Detuning the 2012 Sherco ST290

[pmccand]

The throttle on the 2012 is WAAAY too scary.  Comes on way too hard with small throttle inputs.  What methods are there to calm this beast down?  

1) What alternatives are there to slow the throttle cable twist grip?  I use the Domino side pull (slow) trials version now.

2) Changes to timing?  Advance or retard?

3) Changes to cylinder compression or gasket thickness?

4) Changes to ignition mapping available?

5) Porting mods?

6) Reed mods?

7) Cylinder alternatives? Is there a 250 piston/barrel available that will fit on the 290 engine?

I am 65 years old and a expert-level rider in my previous life, so don't give me this "You gotta train harder and get used to it" approach.  I don't want to shoot up and over 15' vertical steps...I just want to slow things up a bit. 

Edited 3 hours ago by pmccand

[Tr1AL]

Sell it and buy a 250 is the least amount of messing about.

[RonH]

Hey pmcand, I had the exact same problem with my bike. I did three things to help calm my 2023 Gasgas down.

1st - I installed a flywheel weight (it helped some)

2nd - I installed a 1mm head spacer to lower the compression. (It helped a little more, it’s much easier to start too)

3rd - I modified the throttle tube. (This helped a great deal)

Regarding the throttle tube, there is a cam where the cable runs around the end of the tube. Both fast and slow throttles have them. I had tried a slow throttle but the change was very minimal so I bought an aluminum one (slow again) from G2 Ergonomics. It also produced no noticeable change that would work for me. I lived with it for two years until I had the idea of modifying the tube. I simply removed the throttle tube and used a Dremel to ease the cam to a more linear pull. It took me about five minutes to grind it down. I have a photo showing how I modified it in the link below. I put a dashed line in to show what material to remove with a before and after shot. The change from a “scary” throttle response was exactly what I needed. It costs nothing to modify it compared to the other mods I listed. I guarantee this, modifying the tube, will get you what you want. Feel free to ask questions. Good luck!

https://flic.kr/p/2rPhx56

Oh, we happen to be the same age. When you and I were riding trials in the 70s the throttles were linear and smooth. The new age throttles have the cam we didn’t back then. That quick throttle caused me a serious crash with a punctured lung and six broken ribs. I know exactly what you’re going through.

Let me know if the link doesn’t work.

Edited 1 hour ago by RonH

[konrad]

Two cheap, easy, reversible changes:

Retard ignition timing.

Increase squish clearance to ~2mm via additional base gaskets.

 

Additionally, if you are good with the clutch, a flywheel weigh can help slow things down.  

A company called G2 makes a cammed throttle tube called the Tamer: https://www.g2ergo.com/shop/g2-trials-throttle-tube-progressive-rate-sherco/