I've got a Holley 390cfm carb on my 84 300. Does anyone know what size stock primary jets are in those carbs?


Thanks

 

They are 50 or 51's!

 

Is there a way that I can tell what size mine is? I am thinking about putting a size or two smaller in my truck as I think it is running a little rich. I can see black soot on the exhaust.

 

They should be stamped on them. If you believe it is running rich I would rebuild it. You have to pull the float bowl off to replace jets so you might as well spend the 20 or so bucks for a rebuild kit. This will give you a new float and power valve. Also make sure your choke is shutting completely off. If the carb is stock specs their is another problem causing it to run rich. Just changing jets may be a temporary fix but I recomend a rebuild with the factory jets before just swapping pieces and parts to see what works.

T. Roberts
UFD Local 1147

 

Be advised that the jets in the older style Holley carbs (the 4150 and 4160) only control fuel flow at at or near WOT. The float level idle mixture setting and the fixed metering air bleeds control off idle and mid range fuel flow. So don't expect the jet change to do much for your mph.

 

The Carb is brand new.

 

Even if it is brand new carb,it is a 4150 or more likely a 4160(no rear metering block). Go to the Holley site and they have a listing of all the carbs they have made and are making and what jets and other parts are in them. Still, jet changes won't really help the mid-range gas mileage.

 

Oh yeah, that carb comes with 50 main jets. I've got sets of jets 45's thru 102's for my tinkering, but again the jets only limit fuel flow at or near WOT. You might try changing the power valve to a lower number or try a duel stage power valve. They are expensive but do help trucks get better fuel economy with out losing top end power. If you put a duel stage power valve in or if your carb is not equipped with one install a power valve backfire protection valve.

 

Ok, thanks for all the replies. When I installed my carb, I checked the floats, and they looked good. Perhaps I need to look at the Power Valve some.