So I went and looked at another boat today. It was a 98 speedster. I did the compression test and after further investigating I think no i'm sure I did the test wrong. I now use Google to search this site and it has pointed me in the right direction of properly testing. Here is what I did. On cold engine I pulled one plug and left the other in and cranked the ignition for about 5 to 8 seconds until the gauge leveled out. They all tested at about 170 and one of the four was about 160. Which is way over what I was told on here to be normal. What does this mean?
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Newbie mistake.
- Thread starter classy
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It really shouldn't make a difference if you remove both plugs. When you did the compression test did you hold the throttle open? I'm guessing that the high compression is either there is extra lubrication in the cylinders probably from winterizing the ski and fogging the cylinders. Or you have a faulty compression gauge.
You might try starting the boat letting it run for about 30 seconds, let it cool for a few minutes and then re-check the compression.
Lou
You might try starting the boat letting it run for about 30 seconds, let it cool for a few minutes and then re-check the compression.
Lou
1 more thing, not 5 seconds plus , watch the needle on compression guage, the first stroke or fluctuation should be at least 80% of your total psi, then it should only be 3 or 4 total strokes of the piston, not 5 seconds, so, with throttle all the way open, and you should ground plug wires so it doesnt start, and total of 3-4 strokes of the piston, this is your compression, also, motor doesnt have to be stone dead cold either, cause when you run it on the lake, its not cold --- this is something i read here all the time, and im trained to check compression on a warm eng, not a hot eng, just a warm engine --------- if you turn a motor over for over 5 seconds, piston has probably went up and down 20 plus times, so you would be building up compression and not a true reading
people here will tend to argue the point of me saying no more than 5 piston strokes and on a warm eng, but, if it takes more than 5 piston strokes to reach say preferred compression reading, then something is probably wrong then anyways, and me, i wanna see what my compression is warm, and really, theres not much difference anyways
people here will tend to argue the point of me saying no more than 5 piston strokes and on a warm eng, but, if it takes more than 5 piston strokes to reach say preferred compression reading, then something is probably wrong then anyways, and me, i wanna see what my compression is warm, and really, theres not much difference anyways
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You are using a compression tester with a check valve in it? Not no cheap Harbor Freight unit? You will know becuase a good tester is over a $100 and cheap one is like $20(New of course). A cheap one could give you a wrong reading. Doesn't matter if you leave the other plug in or not. It will just turn easier. If the engines are stock the compression should fall within specs of the manual..
bigtexan99
Active Member
Also, a seller who is hiding bad compression may have added oil into the spark plugs right before you got there. Adding lucas oil will temporarily increase compression.
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