FAILED INGITION COIL ON JD #757

I was working on a John Deere 757 with Kawasaki engine # FH721DA59024 miss fire at full throttle under load with blades one. I checked the left spark plug and it was white, checking the right spark plug it was black. So I ohm checked from the laminated center post that the coil goes around to the end of the spark plug wire and came up with 18.6 and 17.6 respectively and Kawasaki says 2-18 ohms are in spec. So I checked a known good coil from another engine and it checked 12.3 ohms. Then I checked a new pair of coils out of the box and found 16.9-19.2.

Well coils must be ok so I put a spark plug tester at the end of the spark plug wire and both coils were firing although the engine would not run of one cylinder. Since it ran good up to full power and wide open throttle I took the carb apart and saw that the butterflies were not opening all the way so I took care of that and richened up the main jets. Still same problem so I installed the new coils and it ran perfect then.

My question is there not a better way to check ignition coils on today's engine that are on so many of products out there?

Thank you for this space.
Coker

Exracer, The coils have power transistors encapsulated inside. I am sure electronic engineers could develop a good tester for dealers which would put the coil under load, but such a tester would be expensive . Further , there is probably little incentive since new sales generate more profit. The transistors used should be screened before mfg of the coils to withstand heat, but some may slip through. This is known as "infant mortality" in the trade. We used to do what is called "burn-in" for 160 hours on military grade parts and still weeded out failures. So I think the poor (AC) tractor and engine owner will always be faced with failures, especially after engine overheat. :smile:

I've been told that a coil may produce spark & still be bad.
If you do the cylinder balance test like you did one coil should keep the engine running. If it doesn't that coil should be replaced.

I replaced both of my coil packs about two years ago. I checked the spark out of the packs and one was bad. So, I spent a wad to replace them both. I would have done it myself, but I didn't have some of the tools to do the job. I bit the bullet. My question to all of your here is, "Where are the jet adjustments"? I can't find any information any where on the World Wide Web. It must be a John Deere Secret. LOL

SnakeDoctor said:

I replaced both of my coil packs about two years ago. I checked the spark out of the packs and one was bad. So, I spent a wad to replace them both. I would have done it myself, but I didn't have some of the tools to do the job. I bit the bullet. My question to all of your here is, "Where are the jet adjustments"? I can't find any information any where on the World Wide Web. It must be a John Deere Secret. LOL

Click to expand...

So you are asking us about jets on a carb ???? What engine do you have and what model is the engine ..... It gets a lil confusing sometimes when a question is asked on an old post from 4 years ago >>>>

Let us know Mon Ami ~!~!

Don't know why you tacked a carb question onto the end of a coil question but the answer is there is no jet adjustments on carbs due to EPA regulations.
Where a low idle adjustment is available, limiting caps have to be fitted.
Ultimately just like cars no carb will be able to meet the regulations & all petrol powered engines will be fuel injected.
Nothing wrong with EFI except it requires a substantially better charging system, cleaner voltage supply and add a significant extra cost that only commercial users will be able to recoup over the service life of the mower.
The big joke is a single jet engine at take off dumps around 200 gallons of unburned JET A1 into the atmosphere and the EPA thinks this is OK but 0.01oz from a mower is a national disaster.

reported