Stock Zuma Looses power at WOT

[Gearbox Paul]

My 02 Zuma (BWS in Canada) looses all power at wide open throttle when I accelerate from a dead start or when I go up hills and the scooter starts to slow down. It "bogs" down as if the engine is running out of fuel. If I maintain the throttle wide open, the scooter will come to complete stop and the engine will stall. However, if I am travel on a level grade, and I gradually bring the scooter to wide open throttle (gradually accelerate) it runs fine. This is consistent and predictable.

The gas tank is clean. I took the carb apart, cleaned the jets and reinstalled. No difference.

I'm stumped.

[g~scoot]

That is an interesting one...It has to be either a fuel or air problem. You've checked the carb. I would suggest looking at your air filter. Never heard of it on a scooter but I had a lawn mower where the air filter got so dirty it would only turn over and then immediately die. You could have something like that going on. It could be just dirty enough to where at wot the flow is restricted enough that the A/F mix becomes super rich. Just a thought. Thats the only thing that comes to mind right now. Ill think on it.

[Gearbox Paul]

Thanks gscoot. I cleaned the air filter when I removed it clean the carb. It was not that dirty. In any event, the scoot runs fine at WOT on a level road. Top speed is good, no problem. It is only a problem when I am at WOT and the scoot revs are low, i.e. going up a hill or accelerating hard from a dead stop.

At first the problem was intermittant. It now happens every hill, and every time I accelerate hard. If I run the scoot at about 1/2 throttle, it runs fine, even going up hills, albeit slower. Once on level ground, I slowly accelerate to WOT giving the scoot lots of time to get the revs up and it runs fine. But as soon as start going up a hill, I have to drop the throttle to 1/2 open. If I maintain WOT, as the scoot revs start dropping, it will "bog" down and loose all power and eventually stop completely.

Hope that helps define the problem.

[j~scoot]

It sort of sounds like the opposite of what you said, you scooter has too much fuel. Is this a stock setup? I know that when i give my scooter too much gas going up a hill it will start to bog down if the revs aren't high enough because i am introducing too much fuel into the cylinder. I have gears though, so i just down shift. Is it possibly a transmission issue, like your torque driver spring isn't stiff enough to get you back into low gear fast enough? or do you think it is something with your cylinder/fuel? Because it mainly happens on hills i would have to lean toward a transmission issue, but without being there i'll have to rely on your opinion.

[Gearbox Paul]

Interesting thought JScoot. Yes this is a stock setup. No mods. If I understand what you are saying, I would be flooding the carb at WOT when the revs are not high enough. It does make some sense. When the scooter bogs down, I release the throttle for a little while and then open it about 1/2 and the scooter runs fine at 1/2 throttle, until I am past the hill and then I can slowly open the throttle to WOT again, giving the scoot time to get the revs up.

The torque driver spring you are referring to, is it the spring that is housed in the secondary sheave (refered to as the clutch spring my manual)? It looks like some special tools are needed to take that sheave apart. Any pointers to give me before I embark on this ?

[g~scoot]

The clutch spring and the torque spring are one in the same. I usually call the large rear pulley spring the torque spring not to confuse it with the small springs actually holding the clutch together by calling it the clutch spring. There is no real secret to taking it apart and changing out the spring. Provoscooter has a pretty good write up on this here in the stage one install how-to (http://www.provoscooter.com/stage-one-installation)

Basically you will need a large wrench and strap wrench or vice to get it apart. just be careful too because the clutch assembly is under a lot of pressure from the spring so make sure you have hold of it or get help when you actually release the nut. Things will go flying if not careful.

[Gearbox Paul]

Thanks GScoot. Once I have removed the torque spring, how will I know if it is not stiff enough ? Should I just replace it with new ?

I noticed in the stage one install how-to that it says to keep the paper-thin washer located next to the variator sleeve. I removed it a while ago hoping to get a little more top speed. I didn't notice a significant gain in top speed but I never reinstalled it. I didn't throw it out though, I still have it. What does this washer do ? Do you think not having it could be related to my problem ?

[j~scoot]

I'm not sure what difference the washer makes, but i would put it back in if you have it. I doubt this would be causing the problem though. Take a look at this thread on transmission tuning (http://www.provoscooter.com/forum/showthread.php?t=9024). If it seems like your scooter is trying to stay in too high of a gear while going up the hill instead of putting you into a lower gear to be able to climb it, then it probably is a problem with the torque spring. You won't know if it is too weak by just taking your scooter apart. you either need to get a new spring (http://www.provoscooter.com/scooters/yamaha/yamaha-zuma-50-horizontal/malossi-torque-driver-spring-yellow.html) to try as a comparison, or just know that you need a new spring by the way your scooter is running.

[Gearbox Paul]

Thanks again GScoot. I'll be away for a few days but I'll get spring, install it and post back to let you know what it did. You've been very helpful.

[j~scoot]

Sure thing! Let us know how it turns out

[g~scoot]

I would put that washer back in as well. I believe it is just for spacing to make sure that everything tightens up how it should. But I agree with J~scoot, I don't think this would be causing your problem. Let us know what happens with the new spring.

[BenG1990]

yea, that washer is to make sure everything tightens up

[st.pete scooter]

check the float needle in the carb see if the spring still has a good amount of tension, and reset your float hight, also try moving the needle on the carb slide down a position that will cause a slightly leaner condition, if your jet needle is adjstable.

[Gearbox Paul]

I installed a new (stock) torque spring and I also put the paper-thin washer back in on the front pulley. When I removed the old spring, I compared it to the new one. I could not tell any difference in the stiffness of either one. Nevertheless I put the new spring in and tried it out. It works great! I am able to accelerate from a dead stop at WOT and I am able to keep WOT going up hills. I don't know if it was the washer or the spring. Like I said the old and new springs looked and compressed equally, I could not tell the difference.

In any event, good call j~scoot and g~scoot. Glad to have my scooter running fine again. G-scoot, I don't know who wrote it but the Stage 1 how-to is excellent and very helpful.

Thanks for all your help.

[g~scoot]

Glad everything worked out for you!! It can be hard to tell the difference between the springs. The stiffness doesn't change much between the different ones. But that little bit makes a difference. I'm sure that both the spring and the washer had an affect on solving the problem. good to hear that the scoot is running great.