Webers Set Too Rich?

[virden]

I have recently acquired a 1996, factory built S3 1700 Super Sprint. The car is very low milage, is in excellent condition and original specification. It goes very well with expected performance, but on anything bar full throttle it back fires and blows back through the carbs(twin 40 DCOEs) When I stop as well as giving off a very strong smell of petrol, both air filters drip what looks like a mixture of black oil and petrol.

 

Are the carbs set up too rich? ☹️

[Nick Chan]

Virden,

 

Webers generate "stand off" where they create a mist of fuel outside their trumpets when on full throttle and this could easily be the reason for the strong smell of fuel. I think a session on a rolling road would be useful or use the spark plug colour to determine whether the fuelling is too rich or not. I put my Xflow Sprint on a RR and it transformed the car and I had built the car from new and had it checked/setup by a Caterham dealer a little while before.

 

Nick

 

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Back in a BEC!

[virden]

Thanks Nick.

Plugs look good, but RR is a sensible suggestion, as it should show up any probs with the timing. My I have been putting off doing it because the nearest RR is some 100 miles away!

[Molecular--Bob]

Might be a timing issue as well. Mine did this when i got it and it turned out to be a loose distributor clamp that had allowed the timing to slip.

[oilyhands]

Stand-off and spit back are different phenomena and have different causes.

 

Stand off will wet the filters and make the engine growl a little and pickup will be slow, spit back is usually caused by lean fuelling or retarded timing.

 

Oily

[stevefoster]

Agree. Spitting is too lean. Check the carb balance too.

Other good things to check (perhaps not part of your problems) - are the jets in tight enough? - not too tight (only into ali) but not rattling around. Do the brass just cover top hats have a working air tight gasket?

Are the carbs able to float on the rubber or spring mountings - they don't like engine vibration. Is the 'O' ring plate doing it's job.

Timing at 12-14 deg advance (from memory - please check).

 

 

Add lightness, says the man with a VX :-)

My 2002/2003 racing pics

here

General pics (mostly of 7's and cars).

here

 

[virden]

Thanks Steve. The car has done less than 10,000 miles and spent long periods in storage so I guess it is possible that gaskets have shrunk.

Lot sto look at .

Thanks guys