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Discussion Starter #1
Picked up a 2002 YZ250 with a California plate. Not only for SM, but also because it seems to open up a lot more offroading opportunities in this state. I have had 2 strokes my whole life but Im new to riding on streets. I would love any advise or tips you have to offer. I am excited to find some track opportunities and also good street rides in southern california.

Braaaap on!
 

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Epic deal picking up that YZ. Nothing like a plated 2 stroke dirtbike. Makes me feel like I'm breaking the law every time I'm ripping around town.
 

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Discussion Starter #3
That is so true! Its legal to lane split here in California and it is possibly the best feeling besides orgasm to braaap past a cop sitting in traffic, or better yet, sit at the front of a light right next to one with my blue smoke fillin their crown vic. priceless haha.

Updated: Bought a KX500 motor last week. It will be put into my YZ250 frame this winter.
 

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Wear full gear! Pants, jacket, gloves, boots, and a leatt brace! I hit a wheel/tire that was in next to the HOV lane on the 405 six weeks ago and got banged up pretty good. It was dark and I didn't see it till last minute. I think it's because of the leatt brace got away with just a compressed t12 and 2 broken bones. Splitting lanes is great, but you need to watch out for things other than cars. But, on the other hand, if I would have swerved around the tire I would have ended up in traffic which would have been much worse.
 

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Picked up a 2002 YZ250 with a California plate. Not only for SM, but also because it seems to open up a lot more offroading opportunities in this state. I have had 2 strokes my whole life but Im new to riding on streets. I would love any advise or tips you have to offer. I am excited to find some track opportunities and also good street rides in southern california.

Braaaap on!
Nice!!
Have you found anywhere to ride yet?
Have you looked into Silverado canyon area?
I have a plated 99 Yz400 that I zip around Tustin with, def allot of fun cruisin past a 50 an watching them do double take till they see that plate.. Lol
I'm also working on getting my 125cc pit bike plated ( just need a brake and lamp inspection)

I almost took the bike out this morning for a cruise, but got lazy lol..
Might go out this afternoon
 

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Discussion Starter #7 (Edited)
Engine swap in progress

The swap is under way! Short explanation: 250 is more than enough for me off road. I'm no expert rider. But it doesn't cut it for road use, and the constant wot takes its toll on the little 250. I sometimes forget that the 250 is NOT the banshee motor I love so much, it just won't put up with the same endless abuse at wot. The banshee motor (my first choice) is really wide which makes everything about a swap into a dirt bike harder so the next best choice is a 500 single. kawasaki style :) what we have here is a 2002 yz250 with a fresh '88 kx500 motor sitting comfortably inside the rails. Zero cutting required. If i tell ya'll how easy it was maybe more people will start to do it :p

The swingarm inside dimension is different so I measured from countershaft sprocket face to engine swingarm bolt surface on both motors. It is 0.375 further on the yz250. This means to line the sprocket back to where it should be, I have to remove .375 from either the inside of the chain side of the swingarm, or the chain side of the kx500 rear engine bolt surface. After disassembling the bearings from the swingarm, it looks like the easiest choice is going to be to cut it from the inside of the swingarm. I just chose swingarm mostly because i can get a whole new one for like 50 bucks on eBay if i mess up. This means that instead of the 2x needle roller bearings that are in there now (on each side), ill need to get either one that is .375 less wide that the 2 current ones together, or 2 bearings that are .1875 less wide each. throw the seals back in and it should all be fine. at that point when the sprocket is lined up properly I need to do the same thing to the other side of the swingarm narrowing the engine or the swingarm. Ive read a lot of people who have done swingarm swaps and they seem to think they have to run a dirt bike bearing so they give up. Come on, theres companies that make bearings to any spec. it may cost 20-30 OMG for that one bearing but who cares. I spend that on premix oil every weekend I ride so that argument is void. In any case, the chain alignment doesn't scare me because 1. I can shim the engine with washers if i have to and 2. the countershaft sprocket is held on with a circlip not bolted like the YZ250 motor is. This means that I have .1875" of forgiveness right there, making my job easier.

surprisingly the stock carb goes into the carb boot and the air boots goes right on the back. too easy! but it shifts the carb upwards like 1.5 inches due to the bigger motor and because of this it puts the throttle cable in a 90 right as it comes out the carb hitting the frame right forward of the rear upper shock mount. the air boot slightly rubs the spring but i could live with that. right now i am looking into early 90's kdx boots. I want to run a lectron carb as well and they are slightly taller apparently.

with the rear motor mount in, i can run a bolt through either the front motor mount, or the bottom motor mount, but not both. When one is aligned, the other is off by .5". This is much better fitment that i thought.

Also the lower rad crossover tube (between the bottom of the 2 rads) is squished between the frame and the engine. In fact, it is sitting .75" above the exhaust port squished by the cylinder just below the head. Maybe Ill go the smaller diameter hose possibly hard line if i have to, or run the hose another location.

Almost forgot to mention that the behemoth 3.2 gallon tank fits flawlessly! ok well not quite but considering how big the motor is i thought Id have to run a pocket flask for a gas tank. Nope! the tank slides right down and stops about an inch up from where it should. Dangit what is it hitting!!! well, its hitting the cylinder head. Fortunately, as I push down on the tank, the cylinder just splits the forks of the tank and the tank settles into its position. After a few heat cycles, maybe the plastic will deform to fit the engine that is stretching it

I think that covers it all, what do you think
 

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Discussion Starter #8
Last night I used a dremel, a file, and tap magic to remove 0.315" from the inside chain side of the swing arm because the kx motor is quite a bit wider at the rear mount that the yz motor. Test fitted, and the sprocket looks like its centered pretty good with the rear sprocket. But there should be a slight gap between the swingarm and the engine. So I will remove material to get to .375" total material removal. This is very easy to do, just slightly time consuming.

Now the holdup and the hard part is removing this 0.375" from the bearing pin. I couldn't even scratch that with my fancy file, it is extremely hard material. Ill have to take that to a machine shop to throw on a lathe. I found a bearing online that will replace the 2 bearings that are currently in each side of the swingarm, except of course it is .375" shorter that the 2 oem bearings total width together.

Once the rear mount is sorted out, I can move on to the front mounts. Then figure out what carb I want to run.

As a side note, there is a slight bit of slop on the flywheel. Like its not tight on the crankshaft and it rotates until the key stops it. I don't have a flywheel puller for this yet but if you guys think thats pretty weird Ill have to just pull the flywheel and make sure the key isn't sheared then lap the crank and flywheel to fit more snugly.

Any thoughts or suggestions are appreciated. I don't know what I'm doing here Smiley
 

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That looks like a lot of fun . . .

Just remember how much those big two strokes vibrate . . .

 

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301 Kit from www.kustom-kraft.com

The swap is under way! Short explanation: 250 is more than enough for me off road. I'm no expert rider. But it doesn't cut it for road use, and the constant wot takes its toll on the little 250. I sometimes forget that the 250 is NOT the banshee motor I love so much, it just won't put up with the same endless abuse at wot. The banshee motor (my first choice) is really wide which makes everything about a swap into a dirt bike harder so the next best choice is a 500 single. kawasaki style :) what we have here is a 2002 yz250 with a fresh '88 kx500 motor sitting comfortably inside the rails. Zero cutting required. If i tell ya'll how easy it was maybe more people will start to do it :p

The swingarm inside dimension is different so I measured from countershaft sprocket face to engine swingarm bolt surface on both motors. It is 0.375 further on the yz250. This means to line the sprocket back to where it should be, I have to remove .375 from either the inside of the chain side of the swingarm, or the chain side of the kx500 rear engine bolt surface. After disassembling the bearings from the swingarm, it looks like the easiest choice is going to be to cut it from the inside of the swingarm. I just chose swingarm mostly because i can get a whole new one for like 50 bucks on eBay if i mess up. This means that instead of the 2x needle roller bearings that are in there now (on each side), ill need to get either one that is .375 less wide that the 2 current ones together, or 2 bearings that are .1875 less wide each. throw the seals back in and it should all be fine. at that point when the sprocket is lined up properly I need to do the same thing to the other side of the swingarm narrowing the engine or the swingarm. Ive read a lot of people who have done swingarm swaps and they seem to think they have to run a dirt bike bearing so they give up. Come on, theres companies that make bearings to any spec. it may cost 20-30 OMG for that one bearing but who cares. I spend that on premix oil every weekend I ride so that argument is void. In any case, the chain alignment doesn't scare me because 1. I can shim the engine with washers if i have to and 2. the countershaft sprocket is held on with a circlip not bolted like the YZ250 motor is. This means that I have .1875" of forgiveness right there, making my job easier.

surprisingly the stock carb goes into the carb boot and the air boots goes right on the back. too easy! but it shifts the carb upwards like 1.5 inches due to the bigger motor and because of this it puts the throttle cable in a 90 right as it comes out the carb hitting the frame right forward of the rear upper shock mount. the air boot slightly rubs the spring but i could live with that. right now i am looking into early 90's kdx boots. I want to run a lectron carb as well and they are slightly taller apparently.

with the rear motor mount in, i can run a bolt through either the front motor mount, or the bottom motor mount, but not both. When one is aligned, the other is off by .5". This is much better fitment that i thought.

Also the lower rad crossover tube (between the bottom of the 2 rads) is squished between the frame and the engine. In fact, it is sitting .75" above the exhaust port squished by the cylinder just below the head. Maybe Ill go the smaller diameter hose possibly hard line if i have to, or run the hose another location.

Almost forgot to mention that the behemoth 3.2 gallon tank fits flawlessly! ok well not quite but considering how big the motor is i thought Id have to run a pocket flask for a gas tank. Nope! the tank slides right down and stops about an inch up from where it should. Dangit what is it hitting!!! well, its hitting the cylinder head. Fortunately, as I push down on the tank, the cylinder just splits the forks of the tank and the tank settles into its position. After a few heat cycles, maybe the plastic will deform to fit the engine that is stretching it

I think that covers it all, what do you think
If your looking for some street power www.kustom-kraft.com makes the 301 Big Bore.
 

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Discussion Starter #12
I am not fully aware of the vibration they exhibit. I was thinking about mixing lead shot with some silicone and filling up the handlebars if it becomes an issue. not worried about it as much as I'm worried about the vibration causing important bolts to come loose. I checked out kustom kraft and was unable to locate a 301 kit. Might have them replate my yz250 cylinder though when I get around to it. Replating is expensive! Gotta put that yz motor to use maybe build me another barstool racer. Had one with a gx390 that was a wheelie beast lol. I was looking into the ESR 325 cylinder but it was just a little bit more to get the 500 so I just did that. I honestly can't believe how close everything is either. Its amazing that 2 bikes from 14 years apart from 2 manufacturers have engine mounting bolts all within half an inch of each other. either thats just the very best way to do it and all mfg's figured out the same thing, or they all copied each other lol. well never know!
 

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301 Kit from www.kustom-kraft.com

I am not fully aware of the vibration they exhibit. I was thinking about mixing lead shot with some silicone and filling up the handlebars if it becomes an issue. not worried about it as much as I'm worried about the vibration causing important bolts to come loose. I checked out kustom kraft and was unable to locate a 301 kit. Might have them replate my yz250 cylinder though when I get around to it. Replating is expensive! Gotta put that yz motor to use maybe build me another barstool racer. Had one with a gx390 that was a wheelie beast lol. I was looking into the ESR 325 cylinder but it was just a little bit more to get the 500 so I just did that. I honestly can't believe how close everything is either. Its amazing that 2 bikes from 14 years apart from 2 manufacturers have engine mounting bolts all within half an inch of each other. either thats just the very best way to do it and all mfg's figured out the same thing, or they all copied each other lol. well never know!
Yep it's under Yamaha 2 stroke YZ250-300 kits

http://www.kustom-kraft.com/collections/yamaha-big-bore-kits/2-stroke-moto?page=2
 

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Lol this is fucking awesome.. Id knock off the set of mounts youre not using and relocate them for sure. Im getting a kick outa this build man.

Ive owned two CR500r's, have fun man.. 2 stroke 500's are a blast to ride.
 

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Discussion Starter #15
Oh thanks for the link snowbison. can't believe i missed that before. Im curious what you think if you have experience running one of these 301's. especially in comparison to eric gorr and eddie sanders big bore 250's. sometimes theres just too many choices!

I would actually like to keep the stock mounts intact if I can in addition to whatever mounts I need for the 500. I know this sounds stupid to some but when we go riding for the weekend it would be sweet to have a spare motor. My buddy lost a ring on his yz250 last time we were out and he couldn't ride anymore. and I don't really enjoy or feel comfortable riding out far alone in case mine breaks down, so I was pretty much done riding at that point too. If we had a spare engine we would have been burnin premix again in an hour! who knows if ill be able to keep the frame like that, but its the goal at least.

Last night I was able to ream the hole in the engine. used a grizzly 43 64 drill bit. (17.07mm, I read about this on the forums as a good overbore to allow clearance, not my idea) sorry my slash button is broken on my computer. its a hss chucking reamer so it was easily able to bore the hole in the soft magnesium. I also started removing .25" of material from the clutch side of the engine mount, so as to let the engine fit in there. I got tired and wanted to eat before I got all the way to .25". I have .125" to go. Unfortunately I am an idiot and in my stupor didn't realize that the swingarm bolt changed from 17 to 18mm from '01 to '02, which my bike is, so the swingarm pivot bolt still doesn't fit in. So I ordered a 23 32 chucking reamer (18.25mm)to bore it again to the next size.

Also, I removed the flywheel, used some valve lapping compound and worked the flywheel on the crank. both the flywheel and crank had surface rust. Now they're polished clean and after a hit with a mallet, it is locked on there. stator looked good, though i have no experience with kx500s so that comment is pretty useless.

Waiting for parts or tools sucks!! Its so close, the hole is going to be very clean indeed. Today i should be able to finish cutting the motor and getting it fit in the swingarm. Cant wait to get this rear mount figured out and get going on the other mounts. hell i can't wait to spark it up.

Im just lost with how I want to fuel it. I have the kx500 carb and the yz250 carb. But I've read that 500's are hard to tune (and I'm nothing special at carb tuning) and I'm trying to spend my time riding not tuning. not to mention if I'm riding at gorman its freezing then I go to barstow or ocotillo and its 100 degrees out. because of that a lectron sounds very appealing. If any one has some advice on this matter, Id appreciate it. Pics to come tonight.
 
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