Backfire Problem

Gecko2345

New User
Hi,
I just registered for this Forum, but have been lurking for years. This is the place I have come for those little issues that pop up from time-to-time. I have a 49 8N with a new problem, and I'm tired if throwing parts at it. The tractor starts just fine, and runs good at low speed. As I advance the throttle, it sputters a little. As I approach the screw on the throttle plate (I don't have a Proof meter) it really sputters and often backfires. I had a retired mechanic, neighbor, look at it, and he is scratching his head. I've replaced the points, plugs, condenser, and plug wires. I'm thinking it is the distributor. My thought is that it isn't advancing the spark. Should I buy a new distributor? What else could it be?
 
" My thought is that it isn't advancing the spark."

That's unlikely.

" What else could it be?"

A few things.

Check the obvious first: misrouted plug wires. 1-2-4-3, CCW. It's easy to connect them wrong at the cap & very easy to cross 3 & 4 on the engine.

Next, adjust the carb.

Make sure the tractor is at operating temp; that usually takes 10 ? 15 minutes at idle depending on ambient temp.

Both Ford and Marvel/Schebler (assuming you have a M/S carb ) say to set both the side-pointing idlemix and the down-pointing mainjet to 1-turn as a starting point. I set the down-pointing mainjet to 1-1/2 turns and don't fool w/ it until the final step.

Then adjust the side-pointing idlemix for fastest idle; not the smoothest idle.

Next, adjust the behind the carb idle-speed set-screw for very slow 400-rpms idle. Do that idlemix adjust for maximum idle at least 3-times.

Make sure that you turn the screws slowly, like 1/8 of a turn at a time & wait a second or two for the engine to catch up. Take your time!

Do it like this:

1. Adjust idle mix jet until RPM increases

2. Adjust idle-mix set screw until the engine nearly stops (as slow as you can get it unless you have a tach that tells you 400 rpm)

Repeat steps 1 - 3 three times.

Remember the side-pointing idlemix is out for lean, in for rich.

If you do not have any problems inside the carb, it is easy to get the idle down to 350 - 400 rpms.

Your last step is to go back to the main jet. Remember, in for lean, out for rich. If you end up turning it OUT more than ? turn for max power (remember, you already had it 1 ? turns out) then stop right there because you have a dirty carb or a fuel problem.

If adjusting the carb doesn't work, post back w/ an update & we can move on to other less likely possibilities.

" Should I buy a new distributor? "

Even in the very unlikely case that it's a distributor problem, never ever buy new component parts for these tractors if the OEM part can be rebuilt. And it's rare when they can't. I?ve been working on old cars, trucks & tractors now for over 50 years. Whenever possible, I get OEM component parts rebuilt. Given the high probability that any new component part purchased for an N tractor is made somewhere overseas w/o adequate quality control, chances are very good that you will be disappointed.
75 Tips
 
(quoted from post at 15:56:26 09/11/16) Bruce,
Thanks for the speedy reply. I'll printed out your instructions, and will post the results.
Gary

Any results with this one?
 

Been going round and round with a 8n and the backfire issue..

This is on a 12volt converted, front distributor 8n. It was already converted when we got it and was running fine.

First off, the coil that came on it was no doubt fried by leaving the key on while charging the battery and such..

Well it turns out that as the 8n was converted to 12Volt we replaced the coil with a 12volt coil unit.. Still backfired...
Upon returning to the parts counter the parts guy gave us a 6 volt coil and said try it..

Bingo... Like magic it did the trick.. Started and runs like a champ now..

Don't know why.. maybe Bruce or someone can explain but even though this 8n had been converter over to 12 volt it only runs correctly with a 6 volt coil..

And Bruce, you contributions to this forum are priceless, I have learned so much from reading your post here.. Thanks a bunch..

.
 
"Started and runs like a champ now.. Don't know why"

How many resistors do you have in your ignition wire?
With a 12V coil on a front mount, all you should need is the
original wire wound ballast resistor mounted to the back of the dash.
If you have an added ceramic resistor you would need a 6V coil.
 
"it really sputters and often backfires."

Backfires through the exhaust or through the carb?
 
" And Bruce, you contributions to this forum are priceless"

You're welcome. Glad to help.

" maybe Bruce or someone can explain but even though this 8n had been converter over to 12 volt it only runs correctly with a 6 volt coil.."

Electrically, the only difference between the 2 coils is the internal resistance. The tractor would "run better" on a 6 volt coil if you have more than the OEM resistor in the circuit.

However......

The difference in coils isn't going to cause it to stop or start backfiring. Misrouting the plug wires would cause it to backfire.
75 Tips
 
Or maybe a 'backfire' is this?
https://www.google.com/imgres?imgurl=https%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2F7%2F79%2FAudi_S1_Pikes_Peak.jpg&imgrefurl=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBack-fire&docid=t4Hrjr7TZJKHTM&tbnid=v4fM7tRY5nVARM%3A&w=1880&h=1249&bih=611&biw=1024&ved=0ahUKEwjZq6jzl6jPAhUo7IMKHbNDBHs4yAEQMwgKKAgwCA&iact=mrc&uact=8
or maybe it is this?

I don't believe either of the first two can be a result of timing being too advanced or too retarded in a running engine. I can't speak for the third..........maybe simply retarded? :lol:
 

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