Questions regarding CVT and mods

OK - I still need to modify my little Burgman 400 a bit but I need to really squeeze the budget too.

I can modify the transmission at a cost of $50 - $550. Even though I've researched on another forum I belong to, I'm still confused on what difference a different spring would make in the clutch housing, etc. This all involves a CVT transmission. What the problem is: I'm getting a bad shuddering when I go through school zones (since I can't downshift).

Is there anyone out there that has a CVT in their machine who can give me some simple, yet concise answers to the most cost effective mods that won't end up eating up the mileage I get now? The J. Costa variator is great, but it can eat your mileage 10%.

Thanks,


Bruce

One quick question, is it in warranty? If so make a dealer address the shuddering when you slow down to school zone speeds.

Otherwise, ensure that the correct stock setup on the CVT is in spec before you tweak it with hard parts. The CVT changes ratios with a variable drive mechanism that is centrifugally triggered. In other words, as you speed up the ratio gears up, reducing engine speed at higher travelling speed. When you slow down the mechanism is supposed to gear down, preventing lugging that you describe. The spring tension controls how agressive or relaxed the shifting is. if it gears up very quickly, then it will stay in the higher gear position longer as you slow down. Conversely if it is slow to gear up, then it will be quick to gear down.

In a nutshell, the gear ratio is determined by the real wheel rotational speed, and governed by the spring tension. Get that spring out of spec and you will either be lugging or racing the engine.

I have no idea what a 'J. Coster variator' is, but if it fools with the shifting rate of the variable transmission it might be contributing to your issue.

Long out of warranty (I'm the third and longest owner).

You mention spring - there is a spring in the clutch housing that I can change out. I can go to a stiffer spring but I'm not sure what it could accomplish. I don't believe, in fact, I'm sure there are not individual springs for the clutch shoes that are changeable - just replaceable with the stock springs.

The main gotcha that I can see is that the clutch is to start engaging around 2,800 rpms according to specs.

However, trying to go through a school zone (and I work at an elementary school so I'm very experienced with these) drops the RPMs to between 1,500 and 3,000 RPMs, depending on whether I've hit 20 mph yet. At 20 mph and with forward movement, I'm hitting around 2,300+ RPMs - this puts the clutch into a tizzy because it wants to engage/disengage constantly. (I wonder if Japan has school zones - if not, then their engineers have no experience with this.) Needless to say, I'm on and off the throttle and brakes trying to keep Mr. Leo from giving me a ticket and yet keep speed up.

A stiffer spring in the clutch might help change things, but I'm not sure (OK, very confused) on how it could change/help.

The J. Costa I mentioned speeds up the lower speed RPMS for quicker take off/shorter 0 - 60 times (shaves about 2 seconds off) but causes a 10+% mileage hit.

My wife has been riding scooters and all of them have had some form of CVT. There is talk on the Vespa forums about replacing the variator to increase performance (probably at a cost of reduced mpg, as you mentioned). I do remember a replacement schedule of the belt on her Aprilia scooter of about 8000 miles - have you checked to see what maintenance is required on the Burg?

I'm still confused by how the durn thing works - on her MP3 the RPM varies maybe 300-400 to go between 40 and 70 mph (always right around 5000).

Start by putting a belt on it
The width of the belt is what the pulleys are set up to grab if its all
factory/try that before anything
rworm

rworm said:

Start by putting a belt on it
The width of the belt is what the pulleys are set up to grab if its all
factory/try that before anything
rworm

Click to expand...

+1 in a big way. Make sure that all of the moving parts on the pulleys are clean and able to move.

The RPMs should stay above that clutch engagement zone by the pulleys changing ratios as you slow down. It sounds from your description as though it does not change down well while under way.

I would suggest consulting a service manual, and getting the mechanism working stock before any modifications are deployed.