Prop question Inline 165
 

I have an Inline 6 mercruiser with a 14.25x17 big ear aluminum prop.
The motor seems to be running strong,timing etc all good yet I am only hitting 3400 rpm,speed around 30mph max with 2 people.
Any ideas if I need to re prop or look for something else to get my rpm's up,or leave as is,TIA.

do a compression test and spark check before you go any further

Will do,thanks

I had the samr srt up on my V and ran a 14x15 prop it was a bit slower on the top eand but I comercil fished t that time and cvarry alot of weight, was great out the hole!!

so i ran a compression test
cyl 1-105
cyl2- 95
cyl3-95
cyl4-100
cyl5-100
cyl6-100

all a little low I would say but pretty equal.This was on a cold engine,i may retry it after running for a bit.

Tested spark all cylinders reading 12kv at the plug.
I also rechecked timing and found it 1.5 degrees retarded so I adjusted that,checked advance and that is functioning.

tested it it hot and got another 5 psi per cylinder,added a little oil and got about 10-15 psi more

Sir What prop did or are you running ? I have a 1974 v-20 step with the inline 6 cly as well. I want to replace prop mine was reworked from several years ago and the co is out of business now . 14" x 19.. If memory is correct had change to 20 degree and some cup added any suggestion would be helpful.. Trans Yank