All Small Six Running Rich

[Maverick57]

Recently bought a 74 Maverick with a 200. Previous owner replaced the carburetor because they didn’t feel comfortable rebuilding the original one. It’s a Carter YFA 7346. Upon purchasing the car we noticed the idle was way too high, so once we got it home I got the idle down to 700-750RPM and realized I could screw the mixture screw all the way in and the engine would still run. In fact it ran best with it all the way “closed”. I got out my vacuum gauge and timing light, and no matter what I did the best I could get was 15-16in of vacuum at best and was still pig rich. After checking for vacuum leaks I’m starting to suspect the main jet is too big. Any ideas?

Update: I measured the main jet and it is .11”

What I’ve done so far.
New carb gaskets
New needle and seat
Set metering rod
Set float
Set timing
New plugs
New cap and rotor
New points and condenser

 

[awasson]

I’m not familiar with the Carter YFA 7346. Does it not have idle or slow speed jets that work with the idle/air mixture screw?

 

[Maverick57]

Yes it has a slow speed tube that’s being fed by the main jet.

 

[Maverick57]

I’m not familiar with the Carter YFA 7346. Does it not have idle or slow speed jets that work with the idle/air mixture screw?

Yes it has a slow speed tube that’s being fed by the main jet.

 

[awasson]

I wonder if you’re right and it’s the main jet. Could be a faulty power valve too. When you screw the air/fuel mixture screw in, you should have been able to lean it right out as long as the choke was disengaged and the butterfly closes properly.

 

[Maverick57]

I wonder if you’re right and it’s the main jet. Could be a faulty power valve too. When you screw the air/fuel mixture screw in, you should have been able to lean it right out as long as the choke was disengaged and the butterfly closes properly.

Very true, the low speed tube only comes in 1 size (17-20) which makes me even more suspect of the main instead of swapping the tube. The main jet is currently a .110” which to my understanding is the biggest jet made for a YF-YFA without drilling it out.

 

[B RON CO]

Hi, since the carb was installed on the big 300 engines, I would go with either the original jet or a little smaller. Are you following the service manual for the metering rod adjustment? Good luck

 

[DON]

Make sure the butterfly valve isn’t open too far. That will render the idle screw nonfunctional