Fuel leaking out the side of walbro carb

[thekingofclubs]

Hi everyone

I have a JD300 with some carb issues. I've cleaned it and gone over it with a fine tooth comb several times. After putting it back on the sled it started up fine but after idling for a few minutes began leaking fuel out the side of the carb from the hole shown in the picture. I have the needle valve lever set just above the carb body. I've got both screws 1 1/4 turn out. I've monkey'd around with the screws and no real improvement. There's quite a bit of fuel going to the vapor return and also some going down the impulse tube.

What have I got wrong here?

Thanks in advance.

[JDT]

do you have the supply and return lines on the correct barb?

supply -center, return-outside edge.

[thekingofclubs]

You bet, fuel lines are all correct.

Yesterday I played with about ten different settings for the metering lever height and saw no improvement on the leak. The longer it runs the more it leaks which tells me it's just flooding and coming out that tiny vent. I don't know enough about the circuitry to diagnose what the cause is. When it starts to flood out and die I can bring it back briefly by choking it.

* I should add, there's a lot of fuel going down the impulse tube too. Not sure if that helps.

[JDT]

There is a paper gasket and a mylar gasket between two of the plates that can get reversed.
You may want to disassemble the carb and confirm that every piece is in the correct position.

Other wise pay close attention to the needle and seat.
It only takes a tiny piece of crud to prevent the needle from stopping fuel flow when it is suppose to.
The needle valve has a soft tip that can shrink or become deformed which will prevent shutoff also.

Maybe replacement of the seat and needle is due. Additional the spring on the metering lever could be weak.

[Matt]

I haven't grabbed a carb yet to look at, but is that hole supposed to be there? Maybe a casting failure?

[thekingofclubs]

Thanks for the help so far guys.

I'm pretty sure the hole is supposed to be there. Without a picture it's hard to explain, but it leads to a cavity inside that plate which leads me to believe its an overflow vent or possibly an air vent? I have two new gasket kits and I've tried fresh gaskets between those plates with no success. This is a bit of a Franken-carb, It's the top end body from one carb and plates from another (both wdb-31). The screw that holds the metering lever down snapped on my original carb, as did the screws holding the circuit plates down. I bought this one and transferred the remaining parts over. The needle looks flawless but maybe the seat is damaged and that's causing the flooding. Is the seat replaceable?

I find working with these ancient WD carbs so frustrating as every time I touch something it just breaks and finding parts is getting harder and harder. How feasible is it to convert the 299 cc to a mikuni or other?

[thekingofclubs]

Some good news,

I spent some time swapping plates from my spare parts bin and new gaskets and finally found a combination that stopped the leak.

But now I still have fuel drizzling down the impulse tube at idle. I'm thinking there is still more leaking going on in the pump stack, even though the diaphragm is in mint shape. Would a worn needle valve/seat cause it to flood down the impulse tube?

[400brian]

My first thought is that if you have fuel going down the pulse line, then your diaphragm is leaking.

[klonteig]

This attachment was in a post a month or two ago and I saved it for reference. VERY useful to have on hand.
I'm no carb expert, but if you are getting a lot of fuel returned down the vapour line, you're pumping lots and if you need to choke it to keep it running, the fuel is not entering the carb, just being returned. Choked it has enough vacuum to draw fuel and run. So would seem the problem would most likely be in the "upper" part of the carb (needle/seat, metering lever, or idle/power needle). That's just from reading the diagrams, though. I haven't had enough of these apart to speak knowledgeably about it...

Edit: Guess I can't attach .pdf's - here's the link to the post:
http://www.jdsleds.com/community/viewto ... ts#p131000