Running rich!

TKlauber · #1 (**permalink**) 12-17-2021, 06:38 PM

Hi all!
I built ERA 427 SC # 491 about 24 years ago. It has about 5000 miles on it. Pete had the 427 SO built locally there.
My single Holley 4160 has been running overly rich with gas dripping from venturis and flooding the plates and pooling into and out onto the medium rise intake. I have adjusted the floats and replaced the perishable components in the carb. The 6.5 Powervalve holds vacuum OK.
I did a pressure test of the fuel pump and came up with over 10 psi. My gauge goes up to 10. The fuel pump is a mechanical Carter 0-3000 that does not have an overflow nipple on the upper half.
I think this car has always run rich but otherwise runs well most of the time.
My solution is to put a pressure regulator on the fuel line between the pump and carb. What regulator would you use?
I would consider lowering the floats a little but am running out of threads on the fuel inlet using a thicker nylon washer on the 5/8 " hex nut.
I have not bent the tang on the float hanger.
Any thoughts?

patrickt · #2 (**permalink**) 12-17-2021, 06:47 PM

If you're really sure that the pressure is 10 psi, then replace the pump -- they're not that expensive and really easy to change out. I run in the upper 5 psi range. Your needle/seats are not built to hold 10 psi.

TKlauber · #3 (**permalink**) 12-17-2021, 07:05 PM

Thanks Patrick! I was wondering your thoughts on this. What mechanical pump would you go with?

patrickt · #4 (**permalink**) 12-17-2021, 07:14 PM

Quote:

Originally Posted by TKlauber

Thanks Patrick! I was wondering your thoughts on this. What mechanical pump would you go with?

Trusty old Carter. Less than a hundred bucks.
https://www.summitracing.com/parts/CRT-M6905

ZOERA-SC7XX · #5 (**permalink**) 12-17-2021, 07:42 PM

I'm on my 2nd fuel pump in sixteen years, a trusty and cheap NAPA unit (about thirty-five bucks).

TKlauber · #6 (**permalink**) 12-17-2021, 08:05 PM

Thanks guys! Gee that was easy. Merry Christmas!

Dominik · #7 (**permalink**) 12-17-2021, 10:17 PM

Your power valves (PV) may be blown. If your carb doesn't react to the enrichment screws on the sides, as in you turn them in and the car still runs, this could indicate my assumption. If you have the older version, the fuel runs our past near the base plate to housing screw and shows randomly all over the intake. Sometimes hours after you stop the engine.

That aside, fuel pressure or float level, or worn out needle/seats.
I suggest to replace them, check pressure and then mess with the PVs which requires opening the float bowls.

TKlauber · #8 (**permalink**) 12-18-2021, 06:23 AM

Thanks for your interest. The power valve held vacuum OK. Tom

patrickt · #9 (**permalink**) 12-18-2021, 09:10 AM

Replace the pump and see if all the problems magically go away. Check your fuel pressure -- something in the sixes is about as high as you can live with. If the richness problem is still there, order the Holley “Fast Kit” #37-1542 which has all of the gaskets, and other rebuilding parts, for the model 4160. When it comes, two of the needle and seats look like they are an exact match. One will be .110 and the other is .097 -- the instruction sheet will tell you that the .110 is the correct match for a needle and seat marked with an “H” on it (which is what you likely have). And put a dab of Vaseline on the black O-ring, that makes the needle/seat valve slip in to the bowl easier. Change the PV even if you think the one you've got is good. Set the float level “dry” so that, when inverted, the brass float is parallel to the bottom of the fuel bowl. IGNORE THE INSTRUCTIONS THAT SAY TO SET THE FUEL LEVEL TO THE BOTTOM OF THE SITE HOLE. With today's gas, and if your engine and carb tilts, you have to set it lower than that. Just set it as high as you can get it, and after each hot run pull the air filter off and see if you're dribbling out the boosters. Turn the floats down a hair at a time until the drips are gone, or pretty much gone. Then, if you are still experiencing richness issues, it is likely the "hot idle blues." There's an easy fix to that and we can walk you through it. But the first step in making a 4160 a wonderful carb is getting the parts not leaking and getting the floats set right. When tweaked properly, a 4160 is absolutely spectacular. Again, IGNORE THE INSTRUCTIONS THAT SAY TO SET THE FUEL LEVEL TO THE BOTTOM OF THE SITE HOLE. Just shoot to get it as close to that as possible without dribbling.

TKlauber · #10 (**permalink**) 12-18-2021, 06:37 PM

I went to Summit and ordered the pump which is backordered till Jan. 3 2022 so I have some time before it arrives. Winter is soon to hit here in SC so I will not be outside as much. I looked at NAPA and their main pump is not available for now. There is an Edelbrock that would work I guess but it is pricey and I will just wait on the Summit Carter.
I will look into the fast kit if no luck with the new pump. I replaced the O ring and lubed it with Vaseline (I saw that trick on a You Tube video also). I have an extra Power Valve and may replace it. I will need to change the oil and oil filter. Maybe replace the coil. It has a Unilite distributor that seems OK. I replaced the cap and rotor (been 24 years) and now I have usable spares.
I could tinker with the float level and bring it down in increments but I am 1 - 2 threads from where the top of the needle seat is even with the carb top and the nut slot is above the seat. I could go back to a thinner washer below the 5/8" nut. The floats are plastic and not leaking. I could bend the tang on the float hanger that engages the needle but I'm not wild about that idea for now. There is just too much fuel flowing out of that carb. and it is not good for the cylinders. I keep a fire extinguisher handy.

TKlauber · #11 (**permalink**) 12-18-2021, 06:43 PM

PS: Hot Idle Blues sounds like a good name for a song. Will keep that in mind. TK

jhv48 · #12 (**permalink**) 12-19-2021, 03:08 AM

Had the same problem. Installed a fuel pressure gauge and found my mechanical fuel pump was putting out over 9 lbs. installed a fuel pressure regulator between the pump and the carb. Pressure dropped to 6 lbs. and no more carb fuel problems.

Tommy · #13 (**permalink**) 12-19-2021, 04:38 AM

I also had the same problem but with an electric pump. New pump (and fuel pressure gauge to confirm) solved the problem.

TKlauber · #14 (**permalink**) 12-21-2021, 07:35 PM

I just had a pop up add from Jegs showing 2 M6905 fuel pumps in stock so I went ahead and ordered one from them and will keep the other as a spare. The weather has turned cold here in the deep South. Maybe it will warm up again by the time it arrives. I appreciate all the responses to my post. I will post the results with the new pump.

bobcowan · #15 (**permalink**) 12-21-2021, 10:47 PM

The fuel pump does not control the pressure. It just pumps fuel. Pressure is created by restrictions after the pump. Just like putting your thumb on the end of the garden hose.

If you're measuring >10psi at the carb, then there's enough restriction at idle to create that pressure. Make me wonder what the pressure is at WOT under a load?

A failing pump will move less and less fuel, and the pressure will drop. Doesn't sound like that's happening here.

I would add a return style pressure regulator as close as possible to the carb inlet. Maintaining a steady pressure with the proper volume is pretty important.

Tommy · #16 (**permalink**) 12-22-2021, 04:17 AM

Quote:

Originally Posted by bobcowan

The fuel pump does not control the pressure. It just pumps fuel. Pressure is created by restrictions after the pump.

Bob,
I admit I don't know much about the design of mechanical fuel pumps, but it seems to me that the restriction you allude to is the float valve in the carb. The problem is that when the valve is closed the pump is powerful enough to raise the pressure above the target 5-7 PSI. My guess is that there is a spring controlled bypass valve at the pump that is supposed to open and release excess fuel back to the intake side of the pump. I consider that to be part of the pump, so by my definition the pump does control the pressure and the OP's pump is bad. .. True, a pressure regulator and return line can solve the problem, but so can a properly functioning fuel pump.

Gaz64 · #17 (**permalink**) 12-25-2021, 05:46 PM

Quote:

Originally Posted by Tommy

Bob,
I admit I don't know much about the design of mechanical fuel pumps, but it seems to me that the restriction you allude to is the float valve in the carb. The problem is that when the valve is closed the pump is powerful enough to raise the pressure above the target 5-7 PSI. My guess is that there is a spring controlled bypass valve at the pump that is supposed to open and release excess fuel back to the intake side of the pump. I consider that to be part of the pump, so by my definition the pump does control the pressure and the OP's pump is bad. .. True, a pressure regulator and return line can solve the problem, but so can a properly functioning fuel pump.

Yes, that is near correct. In a mechanical fuel pump, the diaphragm spring determines the maximum fuel pressure. When volume requirements are low, the fuel diaphragm travel oscillates slowly, and the rocker arm linkage has a spring to allow the cam actuator linkage to follow the cam without moving the diaphragm. As the engine demands more fuel, the diaphragm oscillates more.

If you have high fuel pressure, the pump is the cause. Yes, you can limit the pressure at the carb with a deadhead or bypass regulator, the later needs a return line to the tank.

TKlauber · #18 (**permalink**) 01-05-2022, 01:12 PM

Well both fuel pumps arrived today. Same pump, one from Jeggs and the other from Summit. They are handsome Carter M6905 units and made in USA!
The weather has turned cold here as anticipated. I will try and get one on this week and report back. I will have to put the car up on jack stands and will also change the oil and filter in case there is too much gas in the oil. I may spray paint the black side pipes while it is up in the air if the temperature is high enough to paint.

TKlauber · #19 (**permalink**) 01-09-2022, 05:49 PM

I replaced the fuel pump this weekend. Tricky to get that thing bolted in with the pump lever loaded against the cam. I used assembly lube and some longer bolts to get it started in line and managed to get it in OK being careful not to cross thread the bolts. I tested it and it is a steady 8 psi and I think it helps the situation. I started it and noticed a good deal of gas dripping into the secondary bores almost like the float was stuck. I removed the fuel inlet valve and the "O" ring was in 2 pieces. I replaced it and lowered the float another 1/8 inch and it cranked up and runs fine. Music to hear the car running like it should. I will eventually take the old pump apart to see if I can find anything wrong however it consistently pumps over 10 psi which is too much.
Thanks for all the comments above. They have been most helpful and encouraging.

twobjshelbys · #20 (**permalink**) 01-09-2022, 07:21 PM

Quote:

Originally Posted by TKlauber

I replaced the fuel pump this weekend. Tricky to get that thing bolted in with the pump lever loaded against the cam. I used assembly lube and some longer bolts to get it started in line and managed to get it in OK being careful not to cross thread the bolts. I tested it and it is a steady 8 psi and I think it helps the situation. I started it and noticed a good deal of gas dripping into the secondary bores almost like the float was stuck. I removed the fuel inlet valve and the "O" ring was in 2 pieces. I replaced it and lowered the float another 1/8 inch and it cranked up and runs fine. Music to hear the car running like it should. I will eventually take the old pump apart to see if I can find anything wrong however it consistently pumps over 10 psi which is too much.
Thanks for all the comments above. They have been most helpful and encouraging.

Thanks for giving the follow up. Many people never let us know how right or wrong we are