SBC 6-71 fuel pump problem....

Carter GM4891 - Carter Strip Super Mechanical Fuel Pumps
Fuel Pump, Mechanical, Strip Super Series, Chevy, Small block

This is the pump

 

Something doesn't jive! When you remove the pump and activate by hand does it pump? i.e. does it feel like it's pumping? It will make a definate pumping sound. When you install it (them) was it very difficult to compress? My 1st blush thought is, fuel pump rod too long. Three differn't pumps can't be bad. The fuel pumps don't know there are supplying gas to a carb (s) on a blower,,,,sooo there is something wrong with the pump mounting or to the pushrod. g

 

At the moment I'm leaning towards collapsed filter or pick up sock, something ****ed up to the end of pick up tube or possibly a vent tube with a K&N style mini breather installed too far down on the tube that is behaving more like a reed valve.

 

Thanks!! all good info...

How do I get the push rod out?? Pull the pump and rod out of same hole?

 

Good thought Land See, but Lets eliminate the simple stuff first. Like El Rat points out. Check to make sure you have fuel before the reg. Disconnect and hook a spare line going into a can. If you get fuel now, it should start pulsing gushes as the engine cranks, time to look elsewhere. Carter says 6.9 to 9.5 psi I've got red flag ??? on the reg.

 

If pump is still installed do the fuel test first. Push rod is a pain.

 

Would the regulator let NO fuel by?

 

Could be some kind of weird valve pressure thing, not sure. Just eliminate from the equation for now to trouble shoot.

 

Wanna say they have a ball and seat which would be unlikely to stick shut but can't say it's impossible.

 

I read something about a pressure shut-off on some off the holley pumps. Can't find reasonable info on the Carter.

 

Definitely something strange somewhere. Still feels like heat related because it fails after time down the road. Or vacuum in the line causing the starvation.
Loosen that gas cap when you test.

 

This may be way off, but have you considered lobe wear on the cam?
A friend had this happen on a SBC, aftermarket roller cam didn't handle the fuel pump pushrod and wore the lobe , resulting in th epump not working properly.

Far as I know this is only a roller cam problem.

 

Good point, I thought about the cam lobe but why would a new pump work for awhile again then quit? Cam lobe could wear but, that leads me to think...

Check the bolt in the hole that holds the push rod up when you install a new pump. If that bolt that you put in the hole to seal it is too long it could cause excess pressure against the rod. If the rod sticks in the down position, you will not get any pumping.

 

You said you have filter "right out of the tank" I think you found your problem Mike

 

I don't know why, but my friends problem would appear and disappear, if i recall rpm related. Was hard problem to diagnose because of that.

 

Where should I put it?

 

Why would a new pump fix the problem?

 

Johnny, what's the part # on the Holley pumps you are using? Can you post a picture of your fuel setup from the pump to the regulator to the carbs?

 

But it really doesn't. Only for a short time. It is why some of us think the pumps aren't the real problem.

 

Remove the fuel filter at tank. Its too restrictive for suction side of a mechanical pump.
Install a new filter between pump & carb.

 

You have to narrow down variables in the system. Something changes for awhile when you change out a pump. Time, heat, vacuum, what ever you touch may have impact on the conditions.

• Fuel filter; check the current one for blockage, can you blow through it? Have you replaced it lately, they're cheap.
• Regulator; not seeing it helping or preventing anything at that low of pressure. By-p*** for the time being.
• Gas Cap; is the vent truly adequate?
• Mechanical; does the pump push rod move freely. Need to pull pump to check. If you have not done this, ask how.

 

I agree, unless large enough to not matter. I like to hide them on under carriage, never had a problem when clean.

 

Did you " boost reference " the mechanical pump each time you replaced one? I have a tech sheet on doing this procedure, but I'll be on the flow bench all afternoon, I will see if later I can post that for you, TR

 

Also with those pumps even though they are mechanical, you need to be sure the filters you are using will flow enough volume to support the pumps output, TR

 

Maybe he went diving with your scoobbie for fresh air...

 

Thanks. Thats where I am starting from. My filter was a basic edelbrock and now I stepped up to a high volume filter. Got it tonight and will see what happens.....

 

Here is what I am running....

 

I had the same problem untill I ran a return fuel line from the regulator back to the tank.
This prevents the pump from dead-heading and drawing excess amps.

It worked for me.

 

Enlighten all of us junk, just how many " amps " does your mechanical fuel pump draw anyway?

 

Strange problem. Mechanical pumps should last tens of thousands of miles. Even over 1000,000 is normal.