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Carb tuning...please help.

  • Thread starter Thread starter vipergts
  • Start date Start date
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vipergts

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Had my car set up a a month ago and it was running beautifully....never better.

It has however slowly been deteriorating in so much as the idle speed has become so low it almost stall and the mixture smells very rich at tick over too.

So I think it's mixture is too rich causing it to almost stall.

My carb is a Holley and need to know how to adjust. The pictures below show my carb. Question is the little brass screw nearest the vacume is I believe the low running mixture setting (?) (second pic)

Do I turn it in (both sides) or am I missing something.

Any help would be gratefully received.

Thanks Chaps

vetcarb001.jpg


vetcarb002.jpg
 
The two tiny brass screws on the primary metering block (one on each side) are indeed the idle mixture adjustment screws. Connect a vacuum gauge to a full manifold vacuum source and adjust the screws to achieve the highest steady vacuum reading, working back and forth between the two screws. Re-adjust the idle speed screw on the driver's side (U.S.) linkage as necessary. :)
 
Thanks John.

If I haven't got a vacuum guage can I do it by ear. i.e engine revs rise?
 
A vacuum gauge is a primary tuning tool, and they're cheap - I'd get one. In the meantime, a secondary method is to adjust for highest steady idle, but that's not as reliable.

:beer
 
I agree. If you are going to have a carburator you need a vacuum guage. It's as basic to your tool bax as a hammer.

In the meantime you can get close by turning each screw in clockwise until it seats (lightly). Then back them out 1 1/4-1 1/2 turns. That will give you a good starting point. With the engine warmed to operating temp and idle adjusted to specs, slowly turn the srews out one at a time and listen for rpm increase. If you don't get any turn it in past the start point until the rpm drops and then back out to maximum rpm again. When you get maximum rpm turn the screw back in just a little until you hear the rpm just barely start to drop. This will get you very close and will make for good drivability. You want it right on the edge of where the rpm starts to drop. Alternate from side to side until you can't tell any improvement. You will probably have to reajust the idle during this proceedure to keep it to specs.

Before you adjust for effect you may want to just turn the screws in and out, with the engine running, to change the mix just to get a feel for what you are doing. It will become clear what the screw does right away.
 

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