One cylinder problem
11-07-2009, 07:23 PM
#1
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SuperSport
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Join Date: Aug 2009
Location: Las Vegas, NV
Posts: 731
One cylinder problem
So my bike decided to run on one cylinder today. The weird thing is that it would only do it sometimes.
At idle it would only run on one cylinder. I needed to rev it to 5k and feather the clutch to get it going and keep it from dying.
Once it was going and I kept a steady cruise it would start running on both, however if I got on the gas too much, if I barely gave it any it was fine, it would go back to running on a single cylinder.
And once I passed 4.5k rpm, it would start running on both again.
I tested the front coil with two different plugs and it sparked with both. I don't know how strong the spark should be on the bike though. However I don't think it would be the coil, since it would more likely stop working at higher RPM.
When I pulled the front plug boot it would still run on a single cylinder. When I pulled the rear it would try starting a little, maybe run for a split-second, then die. So obviously the front cylinder is in question.
When I pulled the plug for the spark test, I noticed that the plug was not wet at all. So either there is no fuel or the plug is sparking enough to burn the fuel.
What think you?
I tried opening the gas tank, no help. Sucking on the tank vent hose did nothing either.
At idle it would only run on one cylinder. I needed to rev it to 5k and feather the clutch to get it going and keep it from dying.
Once it was going and I kept a steady cruise it would start running on both, however if I got on the gas too much, if I barely gave it any it was fine, it would go back to running on a single cylinder.
And once I passed 4.5k rpm, it would start running on both again.
I tested the front coil with two different plugs and it sparked with both. I don't know how strong the spark should be on the bike though. However I don't think it would be the coil, since it would more likely stop working at higher RPM.
When I pulled the front plug boot it would still run on a single cylinder. When I pulled the rear it would try starting a little, maybe run for a split-second, then die. So obviously the front cylinder is in question.
When I pulled the plug for the spark test, I noticed that the plug was not wet at all. So either there is no fuel or the plug is sparking enough to burn the fuel.
What think you?
I tried opening the gas tank, no help. Sucking on the tank vent hose did nothing either.
Last edited by Just_Nick; 11-07-2009 at 07:34 PM.
11-07-2009, 08:05 PM
#2
996 new guy
Superstock
Join Date: Jul 2009
Location: Universal city, Texas
Posts: 300
crank it a few times with the front plug out, place a napkin or shop rag in the hole where the plug goes just to "cover" it... if you smell fuel after you pull it out then you are obviously getting it...
11-08-2009, 04:01 AM
#6
Administrator
MotoGP
Join Date: Apr 2006
Location: Kempner, TX
Posts: 4,402
Mine was water in a connection.. every time I washed the bike, or rode in the rain, My tach would die, or I'd run on one cyl, or both. Problem with helping you is,,,, I don’t know specifically what fixed it.. I rode it in to the shop, disassembled the bike down to the frame, and put everything back together cleaning connections and using dielectric grease as I went.
That was two years ago, it’s never happened since. So, check all connections unplug, look for corrosion, signs of excess resistance (melted) clean as you go, and use some dielectric grease.
That was two years ago, it’s never happened since. So, check all connections unplug, look for corrosion, signs of excess resistance (melted) clean as you go, and use some dielectric grease.
11-08-2009, 01:56 PM
#7
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SuperSport
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Join Date: Aug 2009
Location: Las Vegas, NV
Posts: 731
So I just cleaned the carbs. Actually I noticed that none of the jets were clogged to begin with, but I blasted all the ports out anyways.
As a second cleaner, I sprayed some carb cleaner into the fuel line and blew into the fuel line until it felt clear.
When I started it, it ran on both cylinders. And when I pulled out of the driveway it was still on both. But once I was out of the driveway and gave it some gas it went back to two.
I tried the rag over the plug-hole trick and it smelled a little like fuel. Does that mean I'm getting it? Or should the rag have fuel on it too?
As a second cleaner, I sprayed some carb cleaner into the fuel line and blew into the fuel line until it felt clear.
When I started it, it ran on both cylinders. And when I pulled out of the driveway it was still on both. But once I was out of the driveway and gave it some gas it went back to two.
I tried the rag over the plug-hole trick and it smelled a little like fuel. Does that mean I'm getting it? Or should the rag have fuel on it too?
11-09-2009, 08:25 AM
#11
COBB Member
Superstock
Join Date: Jul 2009
Location: NorthEast Connecticut
Posts: 292
I had a similar problem, at a steady 80mph it would drop to 1 cyl. if I let off the throttle then get back into it, both cyl firing. Riding twisties, no problem, lots of on/off the throttle. Found I had a bunch of rust crap in the tank blocking the screen in the tank at steady speeds (like a clogged filter on a car, let off the gas car runs) also found my fuel valve diaphragm torn. Fixed both issues, no problems since. She'll run 120+ for as long as ya got the calzones'
11-09-2009, 09:20 AM
#12
Fastest Color
SuperBike
Join Date: Jul 2007
Location: Lithia, FL
Posts: 2,091
I had a similar problem, at a steady 80mph it would drop to 1 cyl. if I let off the throttle then get back into it, both cyl firing. Riding twisties, no problem, lots of on/off the throttle. Found I had a bunch of rust crap in the tank blocking the screen in the tank at steady speeds (like a clogged filter on a car, let off the gas car runs) also found my fuel valve diaphragm torn. Fixed both issues, no problems since. She'll run 120+ for as long as ya got the calzones'
11-19-2009, 06:47 PM
#16
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SuperSport
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Join Date: Aug 2009
Location: Las Vegas, NV
Posts: 731
Pull the spark plug boots one at the time and see if the way it runs changes.
Once you have identified the "bad coil" you can swap the front and the back coil and see if the symptoms swap coils. If they do, you have ruled out fueling, air, and electrical problems.
Once you have identified the "bad coil" you can swap the front and the back coil and see if the symptoms swap coils. If they do, you have ruled out fueling, air, and electrical problems.
Last edited by Just_Nick; 11-19-2009 at 06:53 PM.
11-19-2009, 10:49 PM
#17
Senior Member
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Join Date: Oct 2009
Location: Newport, RI
Posts: 143
For anyone else finding this thread, another problem that can yield similar "running on one cylinder" behavior is having a messed up enricher (choke) valve. I broke the fitting on one of mine when putting my carbs back in (easy to do, plastic - don't over-tighten, barely more than finger tight). The effect was that the front cylinder didn't start b/c it wasn't choked, but the back one did b/c it was. In theory if I ran it for a while, the front cyl would have warmed up and then done something - but probably not well - since it would effectively have been running with the enricher over-opened all the time.
Also, note that even if you thread the enricher connectors in correctly, you can still accidentally pull the cable out a good inch or so, making the enricher "on" all the time.
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