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General Category >> Rubber Side Down! >> Bad ignition coil?
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Message started by koehlerrk on 06/14/15 at 12:24:23

Title: Bad ignition coil?
Post by koehlerrk on 06/14/15 at 12:24:23

OK, my saga continues... seems my 87 Savage, now with 15,500 miles, is now stumbling right off idle, acts like it's running really rich, carbon fouls the plug quickly, yet it has a #47.5 pilot jet....

Once over 2,500 rpm she smooths out and runs right, but this all new, after I rejetted the carb.

So, neighbor suggested it might be timing or some other electrical gremlin, I started checking and found one item out of spec, the coil.

Clymer manual says the primary side should be between 1-7 ohms, and that between one of the primary terminals and the spark plug terminal I should have 15,000-25,000 ohms. Between the primaries I have 4.6 ohms, between each primary and the plug terminal I have 29,000.

When hooked up and with a new plug grounded to the head, I don't get nice big fat blue sparks, I gets piddly thin yellowish ones.

So, am I on the right track? I'll be calling the local Suzuki dealer tomorrow morning, and if they have a coil in stock I'll send my wife to pick it up. Unless someone here can tell me I'm completely wrong...

Title: Re: Bad ignition coil?
Post by justin_o_guy2 on 06/14/15 at 13:29:09

IF you need a coil AND the OEM coil is pricey, ask around about a car coil.
I dunno how big the coil is.

Title: Re: Bad ignition coil?
Post by koehlerrk on 06/14/15 at 14:47:57

Well Justin, the coil is small.... it fits between the side of the top fame rail and the inside of the tunnel on the gas tank. Car coil might work, but getting it to fit may be problematic.

I can order a new coil online for $12 plus shipping, going to see how badly the local shop gouges for having one on hand. If they come in around $20 then I'll buy it there and have the wife pick it up. Otherwise I'll order it and have it in a few days.

Title: Re: Bad ignition coil?
Post by justin_o_guy2 on 06/14/15 at 14:52:37

That's not painful money. Tear it up.

Title: Re: Bad ignition coil?
Post by Gary_in_NJ on 06/14/15 at 16:38:37

Usually a coil works, or it doesn't. Yours works. Hows the ignition cable look?

Hows your compression. Have you done a leak-down test?

More then likely the poor running is related to your intended or unintended mods. Go back and recheck your work.

Title: Re: Bad ignition coil?
Post by koehlerrk on 06/14/15 at 17:03:24

It works, but not well. Like I said, thin yellowish sparks, not big fat blue ones. Also, my Clymer manual says that if the resistance doesn't fall inside the specified range that you're supposed to replace the coil. The cable to the spark plug looks great, no cracks or signs of arcing.

Have not done a compression test yet, but that doesn't seem to be the problem, the bike fires right up and runs well until a couple days ago. Now it seems to be stumbling when coming off idle, mostly when the engine is warm from running.

Mods... the only one I did was to bolt on a 6" Uni-Pod filter. She already had a Raptor and a Dyna muffler. When I added the filter, I rejetted the carb and all was well. And then it wasn't.

Title: Re: Bad ignition coil?
Post by koehlerrk on 06/20/15 at 03:20:31

I am happy to report that I installed the new ignition coil last night and all my sputter/surge/buck/snort problems went bye-bye!

Would have been a 15 minute fix if I hadn't fugged up the two screws that hold the coil in. Fortunately, the local hardware store was still open and I was able to purchase two new 5x16mm stainless screws to put it back in.

The old gal sounds better, idles much better, and the power delivery is a nice smooth curve now, not jumps and jerks.

I figure I'll go buy another coil and have it sit on the garage shelf... then this one will never go bad.

So, if any of you are having issues idling or coming off idle, check your coil because you may have an electrical problem, not a carb problem.

Now back to playing with jets and washers.

Title: Re: Bad ignition coil?
Post by justin_o_guy2 on 06/20/15 at 10:08:23

Good job of troubleshooting. Odd problem, as noted above, usually, they just fail , or work great till they get warm. The kind of spark clearly matters.
Seems to me lighting the fuel/air mixture off otta be good enough. But, it isn't.

Title: Re: Bad ignition coil?
Post by koehlerrk on 06/22/15 at 03:21:54

Thanks Justin, but I can't take all the credit. A buddy of mine is a retired mechanic, and he grew up tuning cars and bikes with carbs. When I told him about my low-end issues, he suggested I check the ignition system.

Now the old gal is back to a 52.5 pilot, 152.5 main, two washers, and 1.25 turns on the screw. Around town she runs great, time to see how she does on the highway run to work today.