I (with much help from my mechanic neighbour) put the new exhaust valves in the motor and remounted it this past weekend. The engine seems to working fine but the carbs are not. When I took out the engine I just unplugged the electrical connection at the bottom of the carbs and moved them to the side.

I have played with the idle screw and yesterday my neighbour tried playing with that and the other screw whose name escapes me at the moment. Now after starting the bike will idle ok but when you ride it the revs are slow to come down and won't go back down to normal idle. If you play with that other screw you can the initial idle better but makes it much slower for the revs to come down at all. My son is riding it now - better than the inert pile of metal it has been for the last two weeks - but it would be nice to make it run better.

A couple of months ago I had these carbs adjusted by a local shop - new floats, etc - and I didn't do anything to them now other than moving them out of the way while I took out and replaced the engine. I really don't want to take it in to another shop about the carbs - this piece of crap is already proving to be an endless money pit.

I would suspect a loose or missing vacuum hose or cap. Maybe loose carb boot.

Quote from: Paulcet on October 24, 2011, 08:09:10 AM
I would suspect a loose or missing vacuum hose or cap. Maybe loose carb boot.

I made sure the boots were quite secure but I'll double check. I'll also check out the hoses on the carb. I didn't touch any of them, just moved the carb assembly off to the side when I took the engine out/in, but it's possible something go loose in that process.

Yea air entering somewhere - intake exhaust ... and/or throttle cable or choke cable catching.
Cool.
Buddha.

Did you replace your exhaust gaskets, or use the old ones when you 'put the engine back in'?

I think you are also supposed to sync the carbs after a valve adjustment.  New valve clearances will throw the carbs off balance.

The only gasket I replaced was the header gasket. I've seen a mechanic spray the boots/carbs to detect a leak but can't remember what he used. What can you use to spray these things with that won't hurt anything?

I'll look at the syncing if I don't detect any leaks but the last time I tried didn't seem to go too well.

It may just be an incorrectly set idle (long screw) or mixture (two tiny screws on bottom). You have to get the engine warm (15 minute ride) in order to set the idle properly, the mixture screws should be set before hand.

Quote from: thecdn on October 24, 2011, 09:05:10 AM
The only gasket I replaced was the header gasket. I've seen a mechanic spray the boots/carbs to detect a leak but can't remember what he used. What can you use to spray these things with that won't hurt anything?

I'll look at the syncing if I don't detect any leaks but the last time I tried didn't seem to go too well.

wd40, and yes please be careful and dont get much of it on the exhaust. It can and will catch fire. Intake area and cyls it will just sizzle and evaporate.
Synch wont make idle go high. Idle screw will. Valves should be irrelevant to synch, I would rather synch em with the sunlight method than the vacuum method. The valves do affect vacuum, which is counter productive IMHO.

Cool.
Buddha.

I didn't have time to take anything off tonight but I sprayed the carbs/engine with wd and didn't notice any obvious air leaks. The accelerator snaps back into place quickly. The housing for the accelerator cables by the right grip is a bit loose, as are the cables, but they have always been that way on this bike.

When I was checking it in the garage tonight I noticed the revs were slow to come down when you revved it to 6-7000, pausing shortly around 3000 but would go down to an idle of 12-1300. My son told me that when he took it for a ride this morning the warmer/hotter the bike got the longer it would take for the revs to go down from the 3-3500 plateau. Does that symptom mean anything to anyone?

Tomorrow I'll try to have the time to warm it up properly, set the idle when warm, and take the tank off and check out the throttle linkage/adjust the screws.

as stated before, a high idle is indicative of an air /vacuum leak / and/or a lean condition.  When you spray the WD40 or contact cleaner around the areas of the intake (carb boot/manifold/vacuum hose) you should notice a sharp decline followed by a sharp high idle that will hang for a bit.  That symptom would indicate an air leak at that area.  If you have an air leak in the exhaust, you will most likely experience alot of backfiring due to the cold outside air mixing with the hot exhaust gasses prior to the end of the exhaust. 

Are you sure there is no kink/hangup in any of the cables (throttle/choke)?

-Craig