Idle speeds up after warm up

Got the bike running pretty good now. Put in the rebuild kit from Mikes. One of the float needles was noticeably worn, and the rubber parts were hard as a rock. Also one of the floats wasn't quite level so I fixed that. The idle comes back down much quicker now and when it is warm the idle still speeds up a little, but not like it was before. I believe this is normal. Synced the carbs too and the backfiring seems to be gone too. As far as adjusting the mix screws, I took them out and all the parts were there so I cleaned them up, the springs were quite corroded. The washers and o rings were all in tact, cleaned them and put them back in and set them 3 turns out exactly like they were before. So far I am pretty happy with the way its running.:thumbsup: I did try to adjust the mix screws according to the carbguide, but am not sure if I am understanding the dead cylinder method. I took a plug wire off one side, put an extra plug into the cap and grounded on engine. I turned the mix screw on the other cylinder both directions with the engine running, but didn't notice any difference in the idle speed. Also I noticed that both pipes are still putting out exhaust. If one cylinder is dead, shouldn't only one pipe be working?:shrug:
 
Even with the plug off its still pumping air. At idle the difference isn't big since you are burning a very small amount of mixtures.
Don't forget to spray a bit of carb cleaner around the throttle shafts while it's idling, if the engine speeds up it's throttle shaft seal time.

While resurecting my 79 this week I eventually found 7 or 8 make it not run issues. It's tough sorting out so many problems. The final piece of my puzzle was found. The spark looked good on both plugs while cranking. The timing light was intermittent at idle and I could tell one cylinder was dropping out at low idle. I put an in line spark tester on the plug wires and sure enough one coil was weak up and down the range. Swapped in a good coil and life is great. The point is; assume NOTHING, test and verify everything.
 
"The point is; assume NOTHING, test and verify everything."

Very true!!!

I always say to test, in a methodical manner, and never, ever just jump around from one thing to another.
 
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I SAY that, then get my pants in a bunch to meet some self imposed deadline, try to short cut things and pay for it big time......... :shootme:
 
Got the bike running pretty good now. Put in the rebuild kit from Mikes. One of the float needles was noticeably worn, and the rubber parts were hard as a rock. Also one of the floats wasn't quite level so I fixed that. The idle comes back down much quicker now and when it is warm the idle still speeds up a little, but not like it was before. I believe this is normal. Synced the carbs too and the backfiring seems to be gone too. As far as adjusting the mix screws, I took them out and all the parts were there so I cleaned them up, the springs were quite corroded. The washers and o rings were all in tact, cleaned them and put them back in and set them 3 turns out exactly like they were before. So far I am pretty happy with the way its running.:thumbsup: I did try to adjust the mix screws according to the carbguide, but am not sure if I am understanding the dead cylinder method. I took a plug wire off one side, put an extra plug into the cap and grounded on engine. I turned the mix screw on the other cylinder both directions with the engine running, but didn't notice any difference in the idle speed. Also I noticed that both pipes are still putting out exhaust. If one cylinder is dead, shouldn't only one pipe be working?:shrug:

Don't try adjusting the mixture screw (with dead cylinder) at 1200 rpm. Use the throttle speed screw to lower the rpm of the one cylinder down to 300 to 500 rpm i.e. just barely above a stall. In this way the butterflys start to cover up the 3 by-pass holes, which then allows the mixture screw to have some control of the mixture. The change in rpm is not large, so you really have to listen carefully. Go one way until rpm stumbles, then go the other way until it stumbles again. Put the mixture screw half way between the 2 stumbles.

If this does not work for you, then it may mean the butterflys are not sync'ed.
 
I did turn the idle speed down. The only tac I have is the one on the bike, but I had the idle slow enough that it actually died on me a couple of times. Maybe I just need to listen a little better.

Butterflys not in sync?!?! Just when I think I'm getting these carbs figured out, I find out there is more that needs to be checked. Is this something different than syncing the carbs with the manometer?
 
Are you asking if there is more than one syncing operation needed?
If so, then no.
When you sync the carbs you are making both butterflies open up the same amount, at the same time. This ensures both carbs are letting equal amounts of air/fuel mixture into the cylinders. Unfortunately, sometimes while messing around with them they get all boogered up or way off of sync. This is when you might want to remove the carbs and bench sync them, if you are comfortable doing this. That way you can get them close and finalize them on the bike.
The manometer is the best way to sync them while they are on the bike and the bike is running.
 
Yeah, that's what I was asking Littlebill31. I rechecked them on the bike yesterday and they were still right on. Made one myself and use ATF in it and it works great.
 
Okay I'm dealing with this issue right now too. I just cleaned/partially rebuilt my carbs and got them bike on the bike. I was leaking from a few places so I had to replace a float and rebuild the petcock. Bike is running but now I have the high rpm/revving issue.


Here's me question. I attempted a valve adjustment when I first purchased the bike. I swear I watched those videos 40 times apiece because I'm new to this and that was the first thing I'd ever tried. But every time I rotated the engine back around to double check myself and the valve settings THEY WOULD BE OFF! Sometimes all the way up to .10 for the intake! I did the adjustment 5 times apiece on both of the left side valves and then pretty much gave up because I had no idea what was going on. I want to do it again tomorrow because I'm really hoping it will fix the issue I'm having right now. Plus I need to do a tuneup anyways. But I need some input... What's going on? Am i making a rookie mistake? I swear, I thought I was mechanically inclined. Apparently I was wrong.
 
I haven't seen the video, but do you have a manual? It goes over the steps to adjusting your valves.
 
I don't have a manual but there are some really helpful youtube videos. The links are here in the tech section i believe.
 
As the valve stems and the adjuster screws wear the stems get pitted, the adjusters get flat spots. This make adjusting a bit bothersome. You can easily replace the adjuster screws, They just unscrew out of the rocker arms.
You can get them just like the stock ones or one upgrade is to get the ones with a ball in the end. One side of the ball is flattened where it rides on the stem. This flat area covers over the pitting making adjustment easier.
Or remove the engine and tear off the rocker box and do the Porsche elephant foot adjuster mods.
A search on the site will find plenty of info on these mods.
I can't recommend getting a manual enough. You will find it the most used and use full tool you will ever own. I like the factory books. I have then in book form from 70-80 and in downloads from 81 up. I also have the Clymer and Hayne's books. I use them all.
Leo
 
Cros, your advice on the sticky advancer is good advice for those that have them. The sticky advance is often the culprit for a slow to return to idle.
Leo
 
But every time I rotated the engine back around to double check myself and the valve settings THEY WOULD BE OFF!
When you made the rotation you rotated it once or twice to re-adjust?
One rotation would be correct to do the opposite side. Two to do the same side.
 
That may be my problem! Thanks! I figured it had to be something I did wrong, because I got rid of the valve noise on the left side, I just never did the right side bc I thought something was wrong and I was just making it worse. So happy to know that I will be able to have her all tuned up this week. Got the revs to come down too. It was my slides. Used some Vaseline to keep the diaphragms in place this time and that settled it. I am only able to ride with my choke on though but I think thats just my vacuum hose. Its a little to big and I just clamped it down. Going to get a new hose tomorrow and hopefully that will settle it. Thanks again!
 
Use a can of Carb cleaner to check for air leaks. Throttle shaft seals, mount boots, and mix screw holes. Just spray some on each of those points while the engine is running. If all is good, the cleaner should make no difference to how the engine rruns
 
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