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2 cyl's quit after about 10 minutes of riding

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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I have a 79 gs750 that I bought 2 summers ago. Cheap. I got it home and found that I had a bad coil on it... I've replaced the coils with new dyna coils. I replaced the ign with a new dyna II ign, and I replaced the wires on it. Well it will run like a CHAMP for the 1st 5-10 minutes, but when I get on a hgwy and get r goin at high rpm she wont last long. So I took it to a friend of my pops who owns a bike shop and works on older bikes. I thought it was a carb problem, so thats why I took it to him. Last time we talked (last summer) he said he would ride it and it would run fine but soon as it got hot enough cyl 3 and 4 wouldnt fire so he went through the carbs and the problem still exists, he still has the bike. I called him up earlier this week, and now he thinks its the ignition... I know its 1-4 and 2-3, but he said to try to find the old points system and bring it out (which is over an hour away) to try to eliminate the ign problem, and I cant find the old points plate or points and condensers, I think I tossed them. I'm just wondering if anybody has run across this problem with their dyna elec ignition... I'll be damned if I go through another summer without riding it. I've only put maybe 30 miles on this thing since I got it like 2 yrs ago!! Anybody have any ideas!!??
 
750

750

You dont have to do all that, all you have to do is run it till it quits and then check it for spark,(with a spare plug)and if it does then, when it quits next time pop open the gas cap and see if vacuum escapes when you open it up, if so you have a plugged tank vent
 
Doesn't sound like coil or ignition modules to me, because your problems are on 3 and 4, which are seperate coils/modules.
Are the plugs black at 3 and 4?
Any leaking out of the 3 and 4 float bowl overflow lines underneath?
Possible simplist fixes:if the pilot screw (underneath and engine side of the bowl) has been turned out too much, you'll foul the plug. Turn the pilot screw out on 3 and 4 one full turn from LIGHTLY seated for starters. Use a good fitting tool if they're stiff.
Then adjust the side air screws out to 1 1/2 turns from lightly seated.
Then SYNCH the carbs with a vacuum tool. Your VM carbs are very sensitive to vacuum imbalances between cylinders. If you don't have a vacuum tool, then at least try the screw adjustments. Keep a record of where your screws are now so you can return them if you don't like the results. Motion Pro makes a very simple and cheap vacuum tool for about $30/35. Your problem could definitely be a poor synch.
If that doesn't stop the problem, then the carbs should be cleaned, o-rings inspected/replaced, and the float heigths adjusted and the float needle valves inspected/replaced. If you remove the carbs, I recommend replacing the manifold o-rings too.
There's always the possibility that someone changed the jetting too, but didn't do all the carbs the same way for whatever reason. As a bike warms up, it runs richer. If your having richness problems, it will effect the bike more as it warms up and could be causing your problem.
 
#34

#34

Your right Keith I had to go back and reread it, I wonder if he put the old plug caps back after changeing the coils
 
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