yz250 can't figure out
  • rideCR.
    Posts: 152
    I have a 2000 yz250 that was built from the ground up. It was stock bore and really hard to kick over compression wise. the head is shaved as well. I started it up with the second kick and took it out. It rode fine in lower rpm's, but as soon as I opened it up it would bog. (the same kind of bog you get when you start up a 2 stroke and hold the throttle wide open.) I took it down a straight and it finally opened up the whole way, but after that it shut off and lost quite a bit of compression. It has a steel liner in it, so I bought a wiseco piston .040 overbore and put it in after having the cylinder bored. It had the same hard to start feeling as before, but took 6 or 7 kicks to start, and would back fire on a few of the kicks. Ince it started, I had to hold the throttle open a bit to keep it running, and as soon as I opened it up it would do the same thing, just bog. Im running klotz super techniplate oil with 93 octane fuel, 45:1. The coolant leaks a little bit from the head nuts because I forgot to put the copper washers on, and when I open the rad cap after it runs for 5 minutes the coolant shoots out. any ideas? thanks.
  • markyrocks
    Posts: 1,275
    Ummm do whatever you need to do to get head to stop leaking antifreeze. Once antifreeze heats up it builds pressure in the system hence when cap opened that pressure only has one place to go ie it shoots out.

    As far as it bogging down.... sounds like it needs jetted. Also using pressure from feel from the kick starter is not very accurate test, its about as effective putting ur thumb over the spark plug hole.
  • rideCR.
    Posts: 152
    compression reads 185, and I know how to fix the head leak, but Im wondering if that has something to do with it? everyone says jetting but it's not. Ive tried a few different carbs but all three do the same thing. it doesn't bog down and die, it just doesn't go any higher. its like when you hold a cold bike wide open.
  • markyrocks
    Posts: 1,275
    Carb isn't the issue its the jets inside you could of tried three different carbs withe the same exact jet setup in each one..... what's that gona prove. First off what color is ur plug?
  • rideCR.
    Posts: 152
    the plug is just matted silver now. and I actually have a box of jets, which I used to drop the main jet down to a 150. I was reading online about the expansion rate of forged pistons (wiseco) on steel liners. Could it be possible that the piston is expanding whereas the cylinder walls are keeping it compressed?
  • markyrocks
    Posts: 1,275
    I mentioned color of the tip where spark generated. The part that is inside the motor. From my understanding bogging is caused by a too rich air to fuel ratio. If the plug is pitch black then ur rich. If its white ur lean it needs to b like a Carmel color.
  • rideCR.
    Posts: 152
    yes the bridge of the plug is just a matted silver now. its not really the bogging you get when you foul a plug, its the kind you get when you start a cold bike and hold it wide open
  • markyrocks
    Posts: 1,275
    Ya how bout posting a pic. Aaaa NM just take it to a shop. I don't feel like ur qualified to be working on any motorized vehicles.
  • rideCR.
    Posts: 152
    What are you talking about? The bridge, the part in the motor, is matted silver.
  • rideCR.
    Posts: 152
    Look man, Im getting the vibe that you're just being an asshole. You are telling me to try a bunch of stuff I tried a month ago. And if you don't know what the bridge of a spark plug is, you're probably not qualified to own a motorized vehicle. So, if your trying to help I'd appreciate it, but I don't patience for bs. And to set the record straight, I took it to clarion cycle and they don't know how to fix it either.
  • markyrocks
    Posts: 1,275
    I am an asshole. But I do know alot about bikes. If you took it to a shop an they didn't know how to fix it. They're either extremely incompetent, or u just gave them similar attitude your giving me an just left you to you own devices. If the end of the spark plug is still like new the its running lean as can possibly b. But really can't say BC you wont post a pic. Who built this bike from the ground up? If your saying bike hard to kick from cold it has nothing to do with piston expanding. But it could b incorrect tolerance from the start. Good compression shouldn't make bike hard to kick (least no harder than any other bike) if it is a lean condition this will make bike run really hot would explain you coolant problems. If you over heated it could have blown headgasket or even warped cylinder which warped cylinder would prolly put excessive pressure on piston
  • rideCR.
    Posts: 152
    The shop told me I would have to take somewhere that focuses on cylinders. The coolant problem is a simple fix, I just have to get around to buying some copper washers and acorn headnuts. I only mentioned that to see if it could be part of the bigger picture. However, neither surface of the cylinder are warped, the top will set flat on  glass and I can rotate the bottom on glass without it wobbling. As far as kicking it over goes, Its a healthy kick, and compression matches. neither the O rings or the base gasket show signs of a leak into/out of the cylinder. I can't post pics because I have no way of doing so on my Ipod, but the bridge is lightly coated and wet when pulled. The problem that I am leaning for is the expansion rate of a forged piston on a steel cylinder liner. I built this bike from the ground up. It is the fifth one and the second yz250. This is the first time Ive seen something like this and I'm a little stressed out over the severity of it, which justifies my attitude.
  • NZriderNZrider
    Posts: 5,083
    sounds like a weak spark to me. i'd be checking out the stator output voltage
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • markyrocks
    Posts: 1,275
    Ok well let me ask you this. When you redid topend. Did you have anything done to the cylinder? Or did you just look at the piston size an just got the same size piston an ring an just drop it in?
  • NZriderNZrider
    Posts: 5,083
    read again man, its been overbored to match a oversized piston
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • rideCR.
    Posts: 152
    I had it taken to AMs with a Nee piston and it was bored to the piston. But I will check out the spark too, thanks. How can I do this?
  • markyrocks
    Posts: 1,275
    Ok so if they bored it to the piston I'm sure they know the correct tollerences for a forged piston. Unless there was some kind breakdown in communication to where they set you up for standard piston. But I'm gona assume that not the case. Did you do a real tune job? Or did you just swap out some different carbs?
  • rideCR.
    Posts: 152
    The cylinder was fitted to the piston. I have another yz250, same year and everything. It is also bored .04 over. That bike doesn't have a problem like this. it has an iron sleeve which is the only difference. I tried the Carb from that one as well as a spare I have. Neither solve it so I got a box of jets from the shop and experimented with the needle, air screw, and both jets. Nothing I did solved the problem.
  • markyrocks
    Posts: 1,275
    Maybe you have a clog in the petcock or fuel line. I'm gona assume your using fresh gas and that you inspected reeds ect to make sure there good. So I'd say clean an reoil air filter an check exhaust system for obstructions especially the packing in the silencer to make sure it not suffercating the bike. Get multimeter an do thorough tests on cdi ignition coil an crank position sensor. If all that stuff is good. Then your motor is binding up for some reason.
  • NZriderNZrider
    Posts: 5,083
    oooooh muffler packing is a good call. an internally damaged muffler will cause these exact symptoms
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • rideCR.
    Posts: 152
    I have a brand new muffler, new air filter lightly dampened in filter oil, and I bought 2 gallons of 93 octane and mixed it with klotz supertechniplate not even an hour before it was run through the bike. Im taking it out to world of wheels today so they can run the tests that I don't have the equipment for, then I will let you all know what's going on. thanks.
  • rideCR.
    Posts: 152
    They said the same thing. Im going to look more in depth about the expansion and possible have it bored to clear a bit more.
  • rideCR.
    Posts: 152
    http://forums.everything2stroke.com/showthread.php?t=49933

    This is the same thing that is happening to me. It would sputter in the higher rpms, but once I got it to break through I lost my compression. If it is something electrical, why did I lose all of my compression?
  • NZriderNZrider
    Posts: 5,083
    what went wrong the first time you lost compression?
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • rideCR.
    Posts: 152
    I don't know. Haha I got a new std bore piston and put it in and found out it was too small. That's when I got it bored
  • NZriderNZrider
    Posts: 5,083
    wtf? you really should figure out what went wrong when a bike blows up. otherwise you risk rebuilding it and having the same thing happen again.

    did the old piston seize? was it melted or scuffed on the skirts? was the ring stuck?
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • markyrocks
    Posts: 1,275
    Well for what its worth only time my bike sounds like that is when its running out of gas. That why I was so hooked on Carb questions. If your revving out and loosing power at top of gear try shifting up one you'll start all over.
  • rideCR.
    Posts: 152
    Well the piston and cylinder were fine, and I had a brand new piston in the garage so I stuck it in because I figured my rings were bad because there were no other signs of mechanical failure. The bike kicked over fine, just no compression. It did start up with the new piston but still had no comp so I had it bored.
  • rideCR.
    Posts: 152
    Turns out that the guy who sold the motor to me had the wrong set of electricals with it.
  • NZriderNZrider
    Posts: 5,083
    well thats a good find. good job man.
    its a shame you left out the bit that its not the original engine. helps narrow things down a bit quicker.
    *********************
    Winning is 90% rider and only 5% bike, the rest is luck
  • markyrocks
    Posts: 1,275
    Ridecr how did you figure that out?
  • rideCR.
    Posts: 152
    It was a full bike when I bought it, just blown up. I'm thinking the guy bought a different set of electricals when his failed. I just checked serial numbers and got the right ones. I've been on the bike for 3 months now with no problems. 
  • markyrocks
    Posts: 1,275
    Sweet
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