Dhadley you were correct!

[caper_45ca]

I recently posted a question as to why my piston ring broke on my 1995 90 hp v4 Johnson....well powerhead will have to rebored and rebuilt and after the teardown mechanic said it was full of black sticky goo and heavily carboned....manufacturer suggested wot to be 4500-5500..I could get 5100-5300 depending on conditions on any given day.....thought I was ok....but learned the hard way....(going to cost about $3000)anyway I was running a 13 3/4 x15 aluminum prop....I read on here where you suggest to setup engine to run 5600-6000 wot and get 35mph on a 18' sportcraft fish and ski bowrider...how is this done without re-propping.....if I do go to a lower pitch what would you suggest and what will this do to the top end speed?....one thing I forgot to mention...b4 this motor blew I was told by the original owner that there were less than 100 hrs onit....but anyway when I bought it a few months ago it was rough at idle...took it to the dealer and he set the timing at idle as follows..he did a link/sink and using the throttle advance adjustment he set timing to 4*btdc....Thanks again for all the help

 

[willamettejeff]

Re: Dhadley you were correct!

Seems like you probably had a problem other than the propeller size. My 1978 70hp Johnson can spin a cupped version of that same size prop at over 6000 rpms with the cupping making a 15 pitch actually more like a 17 uncupped prop. I would think a 90hp setup correctly would be able to do even better. I assume your trimming the motor to get best rpms and speed. Have you tried changing your motor height? Just some thoughts.

 

[caper_45ca]

Re: Dhadley you were correct!

Originally posted by willamettejeff:<br /> Seems like you probably had a problem other than the propeller size. My 1978 70hp Johnson can spin a cupped version of that same size prop at over 6000 rpms with the cupping making a 15 pitch actually more like a 17 uncupped prop. I would think a 90hp setup correctly would be able to do even better. I assume your trimming the motor to get best rpms and speed. Have you tried changing your motor height? Just some thoughts.

 

[caper_45ca]

Re: Dhadley you were correct!

use trim and tilt and this thing scoots along just great..or least feels good to me....as far as motor height cav plates r about 1'' up from lowest point on the keel....and is in second hole from mounting bracket....

 

[willamettejeff]

Re: Dhadley you were correct!

Just wondering if you ever decarbed that engine? My boat mechanic friend and others here have suggested this be done with some regularity. I did mine after I bought it last year and this year after I burned the fogging oil out of it at the beginning of the season.

 

[caper_45ca]

Re: Dhadley you were correct!

no I never did a decarb..I am new to boating and was unaware of that procedure....it was only after Dhadley had suggested in anearlier post the possible cause of the broken ring...having the engine rebuilt and just dont wanna make same mistakes again

 

[willamettejeff]

Re: Dhadley you were correct!

As a side note, don't necessarily believe your tachometer reading unless you've had it calibrated. For instance, I have verified mine reads around 300 rpms low in the upper range and about 200 rpms low in the middle range. I just keep this in mind for now when using it. Maybe I'll actually calibrate it for next season ..... or not.

 

[Dhadley]

Re: Dhadley you were correct!

We only drop pitch as an absolute last resort. I'd suggest we play with the set up to gain rpms. For the moment lets not change anyting. Lets see how it does after its broke in. Remember, with broken rings you were, obviously, not getting full power from your V4.

 

[caper_45ca]

Re: Dhadley you were correct!

not so sure when im going to get it bk from the shop...but when i do ill post with all the info after break-in and see what needs to be done...Thanks