RXn407

I just got my car dynoed and did 105 HP on a 12 A. I didnt want to hi jack another thread so this question is for you plumbing gurus. I have a holley 650,mallory 140,and EARLS fuel filter. Now what I noticed is to do the plumbing from a reg. gas tank in my 83' you need adapters that are hard to find or you have to rig it up . anyways i got the adapters but my problem is that before I put the EARLS I had a clear one from mr.gasket and i noticed that the tube will fill then drain then fill and drain. Like it was a pulse!? so I thought the filter was too restrictive. So i put the earls on and took it to the dyno. What I found out is that my engine would lean out as I raised the rpm(17.8afr 105hp. @9000+rpm in second gear(which i understand why) BUT TEHN it would PLUMMIT to around 11. AFR.!!!!!!my first pull was in 3rd and i couldnt even make it to 9000 rpm.'s! It stopped @ 7000 and the fuel CUT OFF @ 6000 rpm's. The guy thought i had a fuel injected engine!!!its like the fuel cut i had on my old T2.

So my theory is the fuel will pump then drain then pump then drain. Instead of constant flow. So I thought that the filter is too restrictive, but the problem I have is the pump is rated at 140gph. @12psi. Its only set @7 psi so its around 80 gph. (more or less,right??) SO,WHY WOULD THE FILTER BE THE PROB?(esp. after i changed it)HAS ANYONE EVR HEARD OF THIS?DO I SOUND LIKE A CRAZY!!! the dyno guy told me to clean it up, Do you think my whole system need to be re done? my afr #'s would NOT stay between 11 and 14 through out ANY rpm level? I have a mechanic. But since I have all this FREE knowledge I thought I would give it a shot before i pay and at least i would have a better idea for when i do take it to him. I know its either the carb,pump,or filter,or just my whole plumbing is dirty.I just need to narrow down the prob. before i go spending the money, my explanation really sucks too so, thanks and sorry for confusion.-Erik

IanS

iTrader: (4)

You dont need to got to 9K. 7500 is most likely the highest you would ever need to go unless you have a PP, but then you should have way more than 105 hp. Also a holley 650 sounds a bit much for a stock port motor. What kind of exhaust setup do you have?

trochoid

iTrader: (6)

Did you think you had a V8? The Mallory Comp 140 fuel pump requires a minimum of 3/8" for a returm line. It is twice as much pump as your need for a 12A. The 650 is nearly that much too big too on a stock port, and 7 psi is a little high for the carb.

What other mods are you running? Porting exhaust, etc.

rxtasy3

iTrader: (2)

racing beat's holley for stock port is 465cfm which i ran on an '83 engine and it ran very well. i think some r successfully running 600's but had to install smaller jets and such.

vipernicus42

iTrader: (4)

It seems it's been pretty much covered, but I thought I'd try and bring it all together.

I'm running a Mallory Comp 70. It's more than enough for my needs. The 140 is great, but since it flows so much, you'll want to make sure you have a good Fuel Pressure Regulator to bring the fuel pressure into the range that your carb needs. For example, since I have a rebuilt nikki, my pressure needs to be around 2.5-3psi. So I have a Holley 1-4psi FPR which brings my Mallory's pressure down to the right level.

Which brings us to your carb. General thinking is that for a stock or light street port 12a the Holley 465cfm carb is quite sufficent. The problem with carburetors is that more ISN'T necessarily better.

If you look down your carb you'll notice a little metal ring which contracts in the middle and has a small tube sticking into it. This is the venturi. Here's the basic idea. The air coming in has to squeeze through that tube like water from a garden hose. Since it gets smaller in the middle, it's like putting your thumb over the garden hose, the air goes faster. The velocity of this air creates negative pressure which pulls the gas out of the little tube and atomizes it.

If your carb is too big, the air will be going too slowly through the huge barrels, and will have trouble pulling out fuel. If your carb is too small, you'll have the velocity but not the flow you need at the high end.

I'm no Holley expert, but once you have your fuel pressure under control (and you make sure your return line is big enough to accomodate the excess) I'm sure there's a way you can jet your 650 to work. It won't be ideal, but it'll work. You'll need to see someone who tunes holleys for that.

Jon

darkfrost

iTrader: (1)

Do you have an FPR? If so...which one?

trochoid

iTrader: (6)

If he bought the Mallory Comp 140 from Jegs, it should have come with the 4309 fpr. If he is running the Holley 5-9 psi one, the fpr may be overwhelmed with the volume, and the Holley is a non-return stlye.

darkfrost

iTrader: (1)

Reason I ask, I had a very similiar problem with the dial-style regulator, switched to the 4309 and all problems solved.

trochoid

iTrader: (6)

Most definitely agree with that one. He may still need to upgrade his return line.