Worn valve seats, heavily developed pitting, carbon build up, cracked valves loose or worn valve guides as well as a number of related things also cause low compression symptoms the compression test cannot analyze. If you do your regular maintenance, your 2 stroke carb jetting is tuned, and you run a proper pre-mix ratio, you could see up to 100+ hours of ride time before the compression starts to drop. ... You could have perfect motor and it will show very low compression. I have a 2005 Polaris predator 90 that my 9 year old has ridden the tires off of. 11 Posts . I have 2001 sportsman 400 with low compression were talking 60psi. If you experience low compression on all cylinders, it may be caused by a faulty fitted camshaft timing belt or chain. I know the book calls for 108psi, but I'm not sure how low is too low and if what I'm describing could come from low compression. PDA. Discussion Starter • #1 • May 27, 2009. There are many different low compression symptoms which will cause the engine to run abnormally. If you know that you got low compression after a timing belt replacement, check the timing. My bet is valves are worn out if your having trouble starting it but using a leak-down tester is the best way to tell. Discussion Starter • #1 • Nov 9, 2012. 124 Posts . In fact, it’s not uncommon to see over 200 hours on a 250 … I did a compression test today and it only came up to 75psi. Lastly, owners of 4-strokes should complete a Leak Down Test if a compression test indicates low compression. Help!!!! I had an extra cdi box laying around, tried it, didn't help. Doing a engine compression test will help you locate potential internal problems affecting engine performance. Anyways, if you experience low compression on all cylinders, check the timing. ! Vehicle engines are precision machinery; the movement of many parts must be synchronized carefully to make the engine perform properly. Discussion Starter • #1 • Jul 12, 2012. guys before i took apart my 400ex motor to replace the timing chain i had about 120psi of compression. Intake and exhaust valves are critical components for optimum engine performance. ATV Riders Forum > Sport ATV Model Information > Honda TRX 450R ATV Information > no compression,but good piston and rings? farmer250r. These valves contain mechanisms that must be adjusted correctly to … 1 Posts . These are found between the crankshaft and camshaft. Engine Compression - What Can Cause Low Or No Engine Compression An engine compression test is the most practical way to learn about the mechanical condition of your engine. Moderators - please move this to wherever it should be, couldn't find engine or mechanical section. Flushed fuel out and replaced with new. An engine with low compression in one cylinder will present itself by having a misfire and running rough while no compression in all cylinders will cause the engine not to start. 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