dtskds

This carb we have rebuilt and now it is running really rich. I have checked for a vacuum leak but haven’t been able to find one. I have tried almost everything I can think of. The secondary vacuum diaphragm hasn’t been replaced and I am running .060 jets. I am thinking about unhooking the secondary all together and see if that works and moving to a .041 jet. This is running on a 289 and if anyone can offer any ideas they would be appreciated.

trashline

How do you know it is running rich?

I would start by adjusting float levels, so that fuel just trickles out of the site plug area with a slight bump of the car. then set idle and A/F ratio needles. 1 3/4 turn out from snug is a good place to start. Spray some starting fluid around possible vacuum leaks, the motor will rev if you find one. If the carb ran fine before rebuilding then I wouldnt change jets or any other parts.

You also need to check the needle and seat If the carb sat for a while and didnt change those parts they tend to crap out, it will allow fuel to bleed past them.

dtskds

When it is running at idle there is a lot of black smoke. We have adjusted the float levels and I sprayed starter fluid all over the carb and intake with no change in RPM's. We haven't checked on the needle but plan on doing that tonight.

67mustang302

Where are the idle screws at, what's the idle timing, what rpm is the idle speed at? Don't start disabling the secondaries and making radical jet changes. If you go from a 60 to a 41 jet the car won't even run. Besides, main jets aren't going to do anything to the idle. Is the carb the same one you were using before it was rebuilt? Is the power valve the right size? Is the power valve seated properly with a gasket and not leaking into the vacuum chamber?

dtskds

No this isn't the same carb, I am going from a 2brl to the 4. I am going to have to agree after some reading I saw that the jets have nothing to do with idle. We are going to take the carb off and go through it and make sure eveything is adjusted right.

urban_cowboy

What happens when you tighten the idle screws all the way down?

What happens when they are open just a half turn?

Have you try spraying carb cleaner into the air bleed ports to blow out any dust?

You may try cleaning the air bleed ports on the top of the carb body. If the low circuit air bleed is blocked, you will not get air into the idle circuit which could cause an excessive rich condition at idle.

Also on a four barrel carb, you have to set the idle speed using the front and back throttle plates on some engines. Be sure your transfer slot is not exposed more than .040 front and back. The more transfer slot that is open, the more idle fuel will flow regardless of the idle screws (the transfer slot bypasses the screws).

cprstreetmachines

Sounds your on to something there for sure. That'll tell you if you have an internal fuel leak.