engine overhauld, new valves installed, grinded, adjusted, everything.

Carburators disassembled/assembled, cleaned, iddle speed adjusted, synchronisation adjusted, everything.

problem:

Engine starts/runs on choke, to warm up, when i push back te choke, the engine runs for a little while on normal iddle speed [1000-1300 rpm] and then suddenly refs up to 3500-4000 rpm -for a little while-, but drops back again to iddle speed.

After operation of throttle, the refs again raise, and drop very slowly after little while, but then again, engine reffs up again to 3500-4000 rpm.

WTF could be the problem ???

 

My immediate knee-jerk reaction is sticky floats. Other than the rev issue, everything sound OK? No ticks, groans, buzzes? I'd say you're REAL close....keep the faith!! Sounds like you did a nice job, overall!
(Anybody else have thoughts??)
Welcome to the forums! Hang in there!!

OK; just had another thought...maybe sticky slides (since it's doing it on both "choke" and "throttle?") Can you try it with the carb intakes exposed so you can see if anything is hanging-up? Is the throttle linkage binding anywhere (like at the pivot point on the carb assembly bracket?) Something just hanging-up like it needs lubed?

 

hmmmm, I vote for a vacuum leak as a first thought or bad diaphragm. (spray some either around the hoses to check on the hoses or connections.) As far as the diaphragm it is only a visual check as far as I am aware of.

Welcome to KF and post up some pics of the ride!

 

Diafragm's are ok. checked them all 4, -against bright bulb, underwhile i pulled the diafragm.

 

I allso though about sticky slides, and sometimes it seems to be, do you know how fast they have to slide back when pulled up ?? sometimes i think that above diafragms the air gets out, but not get's in back again, and therefore slides maybe 'sticky' ??

 

I believe the slides should just kinda drop back down when you are off-throttle. They shouldn't drop gradually. Might hit them with a quick spray of very light lube through the intakes. (this might bog your engine for a bit, but will help the slides.) Double check your cables, pivot points, linkage....make sure everything is smooth. (I'm trying to recall if the cable pivot link is in the middle or on the end of the carb rack..??) The cable/linkage spring-loaded pivot should have good "snap" action when you let go of the throttle grip. If the pivot snaps properly but your slides hang up, there's something (crud, dry, out of adjustment) going on with the slides, I would say. Do you remember anything being odd when you cleaned/adjusted the carbs? Let us know...