Friends 8N

[1gr8bldr]

Several mechanics have worked on this thing with no results. It runs good for 10 minutes and then starts to bog and run rough. Everything that can be replaced, has been. Carb just rebuilt. Ran fine as usual for ten minutes. What are we overlooking?

 

[DJ54]

Have you checked the fuel tank cap, to see if it is venting..?? Possibly a vacuum in the tank causing lack of fuel flow..??

 

[MIKE R]

Does it have a inline afternarket fuel filter. They can not keep up with the fuel draw of the engine. Fuel flows through filter, fills the carb bowl and line after filter, runs till fuel can't keep up and starts starving for fuel.

Them aftermarket filters are to resricive. I see one on a old tractor I have to think the tank is rusty and this was the easy fix.

 

[Jerry/MT]

As soon as it dies, and I mean immediately, check for a good spark (FAT AND BLUISH-WHITE, the color of lightning). If you don't have that, it's possible that you have a bad ignition switch. Jumper around the switch and see if that cure it. It's also possible you have an overheated coil. Do you have the resistor in place for the OEM ignition(6V system)?

If you have the requiste spark then you might have obstructed fuel delivery. These old machines have a lot of crap and corruption in the fuel tanks. Remove the plug from the bottom of the fuel bowl on the carb and hold a suitable contaner under it. Make sure trhe tank valve is open. The fuel should CONTINUOUSLY gush out like a cow peein' on a flat rock. If is in intermitent or just dribbles find out why.Have you checked the filter in the sediment bowl and in the fuel inlet elbow to the carb? What about the pulling the tank valve and checking to make sure that the fuel tube9s0 are not plugged. The floats could maybe hanging so a rap on the side of the carb with block of wood will allow them to drop.

 

[LD1]

Why not start by telling us what you have replaced.

Ditto on the fuel test. IF it dont flow out continuously, thats the issue. Take the line off feeding the carb. If it is good there, check that elbow the line hooks into. There is a screen in it. If the flow isnt good at the line supplying the carb, Tank screen and sediment bowl.

Again, what have you replaced.

All this advise is a bit redundant without you giving us the details of what you have done.

 

[1gr8bldr]

All good ideas. I have not seen it but have heard the storys about the attempted fixes that have gone on for the last two years. It stays at his hunting lease so every attempt is in 1 month increments. I'm thinking of going to bring it to my house to work on it here where I can try several different things. It has new spark plug wires, new coil, 2 new coils, switch, distribitor cap, etc. It has been worked on in the field by a tractor mechanic. Been hauled to another tractor mechanic who has worked on a thousand 8n's. They thought they fixed it but did not drive it enough to get it heated up enough to the point where it bogs. Everybody has threw parts at it rather than figure it out. I had searched the net awhile back and had made a list of 20 different things to check. But I have since lost my list. If I recall, I suspect it is a bad resistor. Or starving for fuel, which he says is not the problem. The carb was just rebuilt by a pro mechanic. This because he said that it seemed to do a little better if he choked it. Yesterday, he said something about having water on top of the intake????? I did not know what he was talking about. But I may decide to go get it and bring it into my garage, turn up the air conditioning and tinker with it. They are simple machines. Process of elimination should find to problem

 

[LD1]

IF choke helps, sounds like a fuel problem to me.

A rebuilt carb does absolutely no good if you cannot get enough gas to it.

 

[1gr8bldr]

IF choke helps, sounds like a fuel problem to me.

A rebuilt carb does absolutely no good if you cannot get enough gas to it.

I asked if choke helped after rebuild but he said no. Giving it some thought,.... I suspect that fuel is fine???? It runs good for ten minutes and then starts it's routine. Always the same

 

[cowski]

has the coil been changed? is the dwell set right on the points. when it starts missing, put a little starting fluid to it.if it picks up running good then it is maybe the fuel system. if not changed then check the above.

 

[LD1]

Giving it some thought,.... I suspect that fuel is fine???? It runs good for ten minutes and then starts it's routine. Always the same

That is exactly why I am suspecting the fuel. Picture this:

The carb bowl holes around a cup of fluid. (now I am just going to make up numbers for sake of simplicity.)

So carb holds 8 ounces of gas. While running, tractor wants to consume 2 ounces per minute. Fuel supply screens are restricted and will only allow 1 ounce per minute to be delivered.

After 4 minutes of running, you have consumed 8 ounces of fuel in the bowl, but replaced it with 4 ounces, so tractor will still run.

Another 2 minutes, and you have gone though them 4 ounces but put 2 back in.

Another 1 minute, you use those two ounces and replaced with 1 ounce.

Now you only have about another minute of run time before it quits.

You give up, wait awhile, carb finally fills back up, and you have ~10 minutes to run again.

So the fact that it runs fine for 10 minutes in NO WAY rules out the fuel as being a problem. But it does pretty much say the carb is fine, as all the carb does is meter the air/fuel ratio. So that is working. But you could still be running out of fuel.

NExt time you get to the tractor, you need to shut the fuel off, and take the steel line off at the carb. Then turn the fuel on 2 turns. It should be pouring out about as fast as that line can handle. If anything less than a solid stream flowing pretty quickly, you have a fuel problem.