Fuel Pressure issues with alcohol

[dirttrackrocker]

What should I have for fuel pressure at idle?? I was thinking 3-5... Problem is I have more like 7-8!!! @6000 rpm it goes to 10. The ten seems ok under throttle, but, I'm not liking the 7-8 at idle. I'm running a mechanical fuel pump with a BG regulator that has the idle pressure jet. It had a 76 jet in it at first I replaced it with a 99 and it didn't change anything. I checked to make sure the return line wasn't clogged. I can blow through it and hear bubbles in the tank... Any ideas???

[Roger Williams]

psi

Simply turn down your regulator to 6-7 and run it..
You wont get a pulse punp to idle at a low psi like a belt drive dose.
You don't need 10 psi as long as you have enough volume... PSI and Volume are two diffrent things. 10 is too high and will more than likely cause you to be flooding over when your off the throtle. Your welcome to call me if you need help..
Roger Williams
Williams Precision Engines
765-525-4825

https://www.wpespeedshop.com

[dirttrackrocker]

Thats the problem, I have it backed off all the way.... Will it hurt anything with that much pressure at idle??

[82Motorsports]

To reduce pressure you must turn adjustment screw "OUT" on regulator. Also where do you have your gauge in plumbing sequence?

[dirttrackrocker]

Are you sure??? I had it apart and it looks to me like by turning it in, it puts pressure on the diaphagm and seals off the return creating more pressure. It's a barry grant regulator, mounted to the back of the fuel log, (after the carb) the return line comes out the bottom and the pressure line (gauge) out the back

[joeltjen]

bypass

What should I have for fuel pressure at idle?? I was thinking 3-5... Problem is I have more like 7-8!!! @6000 rpm it goes to 10. The ten seems ok under throttle, but, I'm not liking the 7-8 at idle. I'm running a mechanical fuel pump with a BG regulator that has the idle pressure jet. It had a 76 jet in it at first I replaced it with a 99 and it didn't change anything. I checked to make sure the return line wasn't clogged. I can blow through it and hear bubbles in the tank... Any ideas???

theres your problem.. the diaphram bypass. these are meant for belt drive pumps. you need the mechanical bypass valve thats hooked into the throttle linkage.

[dirttrackrocker]

Nah.. I know lots of guys using this type bypass with a mechanical pump, I've never seen anyone use the ball valve type. BG says they can be used with mechanical pumps but you may need to plug the idle jet if your not getting enough idle pressure. I have the opposite problem. I'm thinking there is something restricting the return.

[GUARDRAIL]

With a mechanical pump, I would put it before the carb on the fuel log plug the idle jet and adjust my pressure to 7-9psi.

[PIERCE3J]

Won't that also restrict the amount of fuel to the carb. at W.O.T.?

[82Motorsports]

I corrected myself. I was thinking of another setup! Anyway, what size line are you using on the return? You have it setup correctly according to BG instructions if I understood you in what you explained. And, yes by changing the jet to larger should affect idle pressure by lowering it, smaller raises idle pressure. Your final pressure you mentioned will be fine, but idle may cause you some flooding.

[kraftkar7x]

isnt the bypass with the idle jet for the belt drive pump and the one without the idle jet supposed to be used on mechanical pump???

[joeltjen]

bypass wrong!!! right from BG

here ya go!!! http://racingarticles.com/article_racing-68.html items 3 and 4

[mherbert]

with a mechanical pump we never could get the idle down to 2-3. we just set it at max. pressure of 8 and it idled close to that. It will sometimes lift the needles off the seats and flood at high rpm, so you really have to pay attention to needle valves and seats. It will also run you out of the shop real quick as it is rich at idle. Went to a belt drive pump and all those problems went away. You can buy a used belt drive pump fairly cheap right now because more and more people are going to gas and selling those belt driven pumps. Look on ebay there is usually at least one for sell every week.

[dirttrackrocker]

No it says never use a throttle bypass with a belt drive pump, it doesn't say not to use a diaphragm with a mechanical. Its been done that way for years.

[dirttrackrocker]

Thats what they say. It says if your using a regulator with a jet in it, you will probably need to plug the jet to get sufficient idle pressure. Started that way and then went to a 76 then to a 99. No change. I've checked everything else, I'm pretty sure it is some kind of restriction in the return line. Some one on the dirt forum suggested that if the return line is hanging down and submersed in the fuel it would create pressure. I'm gonna check that tomorrow when I'm up at the race shop.