Low idle when cold and stutter around 2500rpm

SeaBass

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Aug 7, 2019
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82
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Arlington, VA
Hey peeps,

Since Sunday, I've been experiencing two symptoms that had not been there before.

1st When starting up the S10 from cold (happened after parked overnight and 6 hours at work) the motorcycle will start idling between 1100 and ~850 rpm, and when reaching the lower RPM the second or third time will stall out. Once it has warmed up over 130F no more low idle issue. It starts fluctuating between 1100 and 1000 rpm.

2nd Whichever gear I'm on, when it has to go from 2k to 3k rpm, it's like it hesitates, stutters with what I will describe as a jerk of the shaft and then continue to rev up. This is quite noticeable on the first 3 gears. (this happens on both modes and with and without TC on)

I'm inclined to think it might be Throttle bodies out of sync for the 1st, but have no clue for the second symptom.

Since I got the S10 back in august I've change the oil twice to flush out any old residue, same with the final drive oil; flushed the clutch, changed front pads, check front and back brake fluid and were OK, change the air filter and have run 2 tanks of gas with Yamalube Engine RX. Coolant looks ok too.

I am uncertain if/when the previous owner did a valve adjustment, but the bike is now 49k miles so it might be due. I'm guessing that is the only part of the tune up left, but not sure it will give me those problems.

So, anyone have any insight on what could be happening?

Thank you.
 

Squibb

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Aug 10, 2014
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Could be a whole host of things on a 2013 at almost 50k. Have you checked for codes?

The on road symptom sounds like injectors or coil sticks, but could be a loom issue. The poor idle stability suggests either TB sync, a perished take-off cap or a TP sensor problem.

Anyway, check the diagnostic codes & see if they can provide more of a sense of direction.
 
Last edited:

SeaBass

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Aug 7, 2019
Messages
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Location
Arlington, VA
UPDATE:
The S10 had a shut coil and really rusted spark plug. That cylinder has a 45% loss of compression. They will start tearing down to see if the valves are ok, might need cleaning and adjustment, but they are not too optimistic. So far I'm looking at 1.2k dollars labor cost, 400 for coils and whatever else needs to be replace.

When will you say it will be the point I should tell them to stop and just part the S10? or is it worth to invest on it? The rest of the bike is in great condition, no rust anywhere and electrically flawless.
 

scott123007

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I am going to go out on a limb here and say STOP everything at this point. Get a new spark plug and one coil stick and take the bike for a ride. Then, make a mental note of how it feels. There is no harm in that, engine wise. If it feels normal, then do a compression check. The lower compression "could" have been a "dry" cylinder from too much fuel because of lack of spark. There may be a problem, but you always tackle one thing at a time. Dealerships are too quick to throw out the doom and gloom to make you part with your greenbacks.
 

Squibb

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I'm with scott123007.

I think of it as a wet cylinder, rather than dry - wet with unburnt fuel, that allows air to bypass the piston/rings. So dry of any oil, which could easily create that scenario. Just have the plugs changed & the coil stick replaced & give it a good run - I mean some proper heat cycles through the engine, not a couple of miles around the block.

Personally, if all is good, I would go no further - if she is down on power then you may have to think again.

Good luck - don't get talked into any big spend at this stage.
 

SeaBass

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Joined
Aug 7, 2019
Messages
82
Location
Arlington, VA
I am going to go out on a limb here and say STOP everything at this point. Get a new spark plug and one coil stick and take the bike for a ride. Then, make a mental note of how it feels. There is no harm in that, engine wise. If it feels normal, then do a compression check. The lower compression "could" have been a "dry" cylinder from too much fuel because of lack of spark. There may be a problem, but you always tackle one thing at a time. Dealerships are too quick to throw out the doom and gloom to make you part with your greenbacks.
I'm with scott123007.

I think of it as a wet cylinder, rather than dry - wet with unburnt fuel, that allows air to bypass the piston/rings. So dry of any oil, which could easily create that scenario. Just have the plugs changed & the coil stick replaced & give it a good run - I mean some proper heat cycles through the engine, not a couple of miles around the block.

Personally, if all is good, I would go no further - if she is down on power then you may have to think again.

Good luck - don't get talked into any big spend at this stage.
That is what we are heading, they will get to the valves to check they are ok and adjust them if needed, for now is 2 coils damaged, the cracked one and the one next to it and 2 plugs that need replacement. As it was overdue to valve adjustment, we are proceeding just a little forward, I was planning on doing so soon, now is the time. They will do that today, and call me tomorrow morning to discuss whatever they found and give me the final estimate. The 1.2k is worse case scenario, which involves replacing the valves.

I've been using this guys for as long as I've been riding, and they know that if the fuck me over, I'll stop sending new riders to get their bikes and gears their way. ;)
 

EricV

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A possible contributing factor is carbon build up on the valves. I saw quite a bit of that on my '12 S10 in the 50-80k mile period. I started using Yamaha Ring Free which helped. Now I would consider just using Seafoam instead as it's easier to get and probably cheaper.

I agree with the others, hold off on major work for now.
 
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