350 cc big bore kit for KLX250, Ready to ship!!

Discussion in 'Vendors' started by Bill & Jo Ann Blue, Nov 11, 2008.

  1. Bake

    Bake adventurer

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    Stock gearing is 42/14 a final reduction ratio of 3.0

    42/15 would be 2.8, or 7% higher final drive ratio

    The stock 5th gear is a 1.050 ratio, and that would be considered a final gear, a one to one ratio, for practical purposes.
    6th gear is .904 ratio, an overdrive gear ratio. Which is good, because it allows a lower rpm for higher speed, but the 250 doesn't have the torque to pull it, the acceleration at highway speeds with that ratio is nearly non-existent.
    By going to the 15 t, that changes the ratios for all the speed in gears. So, that means 1st will be taller, 2nd, all the way through to that overdrive 6th. The 351 engine revs so fast, I find that I'm out of 1st gear in a second or two. The stock gearing is fine for trail riding. Many riders go to a 13t, to get the 250 to a higher performance level (at the expense of a lower top speed in 6th)
    But I do quite a bit of street riding on mine also, and for that I think it needs taller gearing. When you get the bike into the overdrive 6th gear, and have an overall ratio also taller, the 351 will have the torque to handle it.
    All that comes down to a bike that will cruise in that overdrive 6th at a higher speed at a lower RPM, and the engine will provide enough torque to have decent acceleration at those speeds, for passing, etc.
    If the 250 runs 7k rpm to achieve 70 mph, then the 351 running the 15t may run 70 mph at 6500...I'm not an expert by any means with all these numbers. I just think the 15t will help the 351 be an overall better Dual Sport performer.
    #81
  2. Bake

    Bake adventurer

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    If anyone is interested in using this new tank, or a 2 tank set, please PM me . I want to keep these talks private at this point.

    Thanks for your understanding.

    Bake
    #82
  3. MaverickAus

    MaverickAus Long timer

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    With the stock gearing and the stock speedo (optimistic) the 250 pulls 60mph @ 6000rpm. When I went to 13/42 it would do 60mph at approx 6600 rpm, so for a guess with the 15 tooth it would be approx 5400 - 5500 rpm @ 60mph which I'm sure the 351 would pull with ease.
    #83
  4. GB

    GB . Administrator Super Moderator Super Supporter

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    I just received my big bore kit today!! I will see about getting installed soon and give you my impressions! Thanks Bill!
    #84
  5. Bake

    Bake adventurer

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    Bill's final report from Colorado came in. Both bikes rode over some rugged, rugged stuff on the single track today. Banged them around pretty good. No cracks, no leaks, everything is fine with the tanks, said he can't even tell it's there while riding.

    Using his 33mm carb, and the 351cc engine, and running a Supertrapp pipe, one bike ran the tank dry at 69 miles and the other 71. Most of that was on winding highway, after filling up in town and heading back to the cabin. Grand total, the tank has been tested for 400 miles, mostly on the trails. This coming week, we'll test for an additional couple of days with tank #3.
    He says they are a go, and the price for the kit is $225.

    I'll get some pictures of the kit on the website early this week.

    Also, I'll be riding with a friend that has an '09, and I'll see what the deal is on fitting our tank to it. We do use the luggage rack bolt; the '09 does not appear to have that bolt. We might need one different bracket. Or all new ones. A bracket change won't be a big deal.

    Thanks
    #85
  6. PeteZ

    PeteZ Adventurer

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    Thanks Bake for the update. Was that 69 and 71 miles running from the new aux tank alone (ie 1.1 gal)?

    Thanks,
    Pete
    #86
  7. GB

    GB . Administrator Super Moderator Super Supporter

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    My 351 big bore kit and Mikuni pumper carb were installed! I haven't done a lot of miles on the bike yet, but it's running very well, it starts easily , whereas with the stock carb it did not. It feels "peppier" too, and gas mileage doesn't seem to have been noticeably affected. Gained 100cc, and more power, without any weight gain.

    The big bore kit is of the highest quality, the mechanic that put it in was impressed with the quality of the piston too, and I really like the way Bill has the idle adjuster on the carb, easy to access as well as the air mixture adjuster.

    Thanks Bill for a top rate product and service!
    #87
  8. rickypanecatyl

    rickypanecatyl SE Asia adventure tours

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    Thanks for the report GB! When you say "peppier" how significant do you mean?

    Bill - anyway to get a confirmation on whether or not the 351 cc kit would fit on a 2001 KLX 300R? Thanks!

    Rick
    #88
  9. GB

    GB . Administrator Super Moderator Super Supporter

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    It's not as sluggish as the 250, and to me it is a noticeable difference. It's certainly no rocket, but it's no slouch either.
    #89
  10. skubidoobie

    skubidoobie Loves to Ride

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    Sweet thread and nice work! Definitely eyeballing that skid plate for my '09, do they fit?
    #90
  11. GB

    GB . Administrator Super Moderator Super Supporter

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    yes, the skid plate fits the 09.
    #91
  12. skubidoobie

    skubidoobie Loves to Ride

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    Sweet! Consider it ordered! :clap Do forum members get a discount? Gotta try lol. Might as well splurge and get the smog plate while I'm at it.
    #92
  13. 67L48

    67L48 Dangerously Incompetent

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    I was wondering if you could provide some insight into the 351 and how it compares to the 331 and 340 kits. I've ridden a 331 and own a stock 250 -- the difference was night and day; it was like a different bike.

    But, For less than 10% more money, a person could step from 331 to 351. There must be some reason that the 331 and 340 kits still exist, right? With all of the good things posted here about the 351, why would a person opt for a 331 or 340? It would be helpful to me if there is some discussion of the tradeoffs between the kits -- torque, horsepower, longevity, difficulty of installation, need for rejetting or carb tuning, etc.

    Thanks.
    #93
  14. GB

    GB . Administrator Super Moderator Super Supporter

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    I don't think Bill is still offering the small kits, he's maxed out the boring to 351.

    Going from a 331 to a 351, I don't think you will notice a huge difference, but going from 250 to 350, well, it's a different bike.
    #94
  15. Bill & Jo Ann Blue

    Bill & Jo Ann Blue Adventurer

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    I still offer the 300, 331, 340 & 351 big bore kits for the KLX250

    Bill
    bandbcyclerestorations
    #95
  16. HalfPlate

    HalfPlate What? Where?

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    Bill,

    I wanted to ask your advice. I installed the 351 kit and re jetted per your instruction. Now the bike starts great, a little choke and we are off, however once its warm it refuses to restart just cranks and cranks, then starts to puff white smoke that smells like maple syrup. I figure the smoke is unburnt fuel but I am not sure whats your thoughts.

    Note: to any perspective buyers this is not a problem with Bills product just my own stupidity.
    #96
  17. Bill & Jo Ann Blue

    Bill & Jo Ann Blue Adventurer

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    We have found that the copper head gasket needs to be re torqued after running the first time. If this don't solve the problem e-mail me.

    Bill
    #97
  18. ZeroGara

    ZeroGara 2strokes & Big Twins

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    I'll second that retorquing recommendation but if the gasket has already developed a good leak you may need a new head gasket. Was your head really clean before you installed the kit? This is common to all heads and more so on singles. Some people even do it three times, once after intial start to full temp and full cooling, and once after 100mi or so.

    The sweet smell comes from coolant that may have gone through he gasket into the cylinder. Once the engine stops and starts to cool down, the pressure from the coolant will force through the gasket and into the cylinder. If it was a big leak or crack somewhere gases from the cylinder would escape into the water passage and force all your coolant off. It will eventually do that even when cold for days.

    So this needs immediate attention and not something to put off. If your head sealing surface is not clean torquing will not fix the sealing problem. If it seems porous it may need a head gasket sealant.

    Your hot starting problem may be totally separate though and be caused by rich jetting not to confuse the issue for others having hot starting problems. If you shut the fuel petcock off and lean the bike a bit to drain some from the carb overflow, then try starting with the throttle steady at 1/8 open. That should clear it up a bit to start.
    #98
  19. ZeroGara

    ZeroGara 2strokes & Big Twins

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    Congratulations for your kit Bill, I admit that it refreshed some interest on the bike I had long lost.

    Q1: What is the outside diameter and depth of the sleeve below the cylinder deck surface? Older KLX250s (I believe of the pre-300 era) had a narrow cavity in the cases that even the 300s sleeve wouldn't fit unless the cases were modified. It was a depth problem as well as the area around the crankwebs was thicker on the old 250s than on later 250/300s. If I remember right the split came around 96-97?

    Q2: I assume this sleeve is not plated, just honed and the piston and rings is meant for such cylinders. Is this a custom made piston or one that exists in the market for other purpose? I know those things run for ever once done right but couldn't help but wonder. I'd assume for such compression rate and valve angles to match it must be custom.

    Q3: Obviously the head is not modified, unless I haven't read all the info here that carefully. Am I correct to assume that area of the piston on the outer top part is meant for the stock 250 head (have the valve sizes changed through the 15 years in production?), would a 300 head work a well with your kit?

    Q4: I remember back from the 250/300 stock parts conersions there was variability in the resulting compression from the swap. Some would use thicker gaskets and some would grind an angled squish band around the head, some would do both to avoid going to high numbers. Have you measured any variability in compression on those 3 prototype engines?

    Q5: Is there a core charge for 250 cylinders? I have a couple good ones from early 250s that I do not see of ever using, a good crank/rod 2 CVs and few other bits and pieces if anyone is interested.

    PS On the aftermarket oversized tanks that existed for the off road only model 250/300 there may be an issue with wiring that goes through under the tank by the front part of the frame as the loom for the street legal bikes is too thick. An other pain in the neck I dealt with since my bike was a Jap version street legal version of the non-kick start enduro bike. There had been so many versions of this bike around the world that even the most fanatic fans get confused. Between USD/conventional forks, electric or kickstart 250s, the D-Tracker, it must have been one of the most spread out models Kawa ever produced. When I saw the recent street legal version coming out my first reaction was "...ohhh no..... NOT Again! This thing will never die!"

    :ricky :eyes
    #99
  20. Bake

    Bake adventurer

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    Bill's website is:
    http://www.bandbcyclerestorations.com

    Contacting him at the email address given on his site would get you information quickly.

    Thanks,

    Bake