Flamethrower 6v coil too much power ?

[M2M]

So I took Purdy's advice and fitted a Flamethrower 6v coil. In the past I've made jokes about how powerful these coils are but it seems those jokes were not too far off.

The issue is, I'm occasionally seeing a large spark from the brass plug wire to the distributor body on the second plug from the firewall. Has anyone else had this issue? I bent the plug wire away from the distributor body to make the gap larger but it still sometimes happens.

Thinking or either covering the brass plug wire with electrical tape (that would look awful) or to replace the plugs with taller ones to make the gap bigger. Plugs fitted currently are the cheap modern ones which I was going to replace anyway with NOS vintage plugs. I have a NOS Route 66 plug and it seems much taller than the ones that are in there now.

[Patrick L.]

Well, that shouldn't happen, but, its not the coils fault.
I think its probably the cap or a bad plug.
I believe the later plug wires/strips are longer which could help.

[Badpuppy]

Swap plugs and wires between cylinders, see if the problem moves. If it does, swap the wires back to isolate the cause. If not, wash the outside of the cap and dry thoroughly. Could be conductive dirt on it.

[Bob-A]

Purdy recommended W-18 Champions to me and I have never had a problem
with them.


Bob-A

[Synchro909]

M2M, that is a common problem. The spark jumps from #3 lead to the body where the internal lead to #4 post is. The spark penetrates the insulation of the body. I prevent this by either making the leads longer by soldering in an extra bit of brass so I can leave a bigger air gap or putting some insulation over # 3 lead. Sometimes I use both methods. The insulation is a short piece of plastic tubing which I slit lengthwise and slip over the brass lead.
It doesn't look original because it is not but IT WORKS! The longer leads are barely noticable and nobody has picked them yet. The insulation is a bit more obvious.

[Bill G]

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Sounds like Sychro's fixes are good pointers. Otherwise, you start with a better spark and have a misfire from the cross-arcing.

[The Master Cylinder]

Originally Posted by Synchro909

M2M, that is a common problem. The spark jumps from #3 lead to the body where the internal lead to #4 post is. The spark penetrates the insulation of the body. I prevent this by either making the leads longer by soldering in an extra bit of brass so I can leave a bigger air gap or putting some insulation over # 3 lead. Sometimes I use both methods. The insulation is a short piece of plastic tubing which I slit lengthwise and slip over the brass lead.

I put some shrink tubing over the leads. Doesn't appear as out of place as a piece of plastic tubing. I believe the Model B leads are ~½" longer than the Model A leads also.

[Synchro909]

Originally Posted by The Master Cylinder

I put some shrink tubing over the leads. Doesn't appear as out of place as a piece of plastic tubing. I believe the Model B leads are ~½" longer than the Model A leads also.

I always thought he longer leads were to allow for the higher distributor which is higher due to the advance mechanism in it.

[Jim Brierley]

It's probably not the coil, no matter the capacity of the coil, it only produces enough voltage to overcome plug gap and compression. a 50,000 volt coil may be only producing the 20,000 (or so) volts as you drive down the road.

[M2M]

Originally Posted by Synchro909

M2M, that is a common problem. The spark jumps from #3 lead to the body where the internal lead to #4 post is. The spark penetrates the insulation of the body. I prevent this by either making the leads longer by soldering in an extra bit of brass so I can leave a bigger air gap or putting some insulation over # 3 lead. Sometimes I use both methods. The insulation is a short piece of plastic tubing which I slit lengthwise and slip over the brass lead.
It doesn't look original because it is not but IT WORKS! The longer leads are barely noticable and nobody has picked them yet. The insulation is a bit more obvious.

Thanks. I will buy some of the longer B wires. The plugs I have are modern Motorcraft, I will try to replace those with taller NOS vintage plugs.

Are 3X plugs taller than Motorcraft?

[Will N]

IMHO, a stock Model A engine, with its 4.2:1 compression ratio won't run any better with a flamethrower coil that puts out 45,000 volts compared to the 24,000 volts of a standard coil. Yes, you do need higher voltage to initiate a spark in a high (like 10:1 high) compression engine, and yes you will get a "stronger" spark with a higher voltage coil. But you don't need 45K volts to reliably fire the spark plugs in a low compression engine, and once the charge in the cylinder ignites from the spark, the strength of that initial spark has no impact on the continuing flame front in the combustion chamber. It's not going to make the gas burn any faster or hotter or more efficiently. Also, the standard Model A distributor body was not designed in contemplation of handling 45K volts, so leakage at that high voltage level is a possibility.

[katy]

The (modern) Champion W-18 are a tall plug and work well in an A.

[Patrick L.]

It is right that these monsters do not need 45K volts to jump that gap, but, I don't think folks buy a coil like that for the voltage. I think they buy the epoxy filled coil so it can be pointed in the original direction.

[Y-Blockhead]

Originally Posted by Will N

IMHO, a stock Model A engine, with its 4.2:1 compression ratio won't run any better with a flamethrower coil that puts out 45,000 volts compared to the 24,000 volts of a standard coil. Yes, you do need higher voltage to initiate a spark in a high (like 10:1 high) compression engine, and yes you will get a "stronger" spark with a higher voltage coil. But you don't need 45K volts to reliably fire the spark plugs in a low compression engine, and once the charge in the cylinder ignites from the spark, the strength of that initial spark has no impact on the continuing flame front in the combustion chamber. It's not going to make the gas burn any faster or hotter or more efficiently. Also, the standard Model A distributor body was not designed in contemplation of handling 45K volts, so leakage at that high voltage level is a possibility.

Originally Posted by Patrick L.

It is right that these monsters do not need 45K volts to jump that gap, but, I don't think folks buy a coil like that for the voltage. I think they buy the epoxy filled coil so it can be pointed in the original direction.

Please read what Jim wrote in post #9.

[Patrick L.]

Originally Posted by Y-Blockhead

Please read what Jim wrote in post #9.

I do read the posts, and Your point is ?

I mentioned in post #2 that the problem was not the coil. Then I Later agreed about the voltage and added another reason [epoxy and position].

[jb-ob]

All the longer 'B' spark plug connectors, taller plugs, high powered coils, duct tape & bubble gum still won't fix a defective / failing distributor body. Time to replace it.......

[Y-Blockhead]

Originally Posted by Patrick L.

I do read the posts, and Your point is ?

I mentioned in post #2 that the problem was not the coil. Then I Later agreed about the voltage and added another reason [epoxy and position].

You are correct Patrick. I was using your post as a concurrence that 45,000 volts wasn't needed and added it incorrectly. I shouldn't have quoted your post at all. Sorry about that.

[M2M]

Originally Posted by jb-ob

All the longer 'B' spark plug connectors, taller plugs, high powered coils, duct tape & bubble gum still won't fix a defective / failing distributor body. Time to replace it.......

It's brand new from Bratton's.

[M2M]

Originally Posted by Jim Brierley

It's probably not the coil, no matter the capacity of the coil, it only produces enough voltage to overcome plug gap and compression. a 50,000 volt coil may be only producing the 20,000 (or so) volts as you drive down the road.

So if you put a larger gap in the plugs the coil will produce more volts?

[Patrick L.]

Originally Posted by Y-Blockhead

You are correct Patrick. I was using your post as a concurrence that 45,000 volts wasn't needed and added it incorrectly. I shouldn't have quoted your post at all. Sorry about that.

Oh OK, no problem.