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Discussion Starter · #1 · (Edited)
Hi,

Here is another question:)

As I wrote in my previous topic I faced some trouble with my GL1200A at high speed (rpm) only. The bike starts perfect and run smooth at low and medium rpm. But at high rpm the ignition timing seems to become "late" (no speed, vibration, shots in muffles). As far as I know the ignition timing depends on vacuum capacity and corrects by vacuum also. If there is some vacuum leakage ignition becomes "late" and effects the problems I always meet with:). This problem always appears exactly at 120 km/h speed (70 miles/hour). So the question is: is there some kind of valve in vacuum line that works incorrect or it's just a small hole somewhere in the line that can cause incorrect timing at high rpm.

I will highly appreciate any ideas, advise or help.

Regards,

Sergey

P.S. Spark plugs, all the filters, ignition wires are new. Carburetors were rebuilded an synchronized
 

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Born in the USSR
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Discussion Starter · #3 ·
I'm not sure it's a coil (coils). I put new plugs in and run about 100 km in different modes (slow, medium and high). When the bike started f**cking my brains I stopped it by kill switch and put the spark plugs off. They were covered by white-grey mixture (mostly white). That means:
1. Overheating (not in my case)
2. Wrong spark plugs (not in my case)
3. Incorrect ignition timing (seems to be my case). But in my case ignition timing is Ok at low and middle rpm. It's incorrect at high rpm only. And ignition timing is corrected by vacuum and depends on ride mode and rpm
 

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Born in the USSR
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Discussion Starter · #5 ·
Hi Cornpone,

1. The carbs are properly synchronized for sure with special professional tools.
2. The intake O-rings are new
3. I did the "spray test" with my friend but found no leaks. But we did not run engine till 2 000-2 500 rpm. We tested it on idle only. Maybe that was our mistake.

Thanks! I will try another "spray test"
 

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Discussion Starter · #9 ·
Ok! I see...If it's not vacuum problem so I don't know what exactly problem I faced:) I think I will start tracing step by step: if spark plugs, filters, ignition wires are new and the carbs are synchronized so I will check coils, cdi and pulse generator. There are no more items to check.
 

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Discussion Starter · #12 ·
The pulse generator send a signal to the cdi to fire the coil at the right time. This is a wasted spark system (two plugs firing off the same coil at the same time). The pg's and the cdi are doing their job correctly, since it doesn't affect the other cylinder fired by that coil.
Let's imagine (in theory) that "some bug" makes ignition timing "late" at high rpm only. What kind of bug could it be?
 

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Born in the USSR
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Discussion Starter · #13 ·
I'm troubled by the "white grey" mixture on the plugs. That to me is an over lean condition. Which would also explain why you can't get any top end speed. It is starving for fuel.

I would do the fuel delivery test in the Factory Service Manual to make sure your pump is putting out enough fuel. I would also change the fuel filter to make sure you don't have a clogged filter.
Hi,

Thanks! But I did fuel pump test. It puts out exactly 0.5L per minute as it must with regards to Service Manual. The fuel filter is also brand new.

By the way if I'm not mistaken with lean fuel mixture the bike runs bad on every gear. In my case on 1st, 2nd, 3d and 4th gear the dynamic speed and torque are excellent but when I reach 120 km/h on 5th gear it seams that somebody or something changes ignition timing in a moment.
 

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Discussion Starter · #15 ·
Thanks for ideas FenderHead. Yes, the problem occurs at the same rpm in any gear at about 4000 rpm. But I can't ride for a long time in 1st gear for example with 4000 rpm.:) and in 2d too:) So let us say this problem appears at high rpm (doesn't matter what gear is switched on).

P.S. Carburator sliders and diaphragms are Ok. Anyway I like your idea to switched vacuum advance unit to another one.
 
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