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grey beard

How Do Bad Coils Act?

55 posts in this topic

Can a 6-volt coil start and run an engine flawlessly but break up only on the top end, like above 2500 rpm? Never saw one do that, but it's about the only remaining culprit I haven't yet replaced. Still got my high speed cut-off point. Just won't accelerate any higher.

Scratched my head on this one so much it's sore . . . . . . and I still got that @#$%^&*()_ miss.

Go figure . . . . . . :confused: :confused: :confused:

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There was a post about the coil overheating, and wrapping it in a wet towel, but that is all I remember.

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Scratched my head on this one so much it's sore . . . . . . and I still got that @#$%^&*()_ miss.

Such language Dave. ;):D

I suppose a weak coil could cause limited RPM. Let's say that the spark is strong enough to light a decent fire at lower RPM's, but at the higher RPM's the saturation time is reduced and could weaken the spark enough to reduce it's effectiveness. However, there's one easy way to test it... replace it. The last coil I bought was under $20 as I remember it.

Merle

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How's your miss coming about? Are you holding your throttle constant, or is it happening under acceleration? 2500 rpm doesn't seem to extreme for either 12 or 6 volt. if the distributor is tanking, it might be robbing you of some power. On my race car i had a ghost in the machine that turned out to be a slightly bent distributor shaft. At 4000 rpm it was trying to shake its self out of the bearings, and compromised the contact points. Otherwise, maybe some vacum leaks are leaning you out. How do the spark plugs look?

48D

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The engine simply will not accelerate above this speed - just like it is running out of gas or spark. Happens sitting in the garage running or on the road. Just no top end. Otherwise starts and runs like a lady. I've checked float level, had the distributor out and looked everything over. All parts are new.

Here's the giggler - before I renewed everything it accelerated perfectly. I sure did fix that one well, didn't I. I'm just so proud . . . . . . :confused:

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Check the wire inside the distributer. I had one that was shorting out when the vac advance kicked in. Took a while to find out what was causing my @#$%^&*()_ miss at higher rpm's.

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Thanks Reg. Been there and done that. Even tried another distributor, and tried it woth the vacuum line disconnected. Still no change.

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If your coil was bad, it's possible that the car would start right up when cold. However, it would then get worse as it heated up. That said, if the coil is bad, the car would not start easily, or at all when it was hot. You would have to let it cool off prior to starting the engine up again. So.........if the engine starts up easily when the engine is good and hot, it's probably not a problem with the coil.

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two things I found

1. Bad coil willwork fine until it gets hot, then it has cool off before it will restart

2, Won't rev or misses, my way the coil wire into the cap, they tend to burn/char over time and need to be cleaned

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Still have my high speed engine problem. Starts and runs and idles perfectly - as good as any engijne I have ever heard. It accelerates just fine up to the magic mark of about 2500 rpm, and then just stumbles and misses and will not increase in speed any further. Tried adding choke, etc., but to no avail.

So far, I've replaced the complete distributor, checked the float level, replaced the fuel pump - electric - and looked everyrthing over very good. Coil, cap, rotor, points and condenser and plug wires are all new, as are plugs. In fact, everything is brand new and engine was just overhauled. It's been run about five miles plus lots of idling around, to date, but of course won't get out of its own way on the road, without full throttle acceleration. Sure does idle around nicely and runs well at part throttle.

Guess I am well and truly stumped. Wish someone else had this problem, then I would be just full of helpful advice. Ain't it a mess . . . . . . :confused:

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Try cleaning up your spark plugs.....run it to 2500 rpm's....check the plugs , and see if your lean or running into a timing problem. If its not the Dist/coil, I'm wonderin' if it's one the carburetor circuits. Hope you get it figured out soon, nice weather is around the corner.

48D

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Still have my high speed engine problem. Starts and runs and idles perfectly - as good as any engijne I have ever heard. It accelerates just fine up to the magic mark of about 2500 rpm, and then just stumbles and misses and will not increase in speed any further. Tried adding choke, etc., but to no avail.

So far, I've replaced the complete distributor, checked the float level, replaced the fuel pump - electric - and looked everyrthing over very good. Coil, cap, rotor, points and condenser and plug wires are all new, as are plugs. In fact, everything is brand new and engine was just overhauled. It's been run about five miles plus lots of idling around, to date, but of course won't get out of its own way on the road, without full throttle acceleration. Sure does idle around nicely and runs well at part throttle.

Guess I am well and truly stumped. Wish someone else had this problem, then I would be just full of helpful advice. Ain't it a mess . . . . . . :confused:

Just some things from the top of my head... Worth everything you are paying for them. :)

I think if I were having this problem, I'd temporarily hook up a vacuum gauge and a fuel pressure gauge so that I could see them as I drove, then take the car out and run it at speed to verify that both are okay. You did not mention fuel line from the tank or the ceramic filter in the tank, so it could be fuel starvation (fuel pressure reading will tell you that).

I'd have to check the manual, but I recall that points and/or plugs set at the wrong gap can also cause high speed issues.

On your newer cars with both vacuum and mechanical advance the plate the points mount on rotates. It is possible that the ground for that plate is not good through its entire range of motion causing the ignition to cut out.

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sounds like coil to me. I have had some small engines that would idle very nicely but would not rev much or at all and it turned out to be a bad coil. I wouldnt think its a fuel issue because you said you tried adding some choke and it didnt make any difference.

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Had this happen to my brothers 49 plymouth, we found pin holes in the gas line replaced the line ,ran fine.

This was many years ago.

You know....I had a 68 Camaro straight six that had a stumble that turned out to be a cracked rubber fuel line. It was a short elbow between the tank and the hard line. It didn't leak, just sucked air at high rpm's......hummmm.

So where you at Greay Beard? Any new info?

48D

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Fuel tank was cleaned out within an inch of its life. Drove around with it in my van for three months. Had one dozen 3/4-inch nuts and bolts floating in 2 gallons of soapy water, followed by an acid bath and a zylene bath and a good air blow-out. Fuel lines are brand splinter new from tank outlet to carb fitting. New electric fuel pump just died last week - it was three years old but was used only a few hours - guess this ethanol really wrecks havoc on fuel pump diaphrams - and am just now replacing it with a new Carter heavy duty pump from NAPA.

If the new pump does not cure this problem, I will next change coils, since the entire distributor has been changed out, to no avail.

Still open to your suggestions, as I have almost struck out here.

Thanks

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Ok...last try. You still haven't told me about the condition of the sparks plugs, BUT....if they are fine and the dist/coil are good....then I begin to wonder if your new feul pump got its rubber parts broken down (ie ethanol=solvent) and plugged small passages in your Carb. Your idle may be good and even your accel/pump....but maybe your high speed circuit, main open throttle circuit, etc. got plugged. If the fuel line is slightly occluded at the fuel filter, the fuel bowl level won't let you know. What I'm sayin is your cholesterol level in the gas (rubber) may have slipped by the filter(liver) and may have caused an infact (dead spot) in your carburetor (heart). Boy....I gotta take more time off work. Good luck GB, I'm out of ideas.

48D

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Welllllll, I have - since my last post - pulled the distrihutor a socond time and replaced the centrifugal unit due to a loose weight anchor pin. I also replaced the condenser, just to eliminate that possiblilty. All pigrail leads inside the distribuor are in fine shape. AND I have replaced a failing Airquip electric fuel pump with a new heavy duty Carter.

After all that work, I am happy to say - I still have exactly the same problem, with no change, whatsoever. Next is a new coil. I'm about ot of possiblilties.:(

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Just put a SECOND new 6-volt coil on this new 218 - problem still exists. So far we've replaced the coil, condenser, points, fuel pump. checked float level and had the distributor apart twice. Still no top end.

Tomorrow we'll take a carburetor apart - again . . . . . . :(

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Just a shot in the dark here but when I first built my truck it wouldn't go very fast either. I don't have a tach to know how fast it was going but anyway it turned out I had mounted the gas pedal funky and it was hanging up long before WOT. Can you run a test with the pedal stuff disconnected and operating the carb by hand?

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Dave;

Are you sucking air into your fuel line prior to the fuel pump? Is there a rubber hose in your fuel line prior to the fuel pump that may be collapsing? Are your valve springs new? Any possibility one or more valve springs are broken? Any intake manifold leaks causing a low vacuum condition?

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Valves were completely reconditioned - seats, faces, guides and springs. Fuel line is new one-piece steel from the electric fuel pump at the tank to the carb - actually I should put a short piece of flex in there somewhere near the front mount - and the few short rubber connectors at the fuel filter and pump are all brand new rubber fuel line.

I'm hoping to find the problem inside the carb today. I'll let yo knowl. Mebby I did something really dumb in there that can serve as a good object lesson for everyone else.

I'll be the goat . . . . . . :confused:

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My guess would be either with Young Ed (linkage problem) or Distributor. If you were working great before you changed all these parts, can you replace them one at a time and see what fixes it ? I'm thinking the vacuum advance is not working properly or the weights on the centrifical advance are wrong springs or something. Should be a spec on the vacuum adv that can be checked with one of those 'suction' thingies that bleed your brakes too.

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