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Old 04-22-2011, 03:33 AM   #4996
David R
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Quote:
Originally Posted by akarob View Post
New 250SF owner here. Picking it up tomorrow.

To the people upgrading to 351 (or 300+) , do you get any head work done? I'd think that some oversize intake valves would be a good idea if your engine gets bigger and carb is getting done and all.

How do the heads in these bikes hold up? Do the stock intake valves last a while?
JUST the 351 makes a huge difference. You get the most bang for your buck. If you want to add a bigger carb or exhaust it will add a little power and quicker response. I ran stock carb with stock exhaust modified by me for a while. It works great. The bug bit me so I had to have the bigger pumper carb which did help with response, but I don't think it added any horse power.

The 351 turned my Street bike from a weed whacker motor to a true thumper. Torque is way up.

No head work or anything else for me. Its fine just the way it is. We started out with DOHC and 4 valves.

David
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Old 04-22-2011, 07:13 AM   #4997
markk53
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The fact is most modern singles will benefit from being "unplugged" at both the intake and exhaust then properly jetted. Unfortunately most exhaust mods make the bike rather loud. It will be nice when someone actually makes a decent flowing quiet muffler. I just wish I had the where-with-all to do the job. It may not be significantly lighter than the stock one would, but it'd flow better and have a bit better tone. There's room under those number plates for sure.

When I sold Kawasakis the trick I learned to really add power everywhere for the KLX300 was to install a carb kit with a larger carb and a larger ID head pipe freer flowing exhaust. About $450 at the time, to pick it up in a big way with bolt on stuff in a few hours.

The same is probably true for the 250. Get it to breathe.

I won't say the big bore isn't a benefit - It absolutely IS. Based on my own experience with only a 27cc bigger engine, the power delivery is pretty much over the same area, but just a lot stronger. It does take more effort and money to do it though in most cases.

I did the big bore and an exhaust at the same time and, oddly enough, I got a 10 mpg GAIN from 50 mpg to 60 mpg. I use a Dial-A-Jet, which automatically compensated for the changes, thus I don't mention jetting. Good consistent plug color and exhaust tip color from sea level at Daytona to 5000 feet in WV, from 20 degrees to 95 degrees.

Do the 250s gain mpg when some of this sort of work is done?
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Old 04-22-2011, 10:31 AM   #4998
TNC
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Quote:
Originally Posted by markk53 View Post
The fact is most modern singles will benefit from being "unplugged" at both the intake and exhaust then properly jetted. Unfortunately most exhaust mods make the bike rather loud. It will be nice when someone actually makes a decent flowing quiet muffler. I just wish I had the where-with-all to do the job. It may not be significantly lighter than the stock one would, but it'd flow better and have a bit better tone. There's room under those number plates for sure.

When I sold Kawasakis the trick I learned to really add power everywhere for the KLX300 was to install a carb kit with a larger carb and a larger ID head pipe freer flowing exhaust. About $450 at the time, to pick it up in a big way with bolt on stuff in a few hours.

The same is probably true for the 250. Get it to breathe.

I won't say the big bore isn't a benefit - It absolutely IS. Based on my own experience with only a 27cc bigger engine, the power delivery is pretty much over the same area, but just a lot stronger. It does take more effort and money to do it though in most cases.

I did the big bore and an exhaust at the same time and, oddly enough, I got a 10 mpg GAIN from 50 mpg to 60 mpg. I use a Dial-A-Jet, which automatically compensated for the changes, thus I don't mention jetting. Good consistent plug color and exhaust tip color from sea level at Daytona to 5000 feet in WV, from 20 degrees to 95 degrees.

Do the 250s gain mpg when some of this sort of work is done?
Mark, mine gained some mpg with the 300 cylinder. At a 250, I had the full Muzzy exhaust...huge head pipe like you describe...modded airbox, and DJ jetting. Still, I had to rev her up pretty well to scoot, which it did OK. With the 300, those other mods probably came more into their own for a performance increase, and I found I could short shift and lug the bike a whole lot more. I think that's where my mileage increase came from.

I also have a totally unsubstantiated theory that the later/current 250 is a tiny bit different from the original 250 that won't accept a 300 cylinder wihtout case machining. I'm suspicious that Kawasaki took the basic 300 model and dropped the bore to 250...marketing, licensing, insurance, and a host of other reasons for a street legal model. When you go back to a 300 cylinder or larger, I'm thinking the combustion chamber and valve layout is more optimum for the bigger bore and therefore provides more/better performance due to being a better "match". One reason I think this is how the valve reliefs are located almost down to the piston ring grooves on the 250. While you can see this occasionally on some engines, it is not really an efficient design for ideal combustion. It seems to me that the power increase of just the 300 cylinder is more than the meager 43cc or so would normally yield. Anyway, just a idea I have about it...worth about .01 cent in today's market.
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Old 04-22-2011, 11:40 AM   #4999
GaryHarris
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Quote:
Originally Posted by redpillar View Post
Why not put on a 13 tooth countershaft sprocket instead? They are much cheaper and no chain length difference.
Besides the look factor I mentioned about, I want the option to gear lower than just using a 13t up front. I feel the bike is way over geared for some of the riding I want to do and from what I understand changing one up front=three in the rear.

If I need to gear back up Ill put a 15t up front.

Ill figure the chain length out.
Thanks.
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Old 04-22-2011, 12:46 PM   #5000
rickypanecatyl
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Sorry I'm too lazy to post pictures but had an amazing ride today!

Just last week I got a motoport airmesh kevlar shirt and pants. To be honest I'm super unhappy with them but they are good for 1 thing and thats riding thru thorns, briars and thickets. Stuff that would rip my tourmaster jacket apart in minutes are no problemo.
And so, dressed for battle I sought to reclaim miles of single track from the ever spreading jungle. I had a razor sharp machete mounted and it was on.
Most of the time there was absolutely no path to see... just a memory burned that it used to be right about here. I lost my front wheel over a 60 foot high cliff and bailed by grabbing the branches and vines above me. The bike didn't go over because liana vines and bamboo shoots were clutching the bars and wrapped around my wheels etc.
Ended up on a motocross/enduro track right next to a river...
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Old 04-22-2011, 02:28 PM   #5001
Dan888
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Quote:
Originally Posted by rickypanecatyl View Post
I lost my front wheel over a 60 foot high cliff and bailed by grabbing the branches and vines above me. The bike didn't go over because liana vines and bamboo shoots were clutching the bars and wrapped around my wheels etc.

!!!!!!!!!!!!!!!! Too bad no pics, I'd love to see the cliff. Sounds like you got lucky.
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Old 04-22-2011, 05:24 PM   #5002
UtahGuido
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Quote:
Originally Posted by GaryHarris View Post
Quick question on gearing guys and gals. I'm currently running the stock 14-42 with stock tires and feel I'm way over geared. Since Ill be soon removing the wheels to change tires, D-606 120/90 rear, I might as well change the rear sprocket while I have the wheel off and this would be a good time to add some "Farkle" since I have a $50 coupon coming.
Quote:
Originally Posted by GaryHarris View Post

http://www.rockymountainatvmc.com/pr...FamilyId=22817

The smallest they offer is a 47T and I have no problem with that since I like the big rear sprocket look, a little color and the old school dirt bike look. The chain guard will be tossed.

I have a decent idea on how the gearing will feel, but I don't know about the chain length. I assume Ill have to get a new chain. Anybody run this set up and can you give me an idea on how many links the chain will need to be?

Thanks.
Hey Gary,

I can help you out I think. I was running a 13/47 setup right (with the 250) and I like that gearing. With the 250 opened up and making power at 7-9K rpm it was no sweat to go down the interstate at an indicated 70 mph. Yeah it was screaming, but it would also chug around and over things really well. The chain is a 108, which works but it puts the adjusters on about 1. In other words the wheel and tire will be in pretty tight. Doable however. I had a real tall Pirelli MT43 on it but a new 606 is just about as tall. Here's what that looked like:



Has kind of a bobtail look.

So I wanted to go to a longer chain so I could move the wheel as far back as possible. I had to mod the adjuster pin to make it work and the axle is back to bitter end of the swingarm - maybe not ideal (the ideal might be a longer swingarm!). Here's the 110 chain and modded adjuster:





Basically that's just a 10x1.25 bolt and some washers.

And sorry about these huge pics.

Another option is 13/45. The 108 chain works well, lots of adjustment, and versatile gearing. Maybe not as rock-crawly but still plenty of low gear.

But now I have the 351 installed and I need to gear up. The low gear is really cool for poking along but I don't think this engine will rev high enough to make the top gear useful. So I'm going back to a 13/42 with the 108 chain. I may go higher.
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Old 04-22-2011, 06:03 PM   #5003
GaryHarris
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Quote:
Originally Posted by UtahGuido View Post

Hey Gary,

I can help you out I think. I was running a 13/47 setup right (with the 250) and I like that gearing. With the 250 opened up and making power at 7-9K rpm it was no sweat to go down the interstate at an indicated 70 mph. Yeah it was screaming, but it would also chug around and over things really well. The chain is a 108, which works but it puts the adjusters on about 1. In other words the wheel and tire will be in pretty tight. Doable however. I had a real tall Pirelli MT43 on it but a new 606 is just about as tall. Here's what that looked like:



Has kind of a bobtail look.

So I wanted to go to a longer chain so I could move the wheel as far back as possible. I had to mod the adjuster pin to make it work and the axle is back to bitter end of the swingarm - maybe not ideal (the ideal might be a longer swingarm!). Here's the 110 chain and modded adjuster:





Basically that's just a 10x1.25 bolt and some washers.

And sorry about these huge pics.

Another option is 13/45. The 108 chain works well, lots of adjustment, and versatile gearing. Maybe not as rock-crawly but still plenty of low gear.

But now I have the 351 installed and I need to gear up. The low gear is really cool for poking along but I don't think this engine will rev high enough to make the top gear useful. So I'm going back to a 13/42 with the 108 chain. I may go higher.

Thanks Guido. I'm thinking the 14-47 set up might be the right compromise for me, but I'm not sure what chain to order.
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Old 04-22-2011, 06:36 PM   #5004
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Gary, I run a 14/47 gearing on my KLX with just a 300 cylinder. With all the other mods and a full Muzzy exhaust, it has lots of low end but still winds out well. I can ride extemely tight singletrack but still cruise at a GPS 60mph all day at a safe rpm. Gearing can be very preferential because we don't all ride the same terrain or the same way. You'll have to take what you hear and try it out to see how it applies to you.
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Old 04-22-2011, 06:50 PM   #5005
UtahGuido
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Quote:
Originally Posted by GaryHarris View Post
Thanks Guido. I'm thinking the 14-47 set up might be the right compromise for me, but I'm not sure what chain to order.
For a 14/47 I'd go 110. I don't think a 108 is long enough. What do you run TNC?
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Old 04-22-2011, 08:23 PM   #5006
TNC
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Originally Posted by UtahGuido View Post
For a 14/47 I'd go 110. I don't think a 108 is long enough. What do you run TNC?
I believe I'm running a 108...wanted to get the wheelbase as short as possible. I'm running on the number "1" snail adjuster. I set it up before I cut the chain, and it works. Most people would probably run a 110.
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Old 04-22-2011, 09:17 PM   #5007
GaryHarris
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Thanks guys. I ordered a DID 116 and don't mind cutting it down. I just didn't want to order something too short or try to be exact since I may run a 15t up front.

Thanks.

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Old 04-23-2011, 04:44 AM   #5008
PunkinHead
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This thread gives chain length for various sprocket combinations.
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Old 04-23-2011, 06:32 AM   #5009
markk53
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Originally Posted by TNC View Post
Anyway, just a idea I have about it...worth about .01 cent in today's market.

I'd sent the .01 cent, but the PayPal fee would be a buck and a half...


You know, it's a shame the manufacturers don't take a page from the old enduro books of the 70s. I remember we had a used beater Hercules 250 enduro (Sachs engine/gearbox, bike looked pretty much like a Penton/KTM) back around 86. It had a seven speed! I have to say it was incredible to ride. Seemed like I never quit shifting it when I test rode it. Makes you wonder why they don't put a seven speed in the smaller dual sport/off-road play bikes. That would give a great low gear and still allow highway speeds with ease. I'd love it in my 650... one gear to pull stumps and another to keep up with traffic on I-71.
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Mark - klx678
95 KLX650C w/Vulcan piston bigbore, Now an 09 KLX250S, selling my 90 Zephyr 550

markk53 screwed with this post 04-23-2011 at 06:38 AM
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Old 04-23-2011, 06:44 AM   #5010
akarob
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I just got a KLX250 for my wife. I took it for a spin and I'm really not used to riding a bike so low on power. I don't think a first gear wheelie is even possible. She'll love it.

I do have a UNI filter, DJ jet kit and a FMF Q4 to put on it. Hopefully that'll pep it up some. I couldn't even put my pinky finger in the stock pipe, talk about plugged up - wow.

Pretty cool bike other than the anemic stock setup.
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