Comet 780

Shepard

Here's some excellent reading material. Did you know that the Comet 780 we run used to be called the 780 Spider.


http://www.vintagesnow.com/Clutch_fi...ShopManual.pdf

BGW

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Jimme T

Thanks shep. I would like to print that

superpro56

Here is further information regarding the 780, taken from the SAE Baja catalog from 2009.

Attached Files

QDS-09BajaSAECatalog.pdf (2.91 MB, 0 views)

raydhd

I used that chart for info on 780 tuning.

Jimme T

Good info. I need to try to figure out how to get my 780 to engage sooner. It don’t engage until 2100. I would love to get it to engage a lot sooner

raydhd

I used the green springs in place of the stock yellow units and lighter rollers in place of the 108 gram items. I was rewarded with less balky engagement at a lower RPM and shift over at a lower RPM.Also note I went to the stock yamaha secondary spring set on B 1 and a wider belt all at the same time.

Shepard

OK - everyone's adjusting there 780 to engage sooner. Anyone notice any changes in the way there clutch shifts out on the top end? The higher the horsepower the heavier the weights should be IMO. The weights provide the clamping force on the belt so it doesn't slip under hard acceleration like when you hit the go fast button. The weight of the machine has a lot to do with the selection of clutch weights. I feel with a cart [weight 660lbs] that if you go with lighter clutch weights you'll risk slip your belt.

Jimme T

I’m not sure about that. This clutch is still pretty new to me. I haven’t messed with it at all since I got it. When I installed the vanguard I went back to the stock driven spring. Set it to b3. I did swap out the belt to a wider extreme duty belt.
It’s a little annoying though because my cart idles at 1100 and it don’t even start to move until it hits 2100rpm. When it does engage it is super smooth I’d just like for it to engage sooner

raydhd

I hate to disagree with Shepard but after a lot of running with the green spring lighter roller weight set up one thing is very clear. Once the clutch shifts over it will stay locked in high as long as your rpms do not fall below where the shift back rpms are. So for example in my case once I cross 3200 rpms the clutch shifts over and I can drop back all the way back to 2200 rpms and the clutch will stay locked in high. Note the shift over and shift back #'s are about 1200 rpms different. I have run with 700 lbs of people on board running into a strong headwind and the rpm/speed ratio stays the same. I might have to use more throttle to maintain the speed but the rpm/speed ratio does not change.I have tried stomping the throttle to make the belt slip once it is locked in and even with the heavy load aboard it does not.In some ways it is like when there is no belt in the clutch and it shifts over it takes some doing to get it to return.I have run most of the season with this set up and found out what it does and does not do.

Shepard

Thanks Ray - I needed to hear that it didn't affect the high end shift. I'm learning as I go. If your setup doesn't slip -- that's the test. I'm concerned about the slippage on the top end with hard acceleration - like 2500 to 4500 rpm in a heartbeat. The model 780 I use is for a heavy machine to start with.