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

[Big Single]

Originally Posted by Bake

I cruise at the torque peak, generally, which on this 351 engine is 6000-7000, so that's about right. The "redline" is 10,000. This big bore engine makes all the power it's going to make at a much lower RPM, at about 8000, you're just making more revolutions. However, it makes close to maximum torque as low as 3500, so it is more of a "tractor" motor than a peak RPM motor. I'm going to gear up a tooth to 15 at the countershaft, because the 351 will pull it at highway speeds. The 250 is just weak, and can't really use the tall 6th gear, in my opinion.

Do you remember the mph at 6000-7000 rpm?

[punkenduro]

with a 120 606 on the back, its almost an even drive (6000rpm = 60mph, ect.) im subscribing to this thread, i would love to do the 351 and tank right now but im having some shifting issues to figure out first.

[Bake]

Tank #1, the very first prototype.

It measured 1.13 gal.

It is a gravity feed tank. It has it's own petcock with NO reserve, so we will run this tank first, then switch to the main tank. It will allow the KLX250 a full 3 gallons of fuel. The coolant catch bottle is replaced with another, slightly smaller bottle, we are making up a mount for it now. The battery isn't affected.
The material is 5052 T3 aluminum. This tank is bolted to the bike in 4 places, the plan is to do it with 3.

The welding is much better on the next 2 tanks, the tank shown previously is #2.

Please bear in mind, these first 3 tanks are for our use, and throughout the month of June, we will be testing them in Colorado for hundreds of miles of trail-riding. After that is accomplished, a decision about this will be made.

[Bake]

Originally Posted by Big Single

Do you remember the mph at 6000-7000 rpm?

The stock speedometer is wildly out of calibration, so it's worthless for a MPH check. I don't use a GPS, so I really can only guess that with stock gearing, 7k rpm would be approx. 70 mph.
One of my priorities is to switch to the 15T countershaft sprocket for testing with the 351 engine.

[GB]

Bake, thanks for the pics and update..

What's the stock gearing on the bike and what will the 15T achieve?

[Bake]

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.

[Bake]

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

[MaverickAus]

Originally Posted by Bake

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

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

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.

[GB]

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

[Bake]

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

[PeteZ]

Originally Posted by Bake

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.

Thanks

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

Thanks,
Pete

[GB]

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!

[rickypanecatyl]

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

[GB]

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.

[skubidoobie]

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