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Another tuning question...fuel pressure, carbs and jetting


Dan B.

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The 358W Ranger had been running OK...not stellar...just OK. Still well enough to run 13.6's and hone tires for impressive distances. But I know this thing is capable of MUCH more. From seeing what other cars are running that are similar in set up...this truck should easily run into the 12.9's.

Dad fired it up the other day for a stroll down street and it died in my driveway. It did the same thing to me last week twice when driving my daughter home from school. Cruising along and it just died. It was getting too much fuel to restart. After shutting off the fuel pump (have it on a switch) and cranking it for a while then it would fire, flip on the pump and it dies. I ended up having to run it for several minutes to clean things out before it would run with the pump pushing fuel. Strange...jetting problem?? After the instance with Dad, it never restarted. It will fire on ether but that's it.

The fuel pump is a Holley Red (second hand to me), regulator is a Holley, lines are Russel Push Lock and are running from the cell to the reg. From the reg is braided Jegs to a Jegs gauge and Holley 750 DP (Jegs reman).

The gauge is giving very inconsistent readings...one time it will be dead on 7#, later it will be 2#, then drop even lower to 1# or less. Next time it may be 6# and stay there. When trying to adjust the reg it will sometimes not go over 5# so I adjust it to where the pressure comes up to 5# then leave it. then check later and it will be 8#.

I'm thoroughly confused and ready to buy a Projection system!! Does it sounds like a pump problem, bad regulator, or ???

Matt...you feel like tuning this thing? :icon_cheers:
 


Will

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Sounds like the float level is set too high. With an electric high volume pump you don't need the float as high.

I much prefer the AFB style carbs (Edlebrock Performer) and a mechanical fuel pump that doesn't require a pressure regulator. You don't need that much fuel and you have built in complications that don't do one damn bit of good. You can burn about 1 gallon per ten horsepower per hour. So if you had 300hp the most you can burn is about 30 gallons per hour with the engine at full load. The fuel pump you have is probably good for 1,000hp.

THIS is all you need. It's probaby going to flow 50gph with pressure on it. Doesn't need a regulator.
 

projectnitemare

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See what kind of pressure the pump is putting out. If it is above 8 psi or so I would use a return regulator. If it is high like that what is happening is the pressure is bleeding past the regulator and flooding you out. I had a similar problem with the standard holley regulator. I wouldn't use a Edelbrock carb, I have one and after you throw some engine mods at it they become difficult to tune. I have to screw with my Performer a few time a summer, then I set if for winter. Every summer I visit a local carb guru and we screw with it for a few hours. Everyone always tells me to toss that carb for a Holley...even the edelbrock guys. I'll be heading to Pittsburgh probably next weekend; if you still have problems I can probably stop by.

Matt
 

baddad457

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Ditto on the regulator if it has no return line to the tank. The Holley red pump has three times the volume you need to run a carb. I run a 30 gal/hr pump and so far it's been plenty to feed a 400+ hp 331 with three carbs.
 

Dan B.

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I thought the Red pump was for street use? Says in the Jegs catalog that it runs at 7PSI and does no even need a regulator. Hhmm. A return regulator and checking the float level may be the trick.

Matt...stop by on your way back through. I'll send a PM with address (right on Route 22).
 

Will

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The AFB is easier to tune. I used Holleys for years. Then I got an AFB on a car I traded for. Once I learned about it (look on bookfinder for ISBN 0-931472-11-3) I decided to keep it. I traded my last 4779 for an old Delta bandsaw.

The main fundctional differences between a Holley and an AFB are in the power enrichment curcuits. The Holley uses a power valve, which is baically an on/off switch on the enrichment circuit. When the manifold pressure drops below a certain point it opens up an orifice in the fuel bowl and lets gas go by. It's on/off. An AFB has metering rods going down through the main jets. These rods can have 2 or three steps on them. They can vary in steps how much fuel is measured in. This is the way people screw these carbs up--just arbitrarily throwing in rods. The last step on the rod stays in the jet so you have to make sure you match the jet to the rod. It's simple, but you have to be aware of it. What it allows is very quick main jetting changes without pulling the jets out. At the track where the power enrichment isn't as important as the main jetting, by asembling a good selection of metering rods and making sure your main jets are over-large, you can do any jet change in seconds.

An AFB is much easier to track tune. You can change jetting (metering rods and springs) without risking fuel pouring out all over your hot engine. The power enrichment parts are not inside the fuel bowl. Once you understand the jets and rods, you can change the enrichment in rate and volume in seconds as well. It makes for a more responsive set-up. On any engine you need to keep track of what you are doing so when you want to make a change you do it in an organized way. An AFB makes you do that.

Another advantage are there are no diaphragms to worry about failing. A Holley has a diaphragm in the power valve and one in the vacuum secondaries, and one in the accelerator pump. The AFB is much more robust--there's nothing in it to fail like that.

Just as a Holley, you can easily adjust the accelerator pump spray.

I have to question how much the people that told you to get rid the the AFB know about them.
 

Dan B.

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I actually had an AFB on this motor for years....it was a PAIN to get running. It took a long time in warm weather to get going. Then it always stumbled and had flat spots.
 

projectnitemare

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That is my problem, the carb is very picky about everything. The lack of support with them and the amount of time in tuning it is worthless to me. I have to tune it spring, fall, summer and winter just for street use. Half of it is the engine but half is also the carb. I'm a EFI fan myself carbs are not my strong suit but I can work with them if need be.

Matt
 

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