Compression Adequate compression of the fuel-air mixture is essential for good starting and running characteristics of an internal combustion engine. Interpretation of Motorcycle Engine Compression Test Result: (1) The final result should be between 125 to 150 PSI per cylinder (refer to your motorcycle service manual for a more precise specification), and (2) On a multi-cylinder engine, the reading for each cylinder should be within 10 PSI of any other cylinder. There are many different low compression symptoms which will cause the engine to run abnormally. Even if there is low compression in one cylinder you will still get puffs of air coming out of the spark plug hole. I would investigate further with any readings under 110psi. So I have following compression test: 1-3# 120 psi dry and cold. Cylinder head warped. Valves that are anything but radically out of spec will have the same immediate symptoms as not changing your oil - NONE - the bike will run perfectly fine. Low compression is not preventing me from starting. Cylinder nuts not torqued properly. As valve clearances shrink (the typical result of valve wear), but not so much minimal clearance … Piston ring/land clearance excessive. My 1997 RMX250 was only hitting 90 psi compression. Lean from what you describe. Imagine a 1/16" hole in one of the valves. Cylinder head nuts not torqued properly. Just to make things interesting, a number of the newer, big single, dirt bikes have an automatic, spring loaded, Compression Release located on the Exhaust Camshaft. Cylinder base gasket not sealing. For this, you have to buy a pressure measure for conducting pressure test. The bike starts and runs 'somewhat' but recently stalled out in traffic a few times. These bikes will have a normal compression pressure that is quite low, because of the Compression Release. On a street engine .040"/1MM is good. Low compression: Spark plug loose or damaged threads. Readings on all cylinders should be within 10% of each other. 150 PSI would be on the high side of OK with pump gas. Compression ratios on modern motorcycles range from as low as 9.5:1, like that on the Suzuki DR650SE, to as high as 14:1, such as on the Ducati Panigale V4. For fixing of low compression problems. Originally I had issues with starting but that is no longer the case. Cylinder head gasket not sealing. I figured my ring was bad so I measured my bore size, it was still stock so I put an oem piston ring in it. For example, the Kawasaki KLX650A should read 50-85 PSI. Most healthy motorcycle engines will have 120+psi. #4-90psi. There were no deep scratches on the inside of my cylinder. Reed valve damaged. The cylinder needs almost zero compression to make that puff of air. For best compression tester: motion Pro 08-0188 compression tester. That's not enough of a leak to prevent that puff of … Cylinder, piston or rings worn or broken. On a racing bike running race fuel I'll run as low as .030"/.75MM but that's for … I have a 1974 Honda CB550 with low compression and blow by from piston #4- with 90psi. I've gotten it to start! Once the motorcycle has started, if the choke needs to be on slightly, the primary jet is either partially or completely blocked. I agree the problem sounds like jetting. Fixing techniques of low compression. Your compression isn't bad. The bike was a barn find and was sitting for 15years and the engine turned over no problem. 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. Engines will need at least 100psi to run, and they might not run well at this low on compression. Once you find the problem of low compression, you need to firstly change the leaking component. My piston was fine. 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