Coil problem?

[jdanoldno7]

77 GS 750- Starts and runs fine for 1 minute, then smokes, dies, and won't start for 30 minutes. Will repeate every hour or so. It has fuel, but I think the spark is just stopping on it?

Thanks for any ideas.

[BigD_83]

77 GS 750- Starts and runs fine for 1 minute, then smokes, dies, and won't start for 30 minutes. Will repeate every hour or so. It has fuel, but I think the spark is just stopping on it?

Thanks for any ideas.

I went back through your older posts to see your history with the bike, and there wasn't a much information.

There's a whole lot that could be going on here other than just a weak/non-existent spark.

I'm sure you've seen the Newbie mistakes thread, which is actually a list of the basic maintenance that should be done when you acquire one of these older bikes. How much of that have you gone through?

Have you pulled the spark plugs and checked for the strength of spark while they are grounded against the head?

The next thing you are going to want to do is get a multimeter and start testing. Check the voltage drop from the battery to the coils. Then check the primary resistance of each coil, and also the spark plug lead to spark plug lead (secondary resistance) for each coil.

Have you cleaned the carbs and checked their function (e.g. slides move up and down without hanging up, carbs don't flood out) yet?

Um...what colour is the smoke you are seeing?

[jdanoldno7]

There really isn't any history with this bike. I got it and did a tune up, drained the gas out of the carbs/ tank, and put on a new rear caliper/ master cylinder. Other than that it's been great till now. It's not a spark issue, the way it was just blowing smoke made me think it was ( it was late, I was tired) It seems that it is just getting way too much fuel and flooding it after it's running. I took the cap off of the air cleaner and it had gas all over in there too. I think it's time to go through the carbs fully on this.

[BigD_83]

Yes. This sounds like the perfect time to dig into the carbs. It could be that you just got some new crud in the needle seats.

How is your gas tank situation? Rusty at all? Old tank liner breaking up?

Old fuel lines chucking rubber?

If you have any doubts, throw a good inline filter on while you are trouble shooting. I've left mine on as insurance because it hasn't affect the running of the bike.

[jdanoldno7]

When I drained the bowls, I expected to fine something, but it was clear. My buddy said that he went through the carbs back in 2009. The tank looks good, but I guess that I'll find out more when I tear into this.

Anything special to watch for? I've gone through many, many carbs in my life. Just not on a bike, my others are fuel injected. This doesn't look any worse other than there are 4 to do.

[BigD_83]

I'm not familiar enough with the VM carbs to give you any specific guidance, but I gather they are a little simpler in setup to CVs.

With these bikes, the common pitfalls are stripped out adjustment needles, or tips of needles broken off due to overtorque.

The other real common issue with these are the o-rings between the intake manifold boot and head. I'm not sure if the 77 750 had them. MisterCinders has extensively documented his carb difficulties, and his Two-faced symptoms thread is worth a read through. He had some particular issues with the bowl gaskets contacting the floats, causing them to hang up and flood. Something I had read about on one of the KZ forums.

The fuel tee o-rings (size and availability) are another problem for the older GSes.

Worn float needles and seats are a less common, but noteworthy issue, and certainly one that would have a real impact on flooding.

Sticking chokes and slides are also not unheard of around here.