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I have a1990 excel and it runs very rich, the previous owner had new jets fitted to get rid of a flat spot. However I would like to refit the old original jets to help get rid of the smell and get the engine running correctly. Will I have to reset and adjust the mixture afterwards, or can I just swap the jets ? Any advise on carbs would be welcome

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You will almost certainly need to adjust the mixture.   I chop & change between 40 & 42 idle jets, the difference between the two is one full turn of the mixture screws for similar levels of CO2 (at idle).   I would go back to the standard jets and report back what misfire problems you are having.   Worth also checking your float heights are spot on

Edited by 910Esprit

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On my 1992 Excel SE I've had the idle jets increased from 55 to 58, to remove slight hesitation ~ 2,800 RPM.

This appears to be somewhat 'standard paractice' on late model SE Excels. The later cars had emmissions control equipement that allowed the engine to just about meet the legal requirements without going over to fuel injection. However, as the engine wears etc a mild flat spot can occur around 2,800 rpm.

I've used Des Hammill's "How To Build & Power Tune Weber & Dellorto DCOE, DCO/SP & DHLA Carburettors ". Excellent book. Tells you everything you need to know about carbs.

Tony

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Hi,

 

thanks, yes mine are the same 55 to 58, but it does run too rich and it smells and will be a problem at the MOT. I have also bought that book it seems excellent, but the bit I worry about is actually changing things for the worst and damaging the engine by going too learn , do people use stuff like colourtune to check the idle mixture,  I may just change the jets and sniff .

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Colortune works great for setting the idle mixture, very accurate & reliable. I doubt you'll get it through the MOT by smell

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