Fuel pressure advice needed for 94 Holleys

[Littleman]

I am running a six two get up. Since this is new to me ,I elected to run the four corners and blocked the center two to start out with. I am running a Holley red electric pump with a Holley 1 to 4 psi. reg. then I put a pressure gage between the reg. and the carbs. I set the pressure at 2.5 psi.. Go run the car and come back and the pressure has changed. I started using a stock mechanical pump at first And got a wild variation in fuel pressure after I set the reg, so I went with the electric set up, which helped alot, but still seems to wonder alittle. I was thinking maybe some sort of return line? I was wondering what has worked with anyone that has played with the multiple carb set ups. I have lots to learn , it is painfull sometimes to look and function kool, but I would not have it any other way,Littleman Thanks

[I go pogo]

BTTT

[Scotch]

How did you "set them up?" Did you go by vacuum (best method), measure the throttle plate angles, count the turns on the adjustment screws..?

If the cars aren't synchronized, they'll not work correctly. Best way to do this is on a dyno with exhaust gas temperature probes in each header primary pipe, and then you can fine tune to get equal temps coming out of weach cylinder. Since your engine is already in the car, this may not be possible, so you have to check the vacuum pull on each carb and read the spark plugs to make sure all 8 holes are getting good and equal fuel.

Yes, fuel pressure is a critical part of this equation, but its far from being the only part...

Let us know what you've done to get the multiple carbs in sync so far, and it'll help us know where you're at and where you need to go.

You may have seen another post about the "temperature ray gun" tool that gives instant temp feedback on whatever you aim it at. This would help considerably if you could use one on your primary header pipes.

If you've got any friends with exhaust analyzers, it would also help to check out the exhaust coming out of each header to ensure you're close to stochio on those and also that they are equal.

You can make this system work very effectively, but you've got to tune it to it's finest point. Like Weber carbs, they work amazingly well when they're all dialed in, but when they're not it sucks total ass.

Let us know where your tuneup is at now, and what you've done so far. Then, we'll be able to help you much more.

Scotch!

[Littleman]

We used a uni-sync, temp gun on the header tubes, as far as street driving the thing works great, it just get a-little pissed off when i put all of my foot into it. I want to first stabilize my fuel pressure then go from their. I do have a couple of cylinders 1 and 2 seem to run alot cooler than the others ? Have not figured it all out yet, still trying to learn the correct name for every part in them.This weekend I reset the float settings to 1 1/4 And jetted down from 50 jets to 48..... right direction I do not know, still runs good on the street. But I would like to take it down the strip. The guy I got the carbs from had the floats set at 1 1/2".......Littleman

[Scotch]

Fair enough. You've done plenty to get them close, and stable fuel pressure is a big deal. So, here's some tips:

You said you had a Holley red and a non-return line regulator, right? Put a gauge both ahead of and behind the regulator to check it's function. Check the voltage to the pump also- if the voltage varies it may be changing the pump speed a little, which may be all it takes to push more fuel past the regulator and then past the needle/seat. Obviously, this kind of diagnosis will require a pal or two to help out and watch gauges etc.

Do you have access to a chassis dyno? I'd LOVE to see what's happening to fuel pressure and pump voltage when you "get into it" and it runs like poop.

It sounds like the idle/midrange stuff is set okay if it runs good in "street driving". This is good and reflects your tuning up to this point. The midrange-to-wide open transition and such seems to be the problem. Let's think about that for a sec...

If cyls. 1 and 2 are both running colder than the rest, that might be reason enough to blame the manifold design. If its designed in such a way that cyls. 3 and 4 are getting a good shot at drawing air/fuel in, but 1 and 2 aren't, you may want to increase the opening between them with a slant toward the forward cylinders, making their ports larger than 3 and 4s so they get a more balanced diet of fuel.

Check your floats to make sure they float at the same level. Sometimes, 2 identical floats will react differently to float level. Also, ensure your float linkages have the same angle in their hinge mechanism. If the floats are closing/opening the needle/seat at different times, the identical adjustments on the metering screws may have vastly different effects. With a single carb you'd never notice such things, but with a multiple setup, this becomes a big deal.

Do I even have to mention checking for vacuum leaks? I spray carb cleaner around the bases of the carb(s) while the engine is idling and listen for any change in the rpm. If you hear an idle rpm change, you've just found a vacuum leak. Spray around the entire circumference of the intake, too..

If you get the fuel pressure dialed in, ensure all the floats and needle/seats are functioning identically, and keep using similar tuning methods as you've already been doing, but on a chassis dyno where you can "drive" the car and see what's happening, whatever problems you have will soon show themselves.

Patience and persistence will win every single time. Don't get frustrated, and keep at it. Soon, it'll run even BETTER than it looks, and it looks pretty fuckin' cool..

Scotch~!

[Littleman]

Scotch, thanks for all the advise, I will check the voltage at the pump, I looked past that. I like your idea to check for leaks also. I learned about a chassis dyno right around the corner from me today and will do alittle more dialing in on this truck and take it to the dyno. Sounds like it will be money well spent, especially if it gets this thing down the track....Thanks again......Littleman

[Scotch]

Keep me informed. If theres anything more I can possibly do to help ya out, I will.

Scotch~!