Ballist Resistor ?

[ronzara]

Hello,
My 1971 351W has developed a miss (Duraspark w/points & Condenser).... I changed plugs,(old ones looked good though) NEW wires and added new Gas with a fuel additive >>> no change.

What are the symptoms of a Ballast Resistor going or gone bad?? Think this could be the problem??

The miss just started one day,...
seems to smooth out once you reach about 4500 rpms, and idle is not bad, but in the midrange (2000- 4000), the motor stumbles pretty bad,.. Any ideas???
BTW: I am running a Road Demon 625 Carb. Carb & Timing seem correct.
thanks
RZ

[Tommy]

My limited experiece with the ballast resistor on my old Corvette is that its purpose is to reduce the voltage to prevent burning up some components (e.g., points and coil). If the resistor failed so the resistance increased significantly, it could reduce the current available to the ignition system and cause the symptoms you described. If you can check the voltage on both sides of the resistor to verify that it is about 12v going in and about 8-9v coming out, it is probably ok. If the voltage coming out is significantly less, that may be your problem.

[Ron61]

I seriously doubt if your ballest resistor is the problem. They will normally go open rather than increase in resistance plus you said it runs good as you get up to a higher RPM. Easy way to elimate it for sure is just strap around it and run the car. It won't hurt anything and that will either eliminate it or point to it.

Ron

[Steve R]

Ron,
If that was my engine, I would start with the basics:
Read the spark plugs to see if all cylinders are burning evenly, and correctly.
Run a compression test of all cylinders.
If those test are o.k., then proceed with trouble shooting.
Keep us informed.
Steve
B.T.W., how many miles are on the engine? I take it this is not the engine in your Cobra?

[Cobra20646]

Ron,

The info you've received above is all good.

To answer your question as to the symptoms of a failed ballest resistor.......

As mentioned the ballest limits current through the points/coil, and as a result, reduces the voltage to the coil.

Your starter solenoid has a set of contacts that bypass the ballest during the time the starter is running.

If the car starts when turning over the motor, but immediately quits when you return the key to the "run" position, that is a sure (if not the only) symptom of a failed ballest.

[Mr.Fixit]

Have you repaced the points and set them recently?

[Rick Parker]

Try spraying some carb cleaner in the air corrector/air bleeds in the top of the carburetor. They are the small brass jets in the tops of the carb mouth.

Rick

[Excaliber]

I KNOW point distributor systems, no way it's the ballast resistor.

Assuming the dist cap, coil, wires and ROTOR are good, I'll bet you money the problem is the CONDENSOR. That little round thing that sits next to the points. The symptoms you describe are classic for a bad condensor. I've seen bad ones that were brand new right out of the box.

Often people replace the points but NOT the condensor. Bad move, it's a very cheap part, not worth risking a problem over.

Ernie

[ronzara]

Thanks for the suggestions guys!

I just changed the condensor today, didn't really make a difference. I will try the carb cleaner, also. I am thinking it maybe junk wires. I installed AUTOLITE PRO series from Advance Auto,... they are 7mm wires and the 1st set basically pulled apart within the 1st week I had them on the car. I am going to run the car in the dark and look for a "light Show'.... maybe crossfiring....??

Yes, this IS the 351W in my Cobra that is giving me troulble. I am hoping this missing problem isn't a sign of a bearing problem or a cam lobe getting wiped !!!!!!???


RZ

[Ron61]

Ron,

Your problem sounds more ignition related than mechanical or fuel. I used to have some problems at higher RPMs until I did away with the points distributor and went to an inductive one. Have never had a problem since. If you can get hold of a different distributor and try it that might be easier than starting to tear into the engine. Most point problems will occur at higher RPMs as that is where you need more voltage. Points have a tendency to bounce after a few runs. I am sure that you have already checked all of your connections and everything. You say the motor stumbles pretty badly at the 2000 - 4000 range but smoothes out at 4500 and above. A cam lobe or anything like that isn't going to go away at any RPM. I am not real familiar with the Duraspark setup but I once had a trigger lead in my Jacobs give me about the same type problem as it had worked loose in the connector.

Ron

[Jim Downard]

Hey Ron,
Jim Downard here. Did you choose to ues the Ford Duraspark because of the CR wiring harness. I was running the Duraspark II ignition and dumped it because of various problems. Screwy timing advance kept making my engine run hot. I would pick up a miss (sometimes) under a heavy load, but always on the right side. I found a loose ground in the distributor, and I also found that the Duraspark II required a specific coil. With those items remedied, I still had a hot running engine. I bought an MSD 6AL ignition, MSD pro billet distributor, and an MSD coil. Problem solved. Engine runs cool, never misses, and runs stronger than it ever did. It's a tough pill to swallow, but dump the Duraspark and go with a quality performance ignition. You'll never regred the change.

Good luck,

Jim

[Excaliber]

It does indeed sound more like electrical. Hmmmmmm.......

Keep us posted!

[MrMagoo]

Points ignition systems can easily be replaced, and probably should. I have a Mallory Unilite distributor on my 351W, with a Mallory promaster e-coil. I use the fatty 8.8mm Accel 300+ wires. Wires are like garden hoses, the fatter they are the lower the "pressure" and less chance for voltage leaks and cross-firing. The Uniite is opto-electric, no points or condenser, no dwell adjustment, etc. Check the plugs for weirdness as has been said, but consider a few hundred bucks for the switch.

[sharpe 1]

your problem sounds like the advance curve in the dist. needs to be recurved to go to full advance sooner.

[ronzara]

Well Guys,

I bought a pertronix electronic conversion set up to install in the distributor, along with it I got the pertronix flame thrower coil, Ford Cap adaptor and rotor to change it over to the HEI style post cap + a set of 8mm wires. The should be here this weekend. We'll see if this changes anything.
Has anyone used the Pertronix stuff??

sharpe 1,
How do you change the advance curve?

Jim,
No, The distributor was in the motor before I got the CR wiring. PS. Havn't made it back to Ohio since New Year's (I am still thawing out for that!)

[MrMagoo]

Tha sounds like a good way to go since you save money on buying a new distributor. I bet it helps. Good Luck.

[sharpe 1]

you must change the advance springs that control the movement
of the mechanical advance in the dist. Lighter springs will allow the timing to advance faster. Depending on the cam you are running many engines need to be at full advance about 36 degrees at about 2500 RPMs Bad timing advance could account for your mid range power loss? The curve can be changed in the car, but the best way is to use a dist. machine.

[sharpe 1]

also the question about the b. resistor. The resistor reduces voltage to the coil. A bad resistor would be either an over heating coil from too much voltage or no voltage at all to the coil. That would not cause a mid range stumble or power loss. It would most likely happen all the time.