Im looking at (if possible) adding performance/hp on my Kohler 25 hp LT. Any tips or suggestions?

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If you have not already done so, tweak the throttle advance to gain a few hundred rpms extra- this usually translates into a 1.5-2 mph gain....ok so this is not a scientific description but use the search feature here and if you do not find anything let me know. Cheap mod. With an LT you reach a plateau of diminishing returns by adding rpms because you are turning the same prop and since there is no gear reduction (as in a shorty SD). I understand a new $400 SS improved flow muffler MAY improve hole shots but I personally don't see enough benefit to justify the cost. Although both the 25/25 HP LT's by various mfg.'s are rated for a 9x7 prop, I find the 9x6 a tad better. I get 20 mph by myself and 17.7 mph two hunters and gear with a 27 HP MB LT on a 1648 grizzly only a few feet above sea level. Yes, elevation is a factor on both prop selection and I suppose carburation. I also suggest, if your air cleaner has one around it, getting rid of the foam "pre-cleaner" so the carb will breathe better. All of the above is conditioned on the usually mild temps here in south Florida so if you are in Utah at 5,000 ft. at 32F there may be radically different suggestions. I have gone to using synthetic oil/grease on my LT and there is noticeable improvement although most scoff at this. I don't care about the doubters, positive frame of mind is useful. I've added steelflex to the bottom and that was worth it. Each motor/ hull combo is different and by now you know the importance of weight distribution. I relocated my battery un front to help this. I can only speak about my LT, I've had three GD's and now an MB. I don't want a shorty thank you, unless I move to Utah/Louisiana.

I have heard of people advancing the timing as well. Just cannot go too far.

bigpun, invest in a tiny tach if you have not already done so. I've had two 25's before the present 27 HP LT so it's ok to tweak the throttle up to 4100-4200 rpm out of the water. Any wear on the prop will slow you down. Though the 25/27 HP's are rated for a 9x7, a 9x6 might push it better. I run at near sea level so no special prop cup or carb setting for me. Each hull is different about optimum load placements fore and aft. As well, you need to find the "sweet spot" of planing depth of the prop/cavitation plate. If you don't have the "trim tab" on the trailing surface of the plate like my MB LT, you can try bending up/down 1/8" at a time the plate itself to find that level. Actually a friend bought a GoDevil 25 some fifteen years ago and put it on a 1648 rivetted MV lowe jon and never has had to adjust the plate. He's got the same motor, albeit with a new rotor, magnets, starter, fuel pump, so they are reliable, and he goes faster than me with my 27 on a grizzly 1648, probably because my hull is 150 lbs. heavier.

P&P heads upgrade the valves(kohler valves are better than briggs valves but every little bit helps) tweak on fuel delivery(i.e fuel accelorator pump dempending on were fuel tank is located) get in touch with a lawn mower racing team they can give you all the performance parts you want

bigpun, before you shell out the moolah, know that after a certain point, more rpms will not help unless you have gear reduction like on a shortail and can turn a bigger prop. I did some quick math, not that I am a math major, but the "big boys" with the modded motors have spent some time as much as $1,000 for each 1 mph gain- man, that is expensive! Then there's the fact the motor won't be under warranty because you've exceeded the stock specs, etc. Additionally, there will probably be more breakdowns and cost of replacing those vroom-vroom components. When I was considering one of the spiffy new SS mufflers the dealer could not guarantee any gain at all. It's like those newer steel shot offerings and reputed hyper-velocities to intercept the ducks...I've actually gone back to the 1400 fps shells as opposed to the 1550 fps high velocity shells because the slower ones pattern better. Speed is no substitute for good old fashioned hand-eye coordination. Anyway, have fun!

Mid west Supercub

563-659-5276

scatters boy 316, what kind of gains did you realize on your GD 27 after doing the head work, cam, etc? Did you go to a bigger prop as well? I've always read and seen the increases on shortails but not on a longtail. Recently a friend souped up a Dixie 14 HP to around 17 and is getting good speed on that shortail. For example as I said I've advanced the throttle to around 4200 rpm out of the water and have even gone beyond that to 4400 rpm but that did not get me any more speed gain so I backed it down to 4100-4200. Just curious is all.

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rangererp, I am not that gifted but let me try. On a longtail you have a straight shaft to a prop, the output is direct. You can increase the rpms but the prop is the same and you can go to a bigger prop but there is a limit on output. The difference on a shortail is that the shaft is connected to a belt (or gear like the PD) and the gearing is different from one to the other (like on a bicycle) and many times adjustable by the mfg. or by the user, so you can turn a larger prop to begin with and this translates into more push/speed at the onset. In other words, if you have two identical hulls and motors and carrying load, the shortail will be significantly faster because of gear reduction, larger prop, efficiency of angle/shorter shaft. Will some engineer please come to the rescue before I further embarrass myself?

The gear reduction is just like down shifting in yer truck. It allows higher RPM's in a lower gear an you can run a bigger prop because of it.

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ok. I was just trying to be clear in saying that expensive mods on an LT engine would be counter-productive as opposed to a shortail, where the gains would be significant albeit expensive ( 1K$ for every 1 mph gain).

^^ Well said.

I have been running a 27kohler MB longtail for a few years and before that smaller HP ones. I have only found 3 things that really affect performance. First, make sure your cavitation plate is adjusted properly. At least on my boats when I first get them the props always want to dig in. Adjust the plate so that it runs just below the surface and you can push down on the handle with just a finger or two and bump it out of the water. This causes the least angle on the shaft and so more of the force from the prop is directed straight backwards instead of down. You can pick up 1-2 mph this way if your prop is really digging in.
Second, try a different prop and make sure the cupping on the ends of your prop is not worn. Once the cupping goes, you can run up the RPM quite a bit and not see much improvement in top end speed. On my 27 I sometimes run a 9x6 if I am going to be hunting light and it gives me about 200rpm over the 9x7 and I might pick up 1-1.5 mph at the top end. I have since gone back to the 9x7 as I think it has better low end torque and I would rather not be stuck than racing a whole mph faster.
Third- it is all about weight distribution with a longtail. When I run big water I move a bunch of my stuff to the back so the bow lifts up higer and helps with the waves and allows me to load the front with more decoys. When I do this however, the rear digs in and I lose about 2 mph. When running light, I can make the dog sit on the bow and he helps level it out and I pick up about 1 mph even though there is actually more weight in the boat. Pods can help if they are installed right.
I tried fancy SS exhaust on a longtail and it didn't do anything for me other than make it easier to maintain when I run in saltwater. If you are thinking about paying for mods to a LT, seriously consider just saving your money and buying a larger engine in the future. When I want to go faster and further- I bring out the prodrive. The longtails are for getting back there where it is real shallow and were never intended for speed. Mods to motors can get expensive real fast and with a longtail whether you have a headwind or tailwind probably has more effect on the top end.

Does anybody know if you can run a 10" prop on a 25 go devil frame? I know the 35s come with one so adding power to your 25 where you can pull a 10 inch prop will give you more speed and launch if you could turn it.

Gearing really doesn't matter that much on boats if you can run your motor to max rpm you need a different prop and if you are loosing RPMs you need a different prop. only two factors that make a surface drive faster is the fact the you can run the prop at a straighter angle and that your not limited to the size prop you can fit. Of course that my .02 cents I may very well be wrong.