Misfire when hot

[Guest]

Hi guys, im new here but read some useful info in the last few weeks which helped me fixed a few issues with my 81 gs 750

But now i got a new problem. This bike is new to me so im not sure what kind of issues it had before. It starts great and runs great until it warms up...about 5 minutes into the ride it starts to misfire and lose power. At first i thought it was an ignition coil/coils but i wanted to ask for your opinions before i waste a few hundred bucks and still have the same problem.

[Grimly]

Coils breaking down when hot are not unknown, so it might be. In a way, it's good that it's doing it every time, as you can quickly remove the tank and check the coil DC resistance when it starts doing it. Of course, such faults have a way of vanishing when they cool down a bit, so you'd have to be quick.
Same applies to the pickup coils, but at least you can check the more accessible end of the harness that goes to them.
The most obvious, and simplest things to check are the plugs, plug caps, and leads - cheaper to replace too, and should be done as a service item in any case.

[Gru]

I checked the resistance when cold and one coil was about 30 and the other 50-60..i dont know what that means but im guessing its not good. Also the spark plugs 1 and 4 are black and the 2 and 3 are brown

[hillsy]

The spark plugs dis-coloring on both 1 and 4 indicates it's most likely spark related.

[tom203]

I checked the resistance when cold and one coil was about 30 and the other 50-60..i dont know what that means but im guessing its not good. Also the spark plugs 1 and 4 are black and the 2 and 3 are brown

You might be having meter reading problems- those are odd ohm readings.. Go here amd read step 10

http://members.dslextreme.com/users/storagecliff/images/electrical_odd-n-ends.html#A17

as mentioned, plug color says there's a problem with 1 and 4

[Gru]

Well i got the new coils installed and still having the issue..once again it misfires only when hot...now im thinking this could be a carb problem