Comet 94c driven adjustment

[roodesign]

Has anyone adjusted their 90d driven pulleys? I am asking because I feel that on my build (see www.roopod.com) that the cvt is not downshifting enough on big hills...I have 9 of the heaviest weight pucks and the lightest spring in the 94c driver pulley, just wondering if anyone has fooled with lightening up the spring predload on the 90d...which should make it downshift easier. right now on a steepish but not crazy hill with me and the missus on board we are lucky to keep going 30mph...but at that speed the engine rpm is 2500-2600 and according to my specs that's closer to 10hp at the engine speed. I think that the cvt should downshift low enough to have the engine going full out at 3600RPM (and 13hp)...any thoughts? also, it just makes sense...by putting all the puck weight in I need to give the 90d more power to overpower all that puck weight (cvt engages at 1450 RPM which is just fine...for starting out) but I think it does make the cvt shift to a higher gear than I want generally...thanks for your thoughts you cvt people!

[albertaphil]

Hey Roo,

Completely awesome build...a great concept, and I congratulate you for your effort and ingenuity.

As for your question...yes, you can change out springs on the 90D to tune it to your engine torque. I can understand your frustration with the setup as it is now. What is your setup geared to top out at? That is, with the engine at 3600RPM and your Comet 94C-90D in high ratio (0.78 overdrive, or close to that, I think) how many MPH is your wheel going?

Also, can you watch your comet when you're driving to see where the belt is running in the 90D?

And are you positive that you have the right distance between the 94C and 90D? If they are too far apart, it will force your belt to ride farther down on your 90D, forcing a faster ratio.

Also, all the pucks and the light spring in the 94C may be your problem too. As I understand it, to get a slower ratio, your drive belt will have to ride lower into your 94C (within limits, of course, so as not to slip) to be able to ride high enough on the 90D to provide the low gear ratio. But then, that whole business is a balancing act between the 94C and 90D...it's all guess and test.

Phil

[DieselFly]

Hey Roo

Here is a like for a CVT tunning manual I had posted in CVT info http://forums.bajasae.net/forum/uploads ... ndbook.zip
It has all of the info you will need. The problem with most CVTs are they are tuned for two stroke RPMs.

[roodesign]

wow, that is some book!
will take me some time to digest all of that! The clutches in there make the 94c look pretty primitive!
Thanks for the link...I will post back when I decide what I want to try first...probably either lighten up on my pucks a bit, or increase the spring preload in the 90d driven...hmm

Thanks again

[DieselFly]

If you have the drive clutch engaging at the RPM you want then go after the driven to control the up shift. I would think you want to start your shift out at 2800-3000rpm to get best torque. I'm running a CVTech setup on my bike that was built for SAE mini baja. This unit is designed for small rear wheels and never fully shifts so I'm running around at 3000rpm most of the time but this is where the engine is balanced to run. Crank up the preload but I think you will need a stronger spring to raise your shift point enought. once I pass about 20 mph when I start to shift then sit at about 3000rpm all the way to top speed which is about 74mph it would be nice to get to 3600rpm as I would gain 4 hp and might get a couple of mph more out of the heap. The thing about CVT's is you are setting your power output not rpm and power togeather when you adjust the throttle kind of like an airplane with a constant speed prop. The cool thing is the power is there right now as the engine does not need to spool up. I was thinking a Morgan three wheeler knock off with a V twin Punsun sticking out the front for my next project with the kids.

Sean

[dieselbikin]

Check out https://www.dieselbikeforum.com/view ... hilit=+94c

I’ve been experimenting with my 94C/90D combo for several years now and I ran into a similar problem. To the best of my knowledge there are no alternate springs, ramps, or adjustments for the 90D so the tuning will have to be done on the driver and final drive ratio.

You are running a heavy vehicle with an engine that builds strong torque at a slow rate, so I don’t recommend going with fewer or lighter pucks. The heavier pucks squeeze the belt harder to prevent slippage and shift slower. You could try the black spring, but my experience is that you’ll just end up with more belt slippage. In other words stick with 9x59g pucks and the pink spring.

I’m confident the primary problem is a high final drive ratio. For example, I have a 10hp engine, 600lbs gross vehicle weight, and a 24” tire. I initially had a 3.90 final drive and tried literally hundreds of puck/spring combos with poor results. Stepping down to 4.60 final drive resulted in a huge leap in performance. Although I’ve run a final as low final drive as low as 5.45, my best results were with a 4.60 final. The Comet can't compensate for a high final drive ratio.

With 10hp and 600 lbs GVW , on a fairly level test course, I hit a top speed of 56 MPH and average 50 MPH. On my alternate test course which has a fairly long and steep hill my speed eventually drops to 35 MPH. In comparison you’re dealing with twice the GVW with only 30% more power, so 30 MPH up a steep hill is not so bad. However, I think with the proper final drive ratio you’ll see a significant increase in performance. Hope this helps.

[toyotaracer9]

Hey Roo ,

I watched your vid a few weeks back , that is a very nice piece of art . As far as the CVT issue goes , have you tried to adjust the throttle to make it rev to maybe 4k ? not saying you need to run it that high just use it to get some more torque when climbing , also you may need to adjust the rack screw to get a little more fuel when climbing . Is it smoking when its loaded ?