Who is going fast with the stock 3/8" fuel lines and Stage 1 pump?

My white car has 3/8 fuel line, sock removed from the pickup in the tank, stock Stage 1 pump, 750 Q-jet, marine filter in the inlet on the carb. I have run as quick as 11.60 @115+.

FYI there are 2 different marine filters which consequently have different diameters. If you are running a 71 or newer Q-jet with the larger inlet you can run either filter. If you are running a 70 & older Q-jet you will need the smaller diameter marine filter that is harder to find.

 

This is the one I just ordered. It's only 1 inch long but specified for 71 & up QJs. They say you still use the same spring in back of it even if you have the 2 inch housing. Look right?

https://quadrajetparts.com/short-mercury-marine-carburetor-fuel-filter-p-433.html

 

That will work on the 71 & newer q-jets with the larger inlet that have the clear seal at the end of the threads.

 

Yup. That's what I have.

 

Well, here's the report after picking the GS up today. Recall that I had the tank dropped, (it was spotless) and installed the RobbMC 1/2" fuel sender, replaced all the rubber hose along the stock 3/8" lines, removed the rubber line under the driver's door and inserted the RobbMC 100 Micron short filter there. (had to cut about 4 inches off the steel line and reflair it) Also, inserted a ball valve into the return line at the fuel pump to adjust the amount of restriction in that line if needed. Road test revealed that fuel pressure was still only 3 psi cruising and dropped to about 1 psi on hard acceleration. Only slightly better than before the work.

So, the fuel pump was bad after all. While waiting for a nearly new Stage 1 pump bought from a forum member, I borrowed a pump from a friend here and installed it. That did it. I now have fuel pressure of 8 psi at idle and cruise and drops to about 5 psi top of each gear. On the way home I was able to go thru the gears without any surge or bog. I'll know better if it's improved my 1/4 mile trap speeds when this terrible 95+ deg. heat leave us. Thanks for all the input, guys.

 

That’s awesome news, still need a known good pump to be sent in the mail?

 

5 psi....your loosing 3 psi in each gear......is the bell not ringing......drop in psi mean less fuel........the warning sign is right in front of you.

I get wanting stk appearing sleeper look etc......but it's too expensive to play around on that ledge.....

Burn down a motor to save a few hundred bucks on a bigger pump and lines. Why risk it........always better to have too much than not enough..........don't forget air quality effects this fuel ratio too........so ot might be ok no . But give it a weather change and it might not be

My car is race only. I have a BG 280 electric....fed by -10 and -8 to carb and return back to the tank........at idle my return line looks like a garden hose spraying........but I see 7.75 from idle to 7000 rpm on the top of 3rd gear

 

Yes, I have to give him back his pump when yours gets here. Just wanted to get one on ASAP while the car was up on the rack this mornig

 

Well, while I appreciate your comments and suggestion that 5 psi means less fuel, I'm hearing that 5psi at full throttle is actually quite satisfactory for my build level. When the FP is 8 psi at cruise the needle/seat duty cycle is less because the need for fuel is less than under load. The drop in FP under load could be the needle/seat is open all the time but fuel voluum is enough to prevent detonation. A friend here in Central Florida has a higher HP combo than me and runs high 11s with similar setup as mine. He has hundreds of runs on his motor with no issues.

Having said all that, I'm still interested in other comments on my experience.

 

Where is your fuel pressure gauge located???

Your gauge or anyone's for that matter only read pressure from that point to the pump, behind it we never really know.....but the pressure come from the other end. So we don't know what the pressure is between the gauge and needle and seat. So let's say a idle you have 8 psi.......everything full happy ect.....now start our hard pull....the pump is playing catch up since why your seeing the pressure drop........but in the end your restriction is the needle and seat. About .125 hole on average........the more pressure you have to push through this hole the better.

If your ok with about a 50% drop in pressure and you can justify that it's good enough because someone else somewhere is getting away with then by all means go that route..........me. I'm not going through a 5k rebuild because I wanted to save a couple hundred bucks on fuel pump and line. In my opinion this is one area where bigger is better......and too much is just the right amount.

 

My gauge tap is located about half way up the fuel line from the fuel pump to the quadrajet. There is a 4 ft. braided line going from the tap to the Summit gauge at the windshield. I do agree that bigger is better and will order the RobbMC mechanical pump if my upcoming chassis dyno runs indicate that air/fuel ratio is getting too lean at the top end. I'll report back later on that. I do appreciate your thoughts on the matter, though.

 

And don’t forget to put a ball valve in the return line

 

Yup. Did it.

 

Do you see a difference in pressure? Jim Weise did it and closed off the line, and the stage 1 pump spiked to 12 psi at idle. I wonder what your failing pump created at idle

 

What I do is not totally close return. Let some back...avoids excessive pressure and helps prevent vapor lock as well

 

Me too, or I used to

 

My fuel pressure at idle with the bad pump was about 5 psi with the return line completely blocked and about 3-4 psi when cruising. I never checked it with the ball valve because we installed my friend loner pump along with all the other mods. On my way home I had the valve open all the way and idle pressure was giggling between 7-9 psi. At cruise it was 8 psi solid and about 5 psi under hard acceleration. I'll be driving it today and will take a look with the valve partially closed and all-the-way closed. I'll get back.

 

Do you still have a filter in the carb housing? At 8 psi you may see fuel seeping near the accel pump