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No 1 plug mis-fires when warm? on a 140?

N

NawlensGator

Member
Replaced: dist cap, rotor, plugs, plug wires and coil wire to dist, coil, cleaned all fuel lines and strainers, good gas flow. It has electronic ignition. Timing light shows steady strobe when pickup is on each of the 4 plugs when engine is cool. Engine runs strong and sounds great. Then, after mowing for 20 to 30 minutes, the engine starts missing. Still runs, and can mow, but with less power and engine sputtering. Back at shed the timing light shows steady strobe on 2,3, and 4, but No. 1 is skipping noticably. Let cool, and sequence repeats.

It looks to me like the No. 1 plug is not getting a steady pulse after the engine gets hot. I'm baffled. Could this be an issue with the electronic ignition? Maybe not an ignition system problem at all? Help!
 
Nawlens- Not familiar with 140 -Is the electronic modular unit separate from the dist? If so try isolating from any engine heat source --sounds like you have heat sensitive component failure in your ign.mod.This is not an uncommon occurance.CO2 sprays on dist housing might also work if mod is internal--hope this helps.--John
 
I guess next step would be put a set of points back in (you did save some, and the terminal post right? I did) and see what happens. It just seems weird that the module would 'know' it is on No.1 and decide to fail to send a pulse to the coil.. You would think it would fail equally on all cylinders. For chuckles, you might try taking the magnet thingy off the distributor cam and turning it 180 degrees to see if the failure changes plugs. I have the Pertronix on a 140 for four years now with no problems. I am curious to see how this turns out.
 
Thanks for the clean thinking John. Elec Ignition module is in the distributor. I would just replace it too, but they're about $100. At worst I would end up with a spare if problem is elsewhere. Is the CO2 to cool the distributor? I have an identical IH 140 that doesn't have this problem.
 
> ...you might try taking the magnet thingy off
> the distributor cam and turning it 180 degrees
> to see if the failure changes plugs.

Good idea. Also try changing the plug.

Could also be that the plug is fouling for some reason.
 
How much distributor bushing wear? Does the distributor shaft wobble (bent)? Did you check the "air gap" between the magnet ring and the module... basically put it as close as you can without it touching and wearing.
 
(quoted from post at 08:04:26 05/03/09) How much distributor bushing wear? Does the distributor shaft wobble (bent)? Did you check the "air gap" between the magnet ring and the module... basically put it as close as you can without it touching and wearing.
Click to expand...

I would bet money this is the right track
 
Check the valve clearance. If the valves tighten up on # 1 & the compression is lower , it may take less voltage to fire & not enough to fire the light??? Just a guess, I don't know.
 
Hi Again --yes the co2 will bring the temp down to very cold if appied for very long--Also here's another thought -why not swap the other tractors module if its working ok? Might be easier to swap dist if your up to the timing chore. just a thought! John
 
Thanks for all the good suggestions. They're much appreciated.


Compared both elec ignitions. Air gap on sputter'n one is noticeably larger. I could only tighten to a gap of about 0.08 inches, but still less than before. Still more than the other. I'll run it and see if it's better (rain permitting).

There is wobble in the dist shaft. In/out about 1/8th inch, side to side not so much, rotation a few degrees (5 or less). How does one replace the bushing? Is this a big job? Can you loosen and pull the shaft out, replace, and reinsert?

I thought about valve adjustment but that shouldn't shouldn't cause spark loss.

Before I try swapping modules I'd probably just get a new one.
 

Just tried and same exact sequence occured after about 20 min. I'll recheck valve clearence later in the week. Maybe the no.1 spark is just a red herring.
 
Did you try the old-fashioned missing cylinder test of pulling each plug wire and listening to the engine? At this point, it just might tell you something the strobe did not. Good luck...
 
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