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2000 Model Johnson 90 hp Prop Recommendations???

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CajunCraig

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Good day, everyone. I have a 2000 model Johnson 90 hp mounted on a Sundance fiberglass center console. When I am running at full throttle, my tachometer shows 4200 to 4300 RPMs. The manual says I should be turning 5200 to 5500 RPMs. Can my prop really cause this kind of decrease in RPMs, or is there something else I'm missing here? I need to know exactly which size and pitch prop I need. I usually run with three men in the boat, including myself, plus a 150 qt. ice chest and tackle. Thanks in advance for any assistance, guys....
 
Step # 1 is to determine the condition of the motor !!!!!----------------If there is something wrong it will not build up the revs.---------------Have it checked on a dynomometer if you must.--------------Is this something that developed suddenly ???-------------New to you motor ???-------New to you boat ?????---------------If all is good you need to reduce pitch by about 4 "
 
The RPM rate is not new, and I have the compression checked twice a year, most recently, one week ago. Compression is good. The motor starts easily and runs well, so there does not appear to be any problems with that. Is there a possibility the tachometer could be reading improperly??? It has been reading this way for at least the past three years. A reduction on the pitch by 4" will increase RPMs, right? How will speed and hole shot be affected by doing this?
 
There is lots of information about props " online " ----------------search for ----------------michigan propeller company---------------Lots of info and easy to read and learn.--------------Many tachometers have adjustable settings for the # of poles on the alternator.--------------Have a shop check the setting !!!!
 
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Now that I think about it, I did have the tach replaced a few years back, and there was an issue with the number of poles on the tach. At least there was an issue with the shop connecting the wires to the wrong poles on the tach initially. That might be why I'm seeing those readings rather thatn what I should be seeing. I'll have to look into that. Thanks!
 
if you have had the rig or a while you should be able to ''hear'' and feel the difference of 1k rpm...just a shot in the dark but i would look at the little roller that advances the timing....they crack and the fibreglass or whatever comes off and all you got left is the metal sleeve inside the roller...it advances but not enough....
 
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