SBC 6-71 fuel pump problem....

I am running a SBC 350 with a bds blower. I have gone through 2 Holley fuel pumps and now 1 carter. They are both mechanical pumps rated at 120gph. The tank is vented and I have a 8psi regulator at the carbs.

Twice they have gone out on the freeway after only 20 miles. The pumps are only lasting 3 months max!!!

What else could be my problem??

 

Have you dissected any to exactly see what failed?

 

Electric motors can go if not enough juice under load. What gauge wire are on them. And the obvious, check you ground is adequate. Some pumps are made to push not pull. Where are they mounted?

 

I haven't gone through any.

They are mechanical pumps

 

What should I be looking for. Never done it....

 

Mounted so direct on the block right? Hmm.

 

So is the diaphragm failing and gas spews out the breather hole?

 

Yea mounted on the block.

No I just get no fuel pressure at the carbs...

 

A failed valve, torn diaphragm, debris from the tank, etc. Did it leak, low pressure or just stop pumping? Are you sure the pumps really went bad or could there be some wierd issue back towards the tank (pulling air) that is causing starvation and losing prime after long distances under load?

 

This smells funny and not like gas.
Mechanical pumps are pretty simple; lever, diaphram, one-way valve.
Thinking...

 

Is there a hidden filter on the ch***is maybe?
What kind of tank? Any baffels in it?

 

It is a model T tank with 2 vents. The tank was 1/4 full so I don't think the gas was moving to get air. I can se the carb bowls and they are bone dry. And If I crank it over after it stalls they don't fill up.

Baffles in the tank and it has a fuel filter right out of the tank

 

Something is weird. Have you talked to Holley? I could be wrong here but have never run a regulator at the carb with a mechanical pump. The carbs should handle the line pressure. Float goes down need and seat opens. Is the regulator recommended for that pump?

 

What pushrod are you using, have you changed it with any of the pumps?

 

Any hoses look collapsed on the inlet side?

 

Good question. Will call bds

The mechanical pump was already on the block so I don't know. Carter said that is one thing to check and see if it is too long and over extending the pump.

All hard lines...

 

Silly question.
Is the bottom of the Tank sitting higher than the pump?

 

Yea.

 

Do you see a Holley # anywhere. Their website has some tech info.
http://www.holley.com/division/Holley.asp#4

Could the fuel line be getting too hot? You say after 20 miles this happens repe***ively.

 

I don't have a Holley on there anymore. Went through 2 and went to carter. That is what is on there now. I have done the math and 120gph should be enough.

 

I can run around town for a good 30 minutes no problems. This last time going to a show I drove 30 miles there early in the morning and no probs. on the way home after 10 miles it failed.

 

I agree in volume but you had what appears to be the same problem with booth brands. The old holley #s might expose some clues.

This feels like supply or heat, maybe both. Hard to believe these pumps are failing.

 

I think it's the pump because now after sitting it still won't start or fill the carb bowls.

Thoughts??

You guys are really helping out!! Thanks

 

Crack the line between the pump and regulator. Thighten and try again. See if you can here any air or witness pressure relief.

 

Also check that carter number. Some pumps do need a reg, some do not.

 

When a pump ****s out, is it just a replcement and then you drive off? No pressure with old pump, good pressure new pump and no other changes etc?
When you pull the inlet fuel line, is fuel flowing freely?
I'm curious about the 8psi, the only fuel pumps i am aware of that need regulator and can get above 8psi are the 160gph race type, none of the 120gph pumps get much over 7psi. I don't think it has anything to do with what is going on, it is just a conumdrum.
I presume you have 3/8ths line to feed the carbs?
Can you rig a gage where you can see it while driving, that might give you an idea of what is going on.
Try cracking the fuel cap in case the vent is plugged.

 

Before the pump too.

 

Good vibrations said that I DO need a regulator but I will double check with carter.

Yea. New pump= start and drive away.

It is all 3/8 hard line...

Could the regulator wreck the pump

 

Nope. Try cracking the line to the pump inlet, tighten it back up and crank it over a bit to see if it starts pumping again.

 

Need to cross check for vapor lock. It is why I asked about heat.
Here is a carter bulletin:
http://www.carterfueldelivery.com/fuelpumps/mp_failure_diag.php