New here first build

AdamGar

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I’ve got this Honda GX270 (9hp) that will be getting dropped into (along with a 40 series torque converter) a Yerfdog Spiderbox or some other 2 person full suspension kart running on 12” fancy golf cart wheels with 19-20” turf tires. I’m perfectly capable of doing the work as long as I start with the correct plan. So I’d like to add electric start to the engine with charging as well. The problem lies in that no one makes a billet flywheel for that purpose (ARC said there’s no demand). SO
1) If I leave the engine completely stock with the govt. still working how fast will this 9hp engine push the kart?
2) Would a stage 2 kit (390 carb, cam, billet rod, HP springs, stainless valves, and maybe porting the heads) make any difference (even for low end torque) if I don’t eliminate the governor (since a billet flywheel isn’t available)?
 

redflash

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speed depends on...rpm...specific gear ratio between drive gear and axle gear....exact tire size...terrain....and weight of kart and rider. once you have thos figures you can calculate approx speed. you notice hp is not included. RPM sets that mark

Da redflash
 

AdamGar

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speed depends on...rpm...specific gear ratio between drive gear and axle gear....exact tire size...terrain....and weight of kart and rider. once you have thos figures you can calculate approx speed. you notice hp is not included. RPM sets that mark

Da redflash
Do you think I’m overthinking this? Most of these carts only came with 150cc engines. Going up to 20” tires on what I believe are billet rims can’t add that much rotational force that ide be stuck with a dog even if I left the engine stock with the governor in place. Right?
 

JimD

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Too many unknows in what you have given us but here is a best guess. The engine is 3,900 rpm (Honda given) , the tire size I took from your notes is 20", the jackshaft 12 tooth going to a 60 and a 7" driven unit you would be going 33mph. Once you give me your exact tire size and what gearing you end up using then I can put it into the computer and kick out the speed.
 

karl

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Well I successfully swapped a gx270 onto a similar kart recently. From the pics I have seen,
the rear swingarm and gy6 engines on yours and my kart should be near identical, would not
doubt we could swap them.

Check out this thread ifya wanna see what your in for.

https://www.diygokarts.com/community/threads/free-buggy-thing.46810/

Mine has 22in tires geared 9 to 1 overall, but a similar gear ratio should be needed.

A jackshaft will be needed, or a new axle to get the correct gear ratio, again read through the thread
on how to achieve this.

Performance will not be great with a stock gx270, or even mildly modified. Expect around 35mph
if you want decent torque.

And since you want to dump $ into this motor for hop ups and electric start/ charging,
your money is wayyy better spend on a predator 420cc, or better yet the new predator 459cc.
Or duromax 440cc, vegas carts 460cc, ect.

Much better performance, path for upgrades, more durability, same or less cost.
 

panchothedog

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karl has you on the right track. Go with the larger engine, 420 to 460. To answer your question about building a motor and not remove the govoner,
a giant waste of time and money. You won't end up with a low RPM torque monster. I built a predator 301, the whole works, rod, flywheel , cam, ported
and milled head, 50 lb springs, header pipe and jetted carb. Left the govoner
in just for the heck of it knowing full well that it would be coming out later.
Seat of the pants driving the kart, could not tell any difference from stock.
Removed governor and it runs strong like it should. Picked up about 18 mph.
 

JimD

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I am sure there is one out there. We wrote our own for in house use to tell people what the speed is based on the variable we know and can throw into the computer. We use a 7" driven because that is what we have and market. The 6" driven Comet used was great for minibike but karts have bigger tires and need more low end torque to get going which is why belt life is shorter on an asymmetric system because of heat build up. Everyone loves speed and I always tell them I don't care how fast you make it go but the important thing is how fast can you stop it.
 

redflash

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in all truth, a 150 motor will not easily pull 20-inch tires, even at a 1:6 gear ratio.....unless you weigh under 50 lbs. You're not over thinking it...youre
just asking too much from small motor, and large tires. I run a 420 stage 2 motor with only 16-inch knobbies, and can't get much over 35 mph.
of course I weigh 210 and ride off road.

Da Redflash
 

AdamGar

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Thanks for all the help. 35mph sounds decent to me as long as it gets there quick (torque). Especially for a cart that will also be driven by my 10yo. And unfortunately a new $500 motor isn’t in the budget when I already have a true Honda that’s free and almost new. Christ, the Moto wheel and turf tire combo alone is $600 but I would assume they weigh less than big knobbies.
 

panchothedog

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If you are staying with the Honda 9 hp look into what is necessary to Safely
remove the govoner. I know a bit about the predators and clones but honestly
can't tell you if the Honda rod and flywheel will safely take the elevated RPM.
I'm sure others with more knowledge about Honda's will chime in. But even in stock form ( header pipe and re- jetted carb ) with the govoner removed will give you more satisfying results without adding any more hot rod parts. Some
stiffer valve springs ( inexpensive ) will get you a few hundred more RPM.
 

Denny

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Has everyone forgotten their roots? You can remove the governor without having to add a billet anythining. Just do not change the valve springs or anything else!! It will give you about 5,000 rpm. It will be fine. If your that worried build a scatter shield also.
 

madprofessor

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Just do not change the valve springs or anything else!!
Ditto, ditto on that. I sent my 12hp. build 212 to Ohio without a governor, and have lost no sleep over the flywheel exploding to maim or kill the new owner. Reason I sleep well is because I did the same thing as what Denny said, I left the stock 10.8# springs in it so it can't spin up much more than 5K rpm. before going into valve float.
Governor delete won't get you any more torque or acceleration than stock, but it will give you the 5K rpm as opposed to the stock 3600 rpm. That only translates to getting higher top end speed above the 3600, doesn't help get to 3600 any sooner.
 
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