Losing Power...

[jpetillo]

I'm trying to figure out why my car loses power late in the race.

What happens is that on the last few laps, the car just loses power and then it comes back and then it loses it again. It feels like loss of fuel. At LRP it only happened on the right hander right before No Name Straight. It would happen pretty much every lap and was like a half-second of no fuel.

This past weekend at NHMS, my daughter claimed the same thing for two sessions. The last two laps the power came and went. After the race she still had over 2 gallons left. One day it was raining & high 50's so we though it might have been frosting of the manifold, since it did show signs of that along the neck of the manifold. But then it happened and even more so during the dry, warmer race the next day. If you know the track, it happened on the uphill in turn four and then the short straight after turn 10. We can't find any correlation. She said it was like she wasn't giving it full throttle - still had some power. We checked the linkage and it's fine - opens the throttle fully.

I checked the fuel cell, and the pickup is right down in the bottom in the rear RHS corner. There is good flow. The breather is fine as well and the fuel call is in god shape - perfectly clean inside.

I can blow through the fuel filter.

The carb float level is within spec (Jim Sching's book).

Carb float valve & seat: is clean.

New battery and it's charged between every session.

There was no skipping, so I don't suspect the ignition. But a hot coil came to mind. I run points still.

Thanks, John

[remmers]

Perhaps check for vapor lock in the fuel pump? It would kinda make sense that you're losing all your fuel in the left hander and then don't have any left in the bowl to accelerate away with. Seems like it would be a long-shot but it could be possible... I had a similar issue at NJMP where I spun and the car died on me, even though I had both feet in. Took me a whole lap to re-fire. When I asked Dave Carr about it he said likely vapor lock in the fuel pump. I also adjusted my fuel test hose to be a high point in the system so that if there's any air bubbles, they go and stay there instead of getting to the carb. Haven't had a chance to test it yet, but I shall find out how well it fairs this weekend at NHMS myself.

[CSatterley]

Was the tach jumping at all? Had an issue at mid-ohio where it ended up being a battery cable connection coming off the wire. It lost power when I shifted and then came back and then lost power again.

[jpetillo]

Thanks for the replies.

I'm looking for long shots! It could be vapor lock, I guess. If so, what do I do to prevent it?

No, there was no tach jumping. I'm pretty certain it's not ignition related. No skipping or tach dancing. I just changed the battery and made sure the connections are all clean and solid. I can't get the power switch or ignition switch to skip a beat by wiggling and giggling them. I'll check the negative cable to the chassis connection, but I doubt that would be a problem only at the end of the session.

Thanks again.

[remmers]

Vapor lock is resolved by replacing the fuel pump with one you know works. (Dave Carr's remedy) I'd also check to make sure you don't have any downward bends in your fuel line where air could get trapped. That's all I can think of to resolve it.

[jpetillo]

Thanks again - I'll give Dave a call.

[Dietmar]

John:

Vapor lock is a condition found on older cars ( like the street VW) where the fuel IN THE LINE actually vaporizes because it is getting too hot before it reaches the carb. Rarely is it a cause of the fuel pump. Since you had this on a cold day, I doubt that it is vapor lock.If the pump is weak, then you will have an issue with the amount of fuel in the bowl, and since you said ONLY ON RIGHT HAND TURNS, I would suspect that it has something to do with the carb- and fuel.

If the power is full on while you are on the straights, but falls off in or shortly after a turn-especially the same direction, I would definitely check the float level. Either you are getting too much fuel where raw fuel is spilling into the carb throat, or you are getting too little and the engine is starving, but comes back on once the bowl fills up. You said needle valve is clean- but does it shut off the fuel?

Fuel pump could be weak, but since it is in the turns, I would suspect the carb.

Would be glad to look at it for you, but I'm going out of town for 2 weeks ( unless you are not in a hurry)

Hope this helps
Dietmar

[smsazzy]

If it were me, I would replace the coil, points, fuel pump and the float switch in the float. All those parts probably will run you less than $150. That is a heck of a lot cheaper than missing a session. Save those parts and mark them as "suspect". As you replace parts, you can use them as spares. Eventually, you will find the bad one.

[kps]

Take a look at your fuel cell vent line. Without outside air pressure the fuel pump cannot receive fuel from the cell. This takes some time to happen as the cell can compress to some degree to compensate. Check for a crimp in the vent hose especially when the fuel level drops and the seat position may change a bit. Make sure the check valve is clear. John

[jpetillo]

All, thanks for the comments - very helpful!

Dietmar, yes I did check the float level, but I agree the valve might not be shutting off. Yes, I can say that the cutting out was always associated with a right hand turn. Certainty idling in my driveway the valve was closing because I was able to check and change the float level. I will change that and the pump! I need to run the car this weekend, so I can't send the carb out. But, thanks for the offer.

Smsazzy, I changed the points - actually the whole distributor - three race weekends ago when it was stuttering at high RPM. That problem went away. I have a new coil and will drop that in, too. I've only seen a coil cause a stutter and not allow higher RPM and/or die completely. Both had to cool before running properly again. So, I'm doubtful of these, but will to the carb changes.

KPS, This could have been it. I did check the fuel cell lines in and out. All flow freely - at least they do now. I blew out the fuel line into the cell and then tried by blowing with my mouth through a hose into the fuel line and the vent line to feel the resistance. My vent line is all new metal encased, so no collapsing/pinching. It all breaths well now. I can push on the cell and push fuel out, or air, depending on which line I block with my finger. Before, when I had the fuel filter (which I'm changing) in line it did not want to push fuel through when I pushed on the cell. I'll try that again with the new filter.

Thanks again, John

[brian]

Everyone has made some great points about fuel lines and vents. I agree with Dietmar on the vapor lock issue, probably not an issue. Make sure there are no air leaks in the fuel line from the tank to the pump. I've seen loose or torn fuel line at the pump inlet fitting cause air instead of fuel come into the system and cause starvation. If you have the pressed in fittings in either the pump or carb, make sure they are tight. Either replace the pressed in fittings or safety wire the hose clamp to the pump or carb to prevent the fittings from falling out. These fittings have been the source of many VW fires.

[SR Racing]

Since you initially said it was ocurring in a corner.. I suspect a carb float level issue. It may show up later in the race simply because you are pulling more G's as you get faster. Most often the failure is due to the counterweight coming off of the float or simply a high float level. This usually causes a short period of flooding (1/2 to 2 seconds). At WOT the carb then clears in a second or two. If the failure is not only in the corners, then it's probably not that. Many times it will only happen in one particular corner, or all heavy rights or all heavy lefts, etc.

[satterley_sr]

I have had smilar problems where it would cut out in turns when hot. One time it was the coil + side grounding on the firewall, my son saw a burn mark and we identified the problem. Another time it was a warped carb cover, it would allow fuel to slosh into the throat and flood the engine. One other time it was a bad condensor but I think you changed that.


Hope this helps, good luck.

Dave

[jpetillo]

Thanks again.

Okay, for the possibility of a fuel line leak leading up to the fuel pump, I'm going to check that the fuel exit plumbing from the fuel cell doesn't have a leak inside. My Fuel Safe has the fuel line exiting about 2" from the bottom. This is very close to my fuel level in the tank when exiting the track. Steve Pastore mentioned this today as well. I'll also check any pressed on fitting.

The float's counterweight is fine. The float level should be fine, but I'll check it again when I put in the new valve.

The thought of going faster and pulling more G's near the end of the race entered my mind, since that's what happened from reading lap times, but one of the days she had the power loss was in the rain, and the G's were not nearly as high.

Thanks again, guys!

[halifax]

Since it was mentioned as a diagnostic rule out earlier in this thread, what are the causes of a jumping tach? Mine gets very bouncy at the higher RPMs.

[jpetillo]

Since it was mentioned as a diagnostic rule out earlier in this thread, what are the causes of a jumping tach? Mine gets very bouncy at the higher RPMs.

Usually that means it's ignition related. For me it was two things. The first thing was a bad battery. I always keep in on a smart charger, so I go out fully charged. It would spin the engine over just fine with the starter, but if I measured the voltage when I came in from a session I had about 10.5 V - not enough to reliably run the ignition at high RPM. You have to check it soon after coming in - before it recovers.

That got me from 4500 RPM to 5500 RPM. But I still had a misfire (jumping tach). I then changed the distributor, and the problem went away completely. Whether it was points or condenser or a crummy distributor, I don't know. John

[brian]

JIm S knows the exact number, but our ignitions can run on very little voltage. Assuming the tach is good and a worn out movement is not causing the needle jump, the most common source of this problem is a worn distributor. Wiggle the rotor and see if it's sloppy. Confirm with a dwell meter. If the dwell reading is all over the place, change the points and recheck. If it's still jumping, replace the dist. I've seen that the drop in electronic units really settle down the uigh rpm dwell as well.

[VDF1]

This sounds remarkably like a tiny air leak into the fuel line where it connected to the fuel filter that I had once. It didn't leak fuel and it only sucked air at high rpms (loss of power)--and it was intermittent (very strange). I never figured out why it was intermittent, but once I sealed the leak by changing gaskets I had power again. I had one of those glass fuel filters (looked cool), but changed to a simple plastic/paper fuel filter after that weekend. Leroy

[Steven McWilliams JR]

My engine would do that at T5, Summit Point, a very sharp left hander, well the only real left hande after full break going down hill. This caused the float and fuel to move forward at that point. take the top of the carb off, and put silicone on the gasket, after I did that, I never had the problem again.

Good Luck,
Steven

[smsazzy]

If you're talking about the gasket between the top and bottom of the carb, I don't think I would ever put silicone on that gasket, but that's just me. Sounds like you may have had a warped carb.

[Dietmar]

Steven Mc:

I agree with SMS... as I too would never put silicone on that gasket.
Take the top off and surface the top and the body on a piece of glass and some wet/dry sandpaper. With the gasket off and the two parts together you should not see any light between the two.
And replace the gasket!
Dietmar
Quixote Racing

[hardingfv32-1]

... And don't over tighten the screws when you reinstall the cover.

Brian

[Steven McWilliams JR]

Dietmar, and SMS--

The carb wasn't warped (cheapest carb I could get from Carr w/ 1 race on it)
we just rubbed a thin layer of RTV on the gasket underneat the top that surrounds the float and another thing (I don't know carbs sorry)

would the negative be that the RTV would get in the fuel?

This didn't happen and it fixed the issue, I'm just wandering.
Steven
P.S. didn't over tighten the scews, thanks Brian

[Dietmar]

Steven Mc:

It might have solved the problem ( or masked it) until the silicone is eaten by the fuel.

Next time you have the top off the carb, simply place a straight edge along the top of the body and look for light under it. Do the same with the top along the edge.

Then again, maybe the screws were not tight enough the first time!

Something to look at as time permits.

Dietmar
Quixote Racing

[brian]

you will have to remove the accelerator brass boss, watch out for the brass ball lurking underneath, and the two brass studs that hold the float shaft in place to finish the car and top. Place some wet and dry on a flat surface, like a piece of glass, and rub the carb and top around on the paper and observe the marks you make. Low spots will show up as no hits and continue to sand until the entire surface hits. Clean well and replace the gasket.