150cc GY6 scooter lost top speed

[Battercake]

For a couple months now, I've been trying to pin down why my scooter, which would usually go up to 62 MPH if I so desired, will usually only go 51 now. This problem began at the same time I had to replace the carburetor diaphragm, so naturally the assumption was that something was affected by that, and a wild goose chase ensued. But this week I had the cover off the CVT and noticed grooves in the variator pulley. I wouldn't have been concerned had they been near the top, but these grooves are only about two-thirds of the way up on the pulley.

I assume my next step is gonna be to remove the variator pulley and see what's going on behind it. Any advice is appreciated!

[sc00ter]

How many miles do you have on the Wolf? What miles are the transmission service suggested? If it was sudden I would check:
Carb diaphragm is it has one. My Buddy 125 has one and they get pinholes in them and make the scoot run weird. Then ensure the new one is seated correctly.
Valve check. My scooter stays pretty set between valve checks. Exhaust can be a tad snug between checks but it'll still run good.
Spark plug check, since you should pull it when checking valves. Also, plug color can tell you how the motor is running. Ashy white=lean. Dark black/wet=rich.
Exhaust for leaks. Plug the end with a damp rag while running. It should stall. Also check for obstruction, kinked pipe or carbon build up.
I just rebuilt my transmission at 8000 miles. I did the following:
New belt.
New V-slides.
New Rollers. Old ones looked good, no major flat spots.
Re-grease torque driver, inspect springs, gently sand glaze from clutch shoes. All good.
Clean bell.
New reduction box oil.
Finally, is you engine oil at the correct level? Over-filled can cause power loss.
My Genuine Buddy 125 has the best health care a scooter can have. I'm very meticulous about services and keeping it clean. But things will fail without warning.
Keep us posted on your progress.

[Battercake]

Originally Posted by sc00ter

How many miles do you have on the Wolf? What miles are the transmission service suggested? If it was sudden I would check:
Carb diaphragm is it has one. My Buddy 125 has one and they get pinholes in them and make the scoot run weird. Then ensure the new one is seated correctly.
Valve check. My scooter stays pretty set between valve checks. Exhaust can be a tad snug between checks but it'll still run good.
Spark plug check, since you should pull it when checking valves. Also, plug color can tell you how the motor is running. Ashy white=lean. Dark black/wet=rich.
Exhaust for leaks. Plug the end with a damp rag while running. It should stall. Also check for obstruction, kinked pipe or carbon build up.
I just rebuilt my transmission at 8000 miles. I did the following:
New belt.
New V-slides.
New Rollers. Old ones looked good, no major flat spots.
Re-grease torque driver, inspect springs, gently sand glaze from clutch shoes. All good.
Clean bell.
New reduction box oil.
Finally, is you engine oil at the correct level? Over-filled can cause power loss.
My Genuine Buddy 125 has the best health care a scooter can have. I'm very meticulous about services and keeping it clean. But things will fail without warning.
Keep us posted on your progress.

That's a lot of questions, but I appreciate your thoroughness. I'll answer what I can.

The Wolf has 6400 actual miles. I've misplaced the manual at the moment. The diaphragm is brand new and perfectly seated. I just checked the valves and they were exactly as you said - the exhaust had worked itself a little tight but they weren't bad. The spark plug looks normal grey, not white or dark. The entire exhaust has been fiddled with repeatedly with no change in performance. The belt is still original with no noticable loss of width or fraying. Engine oil and gear oil have both been regularly changed and are at proper levels.

I have not torn into the variator or clutch because I wanted to solve one problem at a time and until this week I didn't think that might be causing this one.

[sc00ter]

Belts are usually good for around 8000 miles, some will say 10,000. Meansuring a belt is a PITA, so if it's in question just replace it. I save the old belt as a back-up and write the mileage on the old belt with a Sharpie. Never hurts to have a "Oh crap!" spare for emergencies.

You could do the Sharpie line trick on the variator and see if its fully engaging, but then again, if the scooter is restricting itself then the line trick might not go according to plan. If it did the power loss suddenly I would guess going into the transmission and ensuring the V-slides aren't broken/worn/hanging up. And, peek at the rollers for flat spots. It's slightly possible a torque spring may be worn out but at 6000 miles I doubt it. The 3 clutch springs will break sometimes but again, rare at your 6000 miles. I will say this, burnouts will tear a CVT up! So if you do them every now and then like my dumb butt then its possible its trans related.

I hate those stupid diaphragm carbs. Every time I go into one I end up going back into it again! My diaphragm seating skills suck!

Nothing else is popping in my head at the moment.....
Again, keep us posted!

[Battercake]

I looked in my journal and noted that this problem surfaced at 3760 actual miles. I just did the Sharpie diagnostic, and it looks like I've got a good 6 millimeters of pulley going to waste here. I'm too busy this week to take the variator off, but I will when I can and check the rollers and ramps. I guess I've been running the piss out of this thing thinking the problem lay elsewhere.

[sc00ter]

Slightly off subject. I had a Suzuki Burgman 200. It started to slowly suffer a speed loss and would get a bit wonky on the top end. I pulled it apart and found noticeable wear on the variator faces at around 3000 miles, both fixed and the side that contains the rollers. Suzuki wanted mad dollars for a new assembly so I found a used assembly on ebay. Gently used ebay variator suffered the same fate at around 3000 miles as the original one. Turns out the variator faces were not hardened correctly. We have a metals lab at my job and I compared the drive face hardness (or rockwell rating) to a found technical spec from Yamaha. I luckily found a Malossi variator that worked great, I just had to replace the fixed face at every 3000 miles. Thankfully Suzuki lowed the price of that wear item part. Maybe they knew of the problem? That scooter made me hate Suzuki and I'll never buy one of their products again. Impress me with the base/entry level model before I buy a high end model.

I honestly suspect something transmission related as mentioned above. So if everything looks good then you may wan't to consider a performance variator.

[Battercake]

Still no luck solving the problem. I honestly feel like I've put too much time, money, and effort into this already and I'm close to taking a loss and making it someone else's problem at this point. But here's the latest update nonetheless:

Variator was just replaced with new OE type. A crack in the intake duct leading to the carb was repaired. Carb was completely swapped out again. The end result is that nothing has changed, for better or for worse. I still can't get it to go faster than 46 actual MPH, and it occasionally decides to idle much higher than it should.

What else is there left to try? Why am I having such a rare problem that I've been unable to find anything that works?

[sc00ter]

Air leak? Start the scooter and slowly spray some short blast of flammable carb cleaner or equal around the intake and other locations. The motor should not fluctuate in idle. Don't be dumb like me and use a whole can of red Brakleen only to realize the red can is NON-flammable and the green can IS highly flammable!

Nothing else is popping in my head. Without physically seeing it trouble shooting is limited. Otherwise I assume all the transmission parts were in spec?

[Battercake]

Originally Posted by sc00ter

Air leak? Start the scooter and slowly spray some short blast of flammable carb cleaner or equal around the intake and other locations. The motor should not fluctuate in idle. Don't be dumb like me and use a whole can of red Brakleen only to realize the red can is NON-flammable and the green can IS highly flammable!

Nothing else is popping in my head. Without physically seeing it trouble shooting is limited. Otherwise I assume all the transmission parts were in spec?

The only thing I'm finding is a very slight exhaust leak, just enough to feel it with my hand. Could that mean anything?

[sc00ter]

You could have a electric choke issue. It could be partially stuck. I used to be big into Yamaha Zuma 2 strokes. First thing we did, even on a stock one, was bypass the electric choke and put in a manual flip switch style one. The electric choke that comes on them is temperamental and the manual bypass conversion took chasing weird idle/running issues out of the picture entirely.

An exhaust leak on a 4 stroke isn't as serious as on a 2 stroke. But still, its a leak and your'e loosing some back pressure. I see dummies in my 'hood ride a 4 stroke scooter WITHOUT an exhaust. They would rather buy malt liquor and drugs then fix their transportation. The no muffler will eventually burn up the valves in the head because the exhaust, if installed, would have pulled the heat from the head/cylinder assembly. Another thing:

I also see people remove the emission hose that runs from the air filter housing to the exhaust, thinking its a restriction device. Some better scooters that actually meet emissions have a catalytic converter in the muffler, and that hose actually helps supply air that helps heat the cat allowing it to open and flow correctly. Bypass the emission hose and the cat never gets hot enough to properly flow, causing a restriction. My old Zuma 125 had a catalytic converter and it took about a block before it would heat up enough to fully flow. I also recall the Burgman 200 had one, and it kept breaking loose inside the muffler making the scooter run funny. I discovered the exhaust system had a 5 year warranty and had Suzuki replace it 7 times before I gave the Burgman away. That exhaust was a dumb design.

[Battercake]

Originally Posted by sc00ter

You could have a electric choke issue. It could be partially stuck. I used to be big into Yamaha Zuma 2 strokes. First thing we did, even on a stock one, was bypass the electric choke and put in a manual flip switch style one. The electric choke that comes on them is temperamental and the manual bypass conversion took chasing weird idle/running issues out of the picture entirely.

An exhaust leak on a 4 stroke isn't as serious as on a 2 stroke. But still, its a leak and your'e loosing some back pressure. I see dummies in my 'hood ride a 4 stroke scooter WITHOUT an exhaust. They would rather buy malt liquor and drugs then fix their transportation. The no muffler will eventually burn up the valves in the head because the exhaust, if installed, would have pulled the heat from the head/cylinder assembly. Another thing:

I also see people remove the emission hose that runs from the air filter housing to the exhaust, thinking its a restriction device. Some better scooters that actually meet emissions have a catalytic converter in the muffler, and that hose actually helps supply air that helps heat the cat allowing it to open and flow correctly. Bypass the emission hose and the cat never gets hot enough to properly flow, causing a restriction. My old Zuma 125 had a catalytic converter and it took about a block before it would heat up enough to fully flow. I also recall the Burgman 200 had one, and it kept breaking loose inside the muffler making the scooter run funny. I discovered the exhaust system had a 5 year warranty and had Suzuki replace it 7 times before I gave the Burgman away. That exhaust was a dumb design.

I did remove something quite a while back because the tube coming from the head of the engine broke spontaneously. This happened about 1100 miles before I started having this problem though. The internal components of the muffler all disintegrated at some point several months ago and I removed them. Removing them caused no change, but could their disintegration have caused it?

[Battercake]

The hose from the valve cover back to the air box is intact. The last two times I've changed the oil the screen has been rather clean. If replacing and upgrading the exhaust will fix my problem, I'm willing to spend the money, but I've thrown so much money at this already and I've gotten nowhere.

To go back to where this all started, my carburetor diaphragm failed back in January. It would idle, but die as soon as I opened the throttle enough to engage the clutch. That was a simple problem with a simple solution.

But once I took it for a test ride, I noticed it wouldn't go full speed and I've spent the last 3000 miles on a wild goose chase to figure out why. I've replaced the spark plug twice, the ignition coil, the CDI, the entire carburetor twice, the back tire, the petcock, the variator, tried running with the air filter off, tried removing the evap system, reconnected that and tried running with the fuel cap off, and nothing has gotten me any closer to unlocking the top quarter of this machine's ability again.

[sc00ter]

You replaced the whole carb, as in the complete carb assembly? I always keep a known good carb on hand just to help trouble shoot fueling issues. I also keep a few other known good parts on hand for lazy diagnostics.
CDI.
Stator assembly.
Coil.
Only other things I can think of is:

The vacuum hose that opens the petcock might not be seated correctly/clogged or clasping. Rotted/cracked looking? Petcocks themselves rarely fail. I do have a spare on hand though.

Fuel filter obstruction?

Fuel Hose clasping? Can you pinch it shut easily with your fingers? Rotted/cracked?

Is there a earth ground that's disconnected? Mine goes to the lower transmission case bolt hole and if I forget to reconnect it my scoot runs weird.

My brain still says choke issue but if you changed out the whole carb.......

Is the power wire to the electric choke connected? Is it getting power to the choke?

If the scoot was fine before the diaphragm change, then you changed the whole carb, I'm running out of ideas????

Stator might be failing. YouTube has a few good how-to videos on checking the output. If they start to fail they usually affect the top end first, at least on my stator failures. Others have them not hold idle and be hard(er) to start.

Keep us posted please!

[Battercake]

I also replaced the fuel filter a few weeks ago, and today I replaced the entire fuel line. No change. I've replaced the petcock and then went back to the original. I've also tried bypassing it and using manual shutoff valve. No change. The wire to the choke is connected. Maybe I can do a voltage check?

[sc00ter]

Are you sure you have the throttle cable ran correctly, and the slide is opening fully when you twist the throttle wide open? I've seen throttle cables ran wrong before, usually not seated correctly. There is also a barrel adjuster to take out the slack under the throttle. The throttle should only have a tiny bit of slack at idle.

So make sure the slide is completely opening and there is no excess slack in the throttle. I'll keep thinking......