My gremlins are back!

So I was just washing up my 80 750-4 for the first ride to work tomorrow of the year. After I washed it and waxed/polished, I figured I give her one last ride, ya know, just in case. Well, thank god I did. She fired right up. Let it warm up. The first half my ride was fine. Little bit of a stutter at about 1/8 throttle, but it was still cold yet and was getting better. I stop at a stopsign to let some cars go by. I pull out to go and if I got past 1/8, she can't hardly even pull herself let alone me. It's coughing and missing. But, at just cracked throttle, just fine. (maybe 30 mph in second gear). Full tank of gas and filter is clean etc. When I really get on it, I swear I can hear her winding up, but theres no power there, and you can tell when it fires because you get a jolt. It's almost like 2 cylinders are pulling hard, but the other two are missing 85% of the time. I get back to the garage (it actually died at one stop sign, but with a little throttle she started) and the SOB is idling fine. I blip the throttle and it revs, comes down and dies. I start it again and blip the throttle, no problem. I take it back out, and same thing, you can hear two (or so) of the cylinders winding up, but the others only give a kick once in a while.

So, what can cause this? I'm gonna rule out fuel. If it was clogged carbs, the pilots would clogg first, and when I was missing I pull the choke and got crappier results. Also, if the filter was clogged, it would have died from fuel starvation in my garage while idling.

Seems weird it would be the timing advance... just to take a shit like that... but maybe. Here's where I gotta be honest with you fellas. I do have a coil that is cracked, but it's a hairline crack and I have it sealed up with rtv. At idle I pulled a boot and it almost died, so it is firing at idle, but would it make sense it wouldn't at more open throttle? Maybe I got some water in there washing it and when it heated up it started shitting out? Any ideas???

ive seen bad plug wires cause oppisite problem at low speeds then run better at higher speeds when it had more fire.
can you tell what cylinder is doing it?

Nope, I can't. I was gonna pull the plugs...but its damn hot and I more than likely won't be doing my best work because I'm a little frustrated right now.

The plug wires are actually new... I wonder if I pulled one of the cylinders I'm suspecting and then tried to take it for a spin, if I get no change, then maybe I'm on to something?

Water in a crack in a coil?

That's what I'm thinking. I was thinking it was since it warmed up (isn't that when coils usually fail, after warming up?). But maybe it just worked its way in there.

If thats the case, wouldn't it more than likely run ok tomorrow after it has dried overnight?

Hows the humidity where you live? Might want to take them off and put in the oven at say 150 for a couple hours. If you see a crack silicone it for now, and plan on some new coils.

i know this has been said and asked...is the battery new and full and charged.....

Eh, not the worst. I live in central WI. So, it'll get humid, but its not yet. But, I did just wash it, so I'm sure it's higher humidity than if I didn't. As for coils, I'll steal them off my 550 next weekend and see if that fixes it. I'm too cheap to take the dive on some new ones before I know for a fact thats the problem. Plus I'll need to cash my change jar in and save my lunch money so the wife doesn't notice.... :woohoo:

You guys agree it sounds electrical? The first thing I did was think "Oh shit, I didn't lock that jam nut down on my APE cam chain tensioner" haha.

Battery is in tip top shape. Not a year old yet, came out this winter, trickle charge once a month in the house...the whole 9 yards.

Do you have a kickstand switch? Sometimes that acts up and behaves like a bad ignition.

EDIT: I checked a couple 750-4 schematics and didn't see a kickstand switch.

Because of the washing, I'd lean toward an electrical problem as well.

Anytime there is a misfire that comes on after warm up, I look first at the coil. It's a classic symptom of an age related failure of winding insulation. I learned the hard way that old coils are more trouble than they are worth. Getting a "good used coil" from another old bike just delays the problem.... guess how I learned that. Coils don't age well.

apbling wrote: I do have a coil that is cracked, but it's a hairline crack and I have it sealed up with rtv.

That's suspect. Coils are potted to keep air out. If air can get into the windings, it rapidly causes the insulation to fail. Water obviously would also be a serious problem in there as well.

Figured that much... I'm gonna go try it again this morning and see how it acts. I actually hope it's the coils, because at least I know whats wrong! standby for updates.