miss in motor..

[claybill]

installed new fenton head..started right up..still has a miss. changed to autolite plugs, still. didled with dist....same. put a plug 'spark checker' on..all sparking nicely. what do i check next? didnt do points..thought sparker ruled that out..

bill

[greg g]

Put a vacuum gauge on it and watch the needle. a bouncing needle would indicate a sticky valve. Make sure your coil wire is fully seated in the dist, as well as the other wires. The little spark checker will tell you you have a competed circuit but not the resistance in it. What kind of condition are your spark plug wires in. You might want to wait till dark then do a water most test.

Start it up open the hood and most the area around the wires, if you see any spark it not cool. You will also be able to see if there is spark going to the outside of the plug to the head.

Also what plugs are you using and where did you set the gap? the aluminum head will require different plugs with alonger reach.

[norrism1]

Claybill

Sometimes the spark plug insulator has a hairline crack up inside the center conductor. I would suggest swapping plugs and see if the miss moves with the plug or stays in the same cylinder.

[1949P17BC]

Been there done it, make sure the coil wire is good, solid connection, and tight as your brother in law.

[claybill]

interesting......i am using autolite 306..gapped at .30

i looked at ther champion plug..it had an extended electrode..the autolite was flush with the end of the threads.

WHY would the aluminum head require a diffeent plug reach? yu dont mean a long reach plug do you? (longer threads)

bill

[greg g]

On my edmunds head, the plug when properly seated, did not extend into the combustion chamber. It was shielded by the greater thickness of the casting. I don't lnow if your are the same, but look at the stock heads, the plug sits in a depression, on the aluminum heads they are flush with the top of the casting. I think you need a plug with about 3/4 inch of threads to get the electrode into the chamber. Probably isn't an issue right now but with the plug up in the hole, thee is a lot oa places for carbon deposits to start. They would cause hot spots of shield the spark.

If you bear with me a few minutes, I can take a picture and get ir put up. As my paperweight is on the shelf in the garage.

[greg g]

The plug in #1 is the stock heat range plug. It is shielded way to much, and it would run really cold being up in the head and surrounded by cooled alumium. In number 2 is a champion L 80 C which according to their charts is in the same family but longer reach. It is not perfect, but better. Number three is how it should be, but I screwed in one of my MC plugs to that level. Seated all the way it would be too long. The last pic is the L 80 C without the sealing ring. Probably should have measured the thread length but I forgot. You might want to check with Marty, Pete, Robin and other to see what they are running.

3, 2,1 left to right

stock plug up close and blurred (sorry but it shows the concern)

center is the L 80 C without the seal ring and the other showing where the plug probably should be.

[martybose]

Looks like your Fenton head requires a 1/2" reach plug, just like my Edmunds does. I used an Autolite AP425 in mine; a little pricey, but then nothing but the best for my flattie!

Marty

PS You will probably want to chase the sparkplug threads before you put the 1/2" reach plugs in!

[YukonJack]

installed new fenton head..started right up..still has a miss. changed to autolite plugs, still. didled with dist....same. put a plug 'spark checker' on..all sparking nicely. what do i check next? didnt do points..thought sparker ruled that out..

bill

Maybe I'm missing something here, but the way I understood the question there was a miss before the head was installed because he "still has a miss". Would make me think wires, points or condensor. Plugs might be a problem later but this sounds like a problem that existed before the head was changed.

[kencombs]

Is it a continuous miss on one cylinder? an intermittent miss on one? More than one, does it go a way with speed changes? Was it a problem before the new head?

Lot's more info needed before we can accurately troubleshoot this.

[claybill]

claybill here.....

miss with the stock head......still misses with fenton head.

spark checker says all plugs are firing fine.

( checker is a thing that goes on plug and will light up as plug fires, showing even or intermittent firing)

when i loosen the dist. bolt and move dist. back and forth a little..doesnt seem to alter things very much.

comp is 92-97 in all

changed from champion to autolite...still misses.

plug wires are newer and are the radio resistor type....if there was a problem there it would show in the 'plug checker'

miss is noticeable at idle....and when leveling off at higher rpm. accelerates crisp and ok.

i'll check tonite when it is dark to see if spark is jumping about.

engine is on a test stand. out of car. all wired and test/run ready. I use it to test heads, carbs, starters etc etc..

trying to determine if it is...electrical....fuel.....or, timing.

i will check the spark plug depth also. robin has the asme head..hoe he joins in.

claybill

[greg g]

Start your engine and with some insluated pliers, pull on plug wire at a time. If the cylinder is firing properly you will notice the new misfire, it will clear up when the plug wire is reconnected. When you come to one that doean't chang the way the engine is running, they you know which cylinder is miss firing. Then you can check that wire. plug, dizzy cap related to that cylinder for what is causing the problem. A compression test on that clinder is probably in order as well. I would guess it is electrical, but I would also check for a leaking intake gasket. That will give you a lean miss at idle if it is sucking air. Once you isolate where the miss is put a bit of oil or WD 40 or starting fluid directed at the maifold to block connection. If the miss goes away, then you know you need to deal with in intake gasket leak.

You don't need to worry about pistons striking the spark plug. The plug is centered in the combustion chamber between the valves. So it is unlikely there would be any interference with valves either.

[billwillard]

If I had a miss the first thing I would do is remove all plugs and do a compression test. If you find one cyl low reinstall plugs , start engine and set idle up to about 1000 RPM. Remove air cleaner and slowly pour about a pint of water in the carb. If this does non remove the miss you may need a valve job.

[claybill]

interesting ideas are abounding !!! i am trying them all!

last nite after dark i took the flashlight into thegarage and started 'her' up looking for sparks possibly jumping about. none. but it was fun!

this am i will put on new plug wires.

compression is mid 90's all around.

claybill

[claybill]

new wires..better

turned dist all the way clockwise...smoother.

checked thread reach on fenton aluminum head..!YEAH. it requres a longer reach plug for sure..chasing threads this aft. new plugs too.

also. as mentioned some months ago in other discussions......the '41 head, stock, creates higher comp when used on a 230...my guess 10-15 %. it has a shorter and shallower comb area.. WOW!!

bill