Changing speed with sprockets?? Possible??

[Stonewall]

PS how many teeth on the sproket on the sleeve ? What size tires do you have on it right now ? and what is your top speed right now ?
i can do some calculations to achieve your desired speed
I removed 2 teeth and gained about 4 mph for a total speed of 25 mph with 21" tires and still retain enough bottom end power

I currently have the origional 21" Rawhides on it, and with the K341 that (supposedly) runs 4000 RPM I get around 20-22 mph. I don't know the tooth count on the driven sprockets off the top of my head, but I will look and post that tomorrow. I am going to put on 24" Argo tires, and would like to get at least 25 mph, but would prefer more like 30-35 mph. When I put in the CH25, I am not going to use a stock exhaust, I am going for dual straight pipes out the side.

[jerseybigfoot]

but dont you sacrafice alot of reliability and longevity by doing those mods ?? those motors normaly rev about 2800 to 3200 rpm , boosting that to 5000 cant possibly be good for it in the long term , is it ?? and removing the governor doesn't that mean it could be over reved ? it's not like we have another gear to grab in these things to prevent that ?

90% of the time you are driving at the lower speeds. I have performed these simple mods on a number of engines without any issues. The problem with the stock engines in amphibians is they were made for fixed speed applications with fixed timing and fixed mixture carburation and not for motor vehicles. My intent is to not build a racing engine and race it. Although if you build a race engine with mild compression and a mild cam it will probably last as long as a stock engine if not longer. B&S Race engines like Bandolero's or Hodge's will have solenoid shift starters and will have more reliable starting. We recently put a small block Briggs Hodges engine in a Max 2 and not only does it have more usable power but its smoother and easier to control. We were also able to up the alternator size to 20 amp in the same package.
Yes you can over rev the engine the same as you can over rev your automobile.

[Robinhood02]

the difference in top speed in going from 21" to 24" tires is about 11.5% so it should increase your top speed from 22mph to 24.5 mph just by changing the tires ,presuming your rpm remains the same

[Stonewall]

I think that the CH25 runs about 3600-4000 rpm, but I don't know for sure. But it sounds like 35 mph is within reason, maybe 4-6 fewer teeth?

[Robinhood02]

I think that the CH25 runs about 3600-4000 rpm, but I don't know for sure. But it sounds like 35 mph is within reason, maybe 4-6 fewer teeth?

yes it doesn't sound like it can't be done and the 4000 rpm would sugest that it'll have the power to at least come close to maintaining that rpm, 6 teeth may be getting close to the 20% to 25% margin ,i suspect that will be too great of a change for that little motor. but it will really depend on what the count is on that driven sproket.
Dont forget , the SMALLER the tire the less stress on the chains, the smaller the sproket the greater the stress on the chains

[Stonewall]

I'll do some tooth counting and figuring tomorrow. Maybe a combination of 2-4 fewer teeth, and some higher rev mods to the twin will get just what I want.

[Robinhood02]

I'll do some tooth counting and figuring tomorrow. Maybe a combination of 2-4 fewer teeth, and some higher rev mods to the twin will get just what I want.

Im guessing but my guess is youll have roughly 30 teeth , remove 4 teeth and it should give you about 29 mph WITH the bigger tires too, once i get the actuall count i can give you final numbers

[Stonewall]

29 mph sounds great, I just want to make it a little bit more practical for running around fields checking stuff, and more fun of course.

Jersey, I'd like to know more about the higher rev mods that you have done.

[Robinhood02]

Jersey, is there a way to adjust the governor to get say 500 more rpm ?

[jerseybigfoot]

Depending on the engine you are either moving springs or adjusting screws or bending the governor tangs (Briggs vanguard). you should also have a good tach. I have a good induction meter. Another solution is to remove the mechanical Governor and add a small engine rev limiter (they are pricy). Briggs and Kohler v twins have a restricted stock exhaust and can only over rev in neutral or screaming down a hill. There are plenty of engine manuals on line or for sale that describe the adjustment. There have been posts here describing the adjustment for quite a few engines already. I just did a search for governors and there was about 100 posts. lifold did a partial governor bypass that works well. I think he has photos of the mod.