'81 GS750E, Low power, 3 cyliders rich, 1 not happy

[Anonymous]

Hello all!

I've got my some issues with my '81 750E. Last season it ran great! The carbs had just been re-built and dialed-in by a shop for the previous owner. Now, it runs on basically 3 cylinders (2,3 & 4), which run a bit rich. The plugs are a bit sooty. When I changed the plugs just prior to pulling it out for the first time this year, they weren't nearly as black.

Anyway, #1 plug looks almost unused and it runs like crap. Seams to get worse as it gets hot. I changed the plug, swapped #1 & #4 spark plug wires, cleaned the carb (as best I can on the bike) and have sprayed around the intake boot to no avail. I have yet to do a compression check (am borrowing a gauge). I notice that the carb only has one adjustment for air. You can' change any other setting accept sync. The coil resistance is 4.2 ohms on both coils. Not sure what they're supposed to be 3 or 5 ohm. Spark is mediocre, at least not as bright as I've seen on other bikes or autos for sure. I've cleaned all of the connections involved in the loop for ignition. It ran worse prior to that, so at least a good cleaning helped!

Thanks in advance!

Lorne

[shaftzuki]

Before you do anything else, make sure you have a full charge on a good battery - you'd be suprised how an undercharged battery will foul up the works - so to speak ... 8)

[Anonymous]

Hey Mark,

Got lots of juice! Battery's in good shape at better than 13 volts. The charging systems on these leave a bit to be desired, but it's still holding its own.

Lorne

[Anonymous]

OK, I still have yet to get the compression gauge, however, I did the old finger over the spark plug hole and there is at least some compression. #1 feels the same as #4 (like that's much for an acurate test! lol). I'll be getting the gauge tomorrow. Anyway, I did spend some quality time with the electrical system. Seems like it may be a little better and doesn't noticably miss at idle anymore. The battery voltage is around 13.2 VDC. The actual voltage on the positive lead of the coil was down to 11.0 volts (I was surprised at the drop). After tinkering and cleaning, I now have it up to 12.4 volts. When I look at the other lead of the coil, I get 7.4 VDC on a DMM with the bike running. A scope would probably be a better measuring device, but the DMMs handy. Anyone know what the normal voltage is at that point?

Next, one thing I know I screwed up is the sync on that cylinder. What's the vaccuum gauge called to make the take the measurements and where would I rent such a beast? I'm in hopes that once I get her synced up again, the slightly improved spark will make the difference. Thoughts?

Thanks!
Lorne