High idle/desmog

[RonA]

I believe I have a vacuum leak, the bike idles fine in cool weather but increases as the air temperature increases, up to 2500 rpm at 35C. It also surges at idle once warmed up. I am tempted to cap off #1-5 vacuum ports, plug the smog lines, and replace the #6 line to the fuel petcock to solve the leak and minimize future leaks. Is this an acceptable repair or do you have to remove/alter more of the smog equipment?

[sandy]

There are other places where a leak will cause this. Intake runner clamps, exhaust gaskets and O rings under the chrome intake runners can leak. Check all of this for a cure.

[RonA]

Have snugged up the intake clamps and runner and exhaust bolts, no change. This started after I removed the tank to replace the air filter. I suspect the fuel petcock vacuum line, I had to remove it to remove the tank. Looks good from the outside but is hard to inspect. Thought that I might just eliminate all possible leaks now and in the future by capping off all but #6.

[Madmike]

Have snugged up the intake clamps and runner and exhaust bolts, no change. This started after I removed the tank to replace the air filter. I suspect the fuel petcock vacuum line, I had to remove it to remove the tank. Looks good from the outside but is hard to inspect. Thought that I might just eliminate all possible leaks now and in the future by capping off all but #6.

Little bit of starting fluid may help find it

[RonA]

Yeah I have a propane tank with a line for "sniffing" it out, still curious if I can just block off the smog and cap those ports.

[RonW]

To answer your question people have to reach back and remember the purpose for all the tubes when they did their desmog. Might take a while.

[gordonv]

Yeah I have a propane tank with a line for "sniffing" it out, still curious if I can just block off the smog and cap those ports.

What you are describing is called Stealth Desmog. Search for it, and see if anything else is missing in your proposed desmog, I can't remember.

Since you had your tank off, are you sure you got all the intake rubber correctly on the carbs? I would suspect a folded over edge somewhere. An endoscope or a mirror should help out here.

[RonA]

Thanks, will search stealth desmog. I just removed the tank and refreshed the K+N filter. I did not remove the air box, just the lid.

[RonA]

I have eliminated a vacuum leak as the cause, using a propane bottle and hose. I removed #1-5 vacuum hoses/plugs and installed new caps. The #6 line was replaced to the petcock. There was no change. The idle is smooth but low, 500rpm at 15C, smooth at 20C 900 rpm, 1500 rpm at 25C, a bit bumpy at 30C 2000 rpm.

It does this consistently.

I can adjust the idle down to 1000 rpm at 30C, but then it barely idles in cool weather. The throttle cable has the proper free play, the choke/enricher cable also. All of the enrichers move freely, out and in. I checked the carb sync, it was within spec but I touched it up a bit to get it right on. The bike has always pulled strong, maybe a bit smoother at +3000 rpm after the carb sync. All 6 plugs look identical, a light gray color. I replaced the engine coolant temperature sensor, part #36151-MT8-003, no change.

When I purchased the bike last summer it idled perfectly. Since I bought it I have changed the engine and final drive oil, flushed the rad, brake lines, clutch line, set the valves, and refreshed the K+N air filter. It is a great bike to ride, but I am at a loss to figure out this gremlin. My gut tells me it is something simple but I just can't figure it out.

[Jims99]

Maybe try some fuel additives to clean out anything small. If it sat at all, could have slightly clogged up something. I’ll throw some b-12 in on occasion just to make sure they’re ready when I am.  It does sound like something simple.

[gordonv]

Maybe try some fuel additives to clean out anything small. If it sat at all, could have slightly clogged up something. I’ll throw some b-12 in on occasion just to make sure they’re ready when I am.  It does sound like something simple.

B-12 is great, and inexpensive, but only available in the USA. I've used my last bottle, and buy a couple each year for the spring start up and a long ride. ($4USD?)

Techron would be the next I would try, unknown qty/gas for troubled bikes. But I would just do your best to buy fuel at Chevron.

My first thought, how long do you idle for? Forget about it and ride. Unless you stall at a stop, just turn the idle up a little.

[RonA]

I did run a stiff tank full of Gumout fuel cleaner through it. Supposedly with the P.E.A. additives it's one of the better ones available in Canada. It made no difference. When I parked it last fall it was idling great. I topped off the tank, treated the fuel, and drained the carbs. This spring she fired right up. I am not sure when or why this issue started, it showed up when the weather turned hot.

 Your right it's no big deal, just frustrating.  I have been using it as is, it is a great riding bike. Run the idle at a compromise, 400 rpm 10C, 1500 rpm 30C.