speedtigger

iTrader: (16)

As some of you know, I have had a lean tip and cruise problem in problems with 3 different Pro-Systems carbs for more than a year. I finally just gave up and put my home-built Holley 750 on the car and threw the Pro-Systems carb on the shelf.

A quick summary of what the problem was is the car would go dead lean at a low RPM cruise. And had a tip in stumble. The only way to make it drive-able was to adjust the idle pig rich to cover it up.

I tried playing with the bleeds per the techs suggestions and sent it back 3 times. No luck.

Today, I had a thought. I thought I would further restrict the flow of fuel in the idle fuel restriction in the metering block. That did not help either. So, just to go the other way, I removed the restrictor altogether. Now the car would go pig rich at light part throttle. Bam! The first thing I have done that would make it go rich. So, I am thinking I just need to enlarge the restrictor a little at a time until it is exactly what I want.

I had to quit for the night to take the wife to dinner, but I think this will fix it. I can't wait to get the 950 right now. It will be nice to have a $700 carb that I can use.

Doug G

Sometimes its better to be lucky than good

ZONES89RS

iTrader: (25)

Nice work man, hope you get it dialed in perfect.

Thumpn

I have a Pro systems carb and have no issues with it. I did at first but found that the fuel system was lacking, and the Pro System carb is sensitive to fuel pressure or the lack of.

speedtigger

iTrader: (16)

I am a happy camper. Drilling the idle fuel feeds from .035" to .037" solved the problem. Now it will maintain 14:1 from idle to high speed cruise.

All that fuss for a year was solved with one simple procedure.

So, if anyone else ever goes through this with their carbed LS, this might help.

89gmcs15

iTrader: (7)

So with your idle at a happy lean ammount youd slowly get to cruise speed and it would lean way out? mines doin the same thing... So I had to se my idle to a rich 12.2 and it still goes alittle lean gettn to cruising speed. What fuel pressure are you running?

speedtigger

iTrader: (16)

Yes. I had to set my idle ridiculously rich (11-12:1) to get it to cruise at low speeds. Otherwise, it would go off the scale lean at low speed cruise (16:1) stumble and also had a wicked tip in stumble.

I run about 6 1/2 pounds.

Now the car can be set to idle in the mid to low 14:1 range and it holds that all the way through to the main jet transition. Sooooo nice.

89gmcs15

iTrader: (7)

That is exactly what my carb is doing. I spent hours gettin the idle set to mid 13:1 then I took off to drive it and it would go so lean before you stomped the gas it wouldnt rev up. Prosystems recommended 7.5 for the fuel pressure and im at just under 6. Im gunna try and bring it up to their "spec" before I drill the restrictors. I gotta get this thing to stop burnin my eyes at idle haha. Thanks for all the help I was about to go nuts

speedtigger

iTrader: (16)

I know man! Pro-Systems spent hours on the phone with me, rechecked my carb and even built me two new ones. Their conclusion was to set the idle richer because "that is what the car wants".

89gmcs15

iTrader: (7)

Aah the old thats what the car wants ploy huh. Like every engine is so different, like yours is moving air and mine is moving water lol. Exactly what passage did ya drill out? could ya grab a google pic of a metering block and draw a arrow on it with paint or somethin? I dont want to jack one up ha

speedtigger

iTrader: (16)

This is the only picture I could find that had a clear shot to illustrate it. However, Holley factory metering blocks have the orifice in the same location if it is a newer carb.

My carb had a .035" restrictor. I increased mine by .002" to .037". Your carb may or may not have the same size restrictor. You will have to gauge yours first to see what it is to start with.

89gmcs15

iTrader: (7)

Awesome. Yeah I would have drilled the wrong ones haha. Did you do all 4 corners or just the fronts or somethin. Ill prolly go up .002 aswell because I dont think I got a bit that will only be one bigger ha. Thanks for the help again ill post up how it goes after I replace my ripped gasket from takin the block off the carb. Non stick my ***. Whats your idea, red or blue gaskets? Either way im gunna put some non stick stuff on it when I reassemble.

HPbyGD

What I do is drill and tap the passage for a 6x32 brass set screw. That way if you go to big all you have to do is put an other set screw in. You can get 50 screws from McMaster and Carr pretty cheap. The same screws work for air bleeds also. The only thing is that you have to keep the ones that you drill in a plastic bag that is marked so you know what size you drilled them.

Gary

speedtigger

iTrader: (16)

I did all 4 corners. It is not absolutely necessary to fix the problem, but my concern was to make sure I could set all 4 corner's idle mixture equal with the screws.

As for the non-stick thing. Both red and blue fiber based gaskets stick over time. I was just thinking about getting some PAM non stick cooking spray like back in the day before they had "non-stick" gaskets.

streetknight2

iTrader: (10)

Good job figuring it out man. I had a problem at first with the secondaries sticking on my Pro Systems 950, but sent it back and they fixed it. I noticed mine is idling around 12.5. I don't street drive it, but I'd like it to be better. I'll mess with the idle mixture screws first and may try this if it doesn't work.

Kinda OT, but what WOT AFR should you shoot for?

speedtigger

iTrader: (16)

My car runs the fastest ranging between 12.7 to 13.2. My car ranges between those two during a pass, but going through the traps, it is settled in about 13.1:1.

I would speculate that each car is different though. So, YMMV.

streetknight2

iTrader: (10)

Coo man, I appreciate it. I have a FAST dual wideband that will data log, but only made 2 passes with it. So I still have to figure it out.

GC99TA

iTrader: (30)

Good job figuring this out and thanks alot for sharing the info. My Pro Systems carb doesn't have this issue but one of my buddies Biggs carbs does this.

Oh, and back in the day we used to put chapstick on our gaskets to keep em from sticking. Seemed to work OK.

Pop N Wood

iTrader: (1)

That is interesting. My Holley books show the idle feed restrictors being lower in the carb down near the power valve. As per this link

http://www.carcraft.com/techarticles...e/viewall.html

Looks like Holley HP carbs put the restrictors up high while others have them down low.



The article also mentions the interaction of the IFR and the idle screws. Making them larger requires turning down on the idle screws. So for most guys with a standard double pumper with their idle screws less than a turn out you might be better off making the IFR smaller and using smaller ilde air bleeds.

speedtigger

iTrader: (16)

I think this is a revision. Older carbs have them in the location you hae depicted, with newer carbs having them where I have depicted in the photo. I think I read somewhere that this was done for drivability. Although my old 650 (4777) metering plate has them down low and it works great. So, depending on what carb you have, they might be in either place.