8N rough running

Karl_T

Karl_T

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I have a beautiful restored 8N tractor. It started running rough last year. Over time, I have replaced EVERYTHING with no success. It will idle fine for a minute, then almost die, then take off again. Can not drive it around, it will stall and die.

I though it was fuel and replaced a rusty gas tank - no help. BTW, I bought a Chinese one an it was slightly larger than original. Had an AWFUL time shoe horning it in. Then installed a new carb - no help.

Decades ago my dad told me its always the ignition. So even though the parts were not that old I put in (over time and many trials) entire new distributor, new coil, new wires, new plugs. Its ALL new still no joy. Timing is spot on 4 degrees BTDC. No dwell meter but point gap is 20 thou. Visually can see plenty of contact and break time.

Double checked compression, its good and does not leak down so the rings and valves are good.

I thought last night, just maybe there's an intake air leak. But I do not know how to check for this. Ideas?

Or any other suggestions. I am about to give up and scrap it out.
 
I think you spray something around the intake manifold to check for air leaks- don't remember what though- starting fluid?
Sounds like you might have a cracked manifold or something like that- a "tough dog" problem
What about the exhaust? Could it be clogged up somehow?
 
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Check your fuel line. It sounds like it is starved for fuel. The carburetor is gravity fed and it doesn't take much of an obstruction to reduce the fuel flow. The OEM sediment bowl has a screen if I recall correctly. I replaced mine with an in line filter decades ago because of problems with it.

Not likely because of your symptoms but ignition can be a sticky problem on an 8N. On mine, the OEM distributor shaft bushing was worn so much that dwell would change depending upon which way the tractor was leaning on a slope causing the tractor to die if leaning the wrong way. I replaced the distributor and also changed to an electronic ignition system, including a high energy coil. It totally eliminates the messy issue of setting points.
 
The first thing I would do is put a jumper wire from the battery to the coil to eliminate the possibility of a bad ignition switch. When it starts to die, pull the choke out and if it catches and revs back up you will know it's running out of fuel. To check for a vacuum leak I spray the area with SeaFoam.
 
Post 4. Sounds like fuel problem. Rust can move and cause problems. Check from the fuel intake screen and glass fuel bowl and all the lines from the carburetor back. Had a TO 20 that acted the same. Would blow back with compressed air from the carburetor line into the tank. It would run good for a while then the same problem. Good luck. Sometimes just having a second set of eyes on something like this helps. It can sure be frustrating.
 
Have you yanked the spark plugs to inspect the burn in n the cylinders?
Often you can determine the health of each cylinder by the spark plug condition.

Secondly, i would be suspicious of the fuel pump function

Thirdly, an inspection of the distributor and ignition system would come next.
 
I didn't mention it before because I was assuming you had a full tank of fuel. The 8N has a horizontal run in the fuel line and in certain conditions, it can develop an air lock so fuel just dribbles out of the line. This usually followed running out of fuel and putting just a gallon or two in the tank. There wasn't enough of a head to develop enough pressure to push the air bubble through the line and into the carburetor. The solution was to fill the tank. If that didn't work,breaking the fuel line connection at the carburetor was required to clear the bubble and start fuel flowing again. This was essentially eliminated by replacing the sediment bowl with an in line filter.

In fact, I ran out of gas two days ago. Two gallons of gas was enough to get me back in operation. In other situations, I have run out of gas when on a right hand slope due to the tank outlet on the left hand side. This usually happened out in a field where I was a half a mile away from the buildings. If I rolled the tractor around so it was now on a left hand slope, enough gas would flow so I was able to limp back for more. (I know, check the fuel supply before leaving!) That never would have happened with the sediment bowl.
 
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