My car's fuel pressure seems to drop from 6psi to 2.5-3psi after i let it idle or drive slowly for awhile. The fuel pressure goes back up if I drive it hard, do i have to reset the float or is it the problem with the fuel pump? Thank you

 

Why are you running 6 psi on an IDA? If the fuel pressure is varying, it's either a problem with the supply, the fpr or the gauge. What pump, fpr and gauge are you using?

 

Other members had been running 6psi. Do you run an IDA? What do you recommend? I have a Carter 4070 pump, Holley FPR, and the Re-speed gauge.

 

ive seen different fuel pressure recommendations for the webers. it depends on the application and if you've done any mods to increase fuel flow thru the carb top.

in any case, the carburator doesnt really have anything to do with what the pressure is. that is the job of the pump and regulator.

not sure where to start, but if its changing that kind of suggests either a flaky regulator (it happens, look at wall st), or maybe inconsistant voltage to the pump.

 

I think the regulator is fine, I can still lower the fuel pressure but it wont go any higher after it goes down. How can I check for the pump voltage consistency?

 

1st id check the fuel pump ground, and hey maybe its worth adding another or cleaning while you're in there.

to check voltage i'd put a voltmeter on the fuel pump wires and drive around, it should be pretty stable.

 

To run over the rec. 4.5 psi, you need a larger needle/seat...like a #300, or grossejet (not my favorite) and a good reg. Run a return if you want to reduce vapor lock if you live in a hot area...

 

I do have a 300 needle/seat.

 

I'm running the Weber dual DCDs instead of the 2 barrel IDA. Both carbs take 4.5 psi of fuel pressure, not sure where you came up with 6 psi, that pressure is more common for the Holley carbs. The following links will bring you up to speed on setting your IDA. Keep in mind, many of the 48 mm IDAs were set up for street port or larger ported engines. If yours is a stock port, you may need to install smaller venturi and start over with re-jetting. A wideband, along with a vacuum gauge dyno tuning will help you achieve the best tuning, performance, driveability and fuel mileage.

http://www.vintagerotaries.org/index.php?showtopic=17

http://www.vwtrendsweb.com/tech/0308...ce_weber_carb/

http://www.vintagerotaries.org/index.php?showtopic=28

 

Sorry Trochoid, that is not my problem right now, Wackyracer is the one running 6psi and he had been running it for a long time on different cars. My problem is the fuel pressure, which doesn't relate to anything you posted here. The jetting and venturi size is twhat RB recommended for me, I believe it is ok. I am in the process of getting a wideband. Thanks for the info though.

 

I've had a similar problem with my fuel pressure too. I've run 3 different fprs, return and deadhead styles and the pressure doesn't seem to stabilize. When it gets up to 6 psi, the plugs carbon up and I have to change them just to get the engine started. It has gotten to the point that it's become quite frustrating. If Wacky is helping you, great, he seems to be the IDA guru.

As my last resort, I'm beginning to an suspect electrical/voltage fluctuation since I just recently found that the momentary switch for the line-lock has been sticking.

 

I am going to check the voltage first.

 

Is the voltmeter going up when pressure goes up? Is the voltmeter going down when the pressure goes down? Sounds like an alternator prob.

If it's the Holley FPR I've seen those go crazy and need to replace the spring and diaphragm to fix. And, I use the low pressure spring and only use 3psi on the IDA. When I used 4psi the float bowl overflowed.

 

I'm having the same exact problem. I will check voltage as well.

 

I run my race car's IDA at 5.5 psi at idle. It will drop down to about 4 psi after a very long straight on a road race track. The carb is feeding a 13b PP that drinks a gallon of gas every 3.5 minutes.

The Holley regulators are inexpensive items, and sometimes they do act crazy. If your pump voltage is stable, then buy a new Holley regulator. Make sure you have a good high flow rate, low pressure drop filter before the pump and the regulator.

If the voltage to the pump is not reliable, stable 12+ volts, then do like most real race cars do and run a seperate circuit and switch and fuse that only feeds the fuel pump. That circuit should feed directly from your main power source (kill switch.) On my race car, I have seperate, dedicated circuits for the ignition and for the fuel pump. Those are the only two circuits that must work right to make my car cross the race finish line, so I make sure they feed straight from the main power cable.

 

Holley blue regulators tend to go bad after about 1000 hours of use and need to be rebuilt. I just replaced mine with a mallory and it won't lower fuel pressure more then 8 psi, but my IDA runs fine on it. no leakage and gas mile and throttle response hasn't changed one buit so I say fuuk et!

 

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