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12j overfuelling - any thoughts?


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Having a few probs setting up a 12j n/a engine, cant stop the thing chucking out lots of black smoke on anything over a light throttle - it does clear at high revs.

The engine is a recon unit, new oil, new timing belt.

It starts very well, plenty of power and runs sweet, but leaves a smokescreen behind.

I've set the timing and tried advance/retard, and adjusted the fuel screw out a couple of turns.

New air filter, checked for blocks in the airway.

The fuel injection pump came from an older engine - can these wear causing over fueling?

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Mine's a 200 but I had the same problems which I chased for over a year: hard acceleration would leave a swirling corkscrew cloud behind me.

I went through the lot, changed fuel filter, no use, changed air filter, no, still smoking like mad, serviced injectors, not any better. Finally changed fuel, to the more expensive BP premium type and I now have a clean burning engine with a lot less smoke. It runs a bit hotter though, well certainly warms up faster, but I guess the fiercer burn of the higher quality fuel is giving a more complete combustion of fuel so rather than chucking it out the back as smoke its all converted into energy.

Apart from a trial of some more expensive diesel I've no other suggestions! But I'm sure an expert will be along at some point!

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I'm no expert here but perhaps the injector pump needs re-calibrating, advancing/retarding will have no effect on fuel volume delivery it just alters the timing slightly and too far retarded will make the engine harder to start, too far advanced will cause the engine to misfire. An oily air intake system will greatly contribute to chucking out smoke, especially black smoke, take a look at the inside of the air hoses to see how much of a sticky oily coating there is and check out the intercooler, this will also contribute to the problem if it's holding oil..

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It's all as clean as a whistle, so no oil contamination getting in. It's not so bad with engine running stationary, but while driving under any load on anything over light throttle it smokes like billyo till revs are over about 2600 then clears. Someone has tampered with the throttle stops on the pump (removed!), though not the fuel screw as it still had the anti tamper cap on (I've adjusted that out a couple of turns but zero effect on anything).

It starts and runs like a dream, so I'm thinking there's just a bit too much fuel going in rather than an injector problem.

Things still to try are a change of fuel and possibly another oil change as the wrong or old oil can make these smoke as well.

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What about the injectors themselves, have they been changed for ones with larger nozzle holes perhaps? Injectors delivering too much fuel often manifests itself by lots of white smoke which is un-burnt fuel so in this case probably not. I expect there's a quite simple answer but it's just finding it!.

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If it's fitted with MOD parts perhaps it's supposed to smoke, something to do with the following enemy not being able to see you to get a clear target perhaps?

On a more serious note though, I'm leaning back towards it being that perhaps the injector pump is delivering a bit too much fuel and needs re-calibrating or metering rather than cutting it down on the screw.

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Double check the tappet clearances and the timing sprockets (front cover off) to make sure the valves are opening the correct amount and at the correct time - a tooth out on the cam shaft could cause such problems. Black smoke is usually indicative of airflow restrictions, over-fuelling (unlikely if the settings are returned to standard), advanced fuel timing (unlikely if the engine starts easily) or a bad spray pattern from dirty or mal-adjusted injectors.

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