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 December 29, 2025Dec 29 by pmccand

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

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 December 29, 2025Dec 29 by RonH

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/

Edited December 29, 2025Dec 29 by konrad

2 hours ago, konrad said:

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/

Adding 2mm to base gaskets will also change the port timing slightly, whereas increasing the head gasket will not.  Is it your recommendation to lower compression AND change port timing by using a base gasket, or just to lower compression by using a head gasket?

 

2 hours ago, RonH said:

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.

I like your suggestion with the cam.  Thank you for your help.

 

38 minutes ago, pmccand said:

Adding 2mm to base gaskets will also change the port timing slightly, whereas increasing the head gasket will not.  Is it your recommendation to lower compression AND change port timing by using a base gasket, or just to lower compression by using a head gasket?

 

Not suggesting 2mm more base gasket.  Recommending 2mm (or any other value your experiments show to be helpful) total squish clearance.  The squish may already be on the order of 1.2mm.  Yes, it will change the port timing, but I have not seen that small change cause negative side effects.  If anything, it makes the bike slightly easier to kick.  It's also easily reversible. 

The Sherco uses o-ring seals for the head/cylinder interface, which I would leave alone.  Machining the head is another, less reversible, route. 

Increasing the combustion chamber's “blend radius” is another way to soften the hit. I touch on that here: https://www.ossa-efi.com/home/engine/heads 

Also, a bit on reeds here: https://www.ossa-efi.com/home/engine/reed-valves

I'm going to retract my G2 idea based on RonH's experience.  I now see it's intended to be a blend of the slow and fast rates.  Whereas Ron's idea for a “slower than slow” tube is more what you need.  

1 hour ago, konrad said:

Not suggesting 2mm more base gasket.  Recommending 2mm (or any other value your experiments show to be helpful) total squish clearance.  The squish may already be on the order of 1.2mm.  Yes, it will change the port timing, but I have not seen that small change cause negative side effects.  If anything, it makes the bike slightly easier to kick.  It's also easily reversible. 

The Sherco uses o-ring seals for the head/cylinder interface, which I would leave alone.  Machining the head is another, less reversible, route. 

Increasing the combustion chamber's “blend radius” is another way to soften the hit. I touch on that here: https://www.ossa-efi.com/home/engine/heads 

Also, a bit on reeds here: https://www.ossa-efi.com/home/engine/reed-valves

I'm going to retract my G2 idea based on RonH's experience.  I now see it's intended to be a blend of the slow and fast rates.  Whereas Ron's idea for a “slower than slow” tube is more what you need.  

FANTASTIC web site link on the OSSA.  Simply FANTASTIC!  

On 12/29/2025 at 5:18 PM, pmccand said:

I like your suggestion with the cam.  Thank you for your help.

 

Worth checking your throttle tube again to see if it really is the slow version as the black anodized aluminium (aluminum) versions have no cam/ramp and dia should be only slightly larger than your handlebars. An extra carb slide return spring will help avoiding whisky throttle, but at the expense of sensitive throttle adjustments. If you have a coloured S3 cyl head fitted then low compression insert available. Believe the 2012 was the first year of the external stator sensor so adjusting stator plate wont help retard the timing. Ultimately no substitution for time on the pegs. Rick Agans has a wealth of Sherco experience so try to reach out to him.

Shouldn't be too hard to find the same 250 top end on eBay, literally only difference between the 250 & 290 is piston, cylinder & head. 

No head gaskets on Shercos, there are o-rings around the studs on top of the cylinder & a inner & outer o-ring in the head

Not sure how easy it is to fit a flywheel weight as the ignition cover is really close to the flywheel 

12 hours ago, tony27 said:

Shouldn't be too hard to find the same 250 top end on eBay, literally only difference between the 250 & 290 is piston, cylinder & head. 

No head gaskets on Shercos, there are o-rings around the studs on top of the cylinder & a inner & outer o-ring in the head

Not sure how easy it is to fit a flywheel weight as the ignition cover is really close to the flywheel 

Good points. I'll give eBay a go.  Can't imagine I would find anything like that there, given the scarcity of the bike.

 

19 hours ago, tony27 said:

Shouldn't be too hard to find the same 250 top end on eBay, literally only difference between the 250 & 290 is piston, cylinder & head. 

No head gaskets on Shercos, there are o-rings around the studs on top of the cylinder & a inner & outer o-ring in the head

Not sure how easy it is to fit a flywheel weight as the ignition cover is really close to the flywheel 

Flywheel weight comes in a kit with spacer ring and longer ign cover screws, but flywheel puller needed to insert the captive nuts to attach the weight.