Visit The Dirt Forum for More Information

Author Topic:   Help! I am stumped.....
Dirt Forum Champ
Total posts: 968
posted May 02, 2004 06:32 PM  
Got a case of motor gremlins that has worn me out! Scenario---two weeks ago I go out in hot laps and was a rocket. Qualify and the car has a high rpm miss. Before feature I check timing, float levels, and change fuel filter. Feature the car runs perfect. Last week --Hot laps car has high speed miss. Change cap and rotor. check timing. Miss in qualifying. go thru carb Install new spark plugs...great in feature-----miss reoccurs.
At home--blow air thru fuel lines check distributer, This week----good in hot laps. Miss in qualifying- replace carb and's a dog! High rpms it acts like its got a rev limiter at 5000. 2 good DUI distributers. 2 good carbs. Pops and cracks and tack jumps all over the place.
The battery is fully charged and I run an alternator. The power wire to the HEI has plenty juice (checked by running cooling fans off it) What is left????????

Dirt Freak

Total posts: 268
posted May 02, 2004 06:49 PM  
How about your coil. Just a thought.

Dirt Full Roller

Total posts: 52
posted May 02, 2004 07:13 PM  
Check and make sure you have a proper ground on the motor.

Dirt Forum Champ
Total posts: 784
posted May 02, 2004 07:34 PM  
I agree with Pickel it must be something affected by movement or vibrationreally look close at connections and antwhere a wire goes thru something also I always fasren my hot wire to the dist with tie wraps around the dist it keeps the plug ins from vib as much good luck another thought wait until dark and crank and shake wires look for arcs sometimes they are so hard to see as you know a very small abrasion can cause a very big prob

[This message has been edited by Flatlander (edited May 02, 2004).]

Dirt Full Roller

Total posts: 36
posted May 03, 2004 05:20 AM  
I had the same problem last year and it turned out someone put some garbage in my fuel cell. I did all the same things you did. I had a clear fuel filter so i kept checking it... one night i cleaned it out, it was stuffed full of **** again after the warmups, thats when I figured it out... cost me 3 weeks of bad runs. Just stick your hand down in your cell and see if you feel anything other than foam

Dirt Freak

Total posts: 217
posted May 03, 2004 08:33 AM  
i had a similar problem this year. turned out to be electrical related. i found out by
hooking up a volt meter to the distributor, the output wire that leads to the tachometer.

when the car idled, volt meter read around
12.5 volts. when i reved my motor up around 5000 rpms, i saw the volt meter reading drop to about 9 volts.

my problem was a discharged 6 volt battery
in a 6 + 12 volt battery combo i use.

Dirt Forum Champ
Total posts: 521
posted May 03, 2004 10:00 AM  
as mentioned, check your ground (I always like a cable straight from the battery to the engine block).

and ..... one more thing to try would be temporarily removing (or swapping out) your tach.


Ego Racing
Dirt Forum Champ
Total posts: 724
posted May 03, 2004 11:23 AM  
We run a #10 Copper ground wire from the battery cable frame mount up the chassis to the engine and ground the engine there. If you use the small one wire clamps it also gives you something solid to tie any other wiring off to.
I had a tach do the same thing, at 5500 RPM the motor would hit a wall and it was like I was on a rev limiter. I changed cap, coil, wires, plugs, MSD, wiring, MSD chip, Timing retard box, and the switches. When I did the switches it quit and we all were happy we had found the problem, at the track I realised we forgot to connect the tach and I ran the heat race without it. We reconnected it for the feature, Hit the gas on the green and BAM 5500 RPM and the wall was back. I ripped the wiring off during a caution and the car took off when I hit the gas, I almost hit the outside wall looking at the tach and not believeing that was the problem the whole time.

Dirt Roller

Total posts: 12
posted May 03, 2004 12:41 PM  
This is right out of the Speedway catalog...
"-Does the car run out of power or start missing at higher rpm's?
-You tried someone else's ignition and it was still the same?
-Your tach will not work or reads erratically?
-Your engine won't crank over as fast as it should?

One of the leading causes of ignition and guage problems is a bad or improper ground,. Just because you ran the negative cable from the batt. to the frame, does not mean the engine is getting that ground. If you are running rubber or poly motor mounts or have solid mounts that you have painted, you probably do not have sufficient ground.

The fix is simple. Run a battery cable from the frame to the engine. This should be the same gauge size as the other cable because this also supplies the ground to the starter. Also make sure the distributor holddown clamp and bolt are not painted and making good contact with the distributor."

Hope this helps. Good luck -D-bird

Dirt Roller

Total posts: 12
posted May 03, 2004 12:50 PM  
Also as a side note, I would be willing to bet alot of the problems some of the other guys mentioned (shorted out tach, coil etc.) were caused by improper grounding of the electrical system(either by design or damage from vibration). Also I would never recommend disconnecting any electrical or electronic device while it is energized as the voltage spike can damage the component.
Again good luck and be safe. -D-bird

Dirt Forum Champ
Total posts: 968
posted May 03, 2004 07:19 PM  
Thanks for all the replies! I have tried disconnecting the tach with no resolve. I am going to be checking those grounding ideas out. I think whatever it is, the vibration of the car has an effect, because it runs out perfectly in the shop. I will rev it past 5, but cannot bring myself to take it or hold it any higher without any load on it. I did some searching around in the cell, and even designed and installed a "pre-screen" on the pick up tube. My motor guy and Tony at TnT Racecars both told me to swap the battery out....they'd had similar problems and solved it with a new battery. I'll let yall know how it turns out. Thanks again!

neil rucker
Dirt Forum Champ
Total posts: 799
posted May 07, 2004 08:10 PM  
eljojo, ive had the tach cause the same problem. never seen the battery be the cause, but it makes plenty sense. neil


Back to the Archives