GL1200 left side spark plugs

No.
Have you done a carb sync?
If not, sync the carbs and recheck.

Don't know how to sync carbs

Do the left side exhaust pipes get hot real quick when you start the engine? If so you do have some combustion going on in there. If not, then the left cylinders are not firing, even if the plugs are. Could be you are not getting the proper air/fuel mixture into the cylinders (carbs) or you have little or no compression on the left cylinders. Even if the left cylinders are not firing, you would still get something at the exhaust, there is a crossover between right and left, plus if there is any compression it would be pumping air out through the exhaust.

You will need a manual and a carb sync tool to synch the carbs. There may be a "how to" on the forum somewhere.

gold bobber said:

Don't know how to sync carbs

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If you expect to do any diagnosing, or maintain your own bike, at some point you're going to have to make an investment in tools.
The first and best tool is a shop manual.
Second would probably be a DVOM.
As far as I'm concerned, a carb sync tool is a must. (3) You don't have to spend $600.00 on one. A nice one can be had for @70.00. Or, do a search for making your own manometer.
Either that, or find someone close that already has the tools and doesn't mind sharing.

You can make your own synch tool for less than $10, just google (home made carb synch tool). Not fancy but effective and more accurate than gauges.

Noticed glhonda is pretty quick to recommend sharing when he's about as far across the US away as you can get...

dizzy said:

Noticed glhonda is pretty quick to recommend sharing when he's about as far across the US away as you can get...

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Anytime you need help Dizzy, come on out. I'm home most of the day.....:ROFL:

Thanks glhonda...I need all the help I can get.

I have a good old fashioned Motion Pro mercury sync tool that I bought back in '01 or '02, before they outlawed mercury. I'm being very careful with it, I've heard the new ones do not work as well as the mercury type.

I checked the pipes to see if the left side was getting hot like you said, and its not. started it up the right down pipe got hot fast, the left stayed cold. I got a can of seafoam and did like someone else suggested, I took the fuel line off at the pitcock and extended it, put it in the can and let the fuel pump load the carbs till it started to smoke, then shut off, I'm gonna wait a couple days and try it again, if that doesn't fix it, I'll take a compression test, if thats good I guess I'll have to rebuild the carbs. HOPE compression is good.

It's odd that it is only the left side, and both cylinders on the left side. If the compression turns out to be good, and you are sure about the spark, then the carbs are all that are left. Hopefully that is what it is.

I am not familiar with carbed Goldwings. But I believe I read somewhere that the carbs on each side get fuel from a separate place? That the fuel supply to the right and left carbs is separate? Not sure if that is the case or not. If so, it might just be a plugged fuel supply to the carbs, instead of the carbs themselves. On the FI model, the throttle bodies have their own fuel rail for each side.

I'll check on that thanks.

If the linkage between left and right is out of adjustment the throttle valves on the left maybe totally closed.

As said before synchronizing should be your first step.