Okay boys and girls. I have spent the past 3 hours working on my bike to resolve a HIGH idle problem that at first I thought was gone, then it was back, then gone, then back. I went out today to replace some shims and get the carb boots back on (DIY repair) and try to diagnose this once and for all. SO, I get it all back together and the damn thing just runs waaaaay high at idle. It settles around 3200 then it might fall down to around 1400 then maybe 1250 then maybe not.
I have checked and re-checked and re-re-checked until I felt completely ree-ree. Finally, I put the temp. gas tank on checked the cables, sprayed WD40 to check for vacuum leaks, just everything to try and figure this out.
Then I thought to myself, "what have I done just before this all started" and I remembered placing a cover over the left carb nipple which is the vacuum for the petcock. (Since I was going vacuum-less.) I pulled that cover off and my revs dropped down to 900 from around 1500. I then decided to adjust the idle screw back up to where I was running at 1200 and the high revs are gone.
I place my finger on the vacuum nipple and sky high.
SO..... the challenge is this. How many of you who have put a cover over that nipple are having high revs at idle? Go out and take off that nipple cover (The rear of the left carb, not the one on the black covers.) and re-adjust to see if that cures your problem.
I'll wait...............
If that works, someone please explain to me if having that cover over that nipple is necessary for good operation? Is it causing the vacuum internally in the floats? Any possible damage if I leave it off? Right now, testing is running fine. I plan to put the tank back on, and ride a while today. I'll report my results later.
I know that when I accidentally knocked mine off (which I found by the way, when I replaced the chain :o) it ran like crap at low rpm, along with hanging idle sometimes.
That's what I don't understand. You knocked off the hose? or the top vacuum cover? What I am talking about is the rear of the carb (back side not the black plastic top covering the diaphragm but where the fuel vacuum hose connects.)
If I take mine off, the bike runs somewhat better. IF I cover that vacuum port, it surges high and has a very unstable idle.
What has anyone else done? Left that tip uncovered? Do you get a lot of exhaust backfire?
I knocked off the cover on the vacuum port where the fuel vacuum hose connects. My petcock is not vacuum operated.
I also got some backfire when the port was uncovered.
Anyone have any other ideas on high surging idle? I replaced my right intake and left exhaust shims yesterday and almost have them all in the same spec. Right intake and Left exhuast are both at .08mm adn left intake and right exhaust are at .06.
I thought somehow, maybe that would help some of the issue but nothing different other than the motor "sounds" good when running. (Plus it just had to be done.)
Anyway, I have the carbs off and I am going to carefully inspect them to see if there is some trash that has gotten in there. Other than that, it almost seems like a vauum is getting created in the carbs once it runs for a bit and warms up. I litterally hear it surge. Not after giving it throttle but just sitting at a good 1200 idle, it just surges straight to 3200 rpm and sits there.
sync your carbs if your at .06 on 1 intake and .08 on the other your goin to pull more vac from one then the other. you know one carb is flowing through the head better then the other. a good carb sync will get rid of your problem
I will give that a try.
Hanging high rpms- when everything else is ok ( idle adjustment screw/cable etc) is usually a lean condition. If you have the carbs off- you can do a visual "sync" - look at the throttle plates- open the idle screw a little and see if the gaps between the carb body look even- No it's not the prefect or right way to sync a set of carbs but you can see how close they are before you start changing anything (and if you didn't change anything regarding sync before....don't be in a hurry to do it just yet...)
Double check every vacuum hose- make sure your little Orings under the carb tops are there... Did you install new carb boots ( the boots that bolt to the head)? They can look ok and be a big air leak- One of the Gs's I had before had that problem- new boots solved it.
The nipple needing to be on.... well if it's off you are making a big air leak- more air in the air/gas ratio.... Lean...
Did one exhaust downpipe get a lot hotter than the other ( or even glow orange?) ?
Carbs are fun aren't they....
Thanks Jared. I am going to recheck everything today (float height, sync, boots, etc..) Where is the most common place on the boots seem to cause the leak? I had the plastic peeling off the boots at the edge and one thing I have attempted was to seal the edges of the boots. I have sprayed WD-40 around them where initially there was a slight leak but now there doesn't seem to be any. The problem seems worse when I put the nipple cap back on the fuel vacuum line.
The only other thought if everything checks out on the carbs and the sync is good, is that when the engine heats up, the boots also heat up and if there is any crack or gaps, they get bigger?
(ADDED Here from another post just to give everyone good coverage. Thanks to all that have helped me on this.)
Thanks to Jared as well. I finally got "un-lazy" and did the carb sync which helped. Not the total solution for this problem but it definitely helped. :thumb:
I finally believe I have SOLVED my high idle and I bet you will not want to hear what I believe it is.
If you have checked everything over 3 times to make sure the float height is correct, carbs are clean, air mixture screw is set correctly for your carbs (2 turns stock, 3 turns for the K&N / Open exhaust, 40 / 150 jets), carb boots are not leaking, and carbs are synchronized as stated using some oil and 1/4" clear hose from the lumber store, I can almost bet money you have a hanging throttle cable.
I couldn't believe it myself. I wouldn't believe it because I would adjust and everything would be great then all the sudden right on it's own, it would climb straight to 3000 - 3500 and stay there. Almost as if there was some sort of vacuum leak or something.
Well tonight, I got out there in the dark and DID WORK and what I found was this. My float levels were spot on, my air screw was set at 3 turns (no exhaust and K&N, 40/150 jets.) I took the tank off, hooked up my temporary test tank, and fired it up. I let it warm up and fiddled with the idle slightly. Then, i connected the 1/4" hose to sync the carbs. (I thought I did a good job by sight but I was wrong. It was pulling harder on the right carb. (Due to valve clearance differences maybe.) Just touching that darn screw it would easily cause the sync to go the opposite way. I finally got it where I believe it is good based on what I could tell in the dark with my tube.
After that, i decided to ride around the complex a couple of times to see if my problem came back. Nada! Great! So, I started to put the tank on, restarted the bike it idled right at 1200 then like clockwork, 3500.
SO this time, I knew it had to be mechanical. I played around a little with the carb and the throttle and I got lucky and say the cable let the center section of the throttle drop and my idle was normal. I re-adjusted the cable to give as much slack when at idle and that seems to have done it.
I have all the caps on the carbs, I have it synched, and I have it adjusted. I rode all over town for about an hour and the bike ran beautifully.
So take a look at all those things. If you have leaks around the edges of the boots, you might try what I did. Take some high heat black silicone gasket in a tube and clean up the edges peeling off the loose broken plastic. The, cover the edges with a nice smooth bead / glob of silicone. Let it dry overnight and then re-install. Mine seem to be working fine and will buy you some time before you have to buy new ones.
Good luck.