Flathead Quirks

[gary griffin]

I have my flat-head running after a long rest, and a complete rebuild as part of a long restoration.

It refuses to fire number 2 and number 3 cylinders. They are on opposite sides of the distributor cap and 2 is in the front of the right bank and 3 is second on the left bank.

Finding no logical reason that they are not firing. We tried a different distributor, and different wires.

Showing pressure when cranking also. Is there a chance debris is in the inlet manifold? It looks like they share a section of the manifold. Possibly someone put a wad if paper in there??

Focus on that problem tomorrow and should be resolved??

I am surprised how well it runs on 6 cylinders still pretty smooth and quiet.

If they were closer to each other in the firing order I doubt it would run so smooth.

I am running  generic ignition wiring and will order correct harness tomorrow.

Any parallels or suggestions??

[Steve Passmore]

There are 4 cylinders sharing each side of the inlet manifold so I think you would have all 4 down if it were a blockage and I think the Venturi vacuum would drag paper in anyway.
On a newly built engine without knowing what has been done to it its very hard to diagnose a problem.  Have you done a compression check? 
I have seen several engines 'rebuilt'  by professionals only to find they cut the valve seats in so far they loose the 3" clearance the valves stay open!

With the air cleaner off get a light and make sure both throats in the carb have a good jet of fuel when you pull on the accelerator rod.  Sometimes if one side is reduced there's only enough fuel to fire the nearest cylinders to the carb.

[TMoore - NTCLC]

Not Firing?  Do you mean that there is no spark from the distributor to the plug, or are you getting spark but the cylinder is not firing?

My steps would be - am I getting fire from the distributor to the plug?  If yes, is the plug firing (remove from cylinder and check for spark)  If yes, then do I have good compression on the cylinder (i.e. no stuck valves).

If I am not getting fire from the distributor - plug wires?  I noticed you are using modern wires - might be worth switching around to see if that is an issue. Adjust points?  Shouldn't be the issue since other plugs are firing.  Distributor cap - notorious for having issues - try switching it out.

Let us know where the problem starts and we can go from there - and yes, these flatheads will idle like a sewing machine on 6 cylinders - until you put it under load, and then you know it isn't running right.

[harry s]

Gary, When  you say those cylinders are not firing that would mean no spark to me. Assuming you have verified the spark is present to the plugs (and plugs are good) I would check the contact tab on the rotor and also the carbon insert in the inner coil connection. Then the spark plug wire cap contact tabs. Just me on this one, I don't like the  aluminum tabs, much prefer the copper ones. Another totally non scientific test would be to run the engine with all the lights off and look for current leaks. I would also recommend copper core plug wires. Good Luck,    Harry

[gary griffin]

 Thanks for the interest everyone.  As an update, I ordered new spark plug and distributor wiring from Brillman, he is on Ottos's list and they will ship tomorrow, and he knew what I needed, for a nice price of $42.

  I had a friend assisting but he is not here today so I am working by myself. I put a pair of the visible spark devices in the wires to 2 and 3 and they showed sparking during cranking. I did not continue and will work on authenticity issues today.  I poked my inspection camera into the port of my spare manifold but even with the 45 degree mirror I could not see any more than the first passage of the manifold. It will not fit through the vacuum port in the manifold.  After seeing the sparking to 2 and 3 I am focusing on fuel issues. Since 2 and 3 share a passage in the manifold along with the left barrel of the carburetor and the other 2 cylinders sharing the same barrel seem to be O K I am baffled.  It is hard to diagnose alone at his point, need someone in the car assisting. At this point I am thinking that either there is a blockage in the manifold or left barrel of the carb is too lean to provide combustible mix?

[gary griffin]

I finally got back to the car and after trying to figure all of the obscure possibilities I finally fixed it. I put visible spark viewing devices on the plug wires for 2 and 3 which were missing, and figured since they were sparking it was not the plugs so I kept on going to other possibilities. I did a continuity test from the top of the plug to the plug body and nothing happened but so I figured there was not a problem there.  After eliminating all of them I did what I should have done first, I tried two new spark plugs although the others were new and it started right up. Now on to other things. Still hoping to get it to the upholsterers in the next few days. I lost a few days for other reasons also and am in a little trouble for working on the car on Valentines day. Gotta shower up and buy my lady a nice dinner and take mom some flowers on the way.