06:23 PM
#2
Senior Member
Back Marker
Join Date: Sep 2017
Location: FL
Posts: 197
All the settings are basically what I have also minus the 2-1 exhaust. My bike came with one and I got rid of it.
I also went with stock slide holes, stock springs and stock needles.
Maybe an airleak from what I think?
I also went with stock slide holes, stock springs and stock needles.
Maybe an airleak from what I think?
02-19-2020, 06:36 PM
#3
apezman07
Squid
Thread Starter
Join Date: Dec 2019
Posts: 46
Are the stock springs short or long? Short is roughly 5 inches, long is roughly 10 inches. I have a set of each so not sure.
02-19-2020, 07:05 PM
#4
VTR virgin
Superstock
Join Date: Mar 2015
Location: Auckland, New Zealand
Posts: 446
This is from the CV carb tuning guide from FactoryPro; note the last paragraph:
4. Idle and low rpm cruise
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!
4. Idle and low rpm cruise
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!
02-19-2020, 11:23 PM
#5
Senior Member
Superstock
Join Date: Sep 2013
Location: Costa Mesa, CA
Posts: 460
The short ones are from the carb kit, the long ones are OEM. If you are going to run what sounds like a DynoJet kit. You may need to lift your needles up a bit. Check the specs on the Dynojet site. that will give you a baseline.
02-20-2020, 08:50 AM
#6
apezman07
Squid
Thread Starter
Join Date: Dec 2019
Posts: 46
This is from the CV carb tuning guide from FactoryPro; note the last paragraph:
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!
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!
I'm also worried that the needles aren't set correctly being that they're at the lowest setting. I may adjust them and see what happens.
02-21-2020, 01:00 PM
#9
Thread Killer
SuperBike
Join Date: Apr 2013
Location: Geneseo, IL
Posts: 2,021
Gleaned from this forum previously:
From non VTR forum, but should work fine for VTR.
Bring the bike up to operating temperature. Make sure the enrichener is off. Turn the idle speed down using the idle SPEED adjustment screw (the one by the throttle cables on a CV) until the bike is only barely able to stay running, maybe a little higher than that. 800 RPM is a good RPM if you have an accurate tach. With the RPM lower than normal, you will be able to see the effect that adjusting the mixture screw has.
The idea is to turn the mixture screw in until the idle speed drops, then turn the screw back out until the idle speed drops again, and set the screw in the middle of those two points. What you are doing is making the mixture leaner, so lean that the engine does not like the mixture and runs poorly, then you make the mixture richer until it doesn't like that, and the perfect setting is half-way between the point where is falls off either way.
A couple things to remember:
1. If the bike gets overheated during this procedure, you will need to let the bike cool off a bit and try again. If you are already at operating when you start this procedure, running more than about 5 minutes while trying to get the setting correct will make the bike too hot. If the bike is too hot when you set the idle mixture, the final setting will be too lean.
2. The screw should be set at least 1/2 turn out from fully seated, and no more than 3 turns out. If it is less than 1/2 turn out from fully seated when it runs best, you should install a smaller pilot jet and perform the idle drop procedure again. If it is more than 3 turns out, you should install a larger pilot jet and perform the idle drop procedure again. If the screw ends up more than around 3-1/2 turns out from fully seated, the spring tension on the screw is insufficient and there is a chance the screw can vibrate out.
3. A tachometer is helpful for seeing the rise and fall of engine RPM if you are not comfortable listening for the changes.
4. The enrichener should be completely off to perform this procedure.
5. An intake leak will foul these results. If the mixture screw seems to have no effect, you may not be able to perceive the change in idle speed, there may be an intake leak, or you may already be either too lean or too rich and you need a different size pilot jet.
From non VTR forum, but should work fine for VTR.
Bring the bike up to operating temperature. Make sure the enrichener is off. Turn the idle speed down using the idle SPEED adjustment screw (the one by the throttle cables on a CV) until the bike is only barely able to stay running, maybe a little higher than that. 800 RPM is a good RPM if you have an accurate tach. With the RPM lower than normal, you will be able to see the effect that adjusting the mixture screw has.
The idea is to turn the mixture screw in until the idle speed drops, then turn the screw back out until the idle speed drops again, and set the screw in the middle of those two points. What you are doing is making the mixture leaner, so lean that the engine does not like the mixture and runs poorly, then you make the mixture richer until it doesn't like that, and the perfect setting is half-way between the point where is falls off either way.
A couple things to remember:
1. If the bike gets overheated during this procedure, you will need to let the bike cool off a bit and try again. If you are already at operating when you start this procedure, running more than about 5 minutes while trying to get the setting correct will make the bike too hot. If the bike is too hot when you set the idle mixture, the final setting will be too lean.
2. The screw should be set at least 1/2 turn out from fully seated, and no more than 3 turns out. If it is less than 1/2 turn out from fully seated when it runs best, you should install a smaller pilot jet and perform the idle drop procedure again. If it is more than 3 turns out, you should install a larger pilot jet and perform the idle drop procedure again. If the screw ends up more than around 3-1/2 turns out from fully seated, the spring tension on the screw is insufficient and there is a chance the screw can vibrate out.
3. A tachometer is helpful for seeing the rise and fall of engine RPM if you are not comfortable listening for the changes.
4. The enrichener should be completely off to perform this procedure.
5. An intake leak will foul these results. If the mixture screw seems to have no effect, you may not be able to perceive the change in idle speed, there may be an intake leak, or you may already be either too lean or too rich and you need a different size pilot jet.
02-22-2020, 08:48 AM
#12
apezman07
Squid
Thread Starter
Join Date: Dec 2019
Posts: 46
I also wanted to add, in case anyone is looking for this information in the factory service manual:
Carb synchronization is found on page 3-12. Shows you how to plug into vacuum ports on each head. Then while the bike is running, how to sync the carbs. Requires vacuum gauges.
Pilot screw (mixture screw) adjustment is found on page 5-18. Shows you how to perform the idle drop procedure.
Carb synchronization is found on page 3-12. Shows you how to plug into vacuum ports on each head. Then while the bike is running, how to sync the carbs. Requires vacuum gauges.
Pilot screw (mixture screw) adjustment is found on page 5-18. Shows you how to perform the idle drop procedure.
02-23-2020, 12:26 PM
#13
Junior Member
Squid
Join Date: Sep 2017
Location: Chester, UK
Posts: 2
Just to be picky, the pilot mixture adjustment method described above is not the 'idle drop procedure', it is the 'best idle procedure'.
The best idle procedure merely adjusts the mixture to find the fastest (or 'best') idle, or the mid-point between the positions where the too-lean or too-rich condition causes the idle speed to fall (again, as described above). It is better to go with this if you want optimum performance. One can follow the instructions in the workshop manual, but then stop after it says '...to obtain the highest idle speed'.
The idle drop procedure, as described in the workshop manual, means finding the best idle and then leaning out the mixture by a particular amount. This leaning is done for emissions purposes.
Both approaches are described in the Honda Common Service Manual, as follows
The best idle procedure merely adjusts the mixture to find the fastest (or 'best') idle, or the mid-point between the positions where the too-lean or too-rich condition causes the idle speed to fall (again, as described above). It is better to go with this if you want optimum performance. One can follow the instructions in the workshop manual, but then stop after it says '...to obtain the highest idle speed'.
The idle drop procedure, as described in the workshop manual, means finding the best idle and then leaning out the mixture by a particular amount. This leaning is done for emissions purposes.
Both approaches are described in the Honda Common Service Manual, as follows
Last edited by jchesshyre; 02-23-2020 at 12:37 PM.
02-23-2020, 03:31 PM
#14
apezman07
Squid
Thread Starter
Join Date: Dec 2019
Posts: 46
I found the solution to my problem. I'll explain in hopes that it'll help someone else.
I have 2 hawks, one with a blown motor and 1 that runs. 2 different carb setups and 2 of everything so it was easy to swap things in and out to see what worked best. Note the airbox and air horns are factory.
The one that runs, when I bought it, it had dynojet adjustable needles (with the 6 grooves). The needles were on the very bottom groove, as rich as they could go. There was an additional lift hole drilled into the slide & needle retainer. Note that the factory lift holes were covered by the needle retainer. Factory slide lift springs. Front jet 180, rear jet 185. Mixture screws were who knows where. There was an existing idle issue, where the idle would rise above where it should be and not maintain an even idle around 1100rpm.
I took the carbs apart, cleaned everything, and reinstalled the 180/185 jets. I kept the needles on the 6th groove. I installed the needle retainers from my blown hawk- 3 lift holes in the slide and an accompanying 3 holes in the needle retainer (this is where I went wrong). I also installed the dynojet shortened slide lift springs. Mixture was somewhere around 2.5 turns out.
When I fired the bike up, it had the same idle issue but now worse. So after probably 10 times tearing the carbs apart trying different things, many mixture settings, and quite a few full throttle passes, I figured out the issue:
For starters, the needles should not have been in the 6th groove. Every time I adjusted them back (went leaner), the idle issue would get better. I finally settled in the 4th groove from the top- the 3rd grooved required the mixture screws to be turned out too far and it made less power than the 4th groove anyways, regardless of where the mixture screws were at.
Another big issue was I had too many lift holes in the slides. I finally went back to the original needle retainers with only 1 hole drilled (instead of 3). Note there are still 3 lift holes in the slides, but the 2 factory holes are covered by the needle retainer.
I inevitably went back to the longer factory slide lift springs, in lieu of the shortened dynojet ones. However, I'm not sure if this made a big difference or not.
I ended up with the mixture screws 2.75 turns out in the front, and 3.00 turns out in the rear. I'm not saying this is the perfect mixture, but it sure pulls hard as hell and I have power all through the rpms; no dead spots or sputtering. As well as a good, steady idle and perfect running condition in stop and go traffic. Every now and again it'll "cough" when I grab throttle hard at idle with the clutch pulled in or bike in neutral (I figured I can live with this in lieu of the idle issue and the fact that it doesn't happen often anyways). If I go a quarter turn leaner on the mixture, it has a very subtle lean pop from the exhaust. A quarter turn richer and it has a heavy gas smell from the exhaust. That's why I settled with the mixture where it's at.
I have 2 hawks, one with a blown motor and 1 that runs. 2 different carb setups and 2 of everything so it was easy to swap things in and out to see what worked best. Note the airbox and air horns are factory.
The one that runs, when I bought it, it had dynojet adjustable needles (with the 6 grooves). The needles were on the very bottom groove, as rich as they could go. There was an additional lift hole drilled into the slide & needle retainer. Note that the factory lift holes were covered by the needle retainer. Factory slide lift springs. Front jet 180, rear jet 185. Mixture screws were who knows where. There was an existing idle issue, where the idle would rise above where it should be and not maintain an even idle around 1100rpm.
I took the carbs apart, cleaned everything, and reinstalled the 180/185 jets. I kept the needles on the 6th groove. I installed the needle retainers from my blown hawk- 3 lift holes in the slide and an accompanying 3 holes in the needle retainer (this is where I went wrong). I also installed the dynojet shortened slide lift springs. Mixture was somewhere around 2.5 turns out.
When I fired the bike up, it had the same idle issue but now worse. So after probably 10 times tearing the carbs apart trying different things, many mixture settings, and quite a few full throttle passes, I figured out the issue:
For starters, the needles should not have been in the 6th groove. Every time I adjusted them back (went leaner), the idle issue would get better. I finally settled in the 4th groove from the top- the 3rd grooved required the mixture screws to be turned out too far and it made less power than the 4th groove anyways, regardless of where the mixture screws were at.
Another big issue was I had too many lift holes in the slides. I finally went back to the original needle retainers with only 1 hole drilled (instead of 3). Note there are still 3 lift holes in the slides, but the 2 factory holes are covered by the needle retainer.
I inevitably went back to the longer factory slide lift springs, in lieu of the shortened dynojet ones. However, I'm not sure if this made a big difference or not.
I ended up with the mixture screws 2.75 turns out in the front, and 3.00 turns out in the rear. I'm not saying this is the perfect mixture, but it sure pulls hard as hell and I have power all through the rpms; no dead spots or sputtering. As well as a good, steady idle and perfect running condition in stop and go traffic. Every now and again it'll "cough" when I grab throttle hard at idle with the clutch pulled in or bike in neutral (I figured I can live with this in lieu of the idle issue and the fact that it doesn't happen often anyways). If I go a quarter turn leaner on the mixture, it has a very subtle lean pop from the exhaust. A quarter turn richer and it has a heavy gas smell from the exhaust. That's why I settled with the mixture where it's at.
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