Anybody know what bypass jet size is on a APD internal bypass belt drive pump used on a 350 inch small chevy and no I wont call APD they have been less than helpfull this was a new pump and complete setup last year went to a Magna fuel 500- and 4 port regulator and it works fine but have almost a grand in the belt and want it to work

What's the problem? If it has too much pressure put a bigger jet, if too little put a smaller one. It will take some testing but could likely get it in the ball park in the drive way then fine tune at the track.

Sorry forgot to say its on alky and it sets up ok got to 8psi at the recomended 4500 rpm and 3 psi idle but floods over under full throttle and its a 220 mile round trip to the track so lookin for at starting jet its only a 47 from APD

Are the Floats in good shape? The pressures you are seeing are fine, IF the gauge is accurate.

Three different gauges new carbs had them apart new blp needles an seats but at full throttle it would blow alky over the roof no issues with magna fuel pump and regulator goes right down the track just want to make a 1000 worth of APD junk work-lol

is your pump the one with the holley looking adjustment on top/are you 2 to 1 on pulleys.is your adjuster in or mostly out

I've never been able to run that much fuel pressure at 4500 rpm on any of my stuff big block or small block.

Ya well that was where APD said to set it was ok untill you went full throttle then wham fuel would shoot out bowl vents-no good very scary so gave up on the thing but want get it to work as advertized-lol adjuster was out 51/2 turns after APD said three I think it needs a much bigger bypass jet

i would back out on the adjuster ,it doesnt matter what they said but what it takes to make it work.if you come out on screw more the idle bleed may have to be smaller.are you able to record pressure before it blows out.

Gday,
I have an apd belt pump and external bypass reg.
This is how I set mine, I set it up on the bench with a low pressure air reg and a low scale large diameter gauge.
I fit a solid jet where the bypass jet goes and adjust the spring on the reg until the seat is just cracking on the diaphragm at the pressure I'm looking for at Max pressure,
I leave the spring adjustment alone then fit my idle bleed jet, can't remember what size I'm using and I'm not home at present to look at my notes but I know it is pretty large,
My engine is approx 650hp and the.pump they supplied has a 600 thou section width
So it moves a lot of fuel, with mine you have to be carefull not to set the idle pressure too low with the bypass jet being too large otherwise there is too much of a constant bleed at full throttle and it won't hold fuel pressure at hi rpm.
I think the external reg and bypass is a far better set-up than the internal bypassed setup
Float heights need to be set to a height with the bowls off then forgotten about.
Can get that bypass size for you but won't be till next week
Cheers

The bypass jet primarily controls the idle pressure. It can effect the main pressure of it's too large.

This is how it was explained to me. If the pump is to big for the engine you will never be able to run more pressure than the needle and seat can control. The setups that are running 9-11 psi have a properly size pump for the HP and pretty much you are burning fuel fast enough at WOT that the bowl never over fills.

Ok first off I thought 8psi was too high also but have tried it with the magna fuel setup and the needle/seats will hold-currently use 6 1/2 so.. would like to know your bypass jet size when you find it Mr Dilly pump is geared at rate APD sent bought whole kit so...its going to be run with the magna fuel stuff this year as lone as the pump lives current bypass jet is a 47

G,day
By my notes the std bypass jet was 84, not sure what i meant?
an 84 holley jet is .094" or was it .084" not sure on that i can't remember!

However for ages i ran a 92 jet which is .109",
I then increased it to .127" and found that it would drop fuel pressure up top.
went back to .117" and for my hp, idle speed etc it works good and holds fuel pressure wherever i chose to set it in the top end.
Cheers

Thanks for gettin back to me Mr. Dilly also have a external bypass reg. setup to try -thanks again - any info is great

What size are the needle and seats? If it has the bigger 150+ size, 8 psi is high. I have apd pump setup with a return and.160 n/s and I run between 5.5-6 psi.

I will look to see what my bypass jet is.

Hey would appreceate that -currently run 61/2 lbs. at carb n/s are 140 blp thats what pressure APD said to use thought it was high also