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1948 8n runs rough, timing? carb??

Jerry G My 1948 8N is running very rough. It started last year. It would not start at all. It is a front mount distributor. I changed points and it would start but just seemed to be running on only 3 cylinders. I just parked it in the barn until this year.
I got it out, changed the spark plugs, points with new ones(just to make sure I was doing it right). Got the ruler out to check the 1/4" space between the mounting holes. It will still start right up but it is still running very rough, and will accelerate. I found a bad spark plug wire(no continuity), changed all them(checked continuity,OK). The new spark plugs have a black soot on them.
I wanted to see how they were firing, took all of them out, put one in and grounded it about 1/8" from a bolt, spark was white with blue. But each time I tried to ground it out,(with all boots not touching ground), I would get a shock when I pushed in on the starter and held the boot with the spark plug wire to ground.
The engine has probably only 30 hours a year use and was overhauled 15 years ago. It always purred like a kitten and justed sounded great. But now I do not know what it is. I have not messed with the carb setting. I just keep thinking it is in the timing?? Any ideas?? Thanks I am open to any thouhts. Jerry

Jerry G I wanted to add that this is a 6v system. I also took an old sparkplug and opened it to 3/16" grounded it to a bolt, did this on all 4 spark plugs and it jumped the spark.
Bob G wHY DO YOU THINK IT IS THE TIMING? IF YOU SET THE POINTS TO 0.015" AND SET ACCORDING TO THE MANUAL THE TIMING HSOULD BE CORRECT.

Have you checked the firing order? 1-2-4-3.

remove one spark plug wire at atime with it running and listen for any loss of RPMs. there should be.

take a plug and open ethe gap to 3/16' and ground the plug on head and crank over. the spark should be able to jump that far with a blusish spark.

check the main jet settting on the carb. starting point is 2 turns open from full in. some people same to set it at 2 turen and leave it.
let us know what you find
good luck


Check for fuel flow by removing the plug on the bottom of the carb. you shuld get one pint in 2 to 3 miutes .

Bob G Ok that is good, you habve good spark. check for the fuel flow and if that is good you may want to do acompression check. may have a burnt valve.
Bob G just for grins you might check the airfilter. sounds like something is making it run rich.
Jerry G The spark jumped the gap, but it looks white, not blue. It is dark and late, I will try taking off a spark plug wire one at a time tomorrow. And then check the carb. The carb on top looks like has some gas on top, I will check it out tomorrow also. I might have more than one thing wrong.
I just noticed that I left off the round paper gasket that seperates the points from the cap, so I will have to put that back on.

Jerry G To check compression would I take out all 4 plugs and check the compression on each cylinder?? What would be a good reading? Thanks
Bob G Yes remove all the plugs. crank thru at lest 2 -3 compression strokes per cylinder.

above 90 would be a good reading but should run on a bit less. 125 would test. wet is placing some oil in each cylinder before the test. if no change wet then valves, an increase means rings.

Good luck

Bob G One good tst is to run it in the dark and look for a light show. It will show you if the wires are bad.

Jerry G Bob, The comression readings on #1 is 111, #2 is 109, #3 is 100, and #4 is 105. I took a spark plug wire off to see if it made a difference, but I could not notice anything, I did this on all 4 cylinders, one at at time.
I checked to see if I had any shorts, when it was running this morning when it was still dark, nothing. The air cleaner is clean.
One thing I want to make sure is that the #1 cylinder is nearest the front of the tractor and the #4 is nearest the seat and 2 and 3 would be in the middle. Counting 1,2, 3, 4 front to back. And the distributor numbers are 1(top) and 2(bottom) on the left as you are facing the tractor. #3(top) and 4(bottom).
The reason why I ask is that it seems to sound better when I put the #3 cylinder wire on the #4 distributor terminal. Which isn't right, but it just sounds better.
I still have the spark plugs that have a black soot on them. Do you think it is in the carb? I could take it off this weekend and clean it? Thanks for your advise, Jerry

Bob G
Re: 1948 8n runs rough, timing? carb??

The firing oder is 1-2-4-3 with number one cyclinder closest to the fan.

I think what you are saying agrees with picture.
I have to go back and reread our posts and get my mind on the right track. Have you tried leaning out the main fuel jet? in for lean out for rich.

It is a common mistake to get number three and four switched. they run pretty good on 2 cyclinders. yourcomprssion reading sound prtty good so nothing major is going on.
keep at it.

Bob G I would take the carb apart. you may have a stuck float ethat is allowing too much fuel. NAPA auto store should have the rebuild kit. check to make sure the choke is not stuck partially closed. Are you getting black smoke when it is running?
Jerry G Bob, I will clean and overhaul the carb this weekend. yes it is putting out black smoke. Setting the main screw back doesn't help. It isset at 1 1/2 turns. Thanks, Jerry
Bob G Good luck!!
thommoos I had the same problem and i found a cracked manifold, causing it ot miss and back fire changed and now purrs like a kitten.
Jerry G I just checked the manifold. I found a black carbon path just around the manifold as it turns down and heads to the mufffler pipe. It was on the block and blowing by the battery box.
I will start it up tomorrow and see if I can feel anything and then take off the manifold tomorrow and see. I can see where someone welded the manifold already. I have owned the tractor for 20 years. It looks like it is the gasket that is leaking.
Thanks, Bob G and thommoos for your advise. I will let you know what I find out. Jerry G

JerryG Sure enough when I took off the manifold the gasket was blown away right were the carbon deposits were.
Somebody juryrigged a headbolt with 4 lockwashers(closest to the leak), and when I turned it out the whole bolt came out and antifreeze spewed out(I am guessing this is normal??). I will have to get a new stud, but I am wondering should I use some thread compound, antiseize, or just screw in the new stud?? Should I also use new nuts, there were 2 diferent size nut heads? Grade? Thanks, Jerry

Bob G I would use some sealant on the stud and I would use all new brass nuts. I would use grade 8 studs.


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