GS1000G missing

[Rockman]

My 1981 GS1000G starts easily, idles well on all four but misses badly on one cylinder when revved particularly when I'm riding it. Cylinder #3 or #4 I think but its a bit hard to tell on the move.

My initial thoughts were carbies, so I cleaned these out thoroughly (twice) but this made no difference. I've static balanced them. Everything looks pretty good inside.

So I've started looking at the ignition system. I pulled the spark plugs and grounded them. I get spark on all 4 at cranking speed. I did notice all the HT leads have cracks in the insulation so I wrapped extra insulation around these just in case they were arcing out but this made no difference. Plugs are black and a little sooty.

At this stage I'm looking at replacing the coils. I see cheap ones on eb..y in the UK. Anyone used these?

Any other suggestions as to the cause of this?

A bit of info. The bike had this problem when I got it. Its got new plugs, plug connectors. I've also replaced the air filter and the boots between the air box and the carbies. I haven't checked valve clearances yet, but if these were badly out then it would idle properly either. Its got electronic ignition of some sort. Charging system is good and has a 3 phase regulator.

Basically I'm trying to get it to run properly before I start on the cosmetics.

[eil]

Troubleshooting a problem like this isn't easy until you've caught up on _all_ the maintenance, and that includes a valve adjustment. So I'd definitely start there and maybe follow up with a compression test if the problem persists.

Only then would I start looking at the ignition system. It's rare to impossible for a bad coil to only show a problem on one cylinder, however. The standard test for checking coils is to swap them, electrically. Swap the connectors on the primary side going into the coils and then swap plug boots 1&2 and then 3&4. If the problem does not follow, then the coils are good.

The coils rarely go bad, so I wouldn't swap them out on a whim, but if you don't mind a bit of gambling, I guess it wouldn't hurt.

[lemonshindig]

Probably not coils. It's unlikely.

Start with the valve adjustment. Seriously.

And then properly sync your carbs. This is assuming that you cleaned them correctly. If you didn't soak them overnight, then they're still dirty. I guarantee it, even if they look cleaner than a redneck's best moonshine.

[Nessism]

Valve adjustment isn't something you only do when the bike misbehaves. Hopefully you haven't damaged the engine.

[tkent02]

I haven't checked valve clearances yet, but if these were badly out then it would idle properly either.

This is not true. I have seen them idle fine even with burnt valves. Burnt from not being adjusted.

[Rockman]

OK, I'll start with checking the valve clearances. Busy over the next couple of weekends so after that.

The HT leads are definitely cracked through the insulation. Assuming I can dig them out, what do I replace them with?

Incidentally, we cant get carb dip here, only the aerosol stuff. 2 squirts and its gone so it gets expensive to use. What is carb dip made up of?

[Nessism]

Have you look for the Yamaha dip concentrate?

[lemonshindig]

Incidentally, we cant get carb dip here, only the aerosol stuff. 2 squirts and its gone so it gets expensive to use. What is carb dip made up of?

Usually a combination of Acetone, Methyl-Ethyl-Keytone, and Toluene.

There is a lot of people who make their own carb dip by combining the above three ingredients with ATF in roughly 4 equal parts or some deviation.

I just used pure acetone for an overnight soak, and then sprayed out every passage with aerosol afterwards. Regardless of what you use to soak, spraying out every passage after a good overnight soak is a good practice. The soak will loosen the crap up but might not dissolve it completely. Just spraying out passages with aerosol stuff without soaking will leave caked-on gunk behind. Your carb's passages are more than likely restricted by a very thin coat of crap, even if they appear to be flowing. If you have a thin coat of gunk in the passages, it can reduce the diameter of the passage to 40 or 50 percent, which will make the carb function very very poorly. A carburetor is a very finicy, finely engineered device.

[Rockman]

Have you look for the Yamaha dip concentrate?

Nope, don't get that either. Bit of a nanny state here in oz, its probably on some banned list.

[Rockman]

Usually a combination of Acetone, Methyl-Ethyl-Keytone, and Toluene.

There is a lot of people who make their own carb dip by combining the above three ingredients with ATF in roughly 4 equal parts or some deviation.

I just used pure acetone for an overnight soak, and then sprayed out every passage with aerosol afterwards. Regardless of what you use to soak, spraying out every passage after a good overnight soak is a good practice. The soak will loosen the crap up but might not dissolve it completely. Just spraying out passages with aerosol stuff without soaking will leave caked-on gunk behind. Your carb's passages are more than likely restricted by a very thin coat of crap, even if they appear to be flowing. If you have a thin coat of gunk in the passages, it can reduce the diameter of the passage to 40 or 50 percent, which will make the carb function very very poorly. A carburetor is a very finicy, finely engineered device.

Acetone I can get, and probably the ketone and toluene as well so I'll try making up my own brew.

[Big T]

Nope, don't get that either. Bit of a nanny state here in oz, its probably on some banned list.

Hmmm, other OZ members report using the Yamaha stuff

[koolaid_kid]

Hmmm, other OZ members report using the Yamaha stuff

Yes, I thought I saw pete mention it. He said something about it came in a .997 liter bottle, he mixed it 1:1 with water, etc.