How fast should my boat go?

[foilled]

it’s a 1987 OMC 5.7 rebuilt by jasper with an Omc cobra. It’s a cabin cruiser (Larson 250 sport cruiser) weighing about 4300 pounds. V8

 

[Scott Danforth]

About 40-42 would be my guess

 

[Bondo]

Ayuh,.... 40-odd would be Good,....

 

[foilled]

About 40-42 would be my guess

Im getting about 32mph tested off gps. I’m getting about 3700 rpm with trim all the way down. If I start raising it it’ll go up to about 4150 until I here cavitation or whatever and I’m losing speed. Although it’s a rebuild omc the old omc manual does say 4200-4600. Why am I low or am i good since it probably would go to the right rpm range if I kept going up on trim. Any ideas thanks?

 

[Scott Danforth]

You may have the wrong prop. If your motor is 100%, you do have the wrong prop

 

[Bondo]

Ayuh,..... It Could be Alotta things, 'n I know the cause of Yer problem is on This List,......

Yer at the bottom of the accepted rpm range,....
Nearer the Top of the range is better, safer for the motor,.....

 

[foilled]

You may have the wrong prop. If your motor is 100%, you do have the wrong prop

Is there anything I should check specifically engine wise. Engine does seems fine to me. Previous Owner did give me two props both operate at same rpm. Don’t know either size but what size would I need?

 

[foilled]

Okay i see list I’ll check a few things out. What else should I look into for ignition system. New distributor, plugs, wires, and timing have been set. And is there a way to check exhaust flappers?

 

[achris]

Something a lot of people overlook is to check that the carburetor is actually opening open fully. With the engine not running, push the throttle all the way open, then take the cover and spark arrester off the carb and look down the hole.The throttle plate should be fully open (You may have to move the choke plate to see).

Chris........

 

[Scott Danforth]

Is there anything I should check specifically engine wise. Engine does seems fine to me. Previous Owner did give me two props both operate at same rpm. Don’t know either size but what size would I need?

the list that Bondo pointed to is from the stickies

items to check on the motor:
compression
timing
is the throttle moving all the way open

if all that is good

what is your prop diameter and pitch - you may need to drop down a bit in pitch

 

[foilled]

the list that Bondo pointed to is from the stickies

items to check on the motor:
compression
timing
is the throttle moving all the way open

if all that is good

what is your prop diameter and pitch - you may need to drop down a bit in pitch

Timing set at 8 degrees Btdc. A few months back I compression tested it and all cylinders were within 10 percent of each other. And throttle is moving all the way forward. I don’t know current prop dimensions. I could measure diameter but how do I know the pitch?

 

[Scott Danforth]

look at the numbers on the prop, you may have to google it if its only the prop part number.

 

[foilled]

I’ve noticed my electric choke on Holley 4160 has a little movement in the open position that allows it to open slightly more if I push it with finger while in WOT throttle position. It doesn’t open to much more but should I set choke to make sure it’s at the most open position when in WOT throttle position? And how do I make this adjustment. On the choke assembly there is a metal stick sticking out that you put the electric black circle cover over with the spring with a circle in it. Does the metal stick go into the hole in the spring or does the hole in spring go in front on the metal stick?

heres YouTube link to my choke operation. This is a cold engine or will choke fully open when warm?
https://youtu.be/9ADUaiGgdiw

 

[foilled]

the list that Bondo pointed to is from the stickies

items to check on the motor:
compression
timing
is the throttle moving all the way open

if all that is good

what is your prop diameter and pitch - you may need to drop down a bit in pitch

My 3 blade prop is 15 diameter x 17 pitch. And four blade is 15 diameter x 16 pitch. ( four blade is prop I’ve been using for this thread and rpm testing)

 

[Maclin]

Does the metal stick go into the hole in the spring or does the hole in spring go in front on the metal stick?

In the hole.

Choke plate should be held totally vertical by the choke linkage when the engine is fully warmed up. With an electric choke, it heats up even without the engine running if the ignition is on, and should keep the choke plate totally vertical after a few minutes.

There is a mechanism in the linkage that acts as a choke-unloader manually at full throttle, for flooded conditions during starting so the choke won't exacerbate the flooding. But this is almost certainly not an issue with what you are seeing with the choke operation.

 

[foilled]

Does the metal stick go into the hole in the spring or does the hole in spring go in front on the metal stick?

In the hole.

Choke plate should be held totally vertical by the choke linkage when the engine is fully warmed up. With an electric choke, it heats up even without the engine running if the ignition is on, and should keep the choke plate totally vertical after a few minutes.

There is a mechanism in the linkage that acts as a choke-unloader manually at full throttle, for flooded conditions during starting so the choke won't exacerbate the flooding. But this is almost certainly not an issue with what you are seeing with the choke operation.

Sounds good thanks but yea mine was in front of the hole not in it. I’ll switch that