I've got a walbro carb that has given me a small problem since I got it. After I start it, it runs great and has great power and transition. After the flight, if the plane sits for more than 5 minutes, it will start immediately but hesitates and runs unreliably for about a minute. Then no matter what I do, it quits. I have to choke the engine to get it to start again. Then, after it restarts, it runs fine. It happens every time. The line stays filled with fuel all the time. Any ideas? Thanks.

Just a guess, but I'd say "gunky main metering needle", getting hung up..... particularly since re-choking it fixes it. If you're familiar with the innards of one of these, disassemble and clean it like you were in a clean room. Don't tweak on things, just clean every passage you can get to thoroughly.

If problem persists - find a REAL "lawn and garden shop" where the guy knows Walbros and give it to him. If not - buy a replacement carb.

Or do a complete rebuild by buying a full rebuild set....but only if you know your way around inside one of these boys.

(Personally - I'd do the clean and replace.... then a new carb.)

Sounds just like vapor lock, doesn't take much heat, can be as low as 100F..

Marzo,
What engine is it on?

Dave

Marzo,

I've got two 3.2's that do not like to start after a flight after sitting for a few minutes unless they are choked again. Both are inverted installations and the position of the fuel line between the engine and the motor box could easily be creating a small vapor lock issue. Sometimes they will start and run without choking , but usually not. I found it was just a whole bunch easier to choke them every time and go fly since they always run flawlessly after starting. Could your engine be acting along the same line?

Vapour lock has my vote as well, especially if the the engine is mounted in such a way that the cowl does not vent hot air with engine stopped.

@Terry,
can you post a picture of your engine setup?

What should I try to cure vapor-lock? Should I try to run it without the cowl once?

Vapor lock is simply the fuel in the line getting hot enough to convert to a gaseous state either just before or just after entering the carb. The fuel is there, but not in a usable quantity. Choking draws additional fuel into the carb, removing the issue. Look to see if there is a way to let cool air circulate near the fuel lines and carb after landing. A good check to see if that's the problem would be to do as you noted and remove the cowl for a flight to see if the problem continues.

Thanks Silver, I'm going to try that this afternoon. I'll report my findings.

This evening I flew without the cowl. I also wrapped the fuel line with foil where it is near the muffler. No change. It still does the same thing, so I'm thinking it may not be vapor-lock. There is a carb insulator block too.

That seems to rule out the vapour lock.
Check the crankcase for leaks. If that is OK, take the Aerobob route, and clean the carb realy good.

What size engine and what model of Walbro carb do you have? Some Walbro carbs have a screen that is behind a welsh plug. You got to remove welsh plug to clean screen. Thats what my Walbro manual says. good luck Capt,n[:-]