8n ford missfires under load

Hey guys. So my little 1952 8n (side mount distributor) is causing me some stress. It cranks, and runs great in the shop but cuts up something terrible when I take it for a spin and open up the throttle to 1/3 to wide open position. it almost sounds like its miss firing. This is a long story but here goes. It is not a fuel problem. The fuel is flowing fine to the carb. It is not the carb. the tractor acts the same way with 3 different carbs that I tried. I went thru the electrical. New points ,condenser, cap, rotor and 437 autolite plugs. I ohmed the coil and got good reading. I checked spark on all four cylinders with a spark checker and got a good healthy blue spark on all four. I straight wired the ignition switch to check for bad switch. No change. I bypassed the terminal block where ignition hooks up to check for bad terminal block. No change. The points are set at 16 to 18 thousenths as I learned a few years back that the tractor will not run on the factory call out of 25 thousenths. Now a good friend has suggested that I pull the intake/exhaust manifold, that it make possibly have a clog in the intake part of the manifold. He said he had seen that several years ago on a farmall cub. Oh yes just one more thing. I can take the high speed adjust nozzle completely out of the carb and the tractor runs perfect. Remember I said I had tried 3 different carbs and they all act the same way. Pulling the manifold will be my next move I guess unless someone offers something else to look for. Thanks in advance for any help or advice! PS I cant see any sign of a cracked manifold or an exhaust leak.

Have you checked the timing advance mechanism for proper operation? Get a timing light on it and run it through its paces.

I don't see any reference to checking the plug wires. Are they the resistor type? If they are throw them away. Are they solid core wires and if so are they weathered? My Dad had a side mount 8N that would throw fits when the humidity was high (raining here in Utah). A neighbor had a similar problem with his 8N and fixed it with new plug wires. Dad did the same thing and it fixed the problem. Weathered wires will "bleed" the spark to ground or to the other wires and you can't see or hear it. I hope this helps.

Hey! Thanks for the reply. I did have an aftermarket distributor on it which I purchased new and it has ran for 4 plus years now. However I started suspecting it may be the problem because it had a good bit of side to side movement in the shaft. So I ordered a used factory distributor off a running tractor on ebay and installed it. No change. Thanks again for your reply

Thank you for the reply. I have suspected the wires many times through all this. I am not sure if I have cooper wires on mine. I did do a test on mine which was running the tractor with the lights off in the shop but did not get a fireworks show so I figured the wires were ok. However, I did pick up a new set of cooper wires while at a show in gray Tennessee last weekend but I have not installed them yet. Since you said they usually don't show any signs of going bad, I will install them today. The thing that does not make since is that the tractor runs great with the high speed adjust nozzle taken all the way out. It makes me feel their is an air leak some where. Thanks again for the reply.

Misfire under load is usually caused by faulty ignition.

If the spark plug wires are suspect, replace them. Also inspect the distributor cap and rotor.

Of course, the plugs are correct and good?

Dean

+1.................

" I can take the high speed adjust nozzle completely out of the carb and the tractor runs perfect. Remember I said I had tried 3 different carbs and they all act the same way."

I would pull the fuel tank cap off first and see what happens. I would pull all of the fuel screens.
While idling did you try doing a cylinder balance test by pulling killing one cyl at a time? A clogged intake port would not allow the tractor to run perfect just because you removed the high speed screw.

(reply to post at 10:12:15 05/06/18)

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Couldn't edit to add did you ck for vacum leaks at carb and manifold? If you remove the needle screw you are richening the mixture. lean condition will cause a backfire.

cpk, First when you installed the ebay distributor did you set the points at .025? The fact that the after market one wouldn't run at .025 was a red flag. Did you ever run a compression check? Also there is a forum just below this one for 9,2 and 8N's. Lots of guys there that have a lot of experience and knowledge on the 8N's.

OK!!! I think I got it! I apologize for not getting back to you all sooner, but I have been tinkering off and on with my problem for the past week. It turns out the aftermarket distributor was my biggest problem. It had a lot of play in the shaft ( cheap junk!) and evidently was making the point setting go nuts. Anyway I did finally set the points on .025 as advised in the original distributor that I purchased on ebay from a running tractor. There was a good bit of improvement. So next I adjusted the timing (by ear). I think I advanced the timing, at least that's what I think is the proper word, because the engine speeded up slightly when I made the adjustment. After the timing tweeking was done my little 8N is back running GREAT. I just wanted to reply back and thank everyone for their time and input. I am not a mechanic by trade so I always end up learning from the school of hard knocks. I have four restored Ford tractors at present in my collection and enjoy playing with them and taking one out for an occasional evening ride. Thanks again guys!!

OK, I am revisiting the 8N misfire problem that I wrote in about several weeks ago. I thought I had the problem fixed, but I didn't. The tractor still misfires and loses power under load. It seems nothing I do changes it. I can still remove the high speed adjust nozzle from the carburetor and it runs perfect. I put a brand new intake exhaust manifold on it thinking there might be a crack in the original one on the inside that I couldn't see. The only 2 things that I haven't changed is the coil and the wires. Again, nothing I do changes the problem. I'm lost, any advise would be much appreciated if you've gone through this before.

You would be best to start a new thread. this one is way too old to get noticed.
Keith

(quoted from post at 21:14:40 05/26/18) OK, I am revisiting the 8N misfire problem that I wrote in about several weeks ago. I thought I had the problem fixed, but I didn't. The tractor still misfires and loses power under load. It seems nothing I do changes it. I can still remove the high speed adjust nozzle from the carburetor and it runs perfect. I put a brand new intake exhaust manifold on it thinking there might be a crack in the original one on the inside that I couldn't see. The only 2 things that I haven't changed is the coil and the wires. Again, nothing I do changes the problem. I'm lost, any advise would be much appreciated if you've gone through this before.

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ounds like you have swapped out most everything and said you had new wires, so why not install those?