8n will start and idle fine but missfires at half throttle to full! PLEASE HELP

[mbryant51375]

9n/2n/8n tractors are flat head engines. I have been leaning toward valve issue! Guess its time to pull the head!

 

[mbryant51375]

I have tried the points at 18 and at 20 with no change. I know the side to front distributors require different gaps.

 

[mbryant51375]

This is a front distrib!

 

[mbryant51375]

Still missfires under a load. I have disconnected the linkage to the gov from carb and it will randomly smooth out for a split second and back to same!

 

[the old grind]

If compression is good at cranking speed I wouldn't pull the head just yet. Don't bad valves usually give backfires and 'pffts' thru the exhaust (vs misses) and idle poorly? (Proper diagnosis is essential.) Did I ask about plug wires? I guess your mechanical advance checks out ok ...

btw: IMO a governor issue is a very wild guess. Trouble there if you lose rpm under load, but we're not running right 'no-load' yet. ...

I'd have to page back to see about the coil. (similar symptoms..)

 

[sd455dan]

You could try a little propane from a torch as u increase the RPMs by feeding it in at the carb intake if it smoothes out it is lean on the main circuit

Are the plug wires new- have seen bad wires mimic this... OOps see that you replaced them.
What brand of points did you buy ? are they tisco? if so they caused a lot of problems for another owner a while back- some kind of coating or non conductive stuff on the contact surface...

Soundguy is probably your best bet

 

[rsallen]

No no MBRYANTI !
Don't start tearing apart the engine unless you have some clear idea of the whys or what your looking for.
Pulling the head at this point will not tell you anything you don't know already or can't find out with a compression gauge quickly.
If you want to check the valve train access it through the cover plate on the side of the engine.

 

[Utopia Texas]

Start the engine with the distributor body clamp slightly loose. As someone else opens up the throttle a bit at a time manually rotate the distributor a bit to advance the timing to see if that smooths out the engine. If so the mechanical advance needs repair. Be careful to NOT get your fingers too close to the fan blades. I also agree with someone above that many new point sets right out of the box are pure crap and need to be filed to a shiny surface to get a really good clean spark. The Ford Model A (1928-1931) uses a very similar spark system to the 8N and newly made "Ford" points I buy for my Model A are poorly made to say the least.

 

[rsallen]

I'm still of the mind you've got ignition issues.
I only threw out the very rare problems I've encountered over the years. They can and do happen but rarely.

Back to ignition.
I assume the original plug wires were/are solid core wires? You didn't put some after market silicone resistor wires on it did you? Some ignition systems don't like that.
I've run into rotor buttons brand new out of the box that have given symptoms you describe, try another one.
Double check those points.

 

[mbryant51375]

Sounds to me like the centrifugal timing advance is not working properly. Also make sure the coil is wired properly. It will work wired either way but the spark will be much improved if the polarity is correct.

As for wiring to coil,... from ignition to resistor to coil?