How to Compression Test 2 Stroke Engines

[@eddymerkin]

Synopsis: put tester where spark plug goes, put gauge somewhere you can see it like the bars, hold kill switch down, hold throttle fully open, kick engine over until gauge psi stops rising.

[@mooman86]

THANK YOU

[@perpelle]

Warm or cold engine?

[@csheltn]

@@perpelle it doesn’t matter

[@Snurre86]

@@csheltn if the bike has been sitting for a few months it matters allot. If you warm the engine and put a few drops of oil in the spark plug hole. If the compression raises it is the piston rings that is the source off low compression. 1. test cold engine 2. test warm engine 3. test with oil in the spark plug hole It will give you more information

[@josephrogers2898]

Thanks man 🤘🤘

[@jdoyle843]

You don't need to throw away $200-$300 on a compression tester thats ridiculous unless your building nascar race engines then I would understand. $50-$100 will get you a really good accurate compression tester. BTW your mostly paying for that name on your tool when you buy snap-on, Matco, or Mac and that's been proven over and over.

[@MrAlittle5150]

Your right, I have a $30 Craftsman and I have Matco I got from my dad. They both read the same.

[@akilez777]

I am agree with you about this stupid video

[@supersubes]

Thanks for the vid Jeff, very informative. In a future video, can you cover compression and how swapping heads or bumping compression affects engine manners and fuel requirements? Doesn't seem to be a lot of agreement about how a 2 stroke acts when you add compression.

[@raydornbush]

Old post Jeff don't know if you're going to see my comment or not but what's your advice on dirt bikes that don't have a kickstart option.

[@slaverace1]

Push the button.

[@The00MOFO]

great vid, do i need a filter on or open air box ok

[@slaverace1]

You are over-thinking a simple procedure. Just get out your gauge and get on with it.

[@ajmontgomery4564]

Always used the electric start, never an issue, same results with kick or pull

[@mihaidobrescu7430]

Hi Jeff. On the older ktm 200 xcw (2006) we have 12.5:1 comp. ratio. Given a atmospheric pressure of 14.87 psi we should have stock a 14.87 x 12.5 = 185.8 comp. But from 2013 (E-start?) the head on the 200 ktm has changed, do you know the "new" compresion ratio ? Or stock compression range for 2013-2016 models ? I asume lower because of the e-start.

[@Ham_Strokers_Ejacula]

Look at the gauge. If it's labeled somewhere on the face "psia" the gauge is psi-absloute or total pressure, more of a specialty gauge and refers to pressure relative to zero or perfect vacuum. Or it could have "psig" on it or psi-gauge which is measured relative to ambient atmospheric pressure. If the gauge shows psig or a lot of the time nothing (psia/g it's gonna be psig), you won't have to worry about additionally factoring atmospheric pressure into the equation unless you need to.

[@BERZERKERSV4]

engine warm or cold when testing?

[@slaverace1]

Hot or cold the numbers don’t vary much.

[@briannelson2424]

What should the compression be on a KTM xc-w 150 2017?

[@xx3868]

Hi, My little weed eater shows 100+ psi when cold (3 pulls) then after its hot for a while it starts to lose the idle and wont run any more. I quickly tested again and only got 70-90 and coudnt even reach 100 psi after 5+ pulls. Is the engine too worn now to make the 2 stoke cycle work anymore? all coil and fuel and carb has been substituted and bypassed so its not that. also crankcase is airtight after pressure testing it to 9lbs and replacing all gaskets ect. only thing left is a worn engine? also idle Low screw setting wont settle in one place anymore and have to keep using choke to start it even when hot. got full power and the l & H screws can give me more or less fuel , its just after a time 10-20 mins its dies and wont run any more like its starving or air being introduced but i already eliminated all that with total strips and replacement and 3 carbs and emptied tank twice into a container to be sure it wasnt blocking up or the vent valve was closing. I even gravity fed the carb when i removed the pump gasket and blocked off the pulse channel to see if that was losing pulse when hot and it worked great and still stopped exactly the same, so fuel delivery cant be it with 3 diff carbs. Thank for anyone who can help out!

[@theshyguitarist]

So after all that, you couldn't demonstrate it for us?

[@slaverace1]

+theshyguitarist Sorry, my bad. I assumed dirt bikers know how to twist the throttle and kick the lever.

[@theshyguitarist]

+Jeff Slavens Yeah well, my carb is off, and I have a kick start lever on order. Your turn.

[@yanb1981]

poor taste to make assumptions. needs demonstration for a good vid. thumbs down

[@westernapache1700]

I also wanted to see how quickly the needle rises on the first few kicks.

[@solidrockchurchmb]

@@slaverace1 I waited to see the compression test to see if the needle stayed at a certain point, or quickly fell back to zero, and you never culminated the video haha

[@robalva2077]

why is the meter amps dropping while it's still turned off and you have nothing on dropping in seconds

[@slaverace1]

Rob: No idea what you are talking about. This video is about compression, not electrical.

[@DevinHarper]

Great tips, thanks for posting.

[@Sportsmaster222]

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

[@austinpurser]

Did you ever figure out what was causing compression to be this low?

[@PorkChop2D]

Hi im working on a IT 125 2 stroke i cant seem to find to much info on it and im pretty sure its not getting good compression would you know what that actual compression is suppose to be for this bike

[@ITZZaGOBLIN]

I just put a new piston and rings in my 2018 250 xcw that I ordered from the slavens racing website. When I went for my first ride on the new top end o noticed the bike was way easier 2 kick over than the stock piston so I ran a compression test and its reading 140 psi I'm not that knowledgeable on compression so I was wondering if this is 2 low or if I'm good. Any ideas is helpful thanks

[@slaverace1]

Not good. With a stock head at sea level it should be 160PSI. I would pull it apart and find the problem.

[@ITZZaGOBLIN]

@@slaverace1 yea I literally just cranked it with my hand something is wrong could it be something with the rings ????

[@oldmanjimbomiller1713]

Hi Jeff, Great video. does the engine need to be warm?

[@slaverace1]

+Jim Miller No

[@Steveman61]

Yes

[@AWDn0t2]

Using the starter (if you have one) does absolutely no harm to the starter. It would be the same as turning the bike over with the spark plug in it. You just shouldn't crank it for 20 consecutive revolutions. A burst of five revolutions per burst is no problem at all.

[@slaverace1]

+AWDn0t2 The entire starter system is fragile. Any unnecessary use of the starter will cause premature failure. We have the largest inventory on the planet of starters and starter parts. Please ignore my advice and grind away on the starter. We love selling starter parts.

[@01cissy]

LMAO on this reply. Thanks for your vids !

[@Nismo65]

@@slaverace1i know its an old post but people still watch for info. you are exactly right im also a motorcycle electrician of nearly 30yrs in Australia. all these modern style mx bikes have a starter motor the size of a 50cc scooter trying to start a 300 - 450cc. people burn them out all the time especially if they have lost spark or a fowled plug etc etc, but they keep cranking it till the battery is almost dead instead of checking shit, mean while the tiny starter and the tiny brushes and armature get so fucking hot it melts the solder on the brush terminals and generally kills the armature too. i also agree with kicking for a comp test instead of electric depending on the bike because some these day don't even have a kicker. uneducated people think there cranking a car starter motor and just don't have a clue about delicate motorcycle components. at least it's money for us.

[@raydornbush]

​@@Nismo65what's your advice on dirt bikes that don't have a kick start option 2 stroke specifically

[@Nismo65]

@@raydornbush if your engine is still in your dirt bike frame with a kick lever you still use a compression gauge in the spark plug hole and kick it over at least 5 to 6 kicks in a row fast with the throttle wide open that will give you the same result as using the electric starter. you should at least have over 100 psi minimum

[@showerpros]

i guess that doing a comp test is know no longer an option when newer bikes don't have a kickstarter

[@slaverace1]

Hold the throttle wide open and push the starter button until the gauge stops moving.

[@ExtremeSports1200]

hey I have a 2014 ktm 150 xc and it has close to no compression. the guy I bought it from said there is a decompression gear so they aren't hard to start in the woods. is this true?

[@slaverace1]

+Sage Witty No.

[@Sportsmaster222]

Sage Witty Hey man did you ever fix that no compression problem? if so what was the culprit?

[@GyroPyro121212]

Hey, do you know the expected cold compression number for a healthy/stock 1985 CR 500?

[@slaverace1]

No

[@GyroPyro121212]

Jeff Slavens Thanks for getting back to me. I found the specs and purchased the bike.

[@charliesample1773]

6 and a half to tell you nothing

[@henriourricariet4111]

How do you like your dampener bars?

[@slaverace1]

Wouldn't ride without them.

[@ghostttdog]

Hi, what is expected value for 2015 KTM 300 EXC? Thanks

[@slaverace1]

160-165 @ sea level

[@ghostttdog]

Tnx

[@ashleyrogers8010]

Yes budubum, pounds per square inch (PSI). He just said pounds for short.

[@jaydiguardi5096]

Why the hell wouldn't you kick it in the video? Demonstrated all of that, just to stop the video at the exact moment we're all here for smh..

[@solidrockchurchmb]

Haha, I watched the whole video waiting for him to kick the thing over because I wanted to see how the compression registered on the gauge, at least I'll stop now lol

[@timk2482]

He must of only been wearing a tennis shoe at the time

[@jaydiguardi5096]

@@timk2482 I start my 250R and 450R with slippers on no prob lol

[@budubumjohansson9147]

265 pounds. were you taking about PSI?

[@violeman]

NICE Compression Test Kit!!! My Dad is a Mechanic so when I need specialty tools like this, I will borrow from him unless I ended up buying some!! My Dad usually uses Snap-On Or Mac Tools but his compression tester is like 40+ years old now, & is made by a Company called "Sun".. I never worry about spark trying to find ground a different route when my Spark Plug wire is safely placed somewhere to hold the kill switch but that is a good tip especially for newer models !!! I will usually hook up a Spark Gap tester too at the same time on Electric Start Models to kill two birds with one stone!! Well Thanks 4 The Tips !!!

[@samvotaw4144]

My bike when u push on the kickstart jt doesn't turn over it slips and hits the foot peg right away

[@rm25088]

Sam Votaw sounds like it's junk

[@mrredline3940]

It’s stripped

[@EpicMan878]

whats the compression on a ktm 250sx

[@jesseb7022]

I would like to know as well

[@christopherwebber1104]

My starter was worthless after working my 450 out. Built engine, hell to kick. Would have put a decompression valve on it if I had it now.

[@zepplin153]

thanks!

[@ricknelson2214]

Don't have to hold throttle open on 2 stroke.

[@slaverace1]

You are incorrect sir.

[@ricknelson2214]

@@slaverace1 you get the same result open or closed

[@risingeagle915]

Hey Jeff you mentioned the three different models having different PSI specs but I don’t remember you mentioning your bike’s model. I have a 13 300 XC and have the repair and owners manuals but I haven’t been able to find the compression ratio or compression specs for the engine.

[@chrisking4515]

Kick it like you hate it. Love it

[@catalinnicolaevici2061]

SOB... i took the head bolts off for nothing on this yamaha kt100... but noone is giving me a strate answer and a answer with science behind it... im in Cincinnati and it got around 130-135psi.. my buddy whos a master mechanic(im also a mechanic but didnt care to go get my ASE certificate plus i got burned out by ppl bringing in trash vehicles that hasn't had maintenance done on them since the Purchased them... but my buddy o dude that sounds low vehicles are supposed to be around 180-190...idk what vehicles hes talking about cause as good as i am at mechanical im probably 5x better in electronic engineering and microsoldering.(at least with devices you get a nasty one every once in a grate blue moon. Those ppl dont have stuff normally fixed anyways) but i didn't hold the Throttle wide open. The fuel pump vacuum was off and im in Cincinnati ohio... i bet you tha t was a good result for that engine.. i guess ill see what happens when i get new head bolt washers everything else i have more extra of..

[@jimmywaters8929]

Kick it! please

[@chamuko999ify]

$300.00 dlls!!!!🤮😱😭💀 you crazy or you crazy rich I have a home make for $22.00 and work fine very very good!!!