My gremlins are back!

This is one of those problems that every thing needs checking. I would start on the electrical since you are zeroed in there.

Next I would check for water in the carbs. My expierence with water in the carbs," bikes runs good until you open the throttle up" Since water is heaver than gas it will rest on the bottom of the bowls until the flow is increased by opening the throttle more. Then the water is picked up in the pilot jet or blockes the pilot jet until you let off the throttle. Then the water returns to the bottom of the bowls.

The timing advance is a easy check.

My bike was doing basically the same thing last week,except after warming up the bike ran good. Every time I stopped for amy amount of time it would run on two cylinders. My dyna unit was bad on 1+4 cylinder.

Keep us updated.

Roy, you might be onto something!
I did have my seat up last night and some water go into the air intake box (just a little bit), but I figured it would drain out the drain in the bottom of the box.

I did just take it for a spin, no change. I checked my advancer, it was not lubed really well. I didn't have grease so I used silicon spray (figured good enough for now) and took her out... and BIG DIFFERENCE. I can go up to 3/4 throttle, but still acting up at WOT or under super heavy acceleration. It's a start though!

As for water in the carbs... I can just crack the drains and drain each bowl, right?
What kind of grease do you recommend for the advance?

I use whatever I have handy after cleaning off the old stuff. But use the tiniest amount you can to coat the rubbing parts and nothing else. Most of the excess will get flung off and make a mess.

When a coil gets weaker against high voltage breakdown, you will notice it soonest at the higher RPMs, so like Bountyhunter said, that coil is suspect.

I think there is a small chance you can swap a coil over from the 550, if the wires are long enough. (If I recall, your 550 is electronic ignition as well, correct?)


And of course, easy stuff first, drain the bowls if you think water got in. I'm not familiar with the 750 bowl drains. And dry out the airbox.

update... carbs drained, airbox dry... the same. Actually it's not as bad as it was last night, but not as good as it was after cleaning the advance. I think this coil is being the culprit.

Lou-my 550 is electronic yes. And they both have the same screw on compression fitting type fittings to attach the wires, so I could swap wires. I just don't want to smoke my 550 coils or my 750 ignition system.

As for the advance, think silicone will be ok, or should I get some regular ol' grease?

Also, just checked my compression...hot, WOT 135 for 1,3,4 and 128ish for 2. On the low end, but what it was when I was running around fine last year.

Also, I checked the primary windings on the suspect coil, and it measured 2.6 ohms. If it was screwed up, wouldn't it be higher? I didn't get a chance to check the secondary.

apbling wrote: Also, just checked my compression...hot, WOT 135 for 1,3,4 and 128ish for 2. On the low end, but what it was when I was running around fine last year.

Also, I checked the primary windings on the suspect coil, and it measured 2.6 ohms. If it was screwed up, wouldn't it be higher? .

Doubt it. Most of the time the misfiring is from high voltage arc down from the secondary (plug) side to the primary. An Ohm test can not accurately test a coil.

If you have a service manual it will show you how to test your coils and what values you should get if they test ok. Sure sound like a coil to me, i'd start saving for a new set.

Next weekend I can get my hands on my 550's, which I know are good. Then if that solves the problem I'll buy a set.

You guys prefer dyna or accel? I was looking and emgo makes some too, but they aren't THAT much cheaper, and sometimes you get what you pay for...

I think I have a set of good 650 coils if you want them to test. 10 bucks+shipping. Roy

If you have silicone grease easily accessible, I'd use it.

I use Accel 3-ohm coils, but the gray Dyna 2.2 ohm coils should be a better match for the ignition.

I think the Emgo's only come in 4-ohm. That would only be for use with points. Points coils may have problems at higher RPMs because the electronic ignition has less dwell than the points ignitions (which is why the electronic ignitions use faster coils).

I got a hair brained plan here... A local guy has some coils from older Honda/Suzuki bikes that he said he'll let me borrow to see if my coil is in fact my problem. As long as these other coils are off a bike with electronic ignition and measure 2.2 or greate ohms, I should be ok, right? Or am I missing something important?

I'd say borow them & see if any change.