Bike stuttering at constant speeds

[rvkssl]

Hi guy's,

I was wondering if somebodybody could help me out?, since a few weeks i'm noticing a stuttering in the engine at constant speeds, it feels the same as the rev. limiter kicking in but less. Things i've done so far:

- Valve adjustment.
- Replaced igniter.
- Cleaned IACV connector.
- Replaced clutch bearings (nothing to do with this culprit but neccesary due to bearing noise).
- Checked brakes for binding.

I couldn't find anything wrong, the only thing i've noticed was that the clutch compression spring was 4 mm shorter than servicing limits, but i can't imagine that doing the trick. Before swapping parts like crazy i would love anyone pointing me in the right direction, things i'm thinking of are:

- Bad throttle positioning sensor.
- Fuel injector.
- Sidestand switch.
- Chain tensioner.
- Speed sensor.
- Fuel pump.

Bike has run 26000 Km. 2014 LED model with the only right color

Any help will be highly appreciated.

Cheers.

[accyuklad]

you checked belt and rollers im guessing in the 26000km you not checked or replaced

also try disconnect side switch first bypass it

[fish]

For my EFI Kymco, stuttering engine when at a constant speed was a failed throttle position sensor (proven by diagnostic tool)
TPS was replaced. 6 yrs later still running perfectly.
Fish

[you you]

Change spark plug.

[rvkssl]

Checked belt and rollers, bypassed side stand switch, changed spark plug, still no luck...., i also cleaned out de VS sensor, no test ride made yet.
I didn't check the TPS yet Fish, i want to start with the easy stuff before taking all the plastic off ( again )

[you you]

Checked belt and rollers, bypassed side stand switch, changed spark plug, still no luck...., i also cleaned out de VS sensor, no test ride made yet.
I didn't check the TPS yet Fish, i want to start with the easy stuff before taking all the plastic off ( again )

It's been stuttering over a few tanks of fuel, not just one?

[fish]

Checked belt and rollers, bypassed side stand switch, changed spark plug, still no luck...., i also cleaned out de VS sensor, no test ride made yet.
I didn't check the TPS yet Fish, i want to start with the easy stuff before taking all the plastic off ( again )

TPS was avail. only with the $260 throttle body on my Kymco ....fortunately replacement was covered by the 2 yr warranty. Had to get Kymco customer service rep. involved to force dealer to buy the Kymco diagnostic tool to prove it was a failed TPS. Fellow Kymco forum member loaned me his Kymco diagnostic tool...and I posted video on youtube. Got things moving nicely!
Fish

[rvkssl]

Checked belt and rollers, bypassed side stand switch, changed spark plug, still no luck...., i also cleaned out de VS sensor, no test ride made yet.
I didn't check the TPS yet Fish, i want to start with the easy stuff before taking all the plastic off ( again )

It's been stuttering over a few tanks of fuel, not just one?

It’s stuttering over a few tanks of fuel.

[fish]

Yeah, unless you've fueled up at the roadside in Peru. ...these days it's almost never 'bad gas'.

Fish

[Mikes150pcx]

To me it sounds like bad sparking break down, the dia tool would be nice to have so you could see real time reading while you are running. It sounds like the crank sensor is failing and would be what I would look at. If the tps was bad you would see it's values bounce when steady throttle is appiled. You would also see rpm eratic when acting up. You could try pooring water on the crank sensor when it acts up and if the response is instant then that would be for certain. Not all crank sensor will change when water is applied but it doesn't mean it's not failing. Take a hard look at it because a crank sensor will give wild range of repairs with no effect. This is typical of crank sensor fail and miss diagnosis replacing lots of parts for nothing. I hope this helps!

[rvkssl]

To me it sounds like bad sparking break down, the dia tool would be nice to have so you could see real time reading while you are running. It sounds like the crank sensor is failing and would be what I would look at. If the tps was bad you would see it's values bounce when steady throttle is appiled. You would also see rpm eratic when acting up. You could try pooring water on the crank sensor when it acts up and if the response is instant then that would be for certain. Not all crank sensor will change when water is applied but it doesn't mean it's not failing. Take a hard look at it because a crank sensor will give wild range of repairs with no effect. This is typical of crank sensor fail and miss diagnosis replacing lots of parts for nothing. I hope this helps!

Thanks for the tip Mike!, i will try this after my holiday, to be continued in 3 weeks...., i'll keep you guy's updated

Cheers, Ronald.

[fish]

The first "tell" which I had of a bad TPS, was finding a motorcycle blog with this same symptom: ridden a lot at a certain speed, then bucking and missing developed when riding at that speed.
I don't fully understand how the TPS works, but it is like a bad scratch at a spot on a DVD. Speeds lower and faster were perfect, starts perfect, WOT perfect. But, for me, 35mph-ish was a nightmare often.
Fish

[rvkssl]

Update after my holiday:

Read the fault code with the DTC, it said code 1-2 MAP sensor high voltage, followed the troubleshoot guide, all ok. Reset the DTC, fault still present with no mil indications....then i checked the TPS while this is housed in the same sensor and noticed that the resistance from the TPS went from 0 to 1.8 Kilo-ohm (closed-WOT) with a peak of 2.2 Kilo-ohm on 75% throttle postition, the maintenance guide only tells you to check resistance change when moving the throttle within a 0-5 Kilo-ohm range, so that is not very helpfull.
In my opinion a TPS should give a smooth range from 0-5 Kilo-ohm and not peak at 75% throttle position so i think i found the culprit just as Fish suggested. Next step is ordering a new TPS.

To be continued.

[easyrider]

I think that if it was the TPS you would notice some hesitation on acceleration and jerking. At constant level speed perhaps fuel delivery and perhaps coil failure if so equipped on this scoot. Did this first come to light immediately after the valve adjustment ?

[fish]

I think that if it was the TPS you would notice some hesitation on acceleration and jerking. At constant level speed perhaps fuel delivery and perhaps coil failure if so equipped on this scoot. Did this first come to light immediately after the valve adjustment ?

It is all too easy to chase your tail when a TPS is failing! So easy.
Failed TPS is often characterized by : perfect start, perfect idle, perfect acceleration, perfect WOT - stumbles when held in a steady cruise at a certain speed.
Stumble progressed to feeling like ignition being turned off and on when cruising at 33 mph. Engine almost banging off and on.
Eventually I found similar symptoms on several motorcycle blogs and zeroed in on the TPS.
Dealer wouldn't listen until factory customer rep. got involved. I borrowed a factory diagnostic tool and posted the results on youtube! Then everybody listened to me and parts were replaced under warranty. No further issues in 6 yrs.
It was a failing TPS.
Fish

[easyrider]

Hope it is the TPS ..Should be an easy repair.

[rvkssl]

I think that if it was the TPS you would notice some hesitation on acceleration and jerking. At constant level speed perhaps fuel delivery and perhaps coil failure if so equipped on this scoot. Did this first come to light immediately after the valve adjustment ?

No, it started before valve adjustment.

[easyrider]

I read your post again and think you have enumerated most of the causes..Just a matter of checking each one out. Does the PCX have a diagnostics light ? This condition can be caused by a host of conditions and failed sensors some of which mentioned above. We are just guessing but I would check again the ignition circuit ie coil, spark plug, ignition wire, connectors for tightness and condition.Might even try another plug ...clean air filter . The other thing might be fuel delivery ie pressure drop under sustained flow conditions. Fuel filter /sock all can be suspicious as well. This kind of problem can be a bugger to figure out without lots of testing .. Good luck !

[fish]

Really easy to chase your tail with this symptom.(coil, plug, plug cap, grounds & terminals, injector, fuel pump, valves, fuel, pinched line, evap system, tank vacuum, ECU, etc., etc., etc.)
Price of TPS (if it is integral with the throttle valve?) can be expensive.
So, have Honda run a scan on your bike with their diagnostic tool.
Get it fixed and relax, leave your tail alone.
BTDT
Fish

[rvkssl]

So, finally got the parts from Thailand, changed the TPS, did a TPS reset and made a testride, at first i thought the problem was fixed but when the bike warmed up the same thing happend again, stuttering at constant speeds......... , could this kind of symptoms come from the drivetrain?