A Weird One...

JQL

JQL

Growing old disgracefully
Joined
Dec 19, 2010
Messages
837
Location
Val de Marne, France
Bike
2010 NT700 & 2019 FJR1300
OK just had a major service (new PR4 front, spark plugs, liquids, tappets etc. etc. - the EXPENSIVE one) and something doesn't feel quite right. SO before I take it back I could do with some suggestions as what it may be.

Symptoms:

  • Below 3500 rpm the bike is silky smooth
  • Between 3500 and 4000 rpm there's a hint of vibration.
  • Above 4000 rpm there's a definite vibration that wasn't there before so she's definitely "buzzy" at 70 mph.
  • When accelerating relatively hard there can be a hint of hesitation before she picks-up like I'm a quarter of a gear too high.
  • The "feeling" I'm getting through the bars when cruising is like I'm in 4?th not 5th gear - so a very different response to accelerating.

My thoughts are:

  • A dodgy spark plug
  • A Plug cap not fitted properly (I had them changed under the "recall" 4 years ago)
  • Tappets not set perfectly (though she doesn't sound tappety)
  • Have they put a winter fuel blend in the petrol?

I've just checked the front tyre pressure and it's 222kpa - 32.19psi (supposed to be 250kPa - 36psi) so it's possible that it's the tyre pressure - will know tomorrow after a run at the right pressure.

Winter fuel blend
In the US there is a change of the blend of petrol between winter and summer - I haven't found any mention of this in Europe but we do get a similar result with mileage so it probably happens here as well.

The winter/summer fuel blends are due to RVP (Reid Vapor Pressure). In winter the RVP is higher (in the US* about 9 psi) to help the car start and run more easily. In summer it is, therefore, lower (in the US about 7.8 psi) to stop the petrol evaporating in the tank.

Using summer blend in winter could cause the engine to run a little rough as it doesn't vapourise as easily. So it could be this though, the temperature is still in high teens (16? C today - 22? C yesterday), therefore unlikely.


I would welcome any thoughts on the matter especially if you have had similar symptoms on your NT.
 
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Don't make it your problem. You said you paid a lot for the service so they should fix it. It is almost certainly something they did (or didn't do) in the service.

But diagnosing problems is something of interest to us. It is probably something as simple as a vacuum hose not connected.
 
Being a Systems Analyst I have to understand the problem fully before I take it back to the garage.

This also stops the garage from giving you a bull**** response
 
JOhn,

I think your sparkplug, or wire may be a good starting point, also perhaps a botched job of valve adjustment , perhaps a rookie tech who doesn't have the lerned smarts to be working on certain systems! . I know my dealership pretty well and I specify WHO is to work on my bikes if it is into anything tehnical. another possibility might be fuel system adjustments like throttle cable adjustments etc.

I do agree with what Jim said that it is the repairs shop's ob to fix the problem. I do agree with your wanting to know what the problem is if possible!. another thought just flashed through my mind, possibly a safety switch , side stand, or neutral , or clutch safety switch with a possible short in it? I had a very serious problem with a KKLR 650, quit wouldn't run , intermitant firing hesitation etc, I took it to shop and suggested possible fuel contamination/ water but told service manager that was just a though and for them to do complete check out. LOL they went through Carb, cleaned fuels tank and entire system, checked valve adjustment etc. I took it out for a test ride and asme problem came up again, I returned to shop and ask them to humor the old duffer and to disconnect all safety switches, they did and it took off and ran absolutely perfectly. I brought it bckand was telling shop forman about it when shop owner walked up and listened to us, he turned to service manager and ask Why didn't you check that first as it was a common problem on the earlier versions of KLR's. Shop had to eat all of the labor time put into checking , trouble shooting etc!

Eldon
 
In your post you mention the vibes for different RPM ranges. Just a thought since you had a new tire installed, is it RPM related or speed related?
The vibes could be from an improperly balance tire, or worse one that is not seated on the rim, definitly dangerous.
You don't mention any codes showing up, but it could be a poor conection at a sensor, or as you mentioned a bad spark plug or cap.

Brad
 
No codes ATM.

I think it might be the tyre for the vibration but something else for the slight acceleration lag.

More testting today with a 70 mile run on the cards.
 
I filled up, as the gauge was in the red, with brand name gas. After about 30 miles the problems with the hesitation disappeared. So it was probably the cheap supermarket gas causing that problem.

The vibration is still there but, it could be the slightly low front tyre pressure as I wasn't able to pump up the tyres before I left (long and boring story). This I will do in the morning before I set off on another run of about 120 miles.

Will keep you posted...
 
I've heard of mass airflow sensors on cars go slowly bad and cause gradually slowing acceleration but your problem is sudden onset .. check connector ?
 
I admittedly know squat about bikes (but plan to learn and just got the service manual). Just a thought as to tell if it may be engine, powertrain or tires. On a straight stretch with smooth pavement and nobody around, something to perhaps try. Get up to speed so you feel the vibration, pop it in neutral and let the RPMs die down to 0 and see if the vibration is still present. If it's still present I would guess tires, rotation, wheel assembly, etc. and maybe if it goes away then something with the engine or related systems.

On a separate thought, perhaps try a different stretch of road. There is 1-2 mile portion of oddly-paved highway on Interstate 95 here in Maryland that will make your car and bike feel like something is DEFINITELY wrong with the wheel assembly, suspension, or tire vibration... when in fact the road had such subtle dips that it produces vibrations at speeds. Maybe try a different stretch too, see if that varies the effect. Maybe with the new tires it amplifies prior unnoticed subtleties?

Last thought, see if the vibration is present in each gear at the same RPM range and to determine if it's speed related (tire). Might be worth experimenting to see what the vibration range (top/bottom) is in each gear. If it remains the same no matter what gear, then I'd guess something engine-side. If it varies with speed and gas, then something separate influencing the engine - a supporting/feeding system perhaps (air, fuel, electrics, etc.)

Like I said, I know squat but just thoughts to maybe help narrow it down.
 
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OK, I've had the bike back in to be looked at and to do some other work as well.

Prior to her going in she would idle at about 1000 rpm when it was wet and 1400 when dry. So I think it was a sensor not correctly connected. Anyhow they've:
  • reconnected all the sensors,
  • checked the plugs
  • checked out the wiring and tested the electrics
Everything is now OK engine wise. No problems in either the cold or the rain. So it looks like one of the connectors wasn't tight.

While she was in I had the fork oil replaced (I get this done about every 25,000 miles or so) and a new rear tyre (PR4) so they:
  • Checked the final drive unit and splines - A OK
  • Rear wheel bearing assembly - A OK
  • Front wheel bearing assembly - A OK
As the steering head bearings were notchy I had them replace those as well. Having got the bike back I think I preferred the steering head bearings a little nothcy but I suppose I'll get used to the new ease of movement.

As to the vibration. I think it's the difference between the makes of tyre and the Summer/Winter blend fuel (we now have normal winter temperatures!:().
 
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