1st Gen, Fuel starvation?

[ScottNutter]

Well I drove around BeaveRun this weekend, I would say competed but that my draw the rules nerds with my interpretation of compete And I must say that I ran faster than I did in a lapping day, where I noticed the left hand stumble in turn one, but did not notice the stumble this time running 3/4 tank of gas. So I guess my solution for now will be a few dollars/pounds of 87 octane gas. Hopefully I will out grow this patch (ie faster) and will be forced to find another.

I'll see how it works 10/19-10/20 @Nelson where I have had problems in Turn 4.

[bobrx7]

Scott,

I'm new here, but Ive been posting articles with Mazspeed for several years. I have also woked closely with Paul Yaw and we run his carbs on my Solo car and the ITR Mazda I crew for.

Several things come to mind with your problem:

If you have your fuel pressure regulator mounted to the left of the carb, as many people do for convenience, you will have a stumble in sweeping turns. Move it directly behind the carb (it's a tight fit) and keep the hose run as short as possible.

The Holley (Summit) regulators have a bad habit of pressure creep. Add that to most aftermarket guages being WAY off, and I can assure you your are running too much pressure. We have found that 1.75 psi is ideal. Yaw sells a certified gauge for about $50 that is dead-on. There is no brand name on it, otherwise I'd tell you who to call. You can search for gauges. Try to find a certified 1-15 psi unit rated at +/- 5% acuracy.

Last, Grose jets are VERY poor inlet devices. A standard needle and seat lapped with extra fine compound works well. Use the spring loaded type like the originals. These come in the factory carb kits. Set float height to .62 in. using a dial caliper. This MUST be dead on to get good results.

As a fuel specialist, I can assure you good results. Unfortunately, I can no longer endorse Paul Yaw. His customer service has become unacceptable. That's a shame, since he builds a damned good carb.

bobrx7

Crew Cheif
#46 ITR, WHRRI,
Novi, MI

[Scott Nutter]

BobRx7,
Thanks, I have read several of your post and articles from Mazspeed for several years, I even posted a few times, and have used much of your advice. Welcome.

I had another racer give me the same advice about placing the regulator between the carb and the firewall. I was wondering why? Does it have to do with the lateral position of the regulator or the length of the line? With the stock pick up on the carb the line could not be much shorter than it is now.

I have never rebuilt a carb... Oh great another winter project At least I have a street legal Rx7, and a few spare carbs, I can try it out on.

[Dave Damouth]

The column of fluid acts like a manometer when cornering. You end up with the fuel pressure going up when turning left, down when turning right(assuming the regulator is on the driver side). Placing the regulator closer to the carb minimizes the column of fluid. It only becomes an issue on cars that run really low fuel pressure, like ours.

[Scott Nutter]

Thanks Dave,

After a lunch time discussion with a co worker I guess the hot setup would be to have as short as possible run from front to back ( wouldn't want to stumble when I am pulling 1.2Gs accelerating out of a corner ) and make the U from the regulator to the carb have equal length ends to minimize the pressure drop during cornering.

[Quickshoe]

Originally posted by bobrx7:
Yaw sells a certified gauge for about $50 that is dead-on. There is no brand name on it, otherwise I'd tell you who to call. You can search for gauges. Try to find a certified 1-15 psi unit rated at +/- 5% acuracy.

Try:

www.gaugestore.com

I recently bought a very accurate air pressure gauge. They will only sell to those with a resale license. They may just have the perfect fuel pressure gauge. 0-5psi with +/- 1.5% accuracy for $25 or so.

[ddewhurst]

After talking with Paul about the gauges he sells & the fact that he didn't have one to send out a couple years ago I went snooping & found a 0 to 5 psi that is within 1% across the mid 1/3rd range of the gauge. The accuracy is less at either end of the range. Most all gauges that I have viewed have more accuracy through the mid 1/3rd section & are further off at the ends.

Made by Noshok of Switzerland

Try Noshok.com

Sold by McMaster-Car 1-630-833-0300

Have Fun

David