Is it prop or something else

Dwbarger

Recruit
Joined
Aug 29, 2018
Messages
1
Ok put a force 125 on 24' pontoon never gave a thot to check prop before trying it out. On water got 3200 rpms and about 17mph (struggle) got home took prop off to find out it was a 12 3/4x21 pitch ugh. Bought a 14x13 thinking that would get rpms up around 5200 well it only raised it to 4000 at wot. Holeshot is way better and tops out around 23mph but I am still below factory of 4500-5500 rpms. Why if dropping 8 degrees in pitch I only gained 1000 rpms? Should I go to 14x10 or should I be looking somewhere else? Carbs, fuel pump, timing? Engine runs great compression was at 120-127 in all cyls.
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
I would be looking at your engine height. It may be set way deeper than necessary. Need pics showing engine height as compared to bottom of transom and tubes to be of much help.

If the boat is loaded down heavily, that's going to kill speed as well.

Thinking a 125 would turn a 13" prop pretty easily under most conditions.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
An engine badly transom height seated, in a non top running state, badly trimmed, with deck weight badly distributed or overloaded are natural max wot rpm serial killers...

Usually should gain 1 K wot revs dropping max 3 less pitch props from current installed one, engine seems is with issues, check all cylinders have spark, correct carb/time advance synch as check starters.

Happy Boating
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,306
'toons act different than planing hulls

You absolutely need to be at the right engine height. When running, check to see if you AV plate is at the water line. If low, raise up the motor

Then go to the prop and dial in the pitch
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Any engine running at fast displacement speed or on plane with AV plate set even with "water line" will have a poor lower leg water bed height for prop to grab, bite optimum, best top thrust will be lost. On choppy windy water cond prop will aerate badly, including on sharp turns, not on a dime though. It's same as swimming with fingers widely opened.

That setting is only good for slow/fast displacement speed or speeding at straight water courses on calm, flat water cond. Much better is to sit any OB for water flow to skim right under small upper plate for better performance on any water cond, including sharp turns. Test both positions for yourself to find that out..

Happy Boating
 
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