Can't get front mount 8N running right.

[HeyObie]

Front mount 8N

Just can't get my 8N running right. It does no have enough power to cut the grass on a flat surface. I can get more power if I pull the choke out about an inch but it still is not right. When I start it up, it is stronger and gets weaker as it warms up. I have been messing with this on and off for a year and a half. It used to run perfectly

Compression

From cylinder 1 t0 4
Cold dry test 90, 90, 89 80
Hot dry test 90, 90, 90, 90
Hot wet test (dropped oil in the hole) 100, 110, 100, 100

Electrical

I had this problem as a 6 volt system. new plugs, new wires, 2 coils, new condensor cap and rotor. New Bluestreak points. new carb. Didn't change a thing.

I had a problem that I could never get the 6volt generator working so I figured, great time to convert to 12volt.

All new wiring, another set of plugs and wires. Another carb. New alternator and 12 battery. 2 new 12volt coils I fried one).

I also replaced the plate and bearings that the points sit on.

Key switch - I have bypassed the switch by directly connecting the wires to eliminate switch. No different

New oem resistor

Still the same.

Firing order, counter clockwise at front of tractor 1,2,4,3

PLUGS
AUTOLITE 437. It looks like it is burning just right to me. I've pulled pictures up. Definitely NOT rich. Everything is dry. Has dark color on bottom threads of plug. So I think it is right but could be leaning to the lean side

Pulled all plugs and they look the same

Spark - I have an adjustable spark tester that I have set at 1/8inch. All 4 plugs show a nice white spark.

I've changed the timing up and down. Have it in the middle.

FUEL:
I pulled the fuel line off at the carb and the fuel flows. The fuel filter on the carb is clean as it was on ALL 3 carbs that I have had on the 8N.

Summary: It runs about 60% power. Slight Up hill with mower running cutting grass, it can not make it. As I pull the choke out about an inch, the rpms pick up and it is about 75% power and can cut the grass but not strong. With the choke pulled out an inch, the arm on the carb that the choke is attached to is around the 1 o'clock position. This is where he 8N is happiest which means it is almost at the full choke position when it runs best.

NEXT

Since it runs better at a 90% choked position, that means that it wants less air. My thought now is that there is a problem with the intake/exhaust manifold. Either there is a crack or the gasket is bad. AGREE? or any other thoughts?

Thanks for reading.

 

[Lynn Patrick]

Had the same thing w/my "problem child" - 3000 3 cylinder. Pulled the "new" Autolites & installed NGKs & problem solved. I used to run nothing but ALs but now all 6 Fords have NGKs.

 

[Ultradog MN]

I would check the spark when it is
warmed up good after running it for a
while.
Also, remove the plug on the bottom of
the carb and do the flow test.

 

[Jim L WA]

Also, you need to check the spark at 1/4 inch not 1/8 inch. But reading what all you have done, I would tend to agree with you, that the problem must be a vacuum leak around the intake manifold. I've read where you can run an unlit propane torch all around the manifold area and listen for an RPM increase, but I've never had an occasion to do it myself.

 

[Bruce (VA)]

Good troubleshooting.

Re-check your spark; you need at least 1/4".

Yea, you could have a vacuum leak. Get the tractor to operating temp, then run an unlit hand held propane torch around the manifold; if the engine speeds up, you found the leak.

But, odds are based upon the info you have provided that the problem is in your carb. You could have an air leak around the carb metering section. The likely suspects are leaky throttle shaft seals and/or a worn throttle shaft. Or, just a real dirty carb w/ clogged passages.
75 Tips

 

[HeyObie]

I pulled the manifold off today I basically milled it on my 2 foot by 6 inch belt sander. Cleaned the block with a razor blade. Gaskets were tired
And a little suspect. replaced both manifold gaskets and the gasket at the carb I seal both sides of the gasket with a high temp silicone sealer. Took her for a spin. Same result.

I will retest gap at 1/4 and replace plugs with Ndk once I can figure which NDK plug to buy

 

[HeyObie]

I will also run propane test

 

[Lynn Patrick]

I believe the number is NGK B4-L plugs.

 

[Den N Ms]

Lynn Patrick Yup NGK 3112 (B-4L) Best spark plugs.

 

[Hobo,NC]

#1 and the easiest thang to do confirm spark with a spark checker once eliminated move on but not till its a confirmed kill with a spark checker...

Replacement parts today are just flat out garbage new are where you buy them makes no difference...

 

[docmirror]

I vote you aren't getting enough gas. what color are the plugs? Betting they are very cream color.

I've had two diff carbs with partial clog in the main metered circuit. It's a very common failure! If you've had 3 USED carbs on it, suggest you get a known good carb of a good running 8N or buy a rebuilt. Check for vac leaks of course.

Not mentioned yet is the governor. It's unlikely that a governor is sticking as it changes with choke, but set up the governor so that it will go full throttle when needed.