My 69 427/390 running out of fuel at higher RPM

RobRace10

RobRace10

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Joined
May 13, 2008
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So I have started to run my car 69 (427/390 with a little head porting, Comp Cams Extreme Energy XE274H, stock intake) a little harder and it seems to be running out of fuel at about 4000 rpm. It starts laying down and sure feels like fuel starvation. If I lift for a second or so and then step on the gas it will come back for a short period so I assume the bowl is refilling.

So it is a correct original Quadrajet carb for it and I have AN lines and a billet fuel filter. I have checked the fuel filters, the tank was spotless inside, new fuel sock, new stainless lines. I have an older Edelbrock Fuel Pump HD62 that I don't know the history of. Everything else was new since the rebuild. The carb had a fresh rebuild and seems to work perfect otherwise unless I stand on it for more than a few seconds in any gear.


So I opened the carb and the float level was set at about 1/2". I raised it up to about .3" and that seemed to help, but then I started to smell gas. I dropped it down a little and the problem has come back worse than before. I did also open up the fuel pump and don't see anything obvious but I will order a GM Performance pump as I need the opposite side inlet and outlet as on the Edelbrock HD62.


One other thing I have noticed is I'm building pressure in the tank, yet I have a vented cap. Not sure this would cause an issue, but just another FYI.

So anybody have any suggestions as I need to fix this! HELP

Carb.jpg

Carb2.jpg

CarbFloatLow.jpg
 
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Your Q-jet wouldn't happen to have the little filter element in the inlet, would it?
 
I would take it out. The porous sintered ones can look perfect and clog up just as you describe.

It's a longshot but worth a try.
 
I'll pull it and test it out in the morning. I do not believe it is plugged, but certainly could be restricting flow, it is worth a shot for sure.
 
Taking the fuel filter out made a big difference. It may not have entirely fixed the issue, but it certainly was way better than with the carb filter. I will try raising the float back up as I think there was a small leak at the filter connection that may have caused the gas smell.

Update

I think it is all good now. Raised the float back up to where it should be and left the carb filter out and it was pulling past 5,000 rpm with no problem. The little paper filter just doesn't allow enough flow and that combined with the low float level (it was set by the carb re-builder at 1/2" ) and now I'm at about .30 were the two issues.

Here is the filter. It was new, but obviously not a high flow product.

100_5175.jpg
 
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If there is pressure in your tank it is not venting. Check to be sure the vent in the cap is not clogged.
 
The gas cap sat for 25 years along with the car before I rescued it and not to many things worked as they should right off. I took some WD40 and sprayed in the center hole and then some compressed air. It seems like it is opened up now. It must have been stuck or plugged as there was significant pressure a couple of times when I have added gas. I'll find out next time I fill up.
 
That small edelbrock (formerly russell) filter is tiny, get a fram HPG1 or something with a similar element size. They're available w/ a 40 micron stainless mesh filter too. The mesh ones should be rated to well above 100GPH
 
Twin_Turbo said:
That small edelbrock (formerly russell) filter is tiny, get a fram HPG1 or something with a similar element size. They're available w/ a 40 micron stainless mesh filter too. The mesh ones should be rated to well above 100GPH
Click to expand...


I'll get a bigger filter on order, as compared to the carb filter the Edelbrock is huge, but I want to make sure I have fuel flow.
 
Those small filters can be brand new, out of the box but still present a restriction to fuel flow. You're moving in the right direction.

Jake
 
Ive also ordered a new fuel pump. I'm losing all the fuel in the bowl and the line back to the pump, so there must be a bad valve in the pump. Lars says this does happen and I don't believe it is just the fuel in the bowl leaking into the engine, but the entire line of fuel gong back.
Won't be able to get the new pump in for a few weeks as it is back ordered and going racing over the labor day week in Brainard MN.
 
Finally I think I have things worked out. Removed the carb filter, raised the float height and a new GM Performance fuel pump. Now I can keep on it until I want to shift rather than when the motor starts running out of fuel.

:bounce:
 
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