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No Fuel / vapor return line, engine running very rich #2567982
10/22/18 08:07 PM
10/22/18 08:07 PM
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clarks summit pa
73cuda340 Offline OP
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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.


1973 Cuda 528 all aluminum Hemi, 4 speed, 3.23 Sure-Grip, (JA5) Silver Frost Metallic 1973 Challenger Rallye 340 1985 W150 Power Ram prospector 1986 Camaro IROC-Z 305 tpi
Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2568366
10/23/18 02:26 PM
10/23/18 02:26 PM
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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.

Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2568386
10/23/18 03:06 PM
10/23/18 03:06 PM
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71rm23 Offline
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Power valve

Re: No Fuel / vapor return line, engine running very rich [Re: BcudaChris] #2568547
10/23/18 08:17 PM
10/23/18 08:17 PM
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clarks summit pa
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Originally Posted By BcudaChris
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.


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.


1973 Cuda 528 all aluminum Hemi, 4 speed, 3.23 Sure-Grip, (JA5) Silver Frost Metallic 1973 Challenger Rallye 340 1985 W150 Power Ram prospector 1986 Camaro IROC-Z 305 tpi
Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2568555
10/23/18 08:47 PM
10/23/18 08:47 PM
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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.

Re: No Fuel / vapor return line, engine running very rich [Re: tman] #2568565
10/23/18 08:59 PM
10/23/18 08:59 PM
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clarks summit pa
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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.


1973 Cuda 528 all aluminum Hemi, 4 speed, 3.23 Sure-Grip, (JA5) Silver Frost Metallic 1973 Challenger Rallye 340 1985 W150 Power Ram prospector 1986 Camaro IROC-Z 305 tpi
Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2568569
10/23/18 09:14 PM
10/23/18 09:14 PM
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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

Last edited by yella71; 10/23/18 09:16 PM.

71 challenger convertable, 64 sport fury 383 ci with factory air 99 sebring convertable 89 CTD pup
Re: No Fuel / vapor return line, engine running very rich [Re: yella71] #2568576
10/23/18 09:27 PM
10/23/18 09:27 PM
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clarks summit pa
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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.


1973 Cuda 528 all aluminum Hemi, 4 speed, 3.23 Sure-Grip, (JA5) Silver Frost Metallic 1973 Challenger Rallye 340 1985 W150 Power Ram prospector 1986 Camaro IROC-Z 305 tpi
Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2568581
10/23/18 09:42 PM
10/23/18 09:42 PM
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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.

Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2568727
10/24/18 06:15 AM
10/24/18 06:15 AM
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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

Last edited by tman; 10/24/18 06:25 AM.
Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2568729
10/24/18 07:00 AM
10/24/18 07:00 AM
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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?

Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2569007
10/24/18 05:43 PM
10/24/18 05:43 PM
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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.

Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2569097
10/24/18 08:40 PM
10/24/18 08:40 PM
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Again, power valve?????????

Re: No Fuel / vapor return line, engine running very rich [Re: 71rm23] #2569168
10/24/18 11:28 PM
10/24/18 11:28 PM
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Originally Posted By 71rm23
Again, power valve?????????


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

Re: No Fuel / vapor return line, engine running very rich [Re: Challenger 1] #2569175
10/24/18 11:43 PM
10/24/18 11:43 PM
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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.

Re: No Fuel / vapor return line, engine running very rich [Re: Challenger 1] #2569176
10/24/18 11:44 PM
10/24/18 11:44 PM
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Originally Posted By Challenger 1
Originally Posted By 71rm23
Again, power valve?????????


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


Well, sorry Challenger1 or anyone. Just a suggestion

Last edited by 71rm23; 10/24/18 11:44 PM.
Re: No Fuel / vapor return line, engine running very rich [Re: 71rm23] #2569198
10/25/18 12:58 AM
10/25/18 12:58 AM
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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.


1973 Cuda 528 all aluminum Hemi, 4 speed, 3.23 Sure-Grip, (JA5) Silver Frost Metallic 1973 Challenger Rallye 340 1985 W150 Power Ram prospector 1986 Camaro IROC-Z 305 tpi
Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2569238
10/25/18 06:54 AM
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Re: No Fuel / vapor return line, engine running very rich [Re: 73cuda340] #2569359
10/25/18 01:58 PM
10/25/18 01:58 PM
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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.

Re: No Fuel / vapor return line, engine running very rich [Re: tman] #2569485
10/25/18 06:58 PM
10/25/18 06:58 PM
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Originally Posted By tman


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


1973 Cuda 528 all aluminum Hemi, 4 speed, 3.23 Sure-Grip, (JA5) Silver Frost Metallic 1973 Challenger Rallye 340 1985 W150 Power Ram prospector 1986 Camaro IROC-Z 305 tpi






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