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Discussion Starter #1
I have a 1977 GL1000 with low miles, clean carburetors, and new timing belts that was correctly tuned and running great.

Recently it began running very poorly once it would get up to regular operating temperature. The bike gives off the feel that it's running on two cylinders once the poor performance begins. Let it sit for a while and it cools off and goes back to running correctly.

I've checked the surface temperatures of the intake manifolds once it begins behaving badly: Equal on cylinders #1,#3,#4 and notably lower #2.

My feeling is that this is an electrical issue related to the coils, but I'm not certain.

If anyone has suggestions or is familiar with this problem, any input would be helpful.

thanks
 

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Points or electronic ignition?

Both cylinders will not always drop out completely if a lower than optimum charge of the affected coil doesn't happen with points. Resistance plays a role there. One secondary could have more than the other. One cylinder could fire weak and the other not at all, leading to something like you're talking about.

With electronic, both would normally drop out if a module goes bad.

A '77? Plug boots have resistors in them. I've seen them deteriorate to pieces. How are your boots?

A coil could have a problem.. Maybe a crack in its casing. Heat will bring that problem out. If a crack is located closer to one of the secondary wires than the other, then this too could explain why only a single cylinder is dropping out.

Could be a primary wire resistance issue affecting a coil combined with a secondary resistance problem mentioned above. Sometimes a weak spot is noticed further down the line.

Ignition - start at the point housing working towards the coils and then to the plugs.

A fuel problem masked as ignition is sometimes a reality.
 

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simple test:
swap points leads (near battery) and plug caps back-to-front... if problem follows the plug cap it is in the coil

otherwise, pull the synchro port screw of the plenum runner and one at a time see that engine stumbles the same for each cylinder. If only one cylinder is not affecting idle speed problem is likely in that carb(you can also shoot some ether/carb cleaner/solvent into the synchro port and see if idle picks up...definite sign carb is not carb'ing)
 

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Discussion Starter #6
Thank you for the suggestions.

My 1977 is points ignition. The plug boots had an off spec resistance and were replaced.

Update: I installed a brand new OEM replica coil moments ago, replacing the one serving the back cylinders, assuming it to be the offending component. The old one did not seem to be cracked or damaged. I've checked each side for spark which it has.

I now seem to have my coils wired in incorrectly. My engine now will not turnover and gives the occasional back fire.

My coil to cylinder setup is as follows:

Right Coil (old):
Right lead to right-front cylinder #3.
Left lead to front left cylinder #4.

Left Coil (new):
Right lead to back-right cylinder #1.
Left lead to back-left cylinder #2.

I have the resistor attached to the right side with the black wire wired to the side of the resistor with black rubber on it. And the wire with the small brown sleeve attached to the side of the resistor with no rubber.

I seem to have taken a step backwards, are my coils wired wrong? I do have spark. :?

Thanks again. I have a lot of new ideas, but need to get back to my baseline now....
 

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Do you have a manual?
Can get one here.
 

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It aint rocket science
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Update: I installed a brand new OEM replica coil moments ago, replacing the one serving the back cylinders, assuming it to be the offending component. The old one did not seem to be cracked or damaged. I've checked each side for spark which it has.

I now seem to have my coils wired in incorrectly. My engine now will not turnover and gives the occasional back fire. I seem to have taken a step backwards, are my coils wired wrong? I do have spark. :?
Stop replacing parts on assumptions.:gunhead:

Put it back the way it was.

Do the tests above and within 15 minutes KNOW which cylinder(s) are the trouble ones.

Parts REPLACERS very rarely get a successful repair, DIAGNOSIS is key.
 
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