About 5 or 6 years ago I got a free 81 gs550t and a box o parts. I never really had the patience to get it going. Recently I found that some of my problems were caused because I was using the wrong set of carbs:
After getting the appropriate parts, and some fresh O rings, weatherstripping on the airbox, as well as adjusting my valves I was ready to rock! And it fired right up. Awesome!
I spent sunday trying to get it to idle properly, it would stay high after I reved the engine. It seems to really like 2000 rpms. I suspected a lean condition caused by the airbox, the boots are fresh but the box itself is a bit warped in the middle so #2 and #3 don't slide on all the way. I was able to push the center of the airbox out a bit by taking off the air filter and pushing on the inside with a wooden dowel. Sloppy but it worked enough to tighten down the clamps. After a day of slowly backing out the mixture screws to no avail I realized the exhaust pipes from 2 and 4 were cold. When I checked the plugs 1 and 3 were black, 2 and 4 were wet.
Today I got a new battery (had been jumping it from a golfcart), and cleaned the connections to the coil for 1 and 4. (1 being the clutch side 4 being the throttle side just so I'm clear) I snipped the wires back and put on some fresh caps with a little dialectric. Idle was a little quicker to go up and come down, but not great. 4 was getting hot and the plug was a brown color. So I repeated the process for the 2/3 coil. No dice. My box o parts included 2 coils so I swapped one in. Still nothing. Tried swapping the plug with one from a cylinder that worked just for laughs at the end of the day but that didn't work either.
So here I am coming up with a plan of attack for tomorrow night.
-I checked the plugs for spark previously and they all work but I figure replace em anyways because they are cheap.
-I read that a fouled #2 can be caused by a bad petcock. I cleaned mine recently, it gives me gas when I want it, and stops when I don't, but that's another thing I'll give a closer look tomorrow.
-I cleaned all my grounds months ago, probably worth a double check.
-Timing? I know nothing about it, should do something about that.
-I had been focusing on fixing a lean mixture, maybe its been rich all along.
Some more maybe relevant stuff:
-I suspected that #4 isn't firing 100% of the time; when I put my hand behind the exhaust on that side I can feel it stutter occasionally where as the pipe for 1 and 2 is steady.
-Haven't checked the voltage to the coils yet, I assumed that low voltage would cause both cylinders on the coil to not fire rather than just one... another thing on the to do.
-I did not vaccum sync the carbs, just visually as best I could.
-I don't have a gauge for a proper compression check but it gave a decent push when I put my thumb over the spark plug hole.
-I've seen the megawelcome/bikecliff website but was focused on carb stuff. I should probably read up on electrical now.
-Bike isn't very roadworthy at the moment, no rear brake and the clutch doesn't work. (think its just stuck from sitting so long) so I'm not sure if this stuff changes under a load.
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