Bad loss of power on Johnson 140

[Tcorum]

I am just wondering if anyone had any ideas on my problem. I have a 78 Johnson 140 and it has lost 10+ mph suddenly. The boat had some transom repair done but this didn't add much if any extra weight to the boat. It sat for a couple of years unused then once I took it out the boat that use to run a solid 56-58 mph now runs 45 mph. It would not get over 4500 RPMs but I fixed that with a new set of plugs. Now running the same RPMs that use to produce 55+ mph now produces 45 mph. The prop is the same 21" raker and the motor is mounted at the same height. Any ideas?<br /><br />Thanks,<br /><br />Tcorum

 

[Tcorum]

Re: Bad loss of power on Johnson 140

Just a little more information about the motor.. it was rebuilt about 4 years ago and bored out .30 over from what the last owner told me. Could a loss of compression cause a motor to still turn the RPMs as you trim it up but not get the torque required for the speed? I have not yet checked compression on the motor. It runs smooth as silk no misses.<br /><br />Thanks again,<br /><br />Tcorum

 

[sony2001]

Re: Bad loss of power on Johnson 140

I don't think your speed has changed at all. Same prop and same rpm will give same speed. What the transom work probably did was gum up your pitot tube to the speedo. Change it or not and check the tubing for a restriction. Don't blow into,it may damage the speedo. Maybe someone else blew into it.

 

[Tcorum]

Re: Bad loss of power on Johnson 140

Thats a good thought and thanks for the input but I had two different ways I was determining the speed. There is a speedo tube but I also have a speed wheel on my depth finder. Maybe both of them are wrong but I don't think that both went bad at the same time. Thanks for the input... any other ideas?<br /><br />Thanks,<br /><br />Tcorum

 

[JB]

Re: Bad loss of power on Johnson 140

Howdy Tcorum.<br /><br />Seems like your engine is down on power. Maybe lost a cylinder.<br /><br />Run a compression test. If it passes that, try disconnecting, testing and grounding your spark plug leads, in turn. This can be done on the muffs at idle. If you disable a bad cylinder there will be no change.<br /><br />Let us know what you find.

 

[Warmmi]

poblems with a johnson 70 hp 1975

poblems with a johnson 70 hp 1975

after spending the winter in our garage we took the motor for a tune up - guy there tuned it and then told me the water pump is bad as water was not coming out the pee hole but coming out by the prop. put a new impleller in it and seems to run fine - no reverse or nutural due to a missing clamp and it doesn't seem to get hot - took the cover off the engine and there is some gunk here and there that looks like greese that got water in it dont know if or what it is - need to be sure were not running it hot but cant find anyone that can tell me where it vents the water for sure - is it at the bottom of the leg or should there be pee holes? Cant find anyone around here that wants to "waste time" with my older engine and summer is faddig fast. any advice would be much appreciated.