Weber fuel pressure requirments

[kent olsen]

I added a Holley fuel pressure regulator many years ago to my 2.7L. I think I purchased the one that was 4-10psi. The car has always idled poorly, it pops back thru the exhaust.

After reading some of the old posts I'm wondering if I should replace it with the 1-4 psi unit?

I replaced the needle valves in the weber's with "grose" (sp) needle valves after someone told me they were better but I'm wondering if even 4-5 psi is to much and that's why my idle and off throttle sucks?

Comments?

[911pcars]

Kent,
Weber recommends using 3-3.5 psi fuel pressure. Not sure the 4-5 psi is causing your idle problems.

Excessive fuel pressure can overcome the closing force created by the float, then push raw fuel into the throttle bore via the main discharge tube.

You can verify by measuring the float level with the PMO or equivalent active float gauge - the one that screws into the side of the float bowl. A simpler way to confirm is by removing the air filter housing, then with the engine at idle, look into each throttle passage (wear safety glasses). Since idle air/fuel is introduced below the throttle plate at idle, there shouldn't be any sign of fuel; no dripping, no wetness. If there is, the fuel level is too high, either caused by a mechanical adjustment of the float level or by excessive inlet fuel pressure. In addition, the idle circuit also contributes to part throttle operation.

Grose jets were supposed to provide a longer-wearing shutoff mechanism. I have them on my carbs too.

Does your system have a fuel pressure gauge to confirm the output pressure of the fuel pump/regulator?

Hope this helps,
Sherwood

[Fast Corners]

Man it has been a long time since I have messed around with carbs but, from what I remember they liked 3 psi. The grose jets are a very good upgrade. You need to have the float guage and the proper shims to set the jets correctly.

[kent olsen]

Well besides the 'grose' needle valves I bought rebuilt carbs by Harry Beiker. I did the float bowl mod in Bruce Anderson's book. I set the float level with the site glass and shims and adjusted the accel pump shot with the little shot glass.

I have the Holley press reg and the Holley gage and one inline metal fuel filter. The press reg is backed all the way out and I get around 4-5 psi as I remember. Should've checked before I left home for work.

I have added the Mallory MSD, and Pertronix igniter in the dist.

I pretty much run out of ideas and just put up with it over the years. I did find out this 2.7L engine has CIS pistons with I think "E" cams so I figured it's the Weber/CIS mix that is the problem and I will just live with it until I finish rebuilding the 3.0L in my shop.

Other than the idle/low rpm problem this little engine runs great when you put your foot in it. It made about 195HP corrected on the only dyno run I've done. I just would like to figure out what this problem is before I bolt the weber's and headers onto the 3.0L.

[Steve@Rennsport]

Kent,

I've tried the Grose needle assemblies on various cars with no luck and I really prefer the Weber ones.

These carbs run best at 3.5 psi and the float levels should be adjusted after the fuel pressure is set to that value.

[MBruns]

Kent, webbers like between 4-6 psi depending how much power and demand you have, Thats with the weber needles/seats, I don't like the grose jets in the weber/PMO carbs because it seems there is not enough leverage on the float arm to shut them unless the press is 2-3 psi, I have had luck with them in other applications though. your popping at idle is usually a lean condition either mixture or tired throttles/airleaks etc...

Mike Bruns JBRacing.com

[911pcars]

"your popping at idle is usually a lean condition either mixture or tired throttles/airleaks etc...

+1 I forgot to mention that as well. It may well be some of your idle circuits are blocked with debris. Remove the idle jets and blow some compressed carb cleaner through it. Check the idle mixture screws and verify they're in good shape (pointy with consistent taper).

Sherwood

[J P Stein]

I notice you say nothing about balancing the carbs. Are you balancing the carbs side to side properly with a syncometer or the like? An imbalance will cause
"pops back thru the exhaust"?? ...not to be confused with pops back thru the intakes.....which is a lean pop.

If you're coming to the ORPCA AX this Sunday at PIR, look me up and maybe we can fix it.

[aws]

Kent: Be careful putting compressed air into a Weber 40IDA-3C carb, it will collapse the float due to air pressure in the float bowl.------ Ask me how I know this!!! Pressure from a carb cleaner can is OK but nothing more. My opinion is the the poor idle quality is throttle shaft air leaks and adjustment problems--- not fuel pressure. I have always run 4-6 lbs fuel pressure on webers with no problems.

[Nitrometano]

I have the same Holley regulator for 4 to 10 psi. I also add a T fitting and a fuel pressure gauge. With that regulator I can get 3.5 psi to my Webers and I have no problem with the idle.

[kent olsen]

Tks all for your advise.

I just ordered a 1-4 psi holley regulator I'll try. My carbs are total rebuilds by Harry Beiker. I checked, measured the idle jets, they are all 68's. It won't run with smaller idles. I balance both sides with the syncro whatever, the good one.

When I get home this week I'll install the smaller press regulator and recheck the float level like Steve suggested. I've been told part of the problem is the CIS pistons don't like the Webers so if I can hurry up and build this 3.0L in my shop then give it to Steve to tune on their dyno I will finally after 10 years have a strong engine that idles.

One last question, if it is popping thru the exhaust is that lean or rich? I always thought it was rich and the unburnt gasses where being ignited by the hot exhaust!

[Nitrometano]

Popping thru the exhaust is rich, popping thru the weber is lean. Do you know how to set your air/fuel mixture in the webers?

[kent olsen]

Yes I've adjusted the air/fuel mixture and the air bleed adjustments as well. I've even talked to Harry Beiker about finding the right settings.

I'm home so we'll see what happens with the lower fuel pressure and a new filter.