splitshot

I have a 1977 140 johnson motor on my 1986 hydra sportbass boat and i have a problem with it...the cylinders are 110 lbs on the compression test except one it is 90 lbs but my problem is rpms when running the boat it will only do 3200 rpms thats just me and a life jacket in the boat...when i had it in the river i put it in neutral and it would rev to 5000 rpm i only did it once because i know it cant be good without a load on the motor...used a spark tester one of the ones where you screw the gap open or closed to see if the spark is strong enough to jump the gap...itdid jump the 1/2" gap on all cylinders which is what the book said it should do...i dont know what else to check and dont have the $$ for a shop bill right now thanks in advance Jason

Clay-Doh

Might have too much pitch on your prop.

Or your choke is stuck, or burning way to rich. Friends 15 hors Honda wouldnt under load do squat for RPM, turned out the choke was stuck.

Hope that helps

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whipper snapper

90# of compression is a bad piston/cyl situation. that could definitly be the cause. is ita top cyl?

splitshot

cant remember for sure but i think it is the port side top cylinder...i asked a boat mechanic and he said that the prop couldnt be the problem but i was thinking the same that it could be ....choke opens and closes normally...25lbs of compression will make a difference of 2000 rpm ?? oh and the prop is a 13-1/4-17 is what it says it planes good and has a good holeshot just no top end rpm....

Telum Pisces

All cylinders should be within +/- 5% usually. If not, you have a problem. If all your other cyliners are at 110; That means that you can have a 5.5psi swing either way.

jman

Have you checked to see if that cylinder has water in it? If not, just take out the spark plugs, spray some carb/choke cleaner in the hole, and turn the key over to remove any moisture from the cylinders.

splitshot

it has a broken ring the previous owner removed it i guess because there was silicone around the bypass cover (hid by the starter and solinoid)to seal it ....long story short debating on a rebuild...anybody know where i can find an inside micrometer ??? nobody local has one or can get one

whipper snapper

the machine shops aren't gonna hand over a very expensive tool. do you think you are capable of rebuilding? it would prob. bepossible to do yourself for under 1000. easy. if you don't mind breaking 30 out of 40 bolts off in the powerhead, or pay atleast 2500 for a reman.

splitshot

very capable i've rebuilt a few car motors and a50 hpjohnson a long time ago...