KX250 Compression Test (2 Stroke)
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- čas přidán 22. 07. 2024
- www.howtomotorcyclerepair.com/...
Click link above for blog post and service manual.
Checking the compression on a 2 stroke will determine the health of the top end. Low compression can be a sign of worn piston/rings or broken/chipped reeds. My reeds were chipped and saw an increase of 20 psi after replacing them!
Checking the compression often will help you determine when it is time for a rebuild. - Jak na to + styl
Man you don’t know how much this video help me! I’m rebuilding a 1991 kx250 and mine was blownin air back in the tank when I shut it off! Going to put new reeds in it! Holler back at me
I know what you are referring to, the long 14mm adapter. It would give me "more head volume" and probably a lower reading. As you can see I don't have room for that adapter unless I take the tank off.
I wanted to see readings before and after the chipped reeds. Also, I plan on doing this test every 5hrs or so to monitor when I need a new top end. As long as I am consistent on how I do it, the readings will tell me something is up.
Hey Matt I bought a 2000 Kx 250 with almost everything wrong with it with the exception of having a strong top end. I have bought many parts for the dam thing but I am riding so I am happy. I had purchased your rebuild video on the Gumroad app and it has helped me a few times. Thanks for posting your videos now on the remainder of the bike. I am subscribed and much appreciated. Take care and keep her tire side down bro.
Awesome! Thanks for the compliments!
hey how's it going.i want to ask you a question. I just bought a 1989 kx250 that has a rebuilt engine, when I bought it started right up and ran perfect and idled really smooth and now it takes a while to kick start it and when I ride it it like idles high then low then high then low and stays like that even when I hit powerband it does that. I don't know what it could be, I changed the spark plug and put a BR9EIX do you think I need to go to a hotter plug like a br7es.
What do you think is a good price for one in this condition nowadays? Thx
What year make model? What are you trying to accomplish? More bottom, mid, top end power?
Verify or check your gauge with another one to make sure it is reading correctly. Pull your pipe and have a look at piston through exhaust port. Pull reeds and inspect.
Let me know what you find.
This is correct. I've done this same test in shop class all throughout highschool. I've rebuilt snowmobiles, dirtbikes, fourwheelers, lawnmowers, etc. This is correct
I'd LOVE to hear your version on how to do it.
What do you think is worth the money? An aftermarket silencer or aftermarket reeds? Which would you choose over the other for a first mod?
i like your videos thanks for the details, im getting a 01 kx250 on friday but it needs reeds and the power valve is broke appenrantly i also have to put a new piston in thanks for the info hope you dont mind some questions if i get stuck
Yes, that is correct. It is rich from factory and have leaned it out a bit.
Hi! i did compression test also and cold engine was 165 psi and warm engine was about 150 psi and there is stock reeds, i dont know what condition. previous owner said that piston is changed 27 hour ago and only slow forest driving since. what do you recommend to do? i said earlier that my kx250 is 2000 but now i know for fact it is 2001. i bought new FMF gnarly pipe and powercore 2 silencer it did help a bit for the power solution and i changed main jet previous was 178 now 162.
I have a few riding vids I need to edit and upload. I'll be doing a top end vid in the next 6 months.
If my piston ring is bad will I get low compression
Very informative vid man, thanks
ur vids r good man hav u got any of u ridin ur kx 250 nd if u do a top rebuild stick a vid up on ere
how is lean equals to reliabilty?
Twist the tester the opposite way before you screw it on, it keeps it from having so much resistance 👍🏼
Thank you man ! Very informative 👏
Yeah, it's pretty clean and I picked it up for $1100. Check out the blog post "Bought a 2001 KX250" for more pics.
Thanks sailor.
Yes, that can be one cause.
Do you have a video I can purchase on doing a bottom end and top for a 99' kx250 ? Thxs
Yes, here it is www.howtomotorcyclerepair.com/kxenginerebuild/
Nice video I purchased a 2000 kx250 a(2stroke)nd I don't have the compression gage to check it but when I try to kick start its soft like I can crank it with my hand does that mean I'm low compression ?
+LOWPEZ Certainly can be low compression. Mine is very hard to kick and hurts to do so in gym shoes.
The only way to tell for sure is to put a gauge on it.
Here is the one I have and recommend:
amzn.to/1FNoLI5
How does it run otherwise?
is it okay to perform a compression test on a sitting(cold) engine....? need to check a 92cr250 thats been sitting.... any help much appreciated
+Chris 500 Yes, just don't expect the numbers to be as high as a hot engine. My 2nd bike was a 92 cr125.
Thanks! Just did a new top end
Its my kick start that won't go down it's stuck. I already removed my piston and cylinder head. So what would I need to fix it?? Its something de as long with the gears??
Javaris Jones Your kickstarter is seized? Can you rotate crank by hand with trans in neutral?
its a 2003 Yz125. I want power everywhere but mostly mid to top.
No problem!
My throttle wont latch back forward when I pull it back, and everytime I turn it on it automatically accelerates like if the throttle were pull all the way back and nothing is stuck in my throttle nor is idol up, and everytime I pull my throttle back it gets stuck and have to force it back forward while nothing is stuck I it please help
+Angel Govea I responded to this question on another vid you commented on.
Quick question, my motor is locked on my yz125 2005. How can I unlock it? The easiest way possible....
Javaris Jones Start taking it apart. If piston is seized then hit top of piston with wood and slide cylinder off.
01 model and excellent condition wow!!
when I ride my bike in grass feels like am like losing compression but on road it rides fine what could that be
Eddie Edwards Compression won't change based on what your wheels roll on. Please explain your symptoms in more detail.
I got a 1996 KX250 with a Wiseco top end around 250 psi bike runs awesome should that be normal?
Definitely need race fuel to run that compression.
I did this test cold and it was 152 psi would it be more hot ? also I cant get my bike to run it fouls the plug in 10 min and wont start that's why I did it cold .
Re-jet it
Question for anyone who knows, do you need a different compression tester then one used for cars cause I bought a tester from harbor freight that's for cars and I tried it on two bikes cr125 and Yz 125 and the guage wouldn't hold the pressure is kick it would go to like 30 psi then drop both bikes were 30 psi the guage wouldn't hold the pressure so do I need one that's made for bikes I don't get what's going on
Your problem is the HF gauge. I bought that one and there is a design flaw. There is no schrader valve in the end of hose. I highly recommend this one: www.howtomotorcyclerepair.com/compression-tester/
Thanks for posting this comment, I was going to buy on those, until I read your comment
Thanks!
Hey man the reason why it read so high on the compression is the compression tester its self , the way you put it in the bike alows more air to go through the hose (i had the same results with my 125 reading 160) anyway there should be a fitting that goes on to the one that you screwed right into the motor and that will give you correct readings
Didnt mean to ruin it for ya !
Hey. I bought a stock 250R that ran when I got it, but wouldn't idle or accelerate correctly. I cleaned everything, stock settings, checked the reeds, and finally did a compression check. It read 125 psi. My manual says a stock is supposed to be 170 psi +/- 15. My local dealership mic the cylinder and advised getting stock rings, so I bought the whole Wiseco top end kit. It ran a tad better at first, then started fouling plugs. Then it would bog, spit, and sputter. I tested the compression at 140 psi. My local dealership and another bike mechanic said that number was fine. I don't know if they realize this is a liquid cooled, high performance, 2 cycle motor (140 psi would be good for a 4 stroke). I don't know what else can be causing this. Before I drop another $175.00, I really need a wise second opinion. Think if I bore over 1 and get another Wiseco piston/rings, that it would solve my problem? Thanks.
+Chad Adams Lot factors here to consider.
What brand comp gauge?
Reeds in good shape?
Did you hold the throttle wide open during test?
Measure ring end gap?
Power valve operating correctly?
Why can nobody pronounce "Wiseco"? Its not real hard....."Wise-co". Short for Wiseman Piston Company founded by Clyde Wiseman. It's not "Why-see-co" or "Wise-e-co" or "Wise-a-co"
I just did a test on my 99 kx 250. The compression is at 120. I had to keep on kicking it to get the compression up. But once I quit kicking the compression slowly went down as well.
The gauge is leaking, go get another one to try.
today I put in a new plug and it started in two kicks checked compression 152 cold 125 hot after 2 or 3 min at a idle with me keeping the rpm up. I thought it would be more hot or 3 min. wasn't long enough to get it hot so what do you think ....please help
+bob s Bob, regardless those are low numbers. You nee to open it up and see what is going on. Check the reeds first, and go from there.
+MatthewMCRepair ok will do but what did you think of the hot test since it was lower then cold ? should be more hot even if rings are bad don't you think
Typically hot results are greater. I can't explain your results.
I have an 04 kx250 and a 13kx250f and the 2 stroke is much harder to kick. I keep both my bikes well maintained can anyone explain why this, I would think the 4 stroke would be way harder to kick. Thanks
+Zack628 Your 4 stroke has an automatic decompression system that is only active during kickstarting.
You said an operating temp, but your able to touch it with your hand. how long should i run my cr 125 before testing?
I'm mean generally 2 strokes cool off pretty quick externally. Just run it for about 10-15 minutes it should be plenty warm by then, and have all your tools ready to go because these bikes cool off pretty damn quick
danemania001 Just a helpful hint, anit-seize your spark plug threads prior to removing a spark plug from a hot aluminum head or you will possibly have no threads left in your cylinder head
anime2485 I never added any lubricant or anti seize to a 2 stroke plug. I feel that the 2 stroke oil makes it's way to the threads and is good enough. Never had issues this way.
hi, i just made a compression test on my rm250 and it was 100 psi. at wich value should i change the piston. thanks
Assuming you did it correctly, you need a new top end.
thanks for the replay. engine was cold, throttle wide open.
if it's under 150 it needs rebuilt 140 at the absolute lowest
wrench One in this video that you just watched he clearly said that in the service manual spec is 115-172psi. So this means that you can be running at 115psi still but it will likely be hard to start and not have much power left in it plus highly risk blowing the motor top end due to wear on piston rings and the cylinder walls. It causes blow by which creates hot spots around the engine. One will give and meltdown occurs. Reasons for compression higher than new stock usually only happens from aftermarket parts that take the engine closer to its maximum potential. Not trying to take a stab at you. Ride for life!
I have a 1986 Kawasaki kx125 and it won't start I've checked the plugs it had new gas the carb is jetting and everything electrical is solid I just done know why it won't star the compression seems ok but I don't know
You really need a gauge to determine how much compression. Next, install a NEW plug. If it still won't start, see if plug is getting wet with fuel.
Hey man, I have a 1990 KTM EXC 250, I bought the bike off of craigslist awgile ago and ran a compression test and it won't climb over 30 psi, I don't know if I need to plug any certain part of the engine, everything is on the bike and hooked up except for the seat. I'm pretty lost when it comes to working on bikes so I was curious if you knew what could be causing the bike to build almost no pressure...btw the exhaust pipe is not totally secured but is on pretty good and there is a small oil leak, other than that I'm completely lost....any help would be appreciated! thanks
What brand gauge and are you holding the throttle wide open?
MatthewMCRepair it's from Oriely Auto parts, about $40 and yes full throttle. the gauge is on tight as well
Does it run? There is no way it will run with that much compression. Double check the gauge with a known good air source.
MatthewMCRepair no haha the bike doesn't run
Buy one of these cheap cameras and drop it down the spark plug hole: amzn.to/2t7gzRT
Or bite the bullet and start taking the engine apart.
Bike is in beautiful shape
Thanks.....it is because I have no time to ride.
Thank you so much for this video, this helped me so much. I bought the compression tester you advertised and it worked perfectly. Before I watched your video I watched some other D-Bags video saying i need to spend $3-$400 on a compression tester! F$&@ that guy. Your video worked great, thank you so much!!!
I had a 1986 kx 250 and did compression test and third time kic was on 275 on the guage the bike 250 stickers on it but when tooke engine apart it had aftermarket KIPS jug and cylinder head and billet piston the person my cousin got bike race motocross. Yours has 200 psi you can get a lot more compression out of that motor.
Sure but I don't want to run race fuel.
+MatthewMCRepair so I have a 2001 yz250 2-stroke. I just put a new top end on it. now the bike won't start. I had no trouble with it before, It would start up first kick. the bike sounds like it wants to start up the first kick but doesn't. it has spark and everything. need your help.
Does the plug get wet?
yes it does. it's like a black color.
Sounds like you are running an old plug. Try a new one.
it's a brand new plug. it sounds like it wants to start but it does right away. I just don't want it to be the cdi box.
It was running before the top end correct? Then it should not be CDI box. Do you have compression? Fuel/air? Spark timed correctly? If you have all 3 it should run.
on a electric start only dritbike can you still check compression the same way?
Yes, just won't have a tired leg.
okay thanks also do you have any videos for electric start dirtbikes like how they charge or replacing what charges them or replacing starter stuff like that
I watch a lot of your stuff and have learned a lot from them lol
What year make model do you own?
Right now i dont have one but i have been buying and selling bikes for the past year i think next i am getting a kx100 last one was a rm125
Kx100 electric start??? Whaaa
I miss my 01 KX250.
hello, how many bars to replace the piston I have 12.5 bar is ok
I had 200psi, which one would argue is a healthy top end. I took it apart and was completely worn. Pull the exhaust pipe and look at piston. Sometimes you can't tell if it needs a rebuild unless you take it apart.
@@HTMR I mean, despite the compression, it's better to see what with the piston?
@@kolo1367 You would be looking for score marks on piston skirt.
@@HTMR however, I check the piston texture to make sure
@@HTMR thanks for the channel that I like. I like your movies
I recently did a compression test on my cr250 and my gauge showed on both tests 90 psi. idk if the gauge isn't working correctly or what but the spark plug doesn't show a lean condition but a little rich. the low end feels like a rich condition but mid and top feels good.
also it read 90 psi after I rode the bike for a while
+M Pasel What brand gauge? Does it have a schraeder valve at hose end? How does the bike run otherwise?
+MatthewMCRepair I'll have to double check when I get home but it was a cheapo from harbor freight tools. the bottom end feels pretty blubbery but opening up the throttle it clears up and pulls. spark plug after running was black and dark mocha color.
+M Pasel Bingo....the HF unit is junk and gives lower readings. Here is the one I recommend:
www.howtomotorcyclerepair.com/compression-tester/
Buy it here:
amzn.to/1VM4xWc
+MatthewMCRepair awesome thank you so much I just placed a order for that unit and will get back to you asap with the readings.
Does it matter if the throttle is wide open? And gas on or off then? Thanks.
If the throttle is not wide open, it won't pull much air in to compress, therefore resulting in a lower reading.
It is best to run carb dry of fuel before testing. Sometimes fuel entering cylinder can give inconsistent results.
no throttle is not a factor open or closed. gas off just kick it till you see the highest reading on the needle. i do warm and cold tests.
Kevin Stearns Every manual I ever read states WOT. Now it probably will work w/o opening throttle, however you will have to kick it MUCH more. If you feel like you need a quick workout....go for it!
+MatthewMCRepair did you get more when hot or cold ? I have more cold why
+bob s What are the values for hot and cold?
good vids
Doesn’t this have compression lever
No.
Damn I wish I could learn how to do this stuff !!!!!
+doobyboy21 you just did :)
Lean is mean. You can't expect a 2 stroke to live long if you run it lean.
kx 250 backfires woodruff key? spark plug? ideas
Kevin Stearns I've never seen a sheared woodruff key. Pull the plug and let me know what it looks like. Email me here and I can help you through this:
www.howtomotorcyclerepair.com/contact/
Matt
MatthewMCRepair im pretty sure the plug is shit i bought a new one later ill try it. thank you for helping.
Kevin Stearns OK, let me know.
MatthewMCRepair hey matt i took it apart last night the rings were fuked. ring end gap was 3 times what it shouldve.
Kevin Stearns been
Windows Live Movie Maker
Wow clean
Daniel DeMayo Thanks, the way I like it!
yes i know but he said he wanted to lean it for "reliablity" my vote was to NOT!
Now former military, I plan on going to wyotech for Yamaha and Kawasaki dirtbikes.
cool
sorry its a 2002 kx 250
Not holding the kill button or having grounded spark plug can kill your cdi box when kicking it over like that.
You know, I have always heard that, however been doing it for 20+ years and never had one pop on me.
no he didnt, he said it is rich which is more reliable. Then he said he wants to lean it a bit in the future
I don't mean to nitpick, but you forgot to press the kill switch. Since the plug is out, it's not grounded, and you can waste your electrical system.
+jotacalvo I see your point, however never grounded a plug prior to comp test, and never broke any ignition systems.
Whats ignition system and would the bike still run if it was damaged?
+Pizdzirynka1 The bike would not run without spark.
jotacalvo that's not true
throw away that KOSMIC gauge !
what about 100324 PSI? cheap gauge
у меня после трёх качков-11 показывает,а сдесь он маслает 15 раз-14 показывает,если бы я так же маслал-с такой силой и столько раз-у меня бы прибор зашкалил.
Even with google translate I can't understand what you said. Please respond in English.
I have after three strokes-11 shows,and here it maslaiev 15 times-14 shows,if I masel-with such force and so many times-I have the device for free.
That still makes no sense to me. Please restate the question.
reeds have nothing to do with compression
+Don't race me I'm to fast I disagree. The reeds act as a checkvalve, letting air in, not out. As the piston moves up, it sucks air in. When it moves down, the air gets forced into the port leading to the combustion chamber. There may be overlap in the intake tract and port to combustion chamber, therefore air may escape back into carb/airbox during this time. Reeds prevent this.
Bottom line, my reeds were chipped/cracked. My compression test went up 20-25psi with new reeds that help keep more air in the engine.
you foolish berk.
you done compression test with no fuel going through the engine to lubricate, then have the cheek to say the reeds gave more compression ha ha ha . so your engine don't have exhaust then !!! and could never work with a expansion chamber could it,if the reeds give compression ha ha ha you don't have a clue and yet think your an expert.... operating temp on that engine would rip the skin off your hand as well.
this engine is cold,dry and your complete way of testing for compression is wrong...never put petroleum on rubber washers !! why / because it rots them.
if you would have listened to what he said, his old reeds were cracked, thus instead of the reeds closing and not letting that air escape through the carb, it was letting it escape (back pressure) so yeah actually in that case it would.
The residual oil film in engine is good enough to kick a bike over a few times to do a compression test.
To be honest, the engine was warm.
WD40 is safe for rubber.
I'd love to see your compression test video.
Regardless, it has great compression and runs great.
phillnjack shut uppp
phillnjack this was three years ago and I still think that you should pull your own comment. Most of what you said is just dead wrong. Take care and do some research before you speak. Hope you have matured since this. Lol.
Where's your video at smart ass. I wanna critique the hell outta yours.
hey how's it going.i want to ask you a question. I just bought a 1989 kx250 that has a rebuilt engine, when I bought it started right up and ran perfect and idled really smooth and now it takes a while to kick start it and when I ride it it like idles high then low then high then low and stays like that even when I hit powerband it does that. I don't know what it could be, I changed the spark plug and put a BR9EIX do you think I need to go to a hotter plug like a br7es.
No problem!
when I ride my bike in grass feels like am like losing compression but on road it rides fine what could that be
+Eddie Edwards Does it feel like your bike isn't going anywhere in grass? probably just not getting any traction.
Thanks!
hey how's it going.i want to ask you a question. I just bought a 1989 kx250 that has a rebuilt engine, when I bought it started right up and ran perfect and idled really smooth and now it takes a while to kick start it and when I ride it it like idles high then low then high then low and stays like that even when I hit powerband it does that. I don't know what it could be, I changed the spark plug and put a BR9EIX do you think I need to go to a hotter plug like a br7es.
+Jo F Check for vacuum leaks and go thorugh the carb:
czcams.com/video/jRBA1gHlx6k/video.html
What does the plug look like?
Feel free to email me here for more tech support, I respond quicker:
www.howtomotorcyclerepair.com/contact/
Thank you,really appreciate your reply
+Jo F No problem. Go ahead and email me here: www.howtomotorcyclerepair.com/contact/ A lot of people send me pics/vids and that really helps in troubleshooting.
Ok appreciate it, I will take a video