Modern Buddy

A couple of times when starting my scooter and accelerating forward, the engine has failed to return to idle. It basically sounds like it is still in 1st gear trying to move forward and I have to keep the brakes down to prevent it from moving forward.

The first time this happened was over a month ago. I rode it home and decided to look at it there, but when I restarted the engine, the problems were gone.

Today, it happened again. I pulled over the reset the ECU and it was fine. Has anyone else had this happen?

I just had my valves adjusted in April and this sort of sounds like an ECU issue. The first time it happened, I pulled my scooter out of a cold garage and today, my scooter sat in the sun for a couple of hours (normally I keep it in a garage). Not sure if temperature played a part at all.

How many miles on the bike? It could be that the clutch is sticking, but that's unusual unless a clutch return spring has broken. Do you also find that it's shuddering at all on acceleration? Either way, you (or your favorite nearby shop) will likely want to open up the CVT to inspect the clutch.

Thanks. I actually had the CVT inspected when I did the valve adjustment in april. The replaces the rollers and inspected the belt as well.

As Stanza says - the clutch, not the belt and rollers.

Do you mean that the engine speed stays high? If so maybe you have a sticking throttle cable. I don't know how the throttle cable actuates the throttle body on your fuel injected scooter but on my carbed 125 I had a brief problem with the throttle sticking at the carb because a the small rubber boot near the end of the cable got out of place and stuck where the cable ends near where the nipple inserts into the curved cam at the carburetor. If your engine idle speed is sticking high it might pay to check that the cable and throttle body are returning freely at idle.

If the clutch were sticking then it seems that the engine idle speed would decrease at idle and the motor would bog down and maybe stall if you stopped the scooter with your brakes.

Could be a high idle speed.


When it's off can you turn the rear wheel? If the clutch doesn't release, you won't be able to do that easily.

The bike has nearly 25,000mi on it. I can turn the wheel when the scooter is off. I thought about the sticking throttle cable, but the fact that simply restarting the engine fixes it ruled that out.

I don't know about the clutch then. The scooter accelerates very rapidly. On a carburated engine I'm not sure you can tell a difference, but on a fuel-injected one like I have, there is a clear difference between being in gear and being at idle. Whenever I slow down and stop, it's like the engine switches into an idle mode where the RPMs are very low. The problem arises when I slow down, but the engine doesn't switch to its idling state.

If you are turning down the throttle and the engine isn’t fully responding, the fact that it stays in gear is somewhat ancillary because that’s how it’s supposed to behave when it’s running at that speed. Right?

If this is the case you are describing a throttle response problem. Whether it is mechanical or electronic would need to be determined by disassembly to some extent, but i’d personally want to rule out obvious mechanical issues first.

mukaiboston wrote:I don't know about the clutch then. The scooter accelerates very rapidly. On a carburated engine I'm not sure you can tell a difference, but on a fuel-injected one like I have, there is a clear difference between being in gear and being at idle. Whenever I slow down and stop, it's like the engine switches into an idle mode where the RPMs are very low. The problem arises when I slow down, but the engine doesn't switch to its idling state.

The mechanics of the 125 & 170i are the same: when the speed is low enough, the clutch springs overcome the centrifugal force and pull the pads in, thus disconnecting the engine (and spinning belt) from the gears connected to the wheel.

When you're ready to go, give a twist, the engine revs up, and the centrifugal force pulls the pads out to engage and drive the rear.

If the clutch doesn't release, it usually because the engine RPMs never go low enough. Then you're stuck holding the brake and forcing the clutch to slip (which you don't want to do forever).

So, I'd say the bike isn't idling properly 100%. Someone with 170i experience in adjusting that should be along shortly... (you might find out how by searching MB)

When you turn the throttle, is there any play before it starts to rev? Usually there will be just a little bit of twist before it starts to increase engine speed. If your cable is too tight (kinked, sticking), it may be acting as if you're applying throttle all the time even when you aren't. The idle on the 170 is set at the factory, and it uses an automated idle adjust system. If it's not coming down all the way, I'd have it checked out. Last thing you need is for it to rev up unexpectedly.