Originally Posted by achile
Sorry to bug you, but I have a problem that's driving me crazy!
I overhauled the top end of my piggy(piston rings, valves, seats, springs, camshaft bearings...you get the idea).
I dismantled the carb, cleaned it, set the level, needle setting(the needle is new)...etc.
1) the bike starts very hard
2) when it starts, the idle goes wild(from normal to 3000 revs)
3) very litle response from the air screw(new as well)
4) when I rev it, it dies after releasing the throtle
I suspect an air leak due to worn carb body and throtle valve(the only thing I didn't check). The intake boot is new.
I had this problem before the top end work, but it intensified after. More vacum/compression=more air leaking => leaner mixture??
I found crf 450 carburetors(FCR 41) on ebay. I'm thinking about buying one.
What say you?
Hanging idle is usally too tight of cables or the valves are too tight. When the cables are too tight the work against each other to hold the slide up for a period of time, when it does come down the other adjustments may be off not letting it idle. Check the freeplay at the grip and make sure it will rotate back and forth a little bit (ensuring they aren't too tight) To check for a cable prob forcebly close the throttle after a rev so the push cable pulls the slide down, if the revs drops down immediately then it's a cable issue.
If the valves are too tight it makes all kinds of wierd running cond including hanging idle and failure to idle. I've seen some pretty worn carbs that had no adverse effect on the running, I'm sure that could happen esp since we can't really see how bad the carb is but it'd be very unusual.
It's not uncommon for the valves to settle in the head a good bit right after a topend job, that would cause them to tighten up relatively quickly. Tight valves = hard starting also. Im thinking that's the issue.