8N carburetor rebuild and adjustment

KristofMI

Member
1950 8N. I will rebuild my carburetor. Right now the tractor dies if I put the lever lower then half way. Even if the engine is warm. Not sure if the previous owner cared about the maintenance so I decided to rebuild it.
What will be the steps to adjust the carburetor and linkage so it won't die as soon as I place the lever in the lowest position?
 
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.

Lastly, each of us has his own definition of a carb rebuild. If your rebuild did not include soaking the carb 24 hrs in a bucket of caustic carb cleaner &
blowing out every orifice w/ a rubber tipped air gun, you didn't do a rebuild, IMHO. You just replaced parts.



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75 Tips
 
I have the parts needed to rebuild and also I plan to put all parts in my sonic cleaner. Even the new parts , just in case. Should this works? I will blow everything with air when out of the cleaner.
 
i WOULD RUN A SMALL WIRE THRU EACH PASSAGE WAY AND THEN BLOW OUT WITH AIR NOZZLE. Ultra sonic cleaner can't hurt!

This post was edited by R Geiger on 07/27/2021 at 01:44 pm.
 
I'm going to do the wire cleaning , air blow and ultrasonic cleaner. It's not like it's going to take forever to do it.
 
So I took everything out of the carburetor. Does this choke plate looks good? It looks like it's bent.

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(quoted from post at 08:47:04 07/26/21) I have the parts needed to rebuild and also I plan to put all parts in my sonic cleaner. Even the new parts , just in case. Should this works? I will blow everything with air when out of the cleaner.
ltra sonic cleaners work AWESOME.

Given youve had idle issues try to get all the jets (primary, idle, economizer) out of the carb and make sure they are the appropriate jets. These machines are 60-70 years old at this point so only lord knows whats been cobbled on it.

Something else that can effect idle quality is timing. If your tractor is a side mount dizzy make sure you have your timing set right. If you put a light on it and the timing jumps all over the place due to weak advance springs or something binding up it will never idle right.
 
(quoted from post at 10:26:07 08/11/21)
(quoted from post at 08:47:04 07/26/21) I have the parts needed to rebuild and also I plan to put all parts in my sonic cleaner. Even the new parts , just in case. Should this works? I will blow everything with air when out of the cleaner.
ltra sonic cleaners work AWESOME.

Given youve had idle issues try to get all the jets (primary, idle, economizer) out of the carb and make sure they are the appropriate jets. These machines are 60-70 years old at this point so only lord knows whats been cobbled on it.

Something else that can effect idle quality is timing. If your tractor is a side mount dizzy make sure you have your timing set right. If you put a light on it and the timing jumps all over the place due to weak advance springs or something binding up it will never idle right.

I bought the 8N I have now in 1988. rebuilt the engine in 1991. I always had trouble with a stumble just off idle and or a dead spot in the lever travel. Always! No matter I did it was always there.

A couple of years ago I bought my wife an ultrasonic cleaner for Xmas. She restores antiques and I knew it would be useful for cleaning up all hardware etc.

last spring I rebuilt me carb again, it was time, not running terrible but I thought I'd let the rust out.

After the usual degreasing i put both the halves in her ultra sonic cleaner half hour or so. Long story short I no longer have a stumple off idle. the thing now revs up steady and consistant from the idle end of the throttle quadrant to the full load end. In fact the tractor has never ran better in all the years I've owned.

If your one who rebuilds carbs get yourself an ultrasonic cleaner.
 

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