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Hi, I'm a new GS Resources member. I've enjoyed and benefited from reading through a bunch of forum stuff as I resurrected a '77 GS 400 over the last couple of months. So, now I could use some help. Here's the back story.
GS 400 sat for ~ 15 years and ended up in my basement a few years ago. This year I decided to get it on the road. I tore the bike down and got rid of the WindJammer. I cleaned the carbs and put in new seals. I went over all the wiring and replaced suspect connectors. I managed to get the front brake working (master cylinder was frozen), I replaced the brake lines, banjo connectors, pads, piston seals. I replaced the fork seals and fluid. I replaced the fuel line to the carbs and the vacuum line. I cleaned up and painted the frame, tank and tail. I took the valve cover off to check the valve clearance, but I didn't have the right feeler and didn't get one yet. I put everything back together and put in a new battery and plugs. I adjusted the points and statically adjusted the timing. I set the air screws to 1.25 turns open. The bike started right up. I adjusted the idle to 1,200rpm.
The problem is I have a miss at high rpm. Here's the deal. I hooked up the timing light. Set the left timing at 1,200rpm. Checked the left timing at >3,600rpm. I switched the timing light to the right cylinder and set the timing at 1,200rpm. Then I went to set the timing at >3,600rpm and found what I had been hearing, the tach on the timing light was steady at low rpm, then jumped around at high rpm and I could see the same thing, of course, with the timing light (the left doesn't behave like this, nice steady tach reading). But, I could finish checking and adjusting the timing on the right.
So, what I know is that there is occasionally no current in the plug wire at high rpm when there should be current. I checked the wiring to the coil, and checked the voltage at the coil, which was 11 V (same for the left coil). I checked the coil resistance, which was 2 Ohms on each coil. I tried to clean off and check the condensers as described in the Clymer manual, but, without much luck, so I don't know that they are good. I filed the points and readjusted the points and timing which made no difference. Since I had to file the heck out of the points and was having this problem I decided to spring for a NOS set of points and NGK plugs for $20. I put in the new points, adjusted, no improvement. I pulled the plug and checked the spark as I opened the points. The spark looked good to me, but, I already new I'd see something since there is no low rpm miss. I removed the plug wire caps, clipped off 1/8" of wire and screwed the caps back on, no improvement. So, all I can think of is a bad condenser or bad plug wire. Am I wrong in only thinking about the right ignition system? Should I also be thinking about the right carb?
I'll really appreciate any help. I'm having fun riding the beautiful back roads of VA, but, it would be a lot more fun without the miss. By the way the compression in the left cylinder is 115psi in the right 110psi. I'll post a photo soon in case anyone wants to check out the mighty twin.
Mike
P.S. I should mention that the air box lid was missing, so, I fabricated one out of an aluminum for sale sign and some weather stripping.
GS 400 sat for ~ 15 years and ended up in my basement a few years ago. This year I decided to get it on the road. I tore the bike down and got rid of the WindJammer. I cleaned the carbs and put in new seals. I went over all the wiring and replaced suspect connectors. I managed to get the front brake working (master cylinder was frozen), I replaced the brake lines, banjo connectors, pads, piston seals. I replaced the fork seals and fluid. I replaced the fuel line to the carbs and the vacuum line. I cleaned up and painted the frame, tank and tail. I took the valve cover off to check the valve clearance, but I didn't have the right feeler and didn't get one yet. I put everything back together and put in a new battery and plugs. I adjusted the points and statically adjusted the timing. I set the air screws to 1.25 turns open. The bike started right up. I adjusted the idle to 1,200rpm.
The problem is I have a miss at high rpm. Here's the deal. I hooked up the timing light. Set the left timing at 1,200rpm. Checked the left timing at >3,600rpm. I switched the timing light to the right cylinder and set the timing at 1,200rpm. Then I went to set the timing at >3,600rpm and found what I had been hearing, the tach on the timing light was steady at low rpm, then jumped around at high rpm and I could see the same thing, of course, with the timing light (the left doesn't behave like this, nice steady tach reading). But, I could finish checking and adjusting the timing on the right.
So, what I know is that there is occasionally no current in the plug wire at high rpm when there should be current. I checked the wiring to the coil, and checked the voltage at the coil, which was 11 V (same for the left coil). I checked the coil resistance, which was 2 Ohms on each coil. I tried to clean off and check the condensers as described in the Clymer manual, but, without much luck, so I don't know that they are good. I filed the points and readjusted the points and timing which made no difference. Since I had to file the heck out of the points and was having this problem I decided to spring for a NOS set of points and NGK plugs for $20. I put in the new points, adjusted, no improvement. I pulled the plug and checked the spark as I opened the points. The spark looked good to me, but, I already new I'd see something since there is no low rpm miss. I removed the plug wire caps, clipped off 1/8" of wire and screwed the caps back on, no improvement. So, all I can think of is a bad condenser or bad plug wire. Am I wrong in only thinking about the right ignition system? Should I also be thinking about the right carb?
I'll really appreciate any help. I'm having fun riding the beautiful back roads of VA, but, it would be a lot more fun without the miss. By the way the compression in the left cylinder is 115psi in the right 110psi. I'll post a photo soon in case anyone wants to check out the mighty twin.
Mike
P.S. I should mention that the air box lid was missing, so, I fabricated one out of an aluminum for sale sign and some weather stripping.
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