I Really Need a Guru

[NCmau]

My MF202 with a Z134 Continental engine is running rougher than a corn cob. It skips, the higher the RPM the worse if gets. This problem just happened overnight and the weird thing is that once or twice ran okay then back to same problem.
Engine was replaced less than 6 months ago with a totally rebuilt one. New distributor, all new plugs, wires and coil, installed a carb kit. It ran great until last week.

Here is what I have done so far:
• Checked spark at the coil and output of plugs. (Good healthy blue sparks)
• Removed carb, soaked in cleaner and blew all the jets. (I was real clean inside anyway)
• Adjusted air/fuel several times.
• Used a small troubleshooting tank with new gas, just in case.
• Sprayed starting fluid on carb and manifold. (No increase in RPM)
• Checked all fuel filters.
• The carb is getting plenty fuel in the bowl.
• Compression dry test, 110 - 115 psi across
• Adjusted timing at the distributor. RPM goes up and down but problem still exists.

I am pretty sure that after checking and rechecking fuel and spark components, they can be pretty much eliminated.
My uneducated guess points to the timing, but what???... The distributor is almost new. (I didn't pull it and check it). I just hope it is nothing internal.
I tried to follow some sensible troubleshooting procedures, but I am just running out of options.
I just hope you gurus can come up with something.

 

[Anonymous-0]

New engine u say. Try adjusting the valves.I bet it will clearn right up

 

[NCmau]

Uhmmm... ED R that makes mucho sense. I'll do it tomorrow and I'll keep the board posted.

 

[old]

Also on that spark just because it is blue if it will not jump a 1/4 inch gap or more it is not strong enough to run well. Color of the spark is just part of the true picture as to if =the spark is good

 

[mike paulson]

wouldnt hurt to check valve adjustments but you did mention this happened suddenly which makes me question a valve adjustment issue. i would recheck fuel delivery, float, needle valve seat and needle valve ect. and just for the heck of it check you coil ohms after hot to make sure its not breaking down...

 

[Jack in NB]

Could it be a blockage in the air intake system?

A flap loose in a rubber hose connecting the air breather to the carb?

 

[David G]

The breaker bar on the points may have worn down if it was not lubricated.

Check point gap, THEN timing.

 

[Chip812]

My contribution (and worth exactly what you're paying for it): fuel can always be a culprit unless you're very OCD about it... Just a little water in it can cause a pretty severe stutter...

 

[Joe Ferguson]

One possibility is a defective ignition switch
sometimes the switch is as old as the tractor... wear and oxidation/corrosion on the contacts produce switch resistance/bad continuity.

For a test you may bypass the switch (only if you know how) and see if there is some improvement.


My 2¢

Joe Ferguson

 

[MKinOntario]

I'm with Old and say coil too or condensor or plugs. Something electrical.

 

[to_many_irons]

cracked dist cap . as a guess .

 

[Jerry/MT]

I agree with old. Check the advance with a timing light. It may be sticking.

 

[2tractors]

Retorque the head and manifold.With a partial choke does it run better?

 

[mike paulson]

just another quicky, spray some carb spray right into the intake(thru the oil bath air cleaner)or feed the little red stem fro the carb cleaner can right into the carb intake hose. then as she is running crappy just ad little bursts of carb spray and see if it improves. if it does improve with a little spray this will show you that your problem is a lack of fuel/lean condition and you can go from there. if it stumbles worse after a spray you might have a rich condition/getting too much gas or it could be something else.

 

[chuck41]

Two things I would check: broken valve spring or
bent or broken push rod which has come out of
place. Chuck

 

[Used-to-be-iowa-dave]

There's an easy-to-miss in-line fuel filter INSIDE the elbow fitting leading into the carb. Crazy things (like bumble bees) have been known to get in that line and intermittently clog the fuel filter.

Feel the distributor body/cap while it's running. Mine broke the timing gear off the end of the cam and significant vibration was transmitted to the dist. In fact, one dist. ate itself and a new replacement was doing the same until Big Dean correctly diagnosed the symptoms (rest in peace Dean, you're still THE guru and not forgotten here). Hope it's not anything that serious on a recent rebuild.

 

[2tractors]

That will work too Mike but a partial choke will do the same.

 

[MDWK40]

I went threw this a few years back on a grahm bradley. I changed the carb, coil, distributer, manifold gasket, went over all the wiring and gained nothing. when I adjusted the valves it started to run good again. Also had a miss in an M farmall once that turned out to be an internal crack in the manifold. Good luck!

 

[NCmau]

Folks, I haven't seen such response in a long time. It's not just the quantity but also the quality. This is an excellent list for me and many other people to print and keep with the manuals. I can't thank you enough.
At this point I tried and retried everything with exception of the valves. That's what I am doing now and that's where I have a question before I proceed.
I got the valve cover off and measuring the valve clearance, I am finding out that I can slip a .025 gauge (and maybe more) on all valves where they are supposed have a .015 cold instead.
When I slip the gauge it shouldn't have any play, right? Another words if I try to use one or two size bigger than .015, I wouldn't be able to do it, unless those big springs are compressed.
My manual is pretty limited in some of the basic things like this one, so before I adjust these valves, I like to hear from you.

 

[MKinOntario]

That is correct. One or two up should not fit, only the .015, if that's the required gap, but I would think, better a little loose than too tight. So if .016 fits it'll probably be fine too. If I'm wrong, surely others will point it out quick.

 

[MDWK40]

I dont think the tappet gap being .010 to .015 too wide is going to make that much diffrence.I was thinking you had a valve or two that were to tight. Have you sprayed eather or carb cleaner around the intake manifold gaske to see if you have a vacum leak? mabie a broken valve spring?

 

[NCmau]

All the valves are now adjusted to specs and they seem to be working okay from what I can see. Now that I have parts out of the way, tomorrow I'll take a closer look at the manifold.
It really acts like it has an air leakage