Loss of power at high rpm/speed. CVT problem?
 

Hello all,

My buggy is great at low speeds. it has new rollers, clutch springs and torque spring. Problem is, one it gets to a high rpm its as if I loose complete power until the motor slows down. I almost have to come to a complete stop then I get all my torque back and everything is fine. I am not sure what my problem is, thx in advance.

It is a carter bros 150cc gy6 with cvt trans/clutch from northern tools.

is the motor still revving up like its supposed during this time or is
the motor dieing down?

when it happens the buggy seems to quickly loose power and a fully pressed pedal barely keeps it going. The tone of the engine dies and sounds like a whirling in the back. I have to then let the cvt slow to almost a stop then the sound of the motor deepens and I regain power. Without giving it gas it dies.

May be your carburator not getting enough fuel.

Motor will sort of rev but very little if any power actually gets transmitted to wheels to make it move.

It honestly seems mechanical. In my experience with small engines it isn't acting like it isn't getting enough fuel.

The symptoms are hard to explain, but I did as best as I could with text. I could try to get a video today. It just gets to going super fast and it feels like loss of power and the "deep muffler sound" goes away and i just hear whirling back in the back from possibly cvt.

I just rode it. Going fast when the sound difference happens and the whirling starts, if you hold the pedal down you dont completely loose power. But to get the deep sound back and to get the whirling to stop you basically have to completely stop and give it little revs and wait for the deep tone to come back.

its hard to understand your problem too. the only thing I can think of is when your engine is getting to top speed your cvt, belt, etc. is starting to slip, thus the engine is no longer pulling a load so the sound of the engine changes.

That's kinda what I was thinking to Zman.

check your cvt and belt

How can I diagnose the CVT? I have pulled the cover off and done the spring replacements and nothing looked broke( or messed up). The belt looked like it was in good condition.

I drove it today and still the problem exists (no magical fix). Deep tone at start up and around 30 mph the deep tone goes away and I hear a much loader whirrling/gears spinning (with the speed of the buggy, not freely). Just to see, I held the gas all the way down and it got up to about 35-40 mph with only slight power loss. The power loss is much more noticeable at low speeds because it has a lot more low end obviously.

When this happens now, stopping does not just fix it all the time. I rode it some more and after one of the stops I made it sounded normal but then went back to the whirrling sound. I also seem to have to throttle it much more at idle to keep it from dying.

I am still stumped and frustrated. It did not use to do this and I had no issue. I am scared to take it back in the woods now or even out of my yard.

Put the rear end on jack stands and remove tires. Removing tires cuts down the vibration. You do not want it to vibrate off the stands with wide open throttle. Also do NOT use a jack. Use stands. Operate the throttle and watch that the CVT operates in the complete range. In other words the variator at WOT should be at top of pulley and clutch at bottom. When you let off gas variator should return to bottom and clutch to top.
It is difficult to understand your problem so a video would be of help.

So I didn't have time today to take the cover off and check the CVT. I had the fan cover off to tighten a loose bolt on the fan.

This first video is the current state. Today when I started it, it sounded this way. Not running very good and no continuous deep tone.

https://www.youtube.com/watch?v=odtseANgJRY

The next video is revving while under load. (there is some rattle from the roll cage, especially between 30-35 seconds)

Let me explain the sound difference for you to compare. The tone is mostly loud whirling and tinking-link sound. While driving it there is no deep done just loud whirling sort of like you can hear in the second video. With this sound change comes bad idle control/running as you can see and a significant decrease in performance. The deep tone it should have comes in intermittently at a stop while at idle/reving ( such as 18 seconds)
https://www.youtube.com/watch?v=E3vHt1eKD5A

With a load on it, and driving the deep tone is completely gone. Whirling and power loss is very evident.

Ummmm, you've got a big issue going on in that engine. Don't run it anymore. You need to figure out what has let loose. Valve hitting piston, loose wrist pin, shot main or rod bearing on the crank, or something on the starter clutch side come loose. Dat's not a good sound to say the least ...

Agree, doesn't sound good

I had a similar sound when some fans broke on the variator fan. Just might take a good look at that. But should be easily seen once you take cover off. And if you have already did that, then that's probably not it. Or maybe something came loose in one of the clutches. But should be able to tell if take cover off and just listen, and see if the noise coming from the CVT some where.
Agree also, does not sound good.
Very well could be something inside the engine.

Hah, yeah im aware its not a good sound. I am going to look at it this weekend.

Looking at this thing, how the heck would I take the engine out of the frame? Take out the seat and pull it out that way? It is a pain to bend down especially in tight spots.

me personally sounds like the valves are smacking the piston.

Put stands under the main frame (rear of seats) and pull the rear swing arm. Once separated you can pull the engine.

Sounds like the top half of motor. Take the seats out and work on it right there without taking it out.

Could be a bolt backing out of the starter clutch.

So this is results of muffler removal:

Quick 30 second run without:
https://www.youtube.com/watch?v=fP23ibNaG74

Muffler inspection:
https://www.youtube.com/watch?v=OqwIZ1hx_lU

http://i299.photobucket.com/albums/m...psi2ftoiel.jpg
http://i299.photobucket.com/albums/m...pssgcpxz69.jpg
http://i299.photobucket.com/albums/m...pspap3q2gk.jpg

In the second video the clanking noise in the muffler are the baffles rattling around. Inside most of them mufflers are 2 baffle plates one forward the other. In each baffle plate are 2) 1/2" tubes top side of 1st baffle plate and bottom side of second. As the exhaust comes into the muffler the path goes from 4" diameter to 2), 1/2" pipe then into a second 4" chamber then back down to 2), 1/2" pipe than a short distance at 4" than out the 1/2" outlet. Some of the newer mufflers have the 1 1/4" exit out the back of muffler but if it is a California model it could have a converter inside of it and that as well can cause that rattle and cause a restriction which will cause a heavy ping.

Is it supposed to rattle like that though? I don't think it did before.

No as I said something is loose either a baffle or the converter.

that's actually pretty good news for you that it was just something in the exhaust loose. Engine sounds good without it on. As Tom indicates, if whatever's broken free in the muffler blocks it up, it can cause major performance issues. additionally, the exhaust side of the valve looks like your running really rich ...which of course, having a plugged muffler would cause ...

Well I cut the muffler off the pipe and re attached it to the engine. So now its just straight piped and seems to run good, I drove it around a little but it is much to loud for my area. Plus my neighbor is a cop so we don't want any trouble!! hah!

I think my next move is going to be finding a muffler I can put on that pipe. Several of my friends can weld so that shouldn't be an issue if that's what needs to happen. Ive been looking at different mufflers and I really think those performance mufflers different companies sell for the gy6's for several hundred bucks are a complete rip off. Has anyone done something like this? I am meeting my friend after work tomorrow to search for a muffler,possibly at northern tools.

I did find this one, which is supposedly the same thing as the old one but the website may be scam. Has anyone purchased from bmi? http://www.*************/Muffler-Exha...rt_p_2975.html

website is legit but shipping is a scam (i believe BMI are the ones that bought all of yerfdogs parts when they went out of businesses) But like i said their shipping prices are a complete and utter ripoff

I love the hammerhead exhaust, it's a little pricey $250 but it is a nice piece that is stainless steel so won't rust. It is loud but I love the sound it gives the buggy. Has a nice little increase in power also. If you don't want to spend that much I would contact jersey devil on here he makes exhausts for the buggies.

I called BMI up. I found a similar exhaust and explained a few things to them. The exact part listed is what I got. They charged 15 for the shipping for the entire exhaust with muffler from Ohio to va. I didn't think that was too unreasonable. I'm gonna have to do a little tweaking but it works. I think the problem is fixed. The old muffler was not allowing enough flow through and exhaust gas was Building up in it. That explains why it ran good at the beginning. A lot of things were checked and replaced trying to figure out the cause of this but the exhaust issue was the main cause I believe. I'll check in after more riding.

Kid n me was a big help to me on this one. Pointed me right to it. Thanks guys.

15 shipping aint bad for that man but i was gonna order a stock air box for a spiderbox and it was something like 40 for the box (to much) and then like 20 for shipping (ridiculous)