No Fuel / vapor return line, engine running very rich

Is it possible that by not having a fuel return line installed on a carburetor equipped car, the motor would run excessively rich? I don't see how it would be possible, but i just read this recently. The reason that I'm asking is because my motor in my car is running extremely rich and I have taken everything apart and cleaned everything up in both carburetors numerous times and nothing seems to fix the issue. The motor is a brand new 528 hemi with two edelbrock 600's on it. I have a fuel pressure regulator installed and set it at 5 psi, so there's not too much pressure pushing past the needle and seat. I installed the lightest step up springs in the carburetors to help hold down the metering rods at idle. I don't have any vapor locking issues. I'm at a loss at this point of what the problem is and that's why I was even considering this as a possibility. I don't see how this would fix it, but I'm willing to try adding one at this point.

Sounds like you have a dead-head regulator, so shouldn't need a return line. If your tank isn't vented though (your title and post seem to contradict a bit describing a vapor return line and a fuel return line) that can cause problems.

Your car should have a tank with 4 vent tubes on the front, a little 4 tube vapor separator and a 1/4" line running from said separator to the charcoal canister. I am assuming you mean this line by "vapor return line". If this line is plugged, it may cause what you describe.

If you put in a 3/8" or bigger fuel pickup, you'll have a return port on the sender. In my case, I ran a new 3/8" fuel line and used the existing 5/16" line as a fuel return line. I have my vent line connected in the factory manner.

Basically, if the tank vent line is connected and venting properly, I think you can rule this scenario out in your troubleshooting.

Power valve

The regulator that I have is a Holley HP Billet 12-840. It only has an inlet and two outlets with one of the outlets plugged. I have the four vent tubes from the gas tank hooked up to the vapor separator and the line that went to the charcoal canister I have venting to the air since I removed the charcoal canister. I have a 1/2" fuel sending unit that has a return port on the sender that I just plugged since I don't have a fuel return line. Is there any issue with this being plugged? The car has edelbrocks so there is no power valve in the carburetors.

Can you jet it down? Is it rich at idle or under power? Trying to see how you confirmed its running rich. I don't see a return line being an issue. Only way to know is using an afr meter.

It's extremely rich the entire time that its running. It burns my eyes even standing next to it at idle in the garage and if I take it for a ride my clothes will smell like gas by the time I'm done driving it. The car is hard starting and loads up pretty bad when you first go to drive it. I bought a Innovate LM-2 meter to get the actual ratio that it's at; I just haven't gotten around to installing it yet. I never changed the jets since they are the same ones that were in it when the motor was set up on the dyno.

maby your floats are too high...have you gone through the carbs or are they right out of the box? Ive seen a few of those carbs need work brand new to make them right, Im guessing yours are some of those carbs

They claimed that they set the carburetors up when the motor was on the dyno. I've had nothing but issues with it since I bought it.

My '68 Hemi RR was also very rich, stock carbs but big cam (low vacuum signal), chassis dyno guy didn't tune it out although claiming he did...
Later on my racer-guru buddy changed the springs, needles & jets to what he was running in his Hemi Bee (which was more stock) and that cured it. Made more power, too.
Car had lost its separator before I bought it; I ran a Carter electric pump, 1/2" line, mech pump, regulator 6PSI, only the OEM tank vent line. No problems.

I too think you need to check floats. Not too bad of a job, many videos on how to do it. You will have starting and driveability issues with floats too high. This video is not bad and shows how to take top off:

https://www.youtube.com/watch?v=wR_AfQjyT-A

What intake do you have? Does it have the Vankie mod? What size jets and rods? Have you put a vacuum gauge on the intake to see what it reads, that will determine which springs to use. Do you have the Thunder, or Performer series carbs?

No your right it is not because you do not have a return line.

The guy who ran the motor after it was built did not tune it, he can't because it is not in the car under load and in the current weather conditions. He just made sure it ran and and did not leak oil or water. Dyno... is one of those comfort words.

Since you had the carbs apart to clean them, then you must know how to tune them? You got to make changes yourself to find out what is going on, we can't tell you from here.

I have had 2 cars stink to high heaven when idling and both were lean. Lean is what makes them really stink, not rich.


My gosh make some changes to the carbs before damaging your fresh motor. Lean will make it stubble and "load up" too.

Again, power valve?????????

Are we missing something? His carbs do not have power valves.

Recheck the float drop in both directions if you have not done so. Those carburetors are tossed together and out the door they go. Haven't seen one yet that was 100% ready to use.

Hard starting as in starter turns over slow, or as in carburetor is not functioning right? Slow starter speed = recheck the initial timing.

Well, sorry Challenger1 or anyone. Just a suggestion

I checked the float height and drop the last time that I had them apart and set them to edelbrocks recommendation. I guess that I could try lowering them a tiny bit more. The car has two 600 cfm performer series carbs. No vanke mod on the intake and I'm not sure what size jets or rods are in them. The vacuum at idle is very low, I want to say it was at 4 or 5" of vacuum at idle going off of memory. I installed the lightest springs that edelbrock makes for the metering rods. I'll try to get the lm 2 hooked up soon to get some air fuel ratios.

Do you have this tuning guide?

https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf

I used to run an old Carter AFB 625 that I upgraded to Ede calibrations at some point.

My experience was that the Ede float drop setting was good (I don't recall how it compared to the Carter setting) but the float level was slightly lower than the Carter setting, and I had to go another 1/16" lower than the Ede setting to get the mixture right.

Until I did that, it was pig rich from idle up to where it ran out of air at just under 6K on my home brew 302 head 318.

I have the tuning guide that came with the carburetors. I think it's the same one.