1979 1150 thunderbolt merc drive shaft

[Utt2033]

What size boat and what prop pitch are you using?

17 stratos believe a 21 it came with original engine

 

[Chris1956]

You should check your compression and examine the color of the spark plugs, to make sure all are firing. I would expect a bit better top speed.

Are you trimming the motor up to achieve max top speed?

 

[Utt2033]

You should check your compression and examine the color of the spark plugs, to make sure all are firing. I would expect a bit better top speed.

Are you trimming the motor up to achieve max top speed?

Yea I messed with trim last night and it hit 32.6 on garmin gps forgot to look at Rpms. I got some compression checker from Amazon a while back and I put it in the spark plug hole hit the key til it turned over checked and the 3 I checked had 0 so I did something wrong on that but I can tell u this is the smoothest this boat has ran whole time I’ve had it reading up on prop pitches and Rpms

 

[Utt2033]

Yea I messed with trim last night and it hit 32.6 on garmin gps forgot to look at Rpms. I got some compression checker from Amazon a while back and I put it in the spark plug hole hit the key til it turned over checked and the 3 I checked had 0 so I did something wrong on that but I can tell u this is the smoothest this boat has ran whole time I’ve had it reading up on prop pitches and Rpms

The lower I have now I got off a guy who worked for merc racing in Nashville and he said the lower I have is a gear ratio of 2.0 could explain top end but boy she gets up on plane fast with the hydrofoil

 

[Chris1956]

A 2::1 gear case ratio is standard for an IL6 motor. An 850 usually has a lower gear ratio. You can check it easy, by turning the flywheel exactly 2 full turns. See if the prop turns 1 full turn or less.

I would expect 35MPH out of your boat/motor, but that is just an average.

 

[Utt2033]

A 2::1 gear case ratio is standard for an IL6 motor. An 850 usually has a lower gear ratio. You can check it easy, by turning the flywheel exactly 2 full turns. See if the prop turns 1 full turn or less.

I would expect 35MPH out of your boat/motor, but that is just an average.

Thanks for the info I hit 32.6 last night and tach read just under 5 which I think it was 4700rpms but ran smooth until I hit wake and it started ramping kinda scary and noticed fuel usage I’m not use in gas much as before I put some sea form I believe is what it is called and only have ran 1/4 tank of that thru at this point I think just needs cleaning up now May take it for a service before fall fishing starts but thanks for all the Info

 

[Utt2033]

A 2::1 gear case ratio is standard for an IL6 motor. An 850 usually has a lower gear ratio. You can check it easy, by turning the flywheel exactly 2 full turns. See if the prop turns 1 full turn or less.

I would expect 35MPH out of your boat/motor, but that is just an average.

Next thing I’ll do is adjust jack plate up 1/4inch and see what numbers I get