2014 Stumble on accel.

Yesterday, I noticed a flat spot, or stumble, rolling on the throttle. It was so subtle that at first, I thought it was a blast of wind, or a pavement imperfection. The bike idles smoothly, and is behaving normally except for this one spot shortly into the throttle. it doesn't happen at a specific RPM, rather around the same place as I'm rolling on from a closed throttle. It is reliably reproducible. I know it sounds crazy, but the best way I can describe it is that it feels like hitting a very brief wind gust head-on, due to the momentary loss of acceleration. Bike has 27,000+ miles on it. No error codes, no other anomalies that I can detect. I'm going to check the airbox and plugs, but thought I'd see if those smarter and with more time on FJR's than me had a recommendation or diagnosis. Thanks.

Is the engine cold, at normal operating temperature or does it happen all the time regardless of engine temperature?

Next time I'm searching thread tags for engine operating flat spot or stumbling I'll be sure to use nipple as a search term, it's just like your other thoughtful, helpful thread tag words.

Why thank you. The symptom appears whether the bike is cold or at normal operating temperature. I figured it would pass, but alas, it remains.

Test the TPS in diAG screen. See if you can reproduce your flat spot in the digital display response.

There isn't much that can cause a little problem like that at a specific throttle opening or rpm range. As Fred sez, check the TPS, though it can pass the diAG test and still be bad. The other thing that may need testing is the throttle servo that drives the throttle plates.

This may need to be diagnosed via the ECU Diagnostic Port which can dynamically track and store all the related sensor information while the bike is being ridden. The tech can then go through the data plot and should be able to see what's happening. Or, you can spend the ~$650 for the Diagnostic Tool and do it yourself.

Thanks sincerely guys. I'll plot my course based upon your recommendations.

Make sure to check your nipples as well.

Idle rpm set at 1000-1200?

mikep1300 said:

Idle rpm set at 1000-1200?

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Not on a '14. Yamaha took away the adjuster knob and delegated the job to the ECU.

Well dang. It fixed my '11.

Diag read correct values. New fuel and a tank treated with seafoam didn't change anything, so I did what was overdue: Replaced plugs and had TBS done. Both for the first time since the bike left the showroom. The stumble happened once on the way home from the shop yesterday. But I didn't notice any symptoms this morning. Plugs didn't look as bad as I thought they would. A little brown. Shoulders of the electrodes were eroded, and the electrodes were visibly shorter than those on the new ones of the same model. Wish me luck. Tentatively planning on hitting NC and AL this weekend. See you out there.

At what mileage?

Curious since you seem to be laying miles on quicker than me. Might want to do plugs before the 25k valve check

28K or thereabouts. I can't remember when I should have done plugs. Intended to do them last year in conjunction with a coolant change, but shop didn't have that plug in stock when I happened to be there.

Bill Lumberg said:

28K or thereabouts. I can't remember when I should have done plugs. Intended to do them last year in conjunction with a coolant change, but shop didn't have that plug in stock when I happened to be there.

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You have nipples in the tags section...have you checked them lately? Are they a little misshapen or discolored?

Waiting to check them when it's colder...

Bill Lumberg said:

28K or thereabouts. I can't remember when I should have done plugs. Intended to do them last year in conjunction with a coolant change, but shop didn't have that plug in stock when I happened to be there.

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Oh... so you didn't do a valve check yet? The plugs generally come out for that.

Valve check was done at the same time as coolant. Between 21 and 24k. Didn't have plugs on hand. I was too stubborn to leave the bike an extra day for plugs to arrive.

. <blockquote class='ipsBlockquote'data-author="Fred W" data-cid="1308349" data-time="1462544291"><p>
<blockquote class='ipsBlockquote'data-author="Bill Lumberg" data-cid="1308336" data-time="1462542501"><p>28K or thereabouts. I can't remember when I should have done plugs. Intended to do them last year in conjunction with a coolant change, but shop didn't have that plug in stock when I happened to be there.</p></blockquote>
<br />
Oh... so you didn't do a valve check yet? The plugs generally come out for that. </p></blockquote>

Bill Lumberg said:

Valve check was done at the same time as coolant. Between 21 and 24k. Didn't have plugs on hand. I was too stubborn to leave the bike an extra day for plugs to arrive.

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@Bill, so are you saying you had 28k on the original plugs?
--G

Not only were the plugs installed by the factory present at 28,000 miles, but they suffered the injustice of being removed and reinserted at one point when they were already past 20k. Plugs and TBS were the only prescribed scheduled maintenance items that had never ever been done.