Greetings Datto owners,

I have a B310-120Y with the A12 engine, using the stock DCG306 carburettor. A year ago I bought a donor car, exact same model, engine and everything to cannibalize the door due to an accident I had. When taking delivery of the car it ran normally.

Recently I removed the donor carb and tried fitting it on my own engine to see if it would work. The engine wouldnt start and later we found petrol leaking out from the flange where it meets the intake manifold. A look inside and moving the auxillary valve via the counter weight saw petrol PUDDLING inside the secondary barrel.

Took out the donor carb, soaked up the petrol in the manifold, reinstalled the original one, everything was back to normal. I tried Google and some results suggested it could be an out of adjustment float or dirty needle valve causing the level in the chamber to be too high. Anybody experienced this before?

The needle and seat is probably dirty. It works like this, the fuel lifts up the float, which pushes on the needle and stops the flow of fuel until some drains out (i.e. is used by the engine). If the needle and seat does not seal it'll fill till it overflows.

it can be cleaned using a brush and petrol right? I dont have any compressed air.

the needle can simply be wiped clean with your finger. The seat for the needle requires something smaller. you might invest $2 for carburetor cleaner in a pressurised can. that way you don't need air to blow out the passages etc. If the float is touching the side of the float bowl the carb will flood. Plastic floats dissolve in gas containing ethanol. Metal floats develop tiny leaks, fill with gas and sink but they resist ethanol fuel better than the plastic ones. I'd put a new float in the carb. as they are not expensive and it may help. Be sure to adjust it so thefuel level is in the middle of the little float bowl window.

alright, I'll give it a look when I'm free. Are there any other possible causes besides the needle and float?

Electric fuel pumps can cause it. Carburetors like around 3.5 psi, and many pumps exceed that.

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Mine isnt electric. And even if I did have an electric pump my original carb would be overflowing too because both carbs are the same model

If one carb floods and the other does not flood then everything but carburetor trouble is eliminated.
The throttle body, and passages can not cause this sort of trouble ( not unless there is a crack in the float bowl) so all that is left is the float and the float valve.

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gonna have DIY time then (I have two soft copies of repair manuals) . thanks dennis!

I've inspected the carb and I found the following:

1) The needle valve is squeaky clean
2) There's residue at the bottom of the chamber (presumed normal?)
3) When I gave the top cover a few taps, sand/dirt/grit poured out from the fuel inlet pipe
4) The float level was too high (about 6mm clearance at the top compared to the 12mm specs) but was later adjusted.

Could #4 be the cause of it?

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