Hanging revs..

My latest, and hopefully last problem, before getting back on the road.

I took my bike for it's first ride in over a year or two today before work. Not much of a ride. Just down the street and back to test the speedo. On my way back, my revs stayed up high. The previous own took off the tachometer, so I'm not sure how high it was. I'll get one on as soon as I can afford one.

Anyway, sounds like a leak. Right? So now, what's the test methods? I have to go to work early tomorrow. But I'll have a few hours for lunch for test time. What should I try?

Warm up the bike. Once warm, spray WD40 around the carb holders and listen for a lower RPM. Should I rev the throttle when I do this, or just leave it idle? Any other tests? I have never had this happen. The bike has been sitting a while. And I do have new carb to air box boots on order. I just hope that I don't need to order carb holders. I really can't spend that money right now.

Funny thing is I have about $500-700 into this bike. Definitely not a money pit. I just miss riding her. That sounded dirty.

Ideas, thoughts? I'll get back to this tomorrow during lunch. Thanks guys.

LH

No, don't rev it, that defeats the test.

Get the engine warmed up and temporarily set the idle as low as possible without killing the engine (lower than 900 rpm if possible). The lower the better because with the idle very low the slides are nearly shut and the vacuum inside the carb holders is at its highest. Then spray carb cleaner around the carb holders, especially where they mate with the cylinder head and where the carbs attach to them. Carb cleaner works best for this test as it doesn't leave an oily mess with WD40 or evaporate so quickly that it is not drawn into the leaks as can happen with propane or starting fluid (ether). If the engine dies or reacts to the carb cleaner, you need to replace the carb holders. Carb holder leak related problems are noticeable at idle but generally don't have much impact when riding because the throttle is open. If you find you need to replace the carb holders soak the screws with Kroil for a couple days before attempting to remove them, and use JIS standard, NOT Phillips, screwdriver bits, and this will greatly improve the odds that you will not break or strip a carb holder fastener as so many have done. Let me know if you need info on JIS bits, I have a good link for making your own at no cost.

If you find no vacume leaks check the mechanical ignition advancer. It might be gummed up and sticking.

From a few minutes ago. I really didn't find a difference. I used WD-40. I didn't have carb cleaner on hand. I didn't want to use brake cleaner either.

Ed, my carb holders have allen screws. I know about the JIS bits. I read your deal on it a long time ago. Again, spraying fluids didn't change the idle. I'll try again at a lower RPM.

Baldy, how difficult is that check?

Thanks.
LH

baldy110 wrote: If you find no vacume leaks check the mechanical ignition advancer. It might be gummed up and sticking.

Is this what you mean? And if so, is it dry in there where I won't lose oil? What am I lubing up?

It is a centrifugal advancer, the ignition timing advances as the engine rpm increases. Later zx models had an electronc advance built into the ignition box. I had this problem before but it was jerky acceleration, but it is certainly worth checking.

Mark the position of the timing plate on the motor so you can put it back in the same position. Undo the 12mm, then the 17mm engine turning nut underneath it . The ATU advancer will lift off - it is located by a pin in the crankshaft so you can replace it in only the same position on the crankshaft. Step 4 in the factory manual is moving the counterweights against the springs so the rotating pointer lifts off. Give it a good clean with carb cleaner or similar, then lube it with copaslip or moly grease.

If you have access to a strobe timing light you will see the advancer advancing and retarding as the rpms change. They are pretty basic in operation -full advance at around 4000 rpm.

Also check your carb to boot hose clips, they can slack off over the years. The inlet boots sometimes have cracks that are not visisble, but if you take them off and squeeze them a big crack appears. The carb cleaner spray diagnostic should help you narrow down your problem.
Also there are O rings on the carbs , under the boots which often get left off.

.


Nice bike btw.

Maybe your pilot screws are turned out too far on your carbs. When I adjust my carb pilot screws I turn them all the way in, but not tight. Too tight and you will damage them. Then I back them all out 2.5 turns. Then I get the bike running and get the engine warm. If the pilot screws are properly adjusted you should be able to rev the engine and when dropping the throttle the rpm should quickly return to idle. If the rpm drops below idle for too long then the pilot is too lean and the pilot screws need to be backed out more. If the rpm drops too slow then the pilot is too rich and you need to turn the pilot screws in. When adjusting from the starting 2.5 turn position I adjust the screws a half turn at a time between rechecking using the above described method. I always assume that the carbs are matched well enough that each carb does not then need to be individually tuned. I'm sure some will argue about that.

He said it's been sitting a year or two. CV carbs. sounds like sticky slides to me. Everything else checks out.
Steve

swest wrote: He said it's been sitting a year or two. CV carbs. sounds like sticky slides to me. Everything else checks out.
Steve

I did give the carbs a clean a month ago. Won't hurt to check the slides and clean them again. I do have boots coming in so I can get my air box on. That will also help with the rich running. At least in theory.

But I'm stuck at work for now.

I would say if your airbox is off that could be the issue itself.

bromz wrote: I would say if your airbox is off that could be the issue itself.

Airbox was off when I found and bought the bike. It was set up with pods. I got them running pretty good. Did some serious miles on it. It was my daily ride for a year. But I did get an air box for it. And now just waiting on my boots. I've never had the hanging revs. So maybe my slides are a little sticky. Just trying to get time away from work to get to it. I will also loosen the clamps on the carb holders and see if my carbs are not completely seated in the holders.

What else?

But when that is done. I'm done for now. I'll get to making a smaller brat seat for it, or maybe even a second cafe style seat for it. I'm not a fan of this flat tracker seat on it now. It was there when I bought it.

Anyway. Back to work.

Won't hurt to try a temporary fix by coating the carb holders with three bond sealer or some less-worthy sealant. May endure for a week or so, at least long enough for test runs to determine whether or not carb holders are an issue.

One problem with pod filters is that the intake side of the carbs is unsupported, which stresses the carb holders and accelerates their demise.

Carb holders in this condition are pretty much DOA:






The advancer weight pivots are likely accessible for lubing through the timing inspection window.








All this stuff is located under the points cover:




But sometimes more than just lubing is needed, especially if the advancer looks like this:




Good Fortune!