I have been owning a 27 hp PD since September of last year and I am recently noticing my speeds are decreasing. I was running 25 mph in open water with 2 other people in the boat and little to no load, now I am down to 19-20. I have heard that the 27 hp Kohler engines do not offer modifications that can enhance performance; I am going to buy a new prop. Any other suggestions?

well, figure out whats wrong with what you got before you go modding. Do a leakdown test. Also, check your head gaskets. 27 kohlers have been know to blow them. The 27 I had had a fabbed exhaust and Julian at Midwest Super Cub can fix your heads up, but better fix whats wrong first. Could be your prop, too. Good luck.

Thanks for the response. Any advice on how to do a leakdown test?

@Barnes- Yea everything is stock and with a load I was still getting around 22-23 mph. Now I'm afraid I'll be down to 15-18 with a load.

How's the condition of the bottom of your boat? Have you been hitting a bunch of stumps and logs?

@ Owen - No I rarely run logs. The worst it's been through is oyters on a few occasions.

Run much sand? If so, the prop makes a good bit of difference once it looses the cup.

Thanks man will do. And no I never ran in the sand. I think I lost some cup from the oytsers.

25 mph with 2 other guys??? What kinda boat you got? Sorry if it's in your sig but I'm on tapatalk so I can't see.

I'm only bumpin 25 mph and a steady 24 with only me in the boat. And that's after I cleaned carb and got it runnin just right.

I have a 16x48 polarkraft. And yea by myself with about 150 lb load I ran 26 for about 15 minutes.

I'm just afraid that come winter time I won't be able to get on step with my load and 3-4 other guys. seems like it's having trouble with 3 other guys and fishing poles at the moment.

What were ya and what r ya turnin fer RPM's?

shells will destroy a prop...

get the leakdown, valves, and head gaskets checked

my cousin has a 27 on a 14/48 and rcan keep up with me when my boat is loaded and his is empty

rpms haven't changed much was runnin in the 3600s now in the 3500s

Are ya usin the same gps as afore? If ya are, sounds like a prop and or dented/bent hull issue.

I doubt it's a valve or leak issue with bein a Kohler but the head gaskets are a big possibility.

Yea same GPS and I'm thinking it's the prop too, but how do I check the heads?

To do a leakdown test your will need a leakdown tester and you basically pressurize the cylinder with the piston at tdc once it is pressurized you can look at the guage and you will have a percent of leakage. The speeds your claiming are very similar to a customer of mines his was on a 15 44 gatortrax with a hunt deck. I did a headjob and milled the heads some he gain 2-3mph and it cost him under 400.00 I hope this helps.

You haven't mention what your Out Of Water rpms are set at.

I would also run it in a safe area and reach back while underway and make sure the carb is opening all the way. You haven't mention what your Out Of Water rpms are set at.

If your OOW max rpms are lower than 4200-4400 adjust it to that range.

If everything checks out right, (carb opening all the way, OOW rpms adjusted correctly) then do the leakdown test.




If the prop is worn rpms normally increase.

Thanks for all the advice. I did set the out of water rpms to 4250 when I first bought it, but havent checked since. Ill get a new prop and reset the rpms and see what that does. If it still seems off I'll do the leakdown.

Probably the out of water (governor) adjuster mentioned above adjusted itself along with a wore out prop.