Despite this being a genuine Mikuni:
It isn’t holding up too well, considering there are less than 75 hours on it. This diaphragm had gas behind it.
I really like the 106 gram weights with the green springs under all conditions except going up steeper hills. The stock GX390 just doesn’t have the torque to handle the lower RPM operation of the clutch now. Since I already have the 91 gram weights, I thought I should see how they work before possibly going back to the yellow springs.
I was only able to drive around the neighborhood once and there is definitely an improvement on the hills. Tomorrow will be a longer drive to get a better idea on how the combination works out.
So the last few times I have driven the route where I can go 20mph+ for an extended period of time, I have had the problem of the engine dying. I wind up letting the engine sit for a few minutes and then I have to use the choke to get it started again. Fortunately this occurs on my way home and I’m only about one mile from the house. When I get home, I pull the carb to find debris in the bottom of the fuel bowl. After the first time it happened, I replaced both fuel filters. When it happened the 2nd time, I knew the debris wasn’t coming in through the gas line.
I find that there is a vent on the side of this carb. I added a line and installed a filter that I had used on my dirt bikes for the same purpose. I added a filter to the over flow line just because I have several of them. Another ride or two will tell me if this takes care of the problem.
Removed a little bit of material on the CVTech driven clutch and got the sheaves a little closer together. Not a huge difference but a lot of little things add up.
It turns out there are a couple of easy ways to tell if you just received an genuine Comet 780 clutch that was made in the U.S. or a cheap Chinese copy.
A real Comet should come in a box with some paperwork and a couple of parts:
My CVC (Chinese Vegas Carts) came wrapped in bubblewrap.
If you flip the clutch over, on the back of the fixed sheave there should be some numbers cast into the sheave. Here is the back of the Comet:
And here is the back of the CVC:
One other thing you can do to check without touching a thing, the moveable sheave has three tabs that can be seen from the outside of the clutch. Here is the Comet:
This is the worn out CVC moveable sheave that I replaced. Notice no tabs on the outside edge:
If you really want to dig in and start taking things apart, the next thing you can check is what type of threads the clutch is set-up for. If you remove the dome cover, the Comet will have standard threads, in this case 1/4-20. The bolts holding down the pins for the roller weights are the same. My CVC was threaded with metric M6 threads and bolts.
Also with the dome cover removed, you can take a look at the locking plates that are holding the weights in place. Here the Comet has the locking plate folded up:
And then here is the CVC with the flat locking plate.
The Comet moveable sheave will also have some numbers cast into it. This also shows the tabs I mentioned before:
No numbers whatsoever on the CVC moveable sheave:
If you keep going and take the weights off, there is a difference there as well. The weights are designed differently. The CVC on the left has metal guides integrated into the arms of the weight. The Comet weight is on the right. Plastic spacers fit into those larger openings as seen below. So you have metal-on-metal vs. plastic-on-metal.
The first Comet 780 clutch I ordered from eBay arrived damaged.
But the second one showed up in great shape.
I am going to try the 106 gram weights with the green springs. So pretty with all the different colors.
Green springs in.
Despite buying my clutch from a reputable place, it is looking like I have a Chinese knock-off.
I noticed a week or two ago that the moveable sheave of my clutch was wobbling quite a bit. With the engine off, if I grabbed the sheave at the 9 and 3 o’clock position, I could rock the sheave side to side. I ordered a new sheave from beltpalace.com along with some different weights and springs to test out.
My back is still sore and I didn’t want push it by pulling the engine out of the cart. So I dropped the swingarm instead:
The first thing I noticed was that the locking plates weren’t bent over on the bolts holding the roller arms in place.
This is how I pulled the spider off the hub. The 2nd thing that was strange was that I had to use metric M6 bolts to thread into the spider. Glad I still keep a container full of bolts from the Japanese dirt bikes I’ve owned over the ears. I thought that Comet was a U.S. company and expected them to use standard threads/bolts.
And this is how sloppy the hub and moveable sheave are:
The bushings that the guide pins ride in were well worn. The scary thing is that this clutch has less than 75 hours on it!
So finally on to getting the clutch put back together. The hub bushing and casting around the bushing were thicker on the new sheave compared to the original:
I tried to thread the M6 bolts into the new sheave and they wouldn’t go. Turns out the new hub is threaded for 1/4″ – 20 threads. But it wasn’t until I tried to slide the new sheave over the hub that I that it became painfully obvious that this wasn’t going to be an easy project. The new sheave didn’t come close to sliding over the hub, the ID of the bushing was too small.
So I sat back and tried to figure out what to do. The evidence certainly pointed to my clutch being a cheap copy – it wore out very quickly, all the threads were metric and the lock tabs weren’t bent over. I was feeling pretty confident that beltpalace.com was selling OEM parts or at least OEM spec parts. The springs and weights were all bagged as Comet parts.
And if the new sheave wasn’t made by Comet, it was at least a better copy with standard threads. I finally decided to make this sheave work. I doubted I could find a knock-off sheave that would fit my clutch and it wouldn’t be worth it as it would wear out quickly as well. After about an hour of working on it, I finally got the new sheave to fit over the hub. I had to run out to the hardware store to get three 1/4″-20 bolts. And after installing the springs and weights, I made sure to bend over the locking tabs.
I also had to take some material off the sheave so it would slide up high enough and not interfere with the spider.
Now I just need to get the clutch put back on the engine.