Thumper Racing 300 XCF-W Big Bore

2008 250 XCF-W convert to Thumper Racing 300 Big Bore. I took a brand new 250 XCF-W and broke it in. Then hammered it out in the mountains in Northern Arizona. The bike rode great (suspension a little jumpy) but no drama.

Then took the cylinder apart and sent it in to Thumper Racing for the 300 Big Bore Kit. They bored the cylinder to a 300 and provided all the necessary parts to reassemble. After another short break in ride - the bike was taken to Colorado to do some serious trail riding. With the higher altitudes, it is not quite an apples to apples comparison, but the bike definately has more grunt and noticable power delivery throughout the whole powerband. My biggest concern was overheating. Other big bore 250Fs that I have ridden with had trouble overheating - not this one! Roots, rocks, step ups, hills - no problem. No leaks or any other problems to report at this time. I will post more info as time goes on. Right now the suspension is off the bike getting redone, so after that, I will keep you posted!

Please keep us posted with your impressions of this BB kit.

I have a 2008 w/ 14 hrs and will be installing a BB kit. Current options are the Thumper Racing 300 kit or the HT racing 320 kit.

Maybe even the HT 350 stroker kit.

Aside from the obvious displacement and price differences I'm still looking for pros and cons of each.

Thanks

Well, obviously I don't have any first hand experience with the HT Racing kit, but I have heard all good things. So far, the guys at Thumper have been great, the product looks fantastic, and as my post relates, the bike runs great and my biggest fear (overheating), has been a non issue. I will be out of town for a week, but after I get back, I'll do some more riding and let you know how things work out.

I have about 7 hours on my TR 300F.

I am a "C" rider, mainly participating in sanctioned and recreational trail rides and the occasional Northeastern enduro.

What justified the TR 300F kit was I due (over 80 hours) for a rebuild and the cost TR Kit (with the raffle discount) was not much more than a stock piston, rings, and gaskets. Also, years ago I had a XR's Only 430 Kit put my XR400 and I never resented it.

I had a lot of downtime between taking the bike down and riding it with the TR Kit, also I have not been able to ride a stock bike and a TR 300F back-to-back.

After installing the kit, the bike ran crisp with the original JD Jetting (installed when new), but in my first shakedown ride it was a little lean, as noticed on the down hills. This was corrected with the jetting that TR included with the kit.

The bike definitely has more grunt (torque) down low and in the midrange, but I don’t think that revs quite as high as it used to (make sense with a heavier piston), however I rarely ride bouncing off of the rev limiter and I appreciate added low-end and mid-range.

With my current gearing (13/52) with a Z-Ring Chain, the bike easily does throttle only wheelies in 3rd gear and probably will in forth with some effort on my part.

With this added torque I find it easier to get the front end up (for obstacles), especially when traveling at higher speeds. Also, I’m finding the need to shift less in general which is good as I can be a lazy rider. For example, 2 days ago I was in a tight enduro with some surprise vertical hill climbs the added torque definitely helped me with this, as gear selection was not as critical as it was with the stock displacement.

I have about 7 hours on my TR 300F.

I am a "C" rider, mainly participating in sanctioned and recreational trail rides and the occasional Northeastern enduro.

What justified the TR 300F kit was I due (over 80 hours) for a rebuild and the cost TR Kit (with the raffle discount) was not much more than a stock piston, rings, and gaskets. Also, years ago I had a XR's Only 430 Kit put my XR400 and I never resented it.

I had a lot of downtime between taking the bike down and riding it with the TR Kit, also I have not been able to ride a stock bike and a TR 300F back-to-back.

After installing the kit, the bike ran crisp with the original JD Jetting (installed when new), but in my first shakedown ride it was a little lean, as noticed on the down hills. This was corrected with the jetting that TR included with the kit.

The bike definitely has more grunt (torque) down low and in the midrange, but I don’t think that revs quite as high as it used to (make sense with a heavier piston), however I rarely ride bouncing off of the rev limiter and I appreciate added low-end and mid-range.

With my current gearing (13/52) with a Z-Ring Chain, the bike easily does throttle only wheelies in 3rd gear and probably will in forth with some effort on my part.

With this added torque I find it easier to get the front end up (for obstacles), especially when traveling at higher speeds. Also, I’m finding the need to shift less in general which is good as I can be a lazy rider. For example, 2 days ago I was in a tight enduro with some surprise vertical hill climbs the added torque definitely helped me with this, as gear selection was not as critical as it was with the stock displacement.

This is excellent input. I am seriously considering this kit for my '07 250XCF. I'm currently trying to convince the fiance to get it for me as a wedding present! :ride:

More hours hammering on the Thumper Racing 300 Big Bore. Still no problems. Installed an Acrapovic pipe which gave it even more boost throughout the rpm range. Having some jetting issues. Have had the bike in Colorado (went too far on the jetting - too lean), then back to the mountains in Arizona (too fat?? - burbles at low rpm), but getting closer. I think the pipe allows it to breath more, thus it needs more fuel. No reflection on the bb kit. No overheating (except in extreme conditions), no oil burning, no drama or other issues - just more useable power throughout. Nice!

I have had no overheating problems on my HT350 or my HT315 bikes. Love the way they run and they use nikasil cylinders. HT Racing had issues running iron liners in RC4 engines.

Dwight

I have had no overheating problems on my HT350 or my HT315 bikes. Love the way they run and they use nikasil cylinders. There have been issues running iron liners in RC4 engines. Even HT racing refuses to use iron liners for any big bores over 280 cc. The 280cc engine uses an aluminum heat sink to prevent cylinder seizure and cracking problems.

Dwight

I thought this was a TR 300 post? Nice try to bash Travis' kit.

I thought this was a TR 300 post? Nice try to bash Travis' kit.

Dwight cannot resist any opportunity he has to hi-jack a thread and degrade Thumper Racing and give props to HT Racing.

I have had no overheating problems on my HT350 or my HT315 bikes.

Dwight

BS. Any bike can be overworked.

Dwight: Nevermind........................:ride:

Sorry for making a comment. I was responding to the overheating remark, of big bore kits. I made no comment about Thumper Racing. BUT, I will not gloss over a problem area in the RC4 big bore kits of any company.

I know that Thumper has make great kits for years in Honda, Yamaha and past KTM RFS.

Dwight

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