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Intermittently runs on one cylinder?


sesty

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Took the bike out of winter storage this weekend, gave it a wash and a rip around the area. Half way home, starting off on a green light, hit 3rd gear and it the engine would not rev passed 6k and sounded like it was running on one cylinder. On light throttle pulls it was very sluggish until it got a certain RPM or throttle position and the bike would have full power out of nowhere. Rev up to around 6k and fall flat again. Felt like i was driving my old XS400 with a clogged pilot jet.

Made for an interesting drive home. Right side cylinder was about 25 degrees cooler than the left when i got home.

I was hoping it was just old gas, but after draining the tank and topping up with fresh gas it still have the same symptoms. 

Very low mile bike under 3k - will be taking a look at the plugs and intake when I can, 

anything else I should look at?

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M. Hausknecht

Sounds like a spark issue. Once, when I changed my plugs, I wasn't conscientious enough to assure both coils were fully engaged on their plugs. The result was as you describe. The cooler pipe is consistent with that one cylinder working only intermittently.  Also make sure the connectors to your injectors are secure.

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I had a similar problem on another bike. Turned out it was an electrical problem with a connector somewhere. (someone else took a long time to find it). That said, I do not want to lead you astray.....

Just do it! 

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22 minutes ago, Lone Wolf said:

Agreed - easy to verify with spark tester. Harbor Freight has one for $5

I like to do that before throwing parts at an engine, to focus the diagnostic.

assume this tool would only show if the coil was bad, not the plug, right?

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M. Hausknecht
31 minutes ago, sesty said:

assume this tool would only show if the coil was bad, not the plug, right?

Correct (coil or something else before reaching the plug), but since plugs don't go bad unless fouled or physically damaged (both of which are evident when you remove and look at the plug), the tester is ok. I'm old school though; just ground the plug on something when connected to the coil,and thumb the starter. You get a good juicy spark or not. 

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  • 4 weeks later...
  • 1 month later...
On 6/26/2023 at 11:19 PM, Anaya said:

Hi I’m having a similar issue one cylinder will shut off intermittently, did you resolve this?

Just got to it last weekend.. got the plastic and tank off and realized I didn’t have a 14 spark plug socket. Amazons bringing one this week.

got the coils out but the leads on my Klein multimeter are not long enough to test the resistance on the second circuit or bottom connector.

Shoved the lead as far at it will go into the bottom and still registering as open. May just buy the spark tester above 

Edited by sesty
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21 hours ago, sesty said:

Shoved the lead as far at it will go into the bottom and still registering as open.

How about using a piece of wire as an extension?

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  • 2 weeks later...

should have just checked the manual, the bottom caps of the coils just pop off...

Both coils primary and secondary within spec... hoping to get to swapping the plugs this weekend  - and while i have everything off might be worth taking a look at the fuel pump pick up screen / fuel pump

then i guess i am only left looking at the injectors?

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30 minutes ago, sesty said:

then i guess i am only left looking at the injectors?

Once you have determined that you have spark to both cylinders you can move on to fuel problems.

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10 hours ago, sesty said:

....might be worth taking a look at the fuel pump pick up screen / fuel pump...

Here's my experience with failing fuel pump. Also explains how to get to the filter, clogged or not.

That said, I can't see a fuel pump clogging filter or failing pump as a likely cause for the same single cylinder firing/no-fire. 

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  • 2 weeks later...

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