[Pierre1967]

Hi,

My engine bogs during WOT acceleration at 4 500 rpm.

My fuel delivery consists of 1/2 line from trank to pump and 3/8 from pump to Q-Jet. Fuel filter and a return line are between the pump and the carb. I let the fuel filter inside the carb too.

The pump is a Carter M6907 - Carter Street Super Mechanical Fuel Pumps.

Engine has 425 hp approx.

I don't know how much fuel pressure I have, could it be the problem ?

Thanks for your help

[25stevem]

You do not need to have the in carb filter in place if you have a external one, especially so if it’s one of those very restrictive sintered bronze filters!

If you remove that and still have a issue then it’s time for a fuel pressure gauge to be installed where you can see it while driving.
Years ago on one of my street cars with a Q-jet With a fuel pressure regulator I did a experiment to see what level of minimum fuel pressure was needed.

I found that with anything less then 3 psi my 400 cid street Cam’ed motor would idle just fine, but could not even get passed 35 mph on level ground with out back firing through the carb from going lean.

Note that this was with the big .135” needle and seat in the Q-jet by the way!

[Pierre1967]

25stevem,

In term of fuel pressure variation, what can be observed at idle Vs. WOT high rpm ?

[Pierre1967]

Thank you for sharing 25stevem

[sdbob]

I had the SD out today in lays over at top of 2nd. Soo probably new fuel pump. Dont want to derail however what is best stock type mechanical pump so I get needed pressure. The car did it new 48 yrs ago. Stopped when I added small electric pump.

[25stevem]

If a small electric pump helped out then I would say along with a new mechanical pump you need to up grade the fuel system size from the tank up to the pump while being mindful of taking some sharp bends out of the run of the fuel line.
Two 90 degree bends in a line will reduce the available fuel volume by close to 1/3rd so keep that in mind!

[Cliff R]

Any time the engine pulls hard at WOT then bogs out or loses power you aren't keeping it full.

I'd start by installing a high flow needle/seat assembly before looking at more complicated issues. For 425hp you would need at least a .135" seat in the Q-jet to be able to keep it full.

What application and carburetor part number? More information would help.......

[ta man]

Originally Posted by Pierre1967

25stevem,

In term of fuel pressure variation, what can be observed at idle Vs. WOT high rpm ?

Zero variation.

[25stevem]

That’s the way it should be.

[AG]

Originally Posted by Pierre1967

25stevem,

In term of fuel pressure variation, what can be observed at idle Vs. WOT high rpm ?

My race car starts out at the line at 9 psi and goes down to 5 psi at WOT using a Mallory 140 GPH gearotor pump and a 1/2" line to a deadhead regulator, runs 10.0 at 3550#.

[Pierre1967]

Cliff,

It's for street use only, for weekend fun.

Firebird 67 engine combo :

406, stock KRE heads, XE274 cam, 700r4, 3.55 posi, 26" tires.

Pierre

Originally Posted by Cliff R

Any time the engine pulls hard at WOT then bogs out or loses power you aren't keeping it full.

I'd start by installing a high flow needle/seat assembly before looking at more complicated issues. For 425hp you would need at least a .135" seat in the Q-jet to be able to keep it full.

What application and carburetor part number? More information would help.......

[Pierre1967]

Please see attached pictures for part number ..

[sdbob]

I'm looking at Robbmc fuel pump and filter