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Idle problem

Joe Nardy

Joe Nardy

Forum Sage
Past Site Supporter
TGSR Superstar
Guys, Once again I'd like to lean on the unbelievable technical knowledge of this site. I'll 'fess up right now that this problem isn't on my GS but on my '88 Honda Hurricane 1000. I hope you'll still help! Here are the symptoms:

There is a big difference in the idle when cold, warm, and hot. Here's the progression:

Bike starts well with choke, will idle without choke within a few minutes.
When bike is warming up idle is 1200 - 1300 RPM. When throttle is closed RPMs don't seem to drop as quickly as they should.

As bike gets hotter idle drops to around 1000 RPM, RPMs seem to drop quicker when throttle is closed but still not as quickly as they should.
When bike gets hot, like in stop and go traffic, idle will first drop to around 1000 RPM, then drop to 500 RPM or below. The idle drops so low the bike will sometimes stall. Bike will rev easily if throttle is opened quickly, but runs rough until around 2000 RPM if opened slowly. RPMs still seem to drop slowly.

Once bike has heated up, the above symptom remains, even if water temp drops significantly. Today it was very cool and raining and the temp dropped well below normal temp after being hot and the low idle problem was still there.

I adjusted the mixture screws from 2 1/2 turns out to 1 1/2 turns out and the problem seems to have gotten better, but not by much.

Otherwise the bike runs GREAT. It has a Dynojet Stage 1 kit and a K&N replacement filter.

Thanks for any help,
Joe
 
You're mixture is too rich. Trying to compensate by adjusting your mixture screws is not the fix. They should be put back to where they were.
You are either getting the right amount of fuel and not enough air, or you are getting the right amount of air but too much fuel.
IF NOT ENOUGH AIR, what would cause this? Too much slack in the throttle cable(s), dirty air filter, something partially blocking air to the intake, such as an air box seal/foam gasket?, carbs out of synch', I'm not familiar with your carbs but if the throttle valve plate(s) are not in synch' or are sticking a little, this would cause a loss of air intake at low rpm's, if your carbs have a damaged diaphragm you would have a loss of vacuum and therefore a loss of air intake, clogged air passages in the carbs, such as the air-jet and its passage.
IF TOO MUCH FUEL, what would cause this? A vacuum operated petcock with a leaking diaphragm will draw fuel into the carb supplying vacuum, incorrectly adjusted mixture screws, pilot jets too large, loose pilot jet(s),
float fuel level too high, worn/leaking float needle valve(s).
I would also check the sparkplug gaps.
 
Keith,

I think I made some progress today although it will take a long ride to convince me it's fixed for good. I went through your suggestions, here are my findings:

Throttle cable looked good. I made sure the mechanism was returning completely to the stop and that nothing was binding. The cable free play looked good. I looked at the airfilter, it looked great as it is new as of this spring. I checked out the airbox for any restrictions, found none. I checked the carb synch, again good. I pulled the carbs and inspected the diaphragms, slides, made sure all jets were tight, and cleaned out all passages and jets. The petcock is not vacuum operated so this shouldn't be a problem. Before I removed the carbs I drained the float bowls and compared the amount of gas I got out. They all drained roughly the same amount, just under 50 ML, so I think the float levels and needle valves are okay. I pulled the plugs, verified they were the correct plugs as specified in the manual and checked the gap. The gaps were all good and the plugs looked good as well. I was running out of ideas and decided to check the carb boots for cracks. When I did this I found that I could rotate all four boots on the head. They weren't so loose that they were falling off, but it didn't take too much effort to rotate them. I checked the clamp screws and they were all tight. I took a closer look and found that the clamps have a spacer that prevents them from being tightened past a certain point. I took one apart and shortened the spacer from 12mm to 10mm. Now I could feel the clamp tightening into the boot instead of against the spacer. I took all the clamps apart and shortened all the spacers. Now the boots do not move. I carefully re-assembled everything and started it up. I let it warm up then checked the carb synch again. It needed a bit of tweaking and the idle now seems very stable. I checked the Dynojet instructions again and set the mixture screws out 2 turns per the instructions. I'm hoping the loose boots were the cause of the idle problem and possibly why I've been fighting carb issues all summer. Again, I'll have to wait until I can go on a long ride and see how it does.

Thanks so much for the advice!

Joe
 
Hi. I hope it runs good. I know you did'nt find anything on my list that was obvious, but sometimes just tinkering will help. The loose manifold clamps would possibly draw in air which would create a lean mixture. A lean mixture actually fires too soon in the cylinder. Combustion becomes erratic and the rpm's RISE above normal. This is most noticable once warmed up.
You stated that turning your mixture screws in (leaner) seemed to help. This made sense to me (mixture-wise), but adjusting the screws is usually just compensating for the real problem. One thing is for sure, the clamps should not be that loose. I've noticed on several bikes, the clamps do'nt tighten as much as they should.
Anyway, I hope it tests good and your idle is good again.
Let us know if we can help. :)
 
Keith question

Keith question

Keith,
Don't take this as a flame by any means, but after reading this thread I remain a little confused. If Joe was having a low idle condition that would usually indicate being rich. When he turned his idle screws in and it improved the idle a little, that would make one think that it was rich to begin with. If his issue was loose mounting boots it would be lean which would raise idle speeds. Tightening them would (if anything I think) return his mix from lean to normal wouldn't it? :? Bob





If you don't learn something new everyday, you're either stupid or not paying attention:D
 
Bob,

I agree with your logic completely, as I'm sure Keith does. As he mentioned, maybe something else got cleaned up during the process which was the actual fix. I still haven't gone for a long ride so I'm not convinced it is resolved. I'll post my results.

Thanks for the help,
Joe
 
Hi you guys.
If I said something to confuse you, I'm sorry, let me try again.
Joe's low idle condition would indicate to me, a rich mixture. Joe thought so too because he tried adjusting his mixture screws in, to lean it out a little. Then he tried several things I suggested and could'nt find anything obvious. He did find some loose intake boot clamps.
In my second reply, I said that an intake leak caused by loose clamps would make the rpm's RISE. This is of course, the opposite of his problem.
I only was saying that the clamps should not be that loose. There is no indication the loose clamps were allowing air in. The loose boots are not the cause of a low idle. I also said he should put the screws back to where they were because they are not the problem.
As you said, a lean condition will make the rpm's rise, everytime. If it was a serious intake leak (such as not replacing the carb manifold screws used for balancing) the bike would'nt even run.
Joe's problem (I hope it's gone) is a rich mixture.
 
Gotcha now!!

Gotcha now!!

Keith and Joe,
I gotcha now. Joe, would you please pull the ZXR pic from your photos as it has made a big slobbering mess of my keyboard. I saw one of these at the local dealer and immediately fell in love! Now if I only had 2 more jobs and another of me so I could ride with myself on the GS I'd be in heaven :lol: Bob
 
Re: Gotcha now!!

Re: Gotcha now!!

cabinover said:
Keith and Joe,
I gotcha now. Joe, would you please pull the ZXR pic from your photos as it has made a big slobbering mess of my keyboard. I saw one of these at the local dealer and immediately fell in love! Now if I only had 2 more jobs and another of me so I could ride with myself on the GS I'd be in heaven :lol: Bob
Click to expand...

But would'nt the two of you fight over who rides what? :lol:
 
Fighting

Fighting

There wouldn't be any fighting, I'd win. *whisper-No, I'd win* :twisted:
 
Guys,

I finally got out for a longer ride, approx. one hour. The low idle problem returned but just at the very end of the ride. I intentionally rode varying conditions, stop and go, continuous high speed, and a mix of both. The bike got up to full operating temp quickly and I ran it hot and cooler and the idle stayed good until the very end. It did seem more stable than before but there was definitely a 300-400 rpm drop from when it was idling well. So I've still got that monkey on my back.

ALSO, now it seems like the bike doesn't run as crisp. It doesn't seem to accelerate as hard, and even stumbles if the throttle is yanked open. The stumble is worse in higher gears. It seems a logical conclusion that I am now running too rich due to fixing the loose carb boots. What do you guys think? I'm planning to drop the neeedles to see if that helps but I'd appreciate your advice before I jump into it.

Bob, don't worry too much for me, the GS and ZRX are both running SWEET!

Joe
 
Hi Joe. I don't think you should adjust the needles.
Before the low idle problem, the bike ran fine with the needles right where they are, right?
As for the bike not running as crisp, the most likely cause after you worked on the carbs, would be a poor re-synch'. After synching, do you double check by turning the bike off and opening/closing the throttle several times and then re-check the levels? Does any condensation get trapped in your gauge to mess up the levels? I know you know your bike better than me, but I have seen many good running bikes stumble, if the throttle is opened very quickly. The older VM carbs are easier to "fool", but I think the CV carbs also can do this? Granted, the stumble should be fairly brief.
Anyways, back to the low idle. Considering what you've checked, I have a few ideas/suggestions.
This is just a thought, I have no experience with, but does the Hurricane have an accelerator pump? I don't know if I'm correct, but does'nt an a/pump shoot a little extra fuel in at idle rpm's, or do they work only at warm up? If you have one and it was failing, this might cause a rich mixture/low idle?
Another suggestion would be to adjust your air screws for the highest possible idle. Once warmed up, and on the centerstand, adjust your air screws out to achieve the highest idle, then adjust your idle screw knob to the correct idle speed. It's easier to hear the rpm's rise if you adjust 2 at a time in 1/2 turn increments. The jet kit setting you mentioned is only a "base setting".
It's easy for us to blame the carbs for your problem, but a "rich" mixture can sometimes be a weak or intermittent spark. A poor connection can sometimes show itself when hot. Because of the current flow and also engine temperature, the resistance will build up. If you add to this the fact that voltage can drop a bit at idle speeds, you could have a poor connection that would not be noticable at higher speeds, start up, or before it reaches operating temp's.
Try visually checking your plug caps, plug leads, and coil connections.
Clean or replace anything that's not right. You may want to do some resistance/voltage checks when cold and compare them to when it gets hot.
I don't mean to over- explain things, I don't know how much experience you have, so I always try to give as much info as I can.
That's all I can think of right now. Good luck, and let us know how things go.
Keith.
By the way, don't put too much stock into tightening those boot clamps.
There was no indication they were actually leaking. Besides, an intake leak would cause your idle to rise, not lower.
 
Still stumbling

Still stumbling

My GS850 with CV carbs will stumble ever so slightly when whacking the throttle but that's the nature of the beast. My KZ900 with slides doesn't do it as bad but, it's already running a little rich to begin with. The CVs have to wait for the vacuum to lift the slides so that is what causes the stumble. In higher gears with lower revs it sees less vacuum until the revs come up. I think the theory is that this will only pick the slides up to the point that the motor can use for air and fuel, meaning less stumble at lower RPMs. Have you pulled a plug since your ride? Like Keith, I don't know your carbs other than Honda used an air cutoff (on some models..Keihins I think) to stop popping when decelerating. You could have an intermittent problem with your wiring like Keith said also?? Keep after it buddy :) Bob
 
Keith, Bob,
Please help me with terminology here. I referred earlier to 'mixture' screws which you said not to mess with. Now you refer to 'air' screws which I should adjust for highest idle. I think we are talking about the same screws. What I am referring to screws on the engine side of the carbs that (used to) have caps on them that limited their movement. I have disassembled them and they consist of a brass fine threaded screw with a needle point, a spring, a washer, and an o-ring. The Dynojet instructions show a diagram and refer to these as 'mixture' screws. Are we talking about the same screws or are there supposed to be two different screws?

As always, thanks for the help,
Joe
 
Air screws

Air screws

Joe,
There are at least 4(I think) different Mikuni carbs used on GS bikes.
Set 1 utililizes an air screw. This is on the air box side, adjusts air. In to richen.

Set 2 utilizes a fuel screw. This is on the head side of the carb, adjusts fuel. Out to richen

Set 3 utilizes both an air and fuel screw. I know you don't have these.
All 3 sets above are slide carbs, not CV with a diaphragm

Set 4 are the CV carbs. The only adjustment is idle mix or fuel (it's on the head side). Out to richen, In to lean.

We're all on the same page even though the terminology is different. Bob
 
Hi Joe. I only mentioned the air screws (which I have) as a possibility, just like the accelerator pump idea. I can see the confusion over air, idle, and mixture screws. Your description of your screws sounds like the pilot/fuel screws on my bike, very sharp tipped. Mine fine tune the fuel flow for the pilot circuit, and have nothing to do with air flow, I have seperate air screws to adjust the air intake. I don't know if your mixture screws adjust fuel only, or both fuel and air? Do you have a factory manual? I called Dynojet a couple of times and they were helpful with my questions. By the way, if you did'nt know, never tighten down those sharp tipped screws, the tips can break off in the carb body. Just seat them lightly.
You must not have seperate air screws on the side, they are obvious.
Also, I assume now you don't have an accelerator pump either?
What about checking the plug caps/leads/coil connections? Anything?
A weak spark due to a poor connection(s) can show itself sometimes only when hot and/or at low rpm's. A weak spark can easily be confused with a rich condition. How are your plug reads? I have heard it is difficult to get accurate reads at idle rpm's, but have you let the bike idle when hot (with your assistance) and then taken a read? How about the hot and cold resistance/voltage reads?
Going by what you say you've checked, I'm really wondering about your electrical connections. It only takes 1 cylinder to mess up the idle.
 
Keith,

Yes, I do have a Haynes manual for the bike. I plan on looking into plug caps/leads/coil connections. I am familiar with volt/ohm meters but I could use some help with what I should be looking for. I'm guessing cold and hot resistance measurements of coils and wires. You mention voltage readings..........what voltages should I be checking? I also have a timing light that I plan on using to see if any wires are firing irregularly. Any guidance is appreciated.

Thanks,
Joe
 
Joe Nardy said:
Keith,

Yes, I do have a Haynes manual for the bike. I plan on looking into plug caps/leads/coil connections. I am familiar with volt/ohm meters but I could use some help with what I should be looking for. I'm guessing cold and hot resistance measurements of coils and wires. You mention voltage readings..........what voltages should I be checking? I also have a timing light that I plan on using to see if any wires are firing irregularly. Any guidance is appreciated.

Thanks,
Joe
Click to expand...

Hi Joe.
I have been lucky over the years when it comes to most electrical problems, so I really don't have a lot of experience with trouble-shooting.
I would have to look at my manual and try to follow their test procedures too. If you do a search here, I'm sure you'll get some help, or maybe someone else can join this topic.
I do know that hot/poor connections can increase the resistance reads, and decrease the voltage reads. I'm just not sure where the correct places are to take the tests. If you can't find help, I'll try to check out my manual and help you. Maybe I'll learn something. Talk to you later.
PS: To me, a poor connection/coil makes sense. Once the connector/coil gets hot, the resistance builds up, and your spark at the plug decreases.
Also, at idle, the voltage can drop, which can decrease the spark. A weak spark will not ignite the mixture well, so you'll get a "rich" condition.
 
Keith,

As always, thanks. I'm hoping to get some time today to look into this. I'll see what the manual has to offer and take it from there. I'll post my (hopefully successful) results.

Joe
 
Hi Joe. Just had a thought, you never know.
Have you checked the choke assembly? If yours is similar to mine, they are all connected to a shaft, and with vibration, is it possible they are not all adjusted the same? Could 1 or more be hanging up and not fully closing when you turn the choke off? Vibration or dirt/varnish could cause this. Also, if your choke plungers are part rubber (like mine) 1 or more may not be sealing. This would give you a rich condition and it would be most noticable when hot and at idle.
 
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