I have a 1974 Honda CB550 with low compression and blow by from piston #4- with 90psi. 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. 150 PSI would be on the high side of OK with pump gas. On a street engine .040"/1MM is good. I agree the problem sounds like jetting. There are many different low compression symptoms which will cause the engine to run abnormally. Cylinder base gasket not sealing. Originally I had issues with starting but that is no longer the case. Low compression: Spark plug loose or damaged threads. Engines will need at least 100psi to run, and they might not run well at this low on compression. For this, you have to buy a pressure measure for conducting pressure test. For best compression tester: motion Pro 08-0188 compression tester. Reed valve damaged. Once the motorcycle has started, if the choke needs to be on slightly, the primary jet is either partially or completely blocked. So I have following compression test: 1-3# 120 psi dry and cold. Once you find the problem of low compression, you need to firstly change the leaking component. For fixing of low compression problems. 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. Cylinder nuts not torqued properly. My 1997 RMX250 was only hitting 90 psi compression. 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. Most healthy motorcycle engines will have 120+psi. Cylinder head warped. 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. My piston was fine. Readings on all cylinders should be within 10% of each other. These bikes will have a normal compression pressure that is quite low, because of the Compression Release. I would investigate further with any readings under 110psi. There were no deep scratches on the inside of my cylinder. Cylinder, piston or rings worn or broken. Cylinder head gasket not sealing. On a racing bike running race fuel I'll run as low as .030"/.75MM but that's for … As valve clearances shrink (the typical result of valve wear), but not so much minimal clearance … 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. Piston ring/land clearance excessive. Cylinder head nuts not torqued properly. #4-90psi. Lean from what you describe. Your compression isn't bad. 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. Compression Adequate compression of the fuel-air mixture is essential for good starting and running characteristics of an internal combustion engine. Low compression is not preventing me from starting. For example, the Kawasaki KLX650A should read 50-85 PSI. Even if there is low compression in one cylinder you will still get puffs of air coming out of the spark plug hole. The cylinder needs almost zero compression to make that puff of air. The bike was a barn find and was sitting for 15years and the engine turned over no problem. That's not enough of a leak to prevent that puff of … Imagine a 1/16" hole in one of the valves. Fixing techniques of low compression. The bike starts and runs 'somewhat' but recently stalled out in traffic a few times. I've gotten it to start! 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