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Re:HELP...... one piston not firing
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TOPIC: Re:HELP...... one piston not firing
#1025272
jd750ace (User)
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Re:HELP...... one piston not firing 3 Weeks, 5 Days ago  
If you have spark and it is not backfiring through the carb I’d say a stuck exhaust valve. The orange and gray wires that feed the coil have flag terminals on them. I had one contacting the carb cable bracket that shorted the feed to the coil once, so check good under there and make sure nothing is touching them. Mine had a tiny little hole in the cover on the flag terminal. It only made contact when the motor was vibrating.
 
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#1025280
Flashback (Moderator)
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Re:HELP...... one piston not firing 3 Weeks, 4 Days ago  
Probably be a good idea to do a compression test...I'm going with the stuck valve........
 
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#1025298
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Re:HELP...... one piston not firing 3 Weeks, 4 Days ago  
+1 on the compression test like flashback said.. and if you do have svs one thing I've heard of is to shoot some penetrating oil on the valve stems thru the head ports. better yet if you can take the valve cover off let gravity draw it down between the guides.
 
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#1025303
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Re:HELP...... one piston not firing 3 Weeks, 3 Days ago  
Had the exact same thing on my 2000 roadstar. It was a sticking valve. I just poured Seafoam into the intake slowly with the motor idling high then let it sit for about a half hour or so before cranking it up and blowing it out. Worked like a charm!
 
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#1025313
jd750ace (User)
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Re:HELP...... one piston not firing 3 Weeks, 3 Days ago  
Marvel Mystery Oil is magic sauce for sticking valves on air cooled aircraft engines.
 
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#1025357
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Re:HELP...... one piston not firing 3 Weeks, 1 Day ago  
hey all for the reps.... finally got around to my sons and we can safely say it not electrical, plugs all good (new) checked for spark..... leeds coils ignition box all good.... cleaned out the carb just because, fuel filter air filter bla bla.

what i found after cranking it over...... still only one cylinder (rear) firing and absolutely nothing from the front, if i had placed a feather in the end of the pipe it wouldnt have got blown out. no pumping of anything.

so i guess that means svs

now how the f#%k do i fix that, cant get seafoam here but im sure there will be something similar, like to try something easy before pulling anything apart

did find Marvel Mystery Oil.... but it would take too long to ship....

it did backfire out through the carb a few times.....
 
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Last Edit: 2017/11/19 06:55 By masterhermit.
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#1025358
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Re:HELP...... one piston not firing 3 Weeks, 1 Day ago  
masterhermit wrote:
hey all for the reps.... finally got around to my sons and we can safely say it not electrical, plugs all good (new) checked for spark..... leeds coils ignition box all good.... cleaned out the carb just because, fuel filter air filter bla bla.

what i found after cranking it over...... still only one cylinder (rear) firing and absolutely nothing from the front, if i had placed a feather in the end of the pipe it wouldnt have got blown out. no pumping of anything.

so i guess that means svs

now how the f#%k do i fix that, cant get seafoam here but im sure there will be something similar, like to try something easy before pulling anything apart

did find Marvel Mystery Oil.... but it would take too long to ship.... Can you get Yamaha ringfree at your dealer?

it did backfire out through the carb a few times.....
Can you get Yamaha ringfree at your dealer?
 
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Last Edit: 2017/11/19 07:51 By roadiemort.
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#1025630
masterhermit (User)
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Re:HELP...... one piston not firing 2 Weeks, 2 Days ago  
well the decarb spray sh*t didnt work.... pulled the valve cover off and could see that only 3 of the push rods were moving, so going to check the valve lifter on the one thats not moving....?

so why would 3 push rods move and 1 not....? what should i check....?
 
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#1025635
davej (User)
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Re:HELP...... one piston not firing 2 Weeks, 2 Days ago  
Cam/lifter issue of some sort. Is the valve on the non moving push rod stuck open or closed?
 
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Last Edit: 2017/11/25 18:17 By davej.
 
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#1025729
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Re:HELP...... one piston not firing 2 Weeks ago  
davej wrote:
Cam/lifter issue of some sort. Is the valve on the non moving push rod stuck open or closed?

sorry for such a slow reply.... from what my son says, stuck closed
 
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