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Born in the USSR
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Discussion Starter · #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
 

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1984 Aspencade
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296 Posts
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...
 

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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
 

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Born in the USSR
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300 Posts
Discussion Starter · #5 ·
How does one go about dewtermining which of the spark plugs isn`t firing at 90 m.p.h.?
It's very easy! When it happened for the first time I stopped the bike (without switching off the engine) and checked the temperature of each exhaust pipe. The fist cylinder didn't run. Then I switched off the engine, wait for about 30 min while calling my friends, than started the engine and it became OK. Today the situation was just the same. I run for a whole day in different speed regimes (traffic jams, highways etc.) but when I reached 90 mph. I met exactly the same problem with first cylinder
 

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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?
 

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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.
 

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Go do it agine, but a plug socket & wrench inur pocket.Pull plug.& if it's wet replace plug, dry -fuiel delivery.
 

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Junior Grue
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Your float valves have a filter on top of them.
If one of them were mostly plugged you might get enough fuel at idle but not when demand was high.
 

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Born in the USSR
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300 Posts
Discussion Starter · #11 ·
Go do it agine, but a plug socket & wrench inur pocket.Pull plug.& if it's wet replace plug, dry -fuiel delivery.
I did exactly what you say when I met the problem. The spark plug was WET for sure I replace it with a new one. But yesterday the situation was the same. As for carburetors - all the parts inside them (jets, gaskets, valves etc.) are new. I ordered 4 full carburetor's kits from US and changed everything and made them synchronized. Also I can say for sure that there is no vacoom leakage in fuel system (we checked everything). They works perfect. Also we checked all spark plugs wires with a tester (ohmmeter) when assembling the bike. I will change the spark plugs wires today to be sure that the problem is not caused by them and will inform you.

Thanks a lot for help!
Regards,
Sergey
 

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1987 GL1200 Interstate
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23,324 Posts
Most carb rebuild kits are junk. Where did you get it from and what size are the jets? If the bike needs a 108 main jet and the new jet is a 102, that could cause a problem at high speed. Although, a wet spark plug would signify ample fuel.
 

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Born in the USSR
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300 Posts
Discussion Starter · #13 ·
Most carb rebuild kits are junk. Where did you get it from and what size are the jets? If the bike needs a 108 main jet and the new jet is a 102, that could cause a problem at high speed. Although, a wet spark plug would signify ample fuel.
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.
 

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Born in the USSR
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Discussion Starter · #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
 

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1984 Aspencade
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296 Posts
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?
 

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Born in the USSR
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Discussion Starter · #16 ·
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?
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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1984 Aspencade
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That has got to be frustrating. Someone here will figure it out.....

I have been into Khabarovsk quite a few times. Long ways from Moscow......
 
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