NAA losing power

[ClarkR]

Long post, but here's the info. 1954 NAA, 12V conversion, 1-wire 12V alternator, IC14SB 12V coil no resistor, newer points, plugs and wires, MS carb.

Used the tractor about two years ago and it started bogging down while discing. Parked it in the barn and used another tractor. Got it out a few weeks ago and got it going. That's when I put in points, plugs and wires and cleaned the carb (took off sprayed out all ports, etc.), changed oil, etc. Cranked right up, bush hogged for about an hour and started bogging and would only idle, but would idle up and run pretty good with choke under load. Checked for good fuel flow at carb. Removed and cleaned out carb (sprayed out all ports with cleaner). Fired up and seemed to run fine at high idle. I noticed the metal fuel line was close to the manifold so I wrapped with three layers of asbestos line wrap. Mowed for about an hour this weekend and it started the bogging again, would only idle unless you choked it. Went to the house and took a break for a couple of hours. When I came back it mowed for a while and then bogged again, but would idle up on choke. Ran out of time to work on it any more.

My leaning is still the carb, but it's always clean when I open it up. Could it be the coil getting hot and not sending a consistent good spark and the extra gas from the choke making it fire better? Only other thing I suppose could be the condenser. Checked the gas cap and it is venting. Also tried it without the cap, no change. Gas in tank getting too hot? Don't see a heat barrier under tank. Thanks

 

[grhuck]

(quoted from post at 05:43:28 10/07/19) Long post, but here's the info. 1954 NAA, 12V conversion, 1-wire 12V alternator, IC14SB 12V coil no resistor, newer points, plugs and wires, MS carb.

Used the tractor about two years ago and it started bogging down while discing. Parked it in the barn and used another tractor. Got it out a few weeks ago and got it going. That's when I put in points, plugs and wires and cleaned the carb (took off sprayed out all ports, etc.), changed oil, etc. Cranked right up, bush hogged for about an hour and started bogging and would only idle, but would idle up and run pretty good with choke under load. Checked for good fuel flow at carb. Removed and cleaned out carb (sprayed out all ports with cleaner). Fired up and seemed to run fine at high idle. I noticed the metal fuel line was close to the manifold so I wrapped with three layers of asbestos line wrap. Mowed for about an hour this weekend and it started the bogging again, would only idle unless you choked it. Went to the house and took a break for a couple of hours. When I came back it mowed for a while and then bogged again, but would idle up on choke. Ran out of time to work on it any more.

My leaning is still the carb, but it's always clean when I open it up. Could it be the coil getting hot and not sending a consistent good spark and the extra gas from the choke making it fire better? Only other thing I suppose could be the condenser. Checked the gas cap and it is venting. Also tried it without the cap, no change. Gas in tank getting too hot? Don't see a heat barrier under tank. Thanks

My 8N does the exact same thing. I'm positive that the tank's vent is plugged. It's not an uncommon problem. Instead of removing the tank and clearing the vent, while I'm mowing, every half hour or so, I reach over the steering wheel, open the gas tank hatch and unscrew the gas cap & retighten. This allows the tank to replenish a fresh supply of atmospheric pressure. Without the tank being vented a vacuum is created inside the tank which greatly reduces fuel flow.

Try mowing again and well before the time it usually begins to stumble. loosen the cap for a second.

I've found that if I allow the tractor to die, from lack of fuel, it requires bleeding the line to the carb or it's a long crank time

 

[ClarkR]

It has a vented gas cap and the vent seems to be working on the cap (I can suck air through it). I've also tried it with the cap off when it's acting up with no change.

 

[Jim L WA]

Have you checked for a good strong spark, one that can jump a 1/4 inch or more when it's acting up? You said you have another tractor, is it a 12 volt no resister so you could swap coils? Condensers don't cost much, I would try that too. Have you tried bypassing the ignition switch with a jumper wire?

 

[showcrop]

You state that you "checked for good fuel flow at carb" this imlies that you found it to be good. What is good flow to you?

 

[Rusty 2N]

Did you check and clean all 3 screens? 1 on top of sed bowl, 1 in the bowl, and one at carb elbow.

 

[ClarkR]

Yes sir. All completely clean.

 

[ClarkR]

It was a steady flow. Ran a couple of cups in what seemed like a few seconds.

 

[ClarkR]

I haven't checked the spark while it's acting up, but that's a good idea. It just may be difficult since it will barely idle when it's acting up, but I'll give that a try. I'll probably also pickup a condenser. My other tractor is an older IH diesel so no coil to swap, but I can pick one up for testing. I also haven't tried jumping the ignition switch, but that will be easy enough to try. I'm using a heavy duty toggle switch rather than a key. Thanks for the advice.

 

[Jim L WA]

Clark, it doesn't have to be running to check for a good spark. Before it has time to cool off, pull the coil wire out of the distributor and hold that close to the a ground and with the switch on turn it over. We aren't looking for one bad plug or plug wire, but a weak spark. I.M.H.O. I would think that a fuel delivery problem would show up long before an hour.

 

[showcrop]

Clark, what Jim means, I believe, by turn it over is to crank the motor with the starter. There is a situation that has come up here many times where it takes considerable time for a fuel flow problem to have its effect. That is where there is a lot of crud in the bottom of the tank which gets put into motion when the tractor is in use. The screen inside the tank is more than 2 inches tall, and it can take awhile for enough debris to be drawn to the screen to block it. Shut the tractor off and most of it falls away, and the tractor will start and run again.

 

[Jim L WA]

Showcrop, good point, but I believe that screen only comes into play when the shutoff valve is fully open (reserve mode). Please correct me if I'm wrong about that.

 

[showcrop]

(quoted from post at 10:39:30 10/08/19) Showcrop, good point, but I believe that screen only comes into play when the shutoff valve is fully open (reserve mode). Please correct me if I'm wrong about that.

Jim, it depends on how much crud is in the tank.