Diagnosis

[ed mayo]

Looks like the throttle bell crank runs into the orange wire harness. All those filters don't matter if the tank filter is dirty.

[pemz0r]

I also contacted Paul at Performance Oriented to get his help and he is just as stumped as I am, but I did find out that my PMO "Anti-percolation" fix was clogged up on the right bank. I still need to check the left. We both think that won't fix the issue.

[dannobee]

That helps. Check the fuel flow rate after all of the fuel filters. (Or remove the two on the carbs and see if you can blow through them without much restriction). Get an old jug or bucket and measure the fuel flow with the lines disconnected. You should be flowing almost a quart in 15 seconds. If it's a cup or less, it needs to be fixed.
Is your canister filter the Fram HPG-1 or equivalent? If that's the case, that's the only filter you'll need.

[pemz0r]

Originally Posted by ed mayo

Looks like the throttle bell crank runs into the orange wire harness. All those filters don't matter if the tank filter is dirty.

Thanks for spotting that but that was an old photo and probably realized that. Here is the current setup and the fuel filter

[pemz0r]

Here is thing I can't wrap my head around.

In auto X we have 4 runs almost back to back. The 1st and 2nd runs are flawless with the engine, but it's the 3rd and 4th that start acting up and in my mind the only thing that changes within that time is heat.. It's the only variable that changes. I am doing the same turns at roughly the same speed 4 different times.

If it was a fuel flow or any another issue I would experience it within the first and second run..

[Trackrash]

Originally Posted by pemz0r

I also contacted Paul at Performance Oriented to get his help and he is just as stumped as I am, but I did find out that my PMO "Anti-percolation" fix was clogged up on the right bank. I still need to check the left. We both think that won't fix the issue.

Agree. I went through that, with no positive result. In fact one of my carbs has the drillings and one doesn't. Before plugging one set I opened the holes up. Never made a difference.

What did help, is lowering the float levels to the minimum on the gauge.

As mentioned I would get it warmed up so it is exhibiting your problem and check the fuel flow.

Or, set up a method of measuring your gas flow. Measure it. Then use a heat gun on your fuel pump. Measure again.

[dannobee]

Since the pump is electric, check for a voltage drop on both the positive and negative sides of the circuit. It could be an arced connection or poor ground. That would also help explain the heat/time issue. But again, check the fuel flow first. It was my very first thought when I watched your video, and I’ve seen it happen numerous times on the track.

[cmcfaul]

I had similar issue. Was a clogged screen in the fuel tank.

Secondly, would see fuel starvation when running on the track with less than half a tank of gas. coming out a long turn and or hard braking fuel pickup would not be submerged. Fuel tanks back then did not have baffles.

Chris
73 E

[Dave Kost]

Is your fuel tank vented properly?

[Walt Fricke]

A lot of racers connect the rears of the two fuel rails together with a length of hose. The theory is that if some obstruction shows up somewhere in the loop, having access to the float bowls from either end should keep it from causing mischief. Although I am dubious that these straight forward and relatively large passages could have issues like this, I do it on my engines.

With that fuel pressure gauge you ought easily enough to see if there is a pressure difference between starting up fairly cold, and warm and hot running. I suppose you could have proper pressure at idle, but if flow is inadequate from the pump while hot, at WOT the pressure would be lower?

If you have any kind of data logging, it is easy enough to buy a pressure transducer to send a variable 0-5VDC voltage to the data system, where you can convert that to PSI. Then you can record and compare what the 1st run does vs. the final, rough running, runs.

Is your vacuum accumulator connected to the fuel pressure regulator, or is that just a choice of where to mount things?

The vacuum line goes to your distributor? Is that an idle retard? If the distributor centrifugal advance somehow gets sticky when hot, could that cause these symptoms? You might compare how it feels to your fingers when you pull the cap and advance the rotor against its springs when cold, and when hot.

[pemz0r]

I uploaded a baseline video of the fuel pressure before the filters. I calculated 54sec for a 1 and a forth cup.
https://youtu.be/4u870CEjxqQ

Vacuum accumulator is not connected to the fuel pressure regulator, just the location.
The vacuum line does go to the dizzy, I will check to see if there's a difference in feel between hot and cold.

I believe my fuel tank is vented correctly and wouldn't the baffles only work in turns? The fuel exit is towards the back of the tank, so a straight should force the fuel to the back of the tank. I am experiencing the issue straights and turns, plus AutoX is only turns.. and the first couples are flawless (not my driving, the engine) so I don' think it has to do with the baffles.


Here is the fuel pressure regulator around 100F


I guess the next step is too run a gopro inside the engine and see if the pressure falls when it gets hot.

[pemz0r]

I did another test with the filters and it's the same amount within the same time frame.

[Lapkritis]

I believe aftermarket suppliers such as PMO call for higher pressure than 4lbs for track use.

Sent from my SM-N960U using Tapatalk

[Trackrash]

Originally Posted by Lapkritis

I believe aftermarket suppliers such as PMO call for higher pressure than 4lbs for track use.

Sent from my SM-N960U using Tapatalk

Interesting.

FWIW, my pump puts out between 2 and 3 psi. It's an old Facet solid state. I have never had fuel supply issues even after a 20 min session at Sonoma with my warmed up 3.0L.

[dannobee]

There ya go, you've found your problem! Now to fix it. Remove the pump and see what volume it free flows. If it's about the same amount, replace it. If it flows more like a little garden hose, look for a restriction in the tank or a kink in one of the hoses.

Even a modest 200 hp engine at a reasonable BSFC of 0.5 is gonna need 15 gph fuel flow just to make the power. Your fuel system should flow a LOT more than that, just to keep the carb bowls full on heavy acceleration.

[pemz0r]

Dannobee, I don't see how we fixed the issue yet. We determined that fuel flow is about the same with or without the fuel filters. Remember the car runs awesome until it gets to 210 degrees. So tomorrow I will put a gopro in the engine bay and drive it hard. I will keep track of the time/temp and see what happens to the pressure gauge.

[Lapkritis]

Round up to 1.3 cups per minute. Rough math puts the pump performance then at 78 cups per hour.

78/16 cups in a gallon is 4.8gph. That's a problem...

Sent from my SM-N960U using Tapatalk

[dannobee]

A decent fuel pump for a 200hp car should flow at least 50gph. Your 4gph is nowhere near enough. And remember, what you got on your test is the pump's free flow output. Make it pump up a few pounds of fuel pressure and it's gonna drop even further. Given your 54 second test, it should have pumped almost a GALLON of fuel.

You need to fix the fuel flow problem. I know it's not fun or glamorous, but it needs to be fixed before you take it to the track.

[Dave Kost]

I think you have a combination of issues.

Small vent tube on a 1966 912 gas tank. The plastic vent line could be kinked. I don't think the 1966 gas tank had a charcoal system as did the 1969 912 fuel system did. (I think the vent system in a 1966 was just a looped plastic line that vented to atmosphere.) The 1/4 line next to the fuel sender in the gas tank.

Partial blocked gas tank screen. 50 year old gas tank with residue in the bottom.

No swirl pot in gas tank. Chance of fuel pump running dry when fuel gets low in tank. Pulling air into carburetors.

What happens went the gas cap isn't fully sealed? Does the same conditions happen?


I would clean the fuel system starting with the fuel tank and clean and replace all the hoses. OR - pull the sending fuel sending unit out and see if you can see the condition of the filter screen and tank.

Also, check the small fuel hose that goes from the fitting on the gas tank to the tunnel, it could be clogged or collapsed.

Double check the gas tank vent. Does the tank suck in a lot of air when you open the gas cap?

[Lapkritis]

Fuel flowing yet?

Sent from my SM-N960U using Tapatalk