Topic: Intermittent Carb Leak / Rough Start

[Dr. Noisewater]

My bike's a 1975 CB550f, freshly rebuilt carbs with very few miles, new fuel lines, new petcock, and a freshly lined fuel tank.

Sometimes when I let the bike sit for a few days, then turn the fuel on, it'll leak out of one of the carbs. It doesn't leak out of the overflow tube, but somewhere from the bowl (I will check in the morning if my overflow tube is clogged). If I then turn the fuel off, let it "settle down" for a few minutes, then try again everything is cool. No leak. If I run the bike everyday it never happens, only when I let it sit for a few days.

I turn the petcock off when I park it, but I rarely run the carbs out of fuel before turning it off.

Could this have anything to do with the bike running REALLY rough on a cold start? It doesn't always leak, but it always runs rough for the first few minutes of the first startup of the day.

I sync'd the carbs yesterday but when I started it this morning it still acted like a limping dog. It's better after turning the choke off, but still requires working the throttle and raising the idle in order for it stay running. That may sound somewhat normal for a cold start, but the bike does not sound normal. It seriously sounds like everything is missing and nothing is in sync. It's embarrassing how rough it sounds. After it warms up it's totally cool and I drop the idle back down to normal. Idles like a champ and runs great.

Any ideas?

[scharny61]

Hi, I would rule out spark to all cylinders first.  If all have spark id check fuel in each bowl.  The levels should all be the same.
Test each float to make sure that when you push it up gently that the fuel flow stops.

[martin99]

It sounds like you might have a sticking float needle valve. Next time it does it, give the offending carb a couple of sharp taps with the handle of a screwdriver and see if it helps.

[Dr. Noisewater]

Thanks guys. I know the spark is there cause all of the cylinders warm up quickly and evenly.

I'll give it a tap next time, could a sticking float needle cause it to both run like crap when cold and leak occasionally?

[Stev-o]

A sticky float would cause a fuel leak but it normally would come out the overflow tube.
Confirm that is not clogged and if not, your float height may be set too high?

[Duanob]

You should start a new thread for each individual problem, the thread gets confusing if not.

Are you sure the gas leak is not coming from an over flow tube? You need to find out exactly where it's coming from in order to fix it. Are you parking your bike on the side stand or center? Are all the bowl gaskets in place when you tightened them down? If its a sticky float problem that might be related to hard starting and poor running it would be running out the over flows but we don't know where the gas is leaking.