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DCOE Backfiring


Guest Anonymous

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Guest Anonymous

I just installed a single sidedraft 45 DCOE carburetor into a 1976 BMW 2002. The car runs but has a few problems. When I start the car cold it runs at a very low idle as it warms up the idle speed raises but it is not consistant. It runs any where from 400 to 1200 rpms at idle. The other problem that I am having is that the car backfires through the carburetor a lot. Whenever there is a load on the engine, when it is going up a hill for example, the car backfires several times through the carburetor. Another problem that I have is a white smoke that rises from the engine. It has been happening for about a week and it rises from the header's side of the engine. It smells like oil burning. I dont know if it helps but my compression is fine. I tested it and all of the cylinders tested around 130.

I would appreciate any help you can give me.

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Guest Anonymous

Backfire through the carb sounds like timing issue. Oil smoke sounds like exhaust stud issue. Did the car do either of these things prior to dcoe install?

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Guest Anonymous

Where did the carb come from? Is it new or used? I had a similar problem with back-firing with a duel '45set-up(Carbs were used but I rebuitlt them) and it turned out that the return tension thet the p.o. of the carbs ran was too strong and had bent the throttle rods inside the carbs slightly. I spent quite a bit of money and time on them before I found this out trying various things to fix it. Unfortunately I couldn't find anywhere I could buy just the throttle rods and ended up having to buy 2 more carbs. I would try doing all the free stuff first(check timing, ignition system, etc.) before spending any money then, if it's an older carb you might want to pull it apart and check it out. Mine were hardly noticably bent but it was enough to completely screw up the way it ran. It might be worth looking into.

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Guest Anonymous

I know that the car did backfire before I did install the carburetor. It did it so much so that the car would not run. I am not sure whether it made the smoke before i installed the new carb.

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Guest Anonymous

I have to weigh in on this one, given all of the Chris' involved. The

other major factor that causes backfiring/spitting out of the carb

is an excessively lean condition. This could be caused by an

intake system leak. I presume you used new gaskets with the new

intake manifold and carb. Are you using a softmount gasket for

the DCOE? This is easy to screw up if you have it too loose or too

tight.

It is also vaguely possible that you have an obscure problem like a

rocker on an intake valve cranked down too tight, not allowing it

to close all of the way.

Chris B.

'73 ex-Malaga (Single DCOE 45 )

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Guest Anonymous

Do an Internet search for "weber lean best idle" and you will find a

wealth of material describing the procedure.

The first order of business is making sure you have the right idle

jets. What size chokes do you have and what size idle jets are you

using?

Chris B.

'73 ex-Malaga

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Guest Anonymous

Sounds like your idle jets are weak. Try changing the jets to a richer air bleed i.e. f9. Sounds like your progression circuit is becoming too lean when going from idle to starting on main jet. Mine have done that and I took care of it going from f8's to f9's. With a single weber(dual ok) you'll need to jet richer since most carbs out of the box come with 45 or 50 f8's idle jets. Also I would have intermittent backfiring and messing with the emulsion tubes have changed that but that gets expensive. Cold dcoe's always have crappy idle. I pump mine about 4-5 times b4 starting and then I'll have to throttle them until temp goes up. I do not use the choke.

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Guest Anonymous

Your oil burning smell could be exhaust stud leaking or valve cover gasket leaking. If you have fresh clean oil you'll have to look close for the oil leak with engine running.

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Guest Anonymous

It's got to be ignition related, probably wires or a cracked cap, I would do a complete ignition tune up and retime it

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Guest Anonymous

I bought the carb from Top End Performance. I have talked to them and they say it is properly jetted. So I am assuming that they got it right.

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Guest Anonymous

...... MIN. . Back firing before and aftercarb change...., low compression...... - have you:

checked valve clearance ?

cam timing ?

ignition timing with a timing light ?

cylinder leak test ? .

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