Background info: freshly rebuilt 350 (stock specs), Edelbrock intake, Holley 470cfm Truck Avenger, Proform HEI distributor, 9-degrees initial advance, 22" vacuum at idle with a dead-steady needle. Mechanical fuel pump with no return line. Fires right up and purrs like a kitten, but is VERY VERY VERY rich...

I've been fighting what appears to be an over-rich condition, resulting in nasty black stuff shooting out of my exhaust pipes and staining the ground wherever it happens to be idling at the time :mad3: The carb has gone back to Holley and bench verified to be in perfect working order, and I've got the floats set per the Holley instructions. Runs great overall, just waaaaaay rich at idle. My thoughts are to try and plumb in a return line, as I'm thinking the fuel pressure may be too high causing the rich condition (no pressure gauge ot verify, just a theory). I know a return loop will also help with vapor locking, so its a good idea anyways. What is the simplest way to plumb one in? Can I use a different mechanical pump, the ones that have 3 nipples? Or should I use a 'T' fitting somewhere after the pump and before the filter/carb? Or, can I just use a filter from a late-70's Jeep that has the dual outlets? Any input here would be appreciated!!

try the idle mixture screw, my old carb had the same problem.

Forgot to mention that... Mixture screw is only about 1/8 turn out from completely seated, so that's not the issue either.

hollys are rev. set, that could be why it is rich. try treading it out.

Hmmmm, according to the Truck Avenger manual, if you have to mess with the mixture screws (they tell you not to, of course), they tell you to twist it in until you stop gaining vacuum (or idle speed if you don't have a vacuum gauge). I screw it all the way in, and I'm still gaining vacuum and idle speed, and it still runs. That's why I initally thought the carb was bad, because shouldn't it die if the mixture screw is all the way seated? I was thinking it was pulling air from somewhere else internally, but they say it's just fine... So, I left it set about 1/8 of a turn out.

hope you get it fixed. good luck.

Thanks... Any ideas on the return line I'm thinking of?

Have you checked your choke settings? It could be that the choke isn't coming off completely and that is why you are running over rich.
As far as the carb idle mixture screws, if you turn them all the way in it should just about damn near kill the motor.
Also, depending on your altitude, you could be running too rich due to elevation.
Holley TA carbs are jetted and flow bench tested to run at sea level.
So saying you might need to rejet your carb to compensate. There is a guide in the back of your manual that tells what jets to use at a specific elevation.

I live at only about 600ft elevation, so I know that's not the issue :(

As for the choke settings, other than it idling down with a throttle blip, how can I verify this?

Could be a bunch of stuff but you need to adjustment the idle mixture, they don't come set from the factory for EVERY engine. Just theirs.

Could be a bunch of stuff but you need to adjustment the idle mixture, they don't come set from the factory for EVERY engine. Just theirs.

True statement and point well taken. That being said, I've already adjusted the mixture screws and set the floats per the Holley instructions, and I'm still seeing the evidence of a very rich condition. I'm *thinking* my fuel pump pressure is overcoming the needle/seat, which is why I'm thinking about a return line...

So, back on topic, how can I easily plumb one in?

Borrow or rent a guage and verify that is the problem before spending any more $ on it.

If you are thinking return line from the fuel pump would help, that means fuel pressure is to high for the needle and seat then putting too much fuel into the carb and being rich, in the old days they didnt even have a return line from the pump and they all ran Holleys, if you had a needle and seat problem the bowls would be getting full and fuel would be coming out of the vent, maybe front maybe rear, you need to see if the carb is dripping out the venturies by looking down into while running with a flashight, sounds to me like you have a blown power valve or possibly even maybe a reverse idle carb which makes the idle adjustment screws backwards

is it only rich at idle?
does it bog or seem sluggish when you mash the pedal from a stand still?bog =rich,pop = lean
where is the fuel level in the sights when its idleing?should be in the middle.
what jets are in it?
what power valve?-all new holleys in the last eon have blow out protection.
is your idle speed screw screwed in to far? if its too far it will be using the main jet circut and not the idle circut.

is it only rich at idle?
does it bog or seem sluggish when you mash the pedal from a stand still?bog =rich,pop = lean
where is the fuel level in the sights when its idleing?should be in the middle.
what jets are in it?
what power valve?-all new holleys in the last eon have blow out protection.
is your idle speed screw screwed in to far? if its too far it will be using the main jet circut and not the idle circut.

Idle is really the only time I can *tell* that it's rich, other than horrid economy overall. But I'm writing most of that off as the nature of the beast...

No bogging or popping when I mash the pedal whatsoever. It does hesitate briefly just a bit, almost like it cuts out, but it recovers quickly and gets it on.

Per the Holley instructions, at idle the fuel level is at the bottom of the sites.

Jets and power valve are the ones that came in the carb, I have not touched either of these.

The idle speed screw was adjusted enough to get me to roughly 700RPM idle speed, which didn't take much...

Dude thats simple to check for. Haven't you set the floats?? If that's the case they would be unsettable and you couldn't keep the float bowls from overfilling.

But then again it's a truck avenger and they don't operate like a standard holley, the floats aren't as adjustable (I think) as a standard holley.

It's a lot to read but follow these directions and you will achieve holley nirvana :smokin:

http://www.bob2000.com/carb.htm

Dude thats simple to check for. Haven't you set the floats?? If that's the case they would be unsettable and you couldn't keep the float bowls from overfilling.


After I typed that I seen you did check the floats and they are perfect, so no you don't have a problem of high fuel pressure at idle.

Floods can come from a bad power valve and theres a check ball underneath the accelerator pump squirter and if it's missing it will cause a rich condition. I think that link in the last post covers all that, Ive read that entire thing and it's 100% true and correct.