8n backfires

[Mnoble]

I just bought an 8N and haven't had the time to delve into it much. The engine will back fire repeatedly when it is lugged down under load. Also the oil pressure is slightly under 20LBS. Is this likely in need of an overhaul? what should the oil pressure read in an engine in good condition?

 

[Dunk]

"what should the oil pressure read in an engine in good condition?"

Hot??

10 to 40

Turn the big screw on the carb clockwise 1/4 turn at a time, keep up with how much you turn it, so that you can put it back.

You may just be running it to rich.

May also have a sticky valve.

There are some snake oil tricks that may fix that.

 

[old]

When you lug it down do you get black smoke or no smoke?? If you get black smoke I agree with dunk but if you get no smoke then its set to lean. As far as oil pressure I have seen one run for years with just over 5psi when warmed up. These little flat heads for the most part have low oil pressure and do just fine. But I have also seen them run around 50PSI also. Your oil pressure is really good for an old 8N
Hobby farm

 

[Scott1ky]

What year 8N is it? Does it ONLY backfire when it lugs?

Just some things that came to mind: Your timing could be off. If it has a sidemount distributor, you can adjust timing fairly easily by advancing and retarding it some with adjustment. Did you check your firing order? Might have to pull the plug wires and check, it should be 1-2-4-3. I also agree with the others you should check your carb. Might be a good time to tear the carb down and rebuild. The kits aren't too expensive. Good luck.

Scott

 

[Scott1ky]

Oh forgot to add,, I'd save the overhaul as a last resort, it's expensive. Run a compression check to answer that question first.

 

[Jerry/MT]

What distributor do you have? If it"s a sidemount, check your timing.

 

[Mnoble]

The distributor is on this tractor is mounted on the front of the engine. I don't get black smoke when its lugged down until it starts poping, then there's a puff of smoke with each pop. I notice 2 adjustment screws (one big, one small) on the carb. What do they do? thanks for the suggestions

 

[Jerry/MT]

The big one above the fuel bowl adjusts the main jet"s fuel flow. Screw out to enrich the mixture. The one on the side of the carb throat adjusts the idle airflow. To enrich at idle screw in.
before you start, turn the main jet screw in til it stops( do not reef it down!) the scre it out 1-1/2 turns. Not start it and let it warm up.
With the engine warmed up to operating temperature, accelerate the engine. If it coughs and sputters, try enriching the mixture by 1/8 of a turn. Repeat the accel. If the situation gets worse, try leaning it 1/4( since you enriched 1/8 in the previous step). Make 1/8 turn adjustments until it acclerates smoothly from low idle to high idle.

 

[Anonymous-0]

If a spark plug misfires under high engine loads the unburned fuel goes into the exhaust manifold and ignites.As pressures increase a plug can fail to fire.Wide plug gaps and weak spark will case misfires.

 

[Mnoble]

Thanks Coupe all that makes perfectly good sense and is an easy place to start. I always wondered when I was tinkering with engines in the past if conditions in the cylinder where causing miss fire. Iv'e tried adjusting the mixture, but it doesn't seem to have an effect.