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

[mbryant51375]

Recently my uncle and I took on the project of a 8n which had been sitting for several years while the tractor had not been stored properly we do know it ran great up till the electronic ignition had fried.

First we replaced the fuel tank, petcock and fuel line. The carb, which was a aluminum aftermarket version, was soaked thoroughly and rebuilt. We relaced the complete ignition system with new points setup, coil, ballast resistor, wires and plugs. The flyballs in the governor was also replaced. We also have replaced the intake gasket.

Now the tractor starts and idles perfect but will consistently hesitate or missfire once the throttle is adjusted to half throttle or above. We have taken the tractor to the only shop in our area but only to confirm the points was set correctly and the carb was adjusted, but the guy did not like the aftermarket carb so he set us up with the cast iron Marvel carb which I also put a kit in only to run exactly the same. Occasionally the tractor will act as if it wants to run correctly but then goes right back to hesitating.

 

[cqaigy2]

Don't know anything about an 8n, but it sounds at though it's not getting enough fuel at the higher rpm. Assuming float is set correctly along with needle valve and seat are clean, maybe junk along the fuel supply, tank, line, filter.

 

[mbryant51375]

Thanks for the reply, the fuel system is all new and is clean the carb adjustments are set per service guide. However the adjustments have little affect on the way it runs above idle.

 

[Midniteoyl]

Check your distributor, condenser, plugs and timing.. What the coil voltage? Is this 6v or 12v? Are you using a ballast resistor?

 

[mbryant51375]

Thnx for the reply.
Distributor has new bushing, chaged plugs twice and we are running the recommended hotter plugs. It is a front distrib so it only goes one way of course, however the
adjustment only effects the starting and idle. It is a new 12v coil 2.5 ohm. Condenser is fine it will run at idle all day long.

 

[mbryant51375]

We also ran compression check and have 110 to 115 across the engine.

 

[Midniteoyl]

Well, somethings up with your spark, I believe.. Double check the firing order 1243.. advance mechanism free and working?

Do you have an inline spark checker? Timing light?

 

[Midniteoyl]

I dont have an 8n/9n/2n, so hopefully someone with more experience and/or a good IT manual will chime in. But, just from the sound of things, timing/spark is where I would look.

 

[mbryant51375]

Yes we do and it has plenty of spark, however when the throttle is adjusted up it randomly drops cylinders. This does not happen at idle. I was thinking of changing the mechanical advance next?!?! I am at witts end

 

[Midniteoyl]

I must have edited while you were typing..

Unless you did some to mess with the timing, thats about all I have left too. If your timing light have and advance dial, see how much the dist is advancing at RPMs. That'll tell for sure. The manual should also have how to set the timing back to factory if needed..

BTW, what did you set the points and plug gaps too?