Need suggestions for more bottom hit

[preston953]

I have a 2018 250 XC with a FMF Gnarly pipe and I'm a little disappointed with the bottom end response. Has anyone experimented with a Smart Carb on their GG bike? I'm also open to moving around the setting for the exhaust valve or getting a head mod. I just need/want a little more hit off the bottom to loft the front wheel over logs, ditches and trail obstacles.

 

[TGM_OFFROAD]

I have a 2018 250 XC with a FMF Gnarly pipe and I'm a little disappointed with the bottom end response. Has anyone experimented with a Smart Carb on their GG bike? I'm also open to moving around the setting for the exhaust valve or getting a head mod. I just need/want a little more hit off the bottom to loft the front wheel over logs, ditches and trail obstacles.

Start with playing with the pv adjuster since thats free. The Rk tek gave my 300 more power across the board. Or your other option is buying a 300 top end and bolting it on.

 

[frankinberg]

Put a 51 tooth rear sproket set the squish band play with different jetting I like jd jet kit and check power valve setting it will rip then

 

[Zman]

I agree with the previous comments and will add that the STIC metering block will make a great change across the board.

 

[preston953]

Thanks for the suggestions gentlemen, much appreciated.

 

[preston953]

Since I want a little more bottom hit. When I adjust the exhaust valve, I'll want to decrease the pre-load so it opens sooner, correct? So that will be a counter-clockwise adjustment (lefty loosy). What is the stock setting, 2 turns out from closed? What is the suggested turn increments, 1/4, 1/2 or a full turn?

 

[TGM_OFFROAD]

Since I want a little more bottom hit. When I adjust the exhaust valve, I'll want to decrease the pre-load so it opens sooner, correct? So that will be a counter-clockwise adjustment (lefty loosy). What is the stock setting, 2 turns out from closed? What is the suggested turn increments, 1/4, 1/2 or a full turn?

Stock is 2 turns out from full stop. Technically in is supposed to give more bottom end grunt but if you are looking for more of a quicker revving bike then go out. Out makes the pv open sooner. My recommendation is to play with it and see what you prefer.

 

[Jakobi]

Keeping the PV closed will help with off idle power.. If it opens too soon you'll have a more aggressive delivery, which is not necessarily 'more'..

What gearing do you have now?

What jetting do you have?

My experience with these engines is..

13-50/51 gearing
head modification (squish and comp ratio)
quick pull G2 throttle
jetted with Keihin needle for response and delivery (has varied on each engine).

I have used Lectrons and Smart Carbs.. I don't think they offer value for money. They work well enough, but aren't a magic product either. Still require some adjustment and still aren't 'perfect' persay.

The above list I do before I worry about anything else.

 

[(F5)]

For tree roots, throttle response is key. With the wrong needle, in particular the stock needle it will be bogging for long enough for response to be soggy.

 

[preston953]

Thanks again folks. You've given me some excellent starting points, along with good ideas to develop a plan. Even though I haven't specifically said it in this thread I really do like the bike and I'm looking to tailor it's traits to work for me.

 

[reidy]

Another old mod is to take 100mm or so off the silencer or to buy yourself a shorty for the bike. Shorter silencer will give you better throttle response and bottom end snap but with the sacrifice of some top end. But given the type of slow technical riding that most of us do sacrificing top end for better bottom is a small price to pay.

 

[(F5)]

Another old mod is to take 100mm or so off the silencer or to buy yourself a shorty for the bike. Shorter silencer will give you better throttle response and bottom end snap but with the sacrifice of some top end. But given the type of slow technical riding that most of us do sacrificing top end for better bottom is a small price to pay.

Bollocks. Just makes it noisier and loses land access as a result. People equate noise to power. I've added extra muffler section to a high performance 2 stroke racebike where noise restriction was quite stringent and back to back dyno made zero difference.

 

[reidy]

Bollocks. Just makes it noisier and loses land access as a result. People equate noise to power. I've added extra muffler section to a high performance 2 stroke racebike where noise restriction was quite stringent and back to back dyno made zero difference.

100mm off doesn't add that much more noise and it only adds to throttle response not power to the bike. A shorty will make the bike louder but no loader than a worked up 4 stroke! If anything to your theory then the 2 stroke MX bikes must be doing it all wrong when they're all about bottom end punch.

 

[(F5)]

In typical applications there is 200mm of Stinger of smaller diameter preceding the muffler or link pipe. But believe what you want to.

 

[Jakobi]

In typical applications there is 200mm of Stinger of smaller diameter preceding the muffler or link pipe. But believe what you want to.

That's what people do!

I cut 100mm off my 2013 pipe. Made it sound louder. Made it spooge none! But didn't make it any more snappy.

Want some more bottom end? Get rid of the expansion chamber..

Since when do MX engines tune for bottom end? Most are after peak HP with an ability to get into the revs quickly!

 

[rvktm]

the best thing i ever did to get more grunt out of a gg 250 was a adjustable pv cover . didnt do much for the 300 i fitted it to. got a 4 ball 98 pv governor to try in my 05 .the works team had different springs .on ktm and beta the pv gov spring can be changed by undoing a bolt .disappointed that rieju didnt look to improve the pv adjustablity

 

[Doc Brown]

That's what people do!

I cut 100mm off my 2013 pipe. Made it sound louder. Made it spooge none!

Just saw that by chance and feel the urgent need to dig deeper into that, as I have a spooging problem...

So you say altering the silencer or even changing it(?) may solve the problem.

 

[swazi_matt]

I did this to my "banana" exhaust as well, i forget the exact amount that was removed, but there is a formula somewhere for the optimum length of silencer as a ratio of the core diameter