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

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?

Today's progress:

Morning start was tricky and when it finally starts it stumbles a lot, but after warming up it became better. When driving there was quite some moderate jerking. I loosened the idle-mix screw about 1/2 turn, fiddled with the primary slow jet plug but finally re-seating it gently.

Afternoon start up was no problem (left the car for about 5 hours). Jerking was slightly less, idle was smooth, and no more black smoke.

Evening start up no problem (left it for another 4 hours+). Loosened the screw 1 1/2 turn, jerking had significantly reduced, idle was smooth and no black smoke.

If it's dirty inside then why was it running perfectly fine before me and my friend messed around with the idle-mix screw and primary slow jet plug? I'm pretty sure disturbing the screws is what's causing the engine to misbehave...

Btw, what exactly does the primary slow jet plug do, and if I loosen it what exactly happens inside the carb?

Thank you ddgonzal for clarifying. Today after work I tried adjusting the idle-mix and primary slow jet plug, and I managed to get the engine back to its original state (idling, accelerating, everything). I even did a short test drive to be sure, and it still ran fine. About 200m later driving back home the idle became weak again but driving it was normal. Just before I reached home it died on me, had trouble starting, and even if it did start it would die off again.

*Update* I finger tightened the primary slow jet plug (oddly, loosening it kills the engine now) and loosened the idle mix screw quite a bit (I think it's now about 4-5 turns out from bottom, is that a lot?) and the engine is sort of stable. Idle is much better than this evening but still not as smooth as originally. It hesitates/jerks a little bit when accelerating sometimes.

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Thanks for your input. So the pilot screw is supposed to be fully seated in then? I understand that this screw controls the amount of air-fuel mixture going into the engine. So by loosening the screw, am I increasing or decreasing that amount?

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I did adjust it previously (rough idle SOMETIMES, with aircond and lights on) but then my consumption worsened. After calling my dad, and as you said, I turned back out the air-fuel mixture screw (now at about 3 1/4 turns) to make a bit richer. The stalling is now gone.


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As I said, when screwed fully in the engine dies off instantly. Just a quarter of a turn out and it runs fine.

Greetings to all members here. I am new and I joined to ask you guys about a problem I have. I drive a B310/120Y handed over from my dad.

I was tinkering with the air-mix and idle screws to reduce my fuel consumption (it increased after adjusting it previously). This afternoon, I encountered the following problems:

1) Once warmed up, it idles normal. When driving and coming to a stop, the engine dies. I do feel it hesitates slightly sometimes, but maybe it's just the rough road where I test drove it. Fixed!

2) When pressing very slightly on the accelerator pedal, the engine stumbles. Pressing more on the pedal makes it OK again, and sometimes when letting off the pedal it dies. Loosening the idle-mix screw solved it

NEW! 3) I have a bit of black smoke from the exhaust. The choke plate is opened and my idle-mix screw (if it is related to the problem) is about 2 1/4 turns out from fully seated.

4) Previously the engine would idle with a stable *dud-dud-dud-dud-dud-dud-dud* sound. After all this 'screwing' around it has become a slow and sloppy *plop-plop, plop-plop-plop-plop-plop, plop-plop-plop*. Turning in the idle-stop screw doesnt help much. Yes the idle rpm goes up but the plop-plop-plop remains

I found that the third circled screw would kill the engine if turned all the way in, and has a sweet spot about 1/4 turn out.

I'm sure you guys with decades of experience can shed some light on this matter. Thanks!

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