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View Full Version : Fuel pressure issues, I need some help.



AmickRacing
07-31-2011, 12:22 AM
This problem somewhat snuck up on us, I'll give you a brief run down of what went on...

I put a new Willy's carb on around a month ago, prior to that the car was running decent, but only had a couple nights on it this season. It's a steel headed WISSOTA motor belt drive fuel pump off of the front of the motor.

With the new carb on, it seemed to be kinda dead through and off of the corners, kind of blamed the carb, did some tweaking (per Willy's), it helped slightly, but still wasn't great. Paid more attention to the fuel system, noticed the pressure was low, like 2 lbs at idle, and 7 on the high end. Adjusted that a bit, helped some, but noticed that the fuel pressure was bouncing real bad down the straight's. Can't say that it was or wasn't doing that before, but it was noticeably worse.

Put the old carb back on, checked the filter, tank is clean (no pickup, just RR corner fitting), opened the holley regulator and it was clean. Still had the issue.

This week I paid more attention to the gauges, noticed and felt that in the corners it was bobbling really bad, very low pressure in the corners (bouncing between 0-2, then 1-4 on exit, then 6-9 down the straight). We swapped fuel regulators, put a different carb on, checked the filter again, changed fuel pumps. The other fuel pump had a crack where the fitting goes, so we had to re-swap them.

Anyway, main even, same story. Of course the more hooked up the track is the worse it is, but even in the slick I was struggling with it. And of course when the motor isn't putting out the power it should, the car goes to crap.

I'm leaning to believe it's a fuel line that's sucking shut. Today in the shop we ran a short line from the fuel pump into a fuel jug and ran it off that, when you rev it up to 5k, the fuel pressure will go up to around 8.5 or so, it's solid for a couple seconds then starts bouncing around about 2 lbs. I know the shop test isn't as good as the track, but gotta try something. Tried a different gauge too, same thing.

The fuel lines are kind of old, so replacing them wouldn't be all bad anyway.
I'm struggling to believe it'd be the fuel pump, there's really not much to the fuel pumps internally. I'm pretty sure there's no air leaks or cavitation going on... I'm kinda stumped. Any weird things to look for that you guys can think of?

Egoracing
07-31-2011, 09:02 AM
Other than make sure the filter is in correct and the system is clear I think you are on the right track. I do know of one instance when the car would die going into the corner after checking everything the overflow check ball was found in the fuel line to the tank. When the car was running the ball would float in the line but when the RPM was raised to what you would see on the track it would rev to a point and the pressure would drop. The ball would come up the line to the tank fitting and shut the fuel flow off. He found it by blowing air thru the lines from the pump back and the ball popped out.

aaallstar
08-02-2011, 11:54 PM
Had something like this with my modified. First thing I did was have the pump flow tested and it was flowing different with every time they checked it. Turned out to be the o rings on the kse pump were letting in a little air. This was a problem but not the problem. It turned out that my stainless filter became plugged with this real fine black stuff like the inside of the old lines I had. Even though I cleaned it the filter was still plugged. You could really see it if you shined a flash light through it. I fought that one for like a month.

HuckleberryB4
08-03-2011, 01:36 AM
We had a similar problem last year when running a belt drive pump. When we finally tracked it down, the mandrel bolt for the pump pulley on the balancer had loosened up and allowed the balancer to shear the keyway and free spin on the crank snout at higher RPM's. When this happens the motor obviously revs but the pump pulley doesn't spin fast enough to provide the needed fuel pressure.
The easiest way to tell if this is you're problem is to check the timing. If it idles ok but you're timing mark is off there is you're problem. If this does happen to be your problem don't bother just replacing the keyway, you will offset the keyway or shear it every couple of weeks. You lose you're press fit tolerance on the crank's snout and the keyway can't handle holding the balancer by itself. We had to pull the motor down and have the crank sent out and repaired.

Also check the cog's on the belt and both pulleys. Make sure the belt cogs aren't worn real bad and jumping at higher RPMs and that both pulleys aren't packed up with dirt causing it to jump.

If it's doing it from a jug you've already eliminated half of the fuel system from the pump back. And it's not the carb since 2 different carbs haven't fixed the problem and I don't see how a return line would play a factor. So I'm guessing it's something with the pump and it's components or between the pump and carb. Good luck tracking it down.

AmickRacing
08-04-2011, 12:06 AM
I can't say for sure we've figured out what the issue is, but I did get myself a new filter and some new fuel line. In the shop (poor test I know, neighbors might frown on the street test), it seems to be better.

Hopefully this is it, I've got enough problems to fight with out this kinda stuff too!

cfg11
08-04-2011, 02:04 PM
What kind of fuel cell is in your car? We are having the same problem, gets real bad when the track is hammer down. We have swapped fuel pumps, carbs, regulators, filters, checked out fuel lines, and found nothing wrong. next step I guess is tank.


If it is the rolover ball, how did you fix it?

Egoracing
08-04-2011, 02:45 PM
Put the ball back into the cage and screw the fitting back on, the whole thing fell off. If your car is blubbering and popping it can be slightly rich and when you go to get onto the pedal it is dead or acting up then it will clean out and bust the tires loose. I have dropped 1 jet size before and it helped out the problem.

rubbinsracin
08-04-2011, 03:05 PM
we lost the rollover check ball one time. our pickup tube sucked the (not a nice word)(not a nice word)(not a nice word)(not a nice word) thing an inch and a half into the pickup tube as the metal check ball was just a hair smaller than the tube and plugged the (not a nice word)(not a nice word)(not a nice word)(not a nice word) thing right up. burnt out our fuel pump too.

first thing we did when we put the ball back in and screwed the holder back on was to put some blue loctite on those threads as it is supposed to be "fuel resistant"

Egoracing
08-04-2011, 06:28 PM
we lost the rollover check ball one time. our pickup tube sucked the (not a nice word)(not a nice word)(not a nice word)(not a nice word) thing an inch and a half into the pickup tube as the metal check ball was just a hair smaller than the tube and plugged the (not a nice word)(not a nice word)(not a nice word)(not a nice word) thing right up. burnt out our fuel pump too.

first thing we did when we put the ball back in and screwed the holder back on was to put some blue loctite on those threads as it is supposed to be "fuel resistant"

You run in Ga? I had a friend tell me that at Screven there were like 5 cars in 2 weeks that had check ball come out and get sucked up in a few weeks after he had it happen.

AmickRacing
08-05-2011, 12:07 AM
What kind of fuel cell is in your car?

It's a black one... lol
Nothing fancy, just the plastic style bladder that's in a tin can. 90 deg bulkhead fitting in the RR corner, return in the middle, roll over flapper gasket over the tank hole, got a vent line that runs to a mini k&n filter mounted towards the bottom of the tank on the left side, and that line has the check valve in it.