2002 Vmax 600ERG Coil Swap??

M

mcuhan

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Joined
Dec 28, 2009
Messages
21
Age
44
Location
Minnesota
Having fits with a misfiring mag cylinder on 2002 Vmax 600ERG. Carbs are clean, compression is good, however seems like there's intermittent spark only on mag. There's spark when plug is out of the cylinder however apparently that doesn't always mean there's spark when it's under compression.

On the Yamaha parts fiche, clutch and center coil part #s are different (8DF-82310-10-00) than the mag side coil (8DM-82310-30-00). I was hoping I could just swap one to test this issue.

Rode 110 miles and then all of a sudden the last 30 limped in on two. I've tried several rounds of brand new BR9ES plugs. The misfiring plug is hot and always brand new clean looking (not oily dirty).

I'm thinking bad coil or CDI. Any tests for either?


Thanks
Matt
 
A couple of bucks said:
New plug caps??
Click to expand...

Thanks for the reminder - that's next on the to do list too. They are original. My only other thought would be a month or so ago my headlight harness shorted out on the pipe. The fuses blew properly but I wonder if that didn't damage something a little that's causing this too.
 
Changed spark plug caps and plugs, no luck. Must have a cylinder issue. Time to get dirty. Snowing like crazy here. Looks like I'm riding the 86 excel 3 this weekend!!!:sled1:
 
Besides the coil, caps, and verify the compression again as noted above, also take a look inside that cylinder and see what top of piston looks like, and is there any damage around the edges especially on exhaust side. If you have or can borrow an inspection camera, it will help greatly.
Other ideas:
Recheck, reclean carbs, it's not unheard of for them to plug up even if they were cleaned at the start of your season, or even just before your ride.
Check for air leaks at the rubber carb mounts and airbox boots, spray WD40 or carb/brake cleaner around the base gasket area of that cylinder while it's running and see if the engine changes pitch/rpm, indicating an air leak.
 
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A couple of bucks said:
Need to do compression test. Have you tried to move coils and see if problems follow the coil?
Click to expand...

See my original question. Are all the coils the same? The bad cylinder has a different part number than the center and clutch cylinders. Maybe the part number is different because the spark plug wire is longer.

I recleaned the carbs. No difference. Piston looks fine. Not leaking around boots. Tried all tests mentioned above. Only thing not yet done is take jug off which is what I'll do next. When I cleaned the carbs, that idle jet was plugged.
 
Last edited:
image.jpgGood news. The coils are all fine. The bad news...piston missing a chunk! Machine was ripping deep powder all day. Still surprised this happened. Time to jump threads and see what the masses say about a mashed up piston in the crank bearings. Compression was still good. The cylinder might be salvageable.
 
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