ridin420 Posted March 27, 2008 Report Posted March 27, 2008 i just for the heck of it checked the compression on my banshee today the bike seems to run real good pulls strong dosnt smoke but the tester said it had 70psi on both sides was wondering if it would run real good with low compression like that had it out yesterday raced a 2004 kx 250 dirt bike i just to say beat him so i am assuming the banshee is running good i just bought the bike havent rode it that much so i dont know if i am lacking power i am thinking mabey the tester is not right hopefully anyway dont really want to rebuild it Quote
viper1 Posted March 27, 2008 Report Posted March 27, 2008 i just for the heck of it checked the compression on my banshee today the bike seems to run real good pulls strong dosnt smoke but the tester said it had 70psi on both sides was wondering if it would run real good with low compression like that had it out yesterday raced a 2004 kx 250 dirt bike i just to say beat him so i am assuming the banshee is running good i just bought the bike havent rode it that much so i dont know if i am lacking power i am thinking mabey the tester is not right hopefully anyway dont really want to rebuild it make sure that the attachment that you plug into the cylinder is as long as the spark plug and also you need to hold the throttle wide open Quote
ridin420 Posted March 27, 2008 Author Report Posted March 27, 2008 make sure that the attachment that you plug into the cylinder is as long as the spark plug and also you need to hold the throttle wide open ya it was a long one and i did have the throttle open kicked it 4 times Quote
Bansh-eman Posted March 27, 2008 Report Posted March 27, 2008 (edited) it will normnally take 10-15 kicks before the needle stops moving. at 70psi your motor shouldnt be running, and diffenatly not runing well. either you did the comp test wrong or your gauge is wrong would be my guess Edited March 27, 2008 by Bansh-eman Quote
NitroTate Posted March 27, 2008 Report Posted March 27, 2008 usually they wont even start under 100 Are you sure? I just bought one for my wife and it's a mess but I did get it started pretty effortlessly after a few years of sitting outside. The compression is at 90 and 92 right now. I think they are right around 110 stock at sea level aren't they? I'm up in Denver at 5200 ft. so I figured 90-95 would be about normal... It runs and starts fine... Quote
mall0y Posted March 27, 2008 Report Posted March 27, 2008 i just for the heck of it checked the compression on my banshee today the bike seems to run real good pulls strong dosnt smoke but the tester said it had 70psi on both sides was wondering if it would run real good with low compression like that had it out yesterday raced a 2004 kx 250 dirt bike i just to say beat him so i am assuming the banshee is running good i just bought the bike havent rode it that much so i dont know if i am lacking power i am thinking mabey the tester is not right hopefully anyway dont really want to rebuild it 70 is definatley too low and 4 kicks won't give you an accurate reading. Keep kicking it until the needle stops rising. Check out the chart I attached. Remember they are only estimates but it should give you a good idea of what you're working with. Quote
Bansh-eman Posted March 27, 2008 Report Posted March 27, 2008 Are you sure? I just bought one for my wife and it's a mess but I did get it started pretty effortlessly after a few years of sitting outside. The compression is at 90 and 92 right now. I think they are right around 110 stock at sea level aren't they? I'm up in Denver at 5200 ft. so I figured 90-95 would be about normal... It runs and starts fine... Tate, Stock around sea lvl is arounf 125-135 Quote
Dinner Posted March 28, 2008 Report Posted March 28, 2008 Tate, Stock around sea lvl is arounf 125-135 Agreed, after running my motor for a season, I checked my compression. It was around 120 and I am at 900-1000ft above sea level. Oh and 70's seems pretty low to me, should be able to take the kicker in your hands and snap it down and have the engine turn over a few times with that compression... As said above make sure your gauge is actually reading correctly, make sure your fittings are all secure and kick with WOT throttle until the needle stops moving :happy: Quote
dajogejr Posted March 28, 2008 Report Posted March 28, 2008 make sure that the attachment that you plug into the cylinder is as long as the spark plug and also you need to hold the throttle wide open Critical point. If the gauge is not as long as the spark plug reach, your chamber will have extra volume (cc's) and the reading will be off. Also...make sure you're using a quality gauge, not an auto parts store cheapy....and keep on kicking till it don't go up no more. I've had to kick 20 to 30 times on some bikes with higher compression.... 4 kicks definitely ain't gonna cut it. And beating another bike is no indication of how a bike is running. All rider being equal and close to weight, an average modded banshee won't come close to a healthy 250 in a drag race. Quote
nayr742003 Posted March 28, 2008 Report Posted March 28, 2008 SO i bought one of them bull dog compression testers and you are saying that if its not as long as the spark plug it will read wrong? how do i know what my wright compression is then? What kindof compression tester should i get if mine isnt as long as the plug? Quote
dajogejr Posted March 28, 2008 Report Posted March 28, 2008 NO easy way to tell you....honestly. The Snap On gauge I use from a buddy is the same way. I generally add 5 to 10 PSI....to be safe. If the compression gauge isn't taking up all the room as the spark plug would be, there is more volume in the combustion chamber.... Just like when you get smaller cc domes for your head, or get your stock head shaved, you are decreasing the chamber and increasing compression. Same for a comp gauge not as deep as a spark plug but in reverse, you are adding volume. No set formula, unless you want to remove the head, screw in the compression gauge and cc the domes. then you could get an accurate reading.... Quote
fun_on_the_sand Posted March 28, 2008 Report Posted March 28, 2008 You don't need to buy a new one, just keep cranking until the needle stops moving, it should get you in the ballpark 110-130psi I would not recomend to buy a presure test unless you rebuild motors quite often, or if you were using small domes; in that case you need to know what is your compression to use the right fuel. Go and use one from AutoZone or Checkers, or split the price of a goodone with at least other 4 friends Go and spend your money on something else. Quote
Bansh-eman Posted March 28, 2008 Report Posted March 28, 2008 You don't need to buy a new one, just keep cranking until the needle stops moving, it should get you in the ballpark 110-130psi I would not recomend to buy a presure test unless you rebuild motors quite often, or if you were using small domes; in that case you need to know what is your compression to use the right fuel. Go and use one from AutoZone or Checkers, or split the price of a goodone with at least other 4 friends Go and spend your money on something else. i disagree 100%. It doesnt matter if you rebuild motors once a week or once a year. A compression tester is a must have for anyone running any motor. Quote
nayr742003 Posted March 28, 2008 Report Posted March 28, 2008 Yeah i have an bad obsseion with tools my tool payment would pay most of you guys new truck payment I had to have it it was on my list of things that i had to have weather i use it once or never i got it. Quote
dajogejr Posted March 28, 2008 Report Posted March 28, 2008 I would add a compression AND leak down tester are some of the best tools you can buy...they take a lot of guess work out.... Quote
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