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86 GL1200 problems at high speed

1K views 17 replies 9 participants last post by  Midnight Express 
#1 ·
GL1200, 1986. The spark plugs are new, carburetors have been repaired and synchronized a week ago. The engine works very smooth and starts at first press of the button. The cylinders' compression is perfect. But at high speed (about 90 mph) the first cylinder refuses to work:) The spark disappears. If I shift to neutral after that I still hear that only 3 cylinders work. But if I switch of the engine and wait for about 30 min and start it again - everything if perfect again. So the problem is that at high speed the first cylinder doesn't work. Maybe CDI or coils? I would really appreciate any advise!

Thanks in advance!

Regards,
Sergey
 
#2 ·
Probably taxing the engine, creating a lot of heat, which is detrimental to anything ignition related, such as the pulse generators, although if that were the case, seems that it would be 2 cylinders....

Maybe a fragil plug wire, or a cracked spark plug porcelin.... Sounds like something is grounding out, or breaking contact.... Maybe just a dirty gound wire, which when stressed, is failing, but that ostensibly would be all 4 acting up.....

This is from a layman though, so hopefully those with more knowledge will check in...
 
#3 ·
How does one go about dewtermining which of the spark plugs isn`t firing at 90 m.p.h.? Not sure if the 1200s have a vacuum fuel shut off valve, but it sonds like my 1500 when high speeds combined with a hill and extra laod. It would just feel like running out of gas till things slowed down. High load, plus lower vacuum at higher speeds and a vacuum leak = problems.
gumbyred
 
#6 ·
if you are sure its the spark on that cylinder i'd have to go changeout that sparkplug and see if that corrects the problem,if not i'd have to look at either the ngk cap or a leaking wire
you say the carbs were repaired ,if so what was wrong?
 
#7 ·
So all you know is that the front cylinder isn't burning gas. It could also be a carb issue. Since the front two cylinders use the same coil and it was heat related it would shut off both front cylinders. Since it only affects one I'd suggest changing that spark plug or swapping it with another to see if the problem moves to the other cylinder. I think this sounds like a fuel delivery problem and not spark related.
 
#13 ·
Jets are 100% original. Here is another idea: one of Wing owners said there must be some kind of valve connected to air filter and this valve must open at high speed (more then 70 mph). If it doesn't open the bike meets the same trouble as I met. I don't know exactly how this valve called in English.
 
#14 ·
Some other facts: Despite the problem at high speed the bike starts perfect, idling great, has great torque and needs 7-8 l of gas for 100 km (approx. 35 miles per gallon). But as I wrote above at high speed it seems that somebody cuts off fuel and sparks:D
 
#15 ·
If it wasn't just one cylinder, would think someone had installed a speed/rpm shutoff. Or maybe they did, and only wired one cylinder, or only one is working....

Easy fix would be to not go above 89 mph, but that is not what you want to hear....lol

Have you tried the same rpm in 4th gear as 90mph in 5th gear, to see if it still cuts out? I have a 1200, and that must be about 4500 rpms?
 
#16 ·
I did try what you said (4th gear and about 4000-4500 rpms). The result is the same. But today the bike started f**k my brains at medium speed also. I don't know how do you call the process when engine runs on 3 cylinders only instead of 4 in US but in Russia we call it "becomes triple". Strange issue - if it becomes triple and I open the throttle on maximum the engine becomes ok (all 4 cylinders run). We call this operation "to clean engine's ass":). I suspect some vacuum valve or something like that. Something cut off fuel or spark or both of them. I'm more then sure it's not coils.
 
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