365 or 340 bore kit?

[jn2jhavens]

Does anyone hear have experience with both of these bore kits. I am hearing good things about the 340 kit, but was wondering if there are any problems with the low compression 365 big bore kit? ?

[KLeeneX300]

The 340 is a good kit. The 365 is also good, just costs a whole lot more money. It uses the 331 bore plus a stroked crank. If you havn't done any mods to your KLX yet, plan on spending around $1800 for a 365. Less if you already have a pipe and carb. My 365 was a little cheaper because I did all my own motor work.

The best bang for the buck is the 331/340.

[Bill_P]

We're very happy with the 340 that Gary at Thumper just did for us. It didn't make a night and day difference, but definately puts out a lot more than a stock bore modded bike. I've ridden the 365 and it is a Major difference. I wasn't convinced on the reliability issues though, and since we weren't racing, the 340 sounded like a better deal. MUCH! cheaper also.

[brett_h]

My 340 WAS a night and day difference, what else have you done? Carburetion?

[Bill_P]

Already had big gun pipe, dyno jet kit, free mods, etc in place before the 340 kit. It does make a difference - just not night and day. Very happy with it though.

[jn2jhavens]

I already have the carb, header, hotstart, etc.. If I am not going to notice a marked improvement in power then I may go for the 365 kit. I am only worried about the maintenance of the bike. Do I need to worry about rebuilds every year, and more vibration or not. This is what I am mainly worried about. I do not race, I only ride in the woods, but would like more power for the hill climbs and stuff like that. What do you think?

[KLeeneX300]

So far I have only had to do basic maint. on my 365. I change my oil every other ride and clean my air filter every time I go out. I haven't noticed any more vibration over stock. The one thing I have noticed is that I run through the gears really fast with the stock 14/50 gearing. My top speed in 6th was only about 55-60. The engine felt like it wanted a seventh gear. A change to 15/50 helped a lot. I still have plenty of low end grunt for the tight woods. The best way I can describe the 365's power is to think KTM 400, very similar. An all out 365 can dyno about 42-43 hp.

[Bill_P]

I'd suggest talking with Gary at Thumper Racing and with Jerry at Four Stroke Works and use that to help you make a decision. All I can say is that the 365 that I rode was a monster. It had pumper, pipe, and almost every mod that you could - to the tune of 7k extra! Thumper suggests that the 340 use the stock CVK. This could account for a lot of the "feel" difference. I'm sure you could put a pumper on the 340 if you wanted to deal with the jetting issues.

[Bill_P]

OK, my son Corey who rides the 340 just saw this thread and wanted to kick in his $.02. Here goes:

I love my 340 kit. Just before I got it I bought a Big Gun exhaust system. I only had about 2 rides on when I realized that my valves were way out of spec and had to get new ones and the valve seats ground. It was going to cost me $400 to fix it locally so I sent it off to get the kit because it was going to cost almost as much as just fixing my valves. Long story short this thing strait up rocks. I can ride a gear higher in all situations and going through whoops is so much easier because I can lift the front end in fourth without even having to pull up on the bars. In my opinion this is the best thing you can possibly do to the KLX besides a new exhaust to give it more power. As the old saying goes "Bigger is Better"

[brett_h]

Bill; what main jet are you using?

[Bill_P]

Dynojet MJ - 135 or 138. Can't remember, but I think it's a 138. DJ needle in 4th clip I believe - whatever DJ recomends in their literature. 2.5 turns out on the pilot screw. 3000 feet elevation (So Cal Dez). Right now it's running a tad lean due to the weather, but still OK. I think a bigger MJ might be in order.

[Bill_P]

Oh yeah, that's a CVK with Dyno Jet mods.

[brett_h]

Hmmm... I have tried bigger jet's (132-138) and it has always lost power. I make note of all modifications in the back of my manual and no matter if my bike was stock, 331, or 340, with or without the DJ needle, it has run best with the stock 128 or 130 m.j. I think some guys assume that when they modify their motor that a bigger m.j. is in order, sometimes this is true, but the KLX-300 is the one bike that (for me) this has not been the case. Have you ever tried a smaller m.j.? We are at similar elevation and it is at least as cold here (last ride 28 degrees) and I have a 130 currently. The previous ride with a 132 it was noticeably less powerful.

[Bill_P]

Well..... The guys at BG told me to put in a 150!! I thought they were out of their minds. I presumed I would have to go bigger than the 128 it had in it prior to the BG due to the increased flow. I had a 132 in before, so we started bigger. We went up to a 138 which I think was the biggest I had at the time. Each time checking with the bike held WOT and checking the plug. Each time with the plug looking lean. From what I've learned subsequently, I guess the plug test is not all that accurate. So you think I should go back down and try it there??? I'm not noticing any bog or anything like that. Not smoking either. I'm no jetting expert. Any ideas Brett???

[Bill_P]

Brett, are you running the stock exhaust??? If not what are you running.

[Stroker340]

All I can say is that my bike was one of the two bike LArry Rossler built up for the 1996 issue of Dirt Rider Magazine and pictured on the front cover of April's issue that year. Below are the modifiaction done to the bike with full dyno testing done for the article as well. I am 6' 3" and 235lbs and this bike in every gear with me on it kicks ass!!!!! I just did a few rides this weekend up in Washington State and logged some 60+ miles of Sandy,Extreem Water, and Rocky Terrain and had a blast. I know what my Stroker 340 can do and as far as responsiveness and power goes I don't need a damn bit more! Hell, save money and go with the 340! Take heed in what I say Grasshopper I am still a newbbie as far as this stuff goes but I knnow what I like!!!!!!!!!!!!!

[Bill_P]

I was under the impression that Stroker (and now Four Stroke Works) only did 331's and 365's. Gary Hazel at Thumper Racing does the 340's and has a whole different philosophy - stock CVK's w/ jetting changes, Lower compression instead of higher, stock cams, etc.. Anyway, I can assure you that if it's a LR KLX. it bears no resemblance to any normal 340 that Thumper builds! ;-)

[KLeeneX300]

Stroker did do 340's. The very first magazine write up I saw about Stroker mentioned them. They even said Stroker did some 350's before ending up with the 365. A Stroker 340 is not the same as the Thumper 340. The Stroker motor has a stroked crank. The Thumper kit is just a big bore kit. The Stroker motor starts as a 250 then bored to 307. After that you stroke the crank for 340.

I still have that magazine article as well as every Stroker write up I could find.

[Bill_P]

Hmmmm, very interesting Brandon. Like I suspected, a Stroker 340 is nothing like a Thumper 340.

[brett_h]

I have a complete Stroker exhaust. I am just suggesting that if you have not tried a smaller m.j. that you might want to. If you have a 135-138 try a 130. When I built my motor the first time (stroker 331) L.R. himself told me to run a 128, when I made it a 340 Thumper Racing suggested 135-138. Gutless, pig, dog. So I started going smaller with the m.j. and it just keeps getting better. I dont look at the plug but I do look inside the muffler. When I had the bigger jets it was black and sooty inside, now it is grey. The throttle response is much quicker and the hi-rpm power is a handful. If you want to be cautious you can go down one size at a time but if you have a 138 start with a 132. If your bike is as rich as mine was you will notice right away the response and power and you will go a lot further an a tank. Brett.