Aside from the obvious effect of load, Cam timing would limit the power band. Altering the cam timing could advance your power band upward, at the expense of low end power.

You really need a different powerplant.

I'm looking at a used Honda GX390 13hp I found on CL. I think if it's still available I can snag it for $100. My other choice is an 18 hp Briggs that I think I could offer my brother $100 for or maybe even snag it for nothing. I like the idea of the 18 hp but it'll take a bit more work to install than the 13 hp Honda that would be almost a drop in.

Think bigger, man. 13 hp isnt going to matter, 18 sounds nice but really doesn't get you anywhere in a vehicle that heavy. Those types of engines are made for running lawnmowers, cement mixers, generators. They aren't all that fun when put on the back of something with four wheels.

I get what you're saying but ultimately my quest for more power is really a quest to get this thing capable of running up around 40 mph which I think I could do with gearing but that would ultimately hurt the low end. With the drive system it has it will never be a neck snapper so really anything short of getting rid of the two jackshafts and installing a full engine trans combo that I and tie into the axle isn't going to be much fun.

It's really not all that hard to swap an engine into something like that. Junkyards are full of motorcycle engines. Thousands of them have been used in minisprints and other things. Any halfway decently equipped shop could do it in a weekend.

About 35 years ago, my brothers and I bought some Honda Odyssey's, which were similar in concept but powered by two-stroke engines. We modified them extensively, they ended up much lighter than what you're riding in and the engines were enlarged and made probably four or five times the power that yours does. They were fun for a while but it didn't take long to get used to the power to weight ratio and want something much faster.

It's up to you. You've put a lot of time and effort into trying to get another half horsepower out of the one you have. I'd rather you see you expand that same sort of effort to get five times the power that you have.

Think big

I don't know... I think I'm going to tackle gearing as others have mentioned and keep playing around to maximize the power I can get out of the engine I have. It's just too easy to make something faster by going out, getting another engine and dropping it in, anyone can do that. But not everyone can get the maximum power out of the engine they have as well as maximizing the gearing to make the best use out of the power they're producing. That to me is where the real fun is at.
So I'm going to play around with plug gap, air/fuel, and ignition timing advance this morning as I know it can make a big difference.
On gearing, since a 60T seems to be about as big as I have found for the driven sprocket, I'm going to look into a different sprocket on the jackshaft. I have seen where more efficient gearboxes having F/N/R with F being a 1:1 can be had for around $160 to $175. I think I could go from the Driver clutch to the gearbox with the driven pulley then out of the gearbox down to the axle and cut out one chain, one jackshaft and two sprockets which should reduce power loss through the drive system as well.

I saw those... and they don't cost much. I still think though that even with more power my gearing and the inefficiency of the drive system in general is going to be a limiting factor. I keep going back to gearing as one of the things because my friend's Helix 150 clearly has fewer chains and sprockets while still using a TAV2 belt driven setup going into a gearbox. His 150 is about 200 lbs lighter as I mentioned but his engine doesn't produce 9 hp until he hits 7500 rpm YIKES! When we were playing around he wasn't over 4000 rpm so he wasn't even close to maximum HP and he still pulled away. After thinking about this a bit more and reading more as well as taking into account the opinions here and on a Karting forum I think I'm going to play with gears and look at putting a more efficient gearbox on it so I'm not losing as much power in the drive system. If I can't get happy after that, I'll look at putting more power on it but as javadog mentioned I think I'd go for a 4 wheeler or motorcycle engine.

Here is how I would spend your money (something like).

https://www.ebay.com/itm/Engine-Motor-Runs-YZ-250-Yamaha-94-yz250-R2-/112590437119?_trksid=p2385738.m2548.l4275

Is it a CVT? I'm wondering if hte trans is putting it in too high of a ratio once there is resistance. I'd start by adjusting that.

Yeah it has a belt driven CVT. I have played around with the driven pulley spring tension to try to keep the driven pulley closed a bit longer. I think I'm going to revisit that as well.
I just took it out of the barn for the pic below and was playing around in reverse. It has to be gearing. In reverse I can wind this thing out.

So here's what I'm dealing with for the drive system.


http://forums.pelicanparts.com/uploa...1508603069.jpg

I just opened the plug gap to .032 from a .026. I jacked the back up and wanted to see if my tach was showing above 3200 rpm. With the tires off the ground I could wind it up to 5500 rpm. I put it on the ground and in reverse I could easily go above 4500 rpm. Flat out across the field.. only got up to 3200 rpm. I'm not sure what the gearbox ratio is in forward or reverse so I'm going to try and find some specs on that. I'm still going to tinker with advancing the timing but all roads are leading me toward gearing to get more rpm.

Something else I paid close attention to was when the driven pulley was opening up, it seemed to be fully open at 2800 rpm which would seem to make sense when the maximum torque the engine produces is in the 2600 to 2800 rpm range.

Update:
I removed the muffler, man! this thing is loud. I then leaned out the idle mixture screw until I got a lean stumble. I then gave it about 1/2 turn out from the lean stumble and it seemed to really wake up. I'm thinking I might get another main jet and bring it up about 2 bit sizes smaller than where I'm at now. Anyhow, I took it out on the road with the muffler off and carb leaned out a good bit and hit 37 mph @ 4200 rpm... progress!! My best in the same distance run before was 34 mph. I'm going to put the muffler back on and do a run tomorrow to see how it does.
Ideally I'd like to gear it so it does better in the dirt. The added friction of grass or bean stubble knocks me down about 10 mph and almost 900 rpm.

tcar,
I'm thinking about going a bit narrower as well as going down about two inches in diameter. The problem is, I'll need to find the rims to do it.

^^^I understand - from the picture / description it appears there are in fact 3 drive units working in series from the engine to the axle. I would concentrate on which set of chain / sprockets are the easiest to change. Most likely it's the last set - where the large sprocket is on the axle. On that set you could add 4 teeth on the axle sprocket or add 1 tooth on the small sprocket.

You'll need to figure out what chain/ pitch you have on that set. It may say in your owners manual if not, remove that chain, look on the side of the links - there should be a number stamped.

There are several companies that manufacture / stock many sprockets with the tooth number and then inside diameter bolt style to fit the shaft on which it is mounted

Yeah... this drive system is weird to me. The driver pulley and driven are variable based on RPM. They can change the gear ratio based simply on RPM. I don't recall what the factor is but even if you calculate the final drive ratio from the gearbox to the axle sprocket, that ratio can be changed by the belt driven pulleys that vary as RPM changes. Right now I think I might look into a more efficient gearbox. The gearbox on the Helix 150 my friend has, has a more efficient gearbox setup. His comes from the driver to the driven on the gearbox by belt. Out of the gearbox it goes to a chain down to the axle. One less chain and a lot different pulley diameter for the driven. I think if I change sprockets I can definitely change the speed in a field or on grass for the better.

Your issue is not gearing, it's clutching.

From my snowmobile clutching experience, I'd check the spec on that drive belt....Look at that gap between the belt and sheave in the primary clutch (the one with the fan on it).......You can look up the belt number and see what the proper width is. This belt looks totally worn out.

If the belt is worn out, it's like you are always in too high of a gear and the engine will bog; never reaching max rpm....You can put the belt number in ebay or amazon and get a new one. The belt in your picture is so loose, it may not even be the correct belt?

The clutches are also out of alignment. There are usually shims on the shaft behind the secondary clutch to move it left or right so the two are in alignment.

Looks like your current top speed is within spec:

10hp Double Seat (Electric Start w/Reverse) Go-Kart / Buggy

265cc, air-cooled, OHV/OHC engine for longer life and quieter operation.
Keyed electric start for convenience.
Approximate (and conservative) top speed is 30 - 32 mph.
CVT drive with reverse designed for hills, slopes, grass, mud and sand.
Hydraulically damped coil over shocks for a comfortable ride.
Rack and pinion steering for easier handling.
Front and Rear hydraulic disc brakes for reduced stopping distance.
Dual 3 point retractable lap/shoulder belts.
Brush Bars for additional protection.
Mud guards and full front plate.
Dual running lights and whip flag for increased visibility.
Comprehensive operator's manual and video for proper maintenance and safer operation.
Ages 16 & up
Proudly made in the USA!

Engine
Air Cooled, 4 cycle, OHV/OHC Single Cylinder, 265cc

Starting System
Keyed Electric Start w/Pull Recoil and Manual Choke

Air Filtration
Dual Element

Exhaust System
Aluminized Muffler with Heat Shield

Fuel Capacity
2.0 gal.

Oil Capacity
36 oz. SAE 30#

Spark Plug
Champion/RL86C or NGK/BR6HS

Transmission Type
Dual Wheel Drive CVT with Planetary Reverse

Tires & Wheels
Front & Rear 19"x7"x8" 20"x11"x8"

Frame Type
Heavy Gauge - Jig Welded Multiple Diameter/Gauge

Finish
Baked Powder Coat

Brakes
Foot Operated, Hydraulic Triple Disc, Two Front/One Back

Performance
Max Speed Approx. 30 - 32 mph

Fuel Consumption
30 - 50 mpg

Steering
Rack and Pinion

Suspension
Adjustable Coil Over Shocks

Terrain
Hills, Slopes, Grass, Mud and Sand

Special Features
Seat Independent Bucket Seats
Restraint System 3-Point Shoulder/Lap Belts w/Retractor
Engine Stop Switch On Engine and In Steering Wheel
Brush Bars 1.25 and 1.5" HREW Steel
Safety Dual Running Lights, Whip Flag
Miscellaneous Speedometer, Rear Rack

Dimensions
Curb Weight 675 lbs.
Max rider Weight 400 lbs.
Gross Vehicle Weight 1075 lbs.
Wheel Base 72.25"
Seat To Pedals 35"-39"
Vehicle - Overall 99"Lx57"Wx56"H

Retail Price
$3299

The belt is 7/8 wide and of proper length based on the manufacturer recommendations. I had to measure Center to Center of the driver and driven to get the proper length.

On alignment, there is supposed to be a slight offset between the two because of the way both pulleys move. On the driver, the outside sheave moves toward the engine. It's a symmetrical pulley so both sides are tapered equally. As the driver closes and the driven opens, the two will be perfectly aligned. This is normal setup and operation for a Comet Series 40 drive system. If I line the two up perfectly center for center, I'll chew up a belt within minutes.

From your other post, Yeah... I know I've got this thing maxed as far as speed but my problem is, when I get in the grass I drop down into the 20's. I want 30's out of it off road.

For fun, later this morning I'm going to put up a video of this thing running as my brother would like to see just what I'm dealing with here. I'll keep the muffler on!

I still think I'm losing power through the inefficiency of the drive system in general. The more chains you have, the more power loss you'll see.

What air pressure are you running in the tires?

Manco recommended 10. Tire is rated for a max of 36. I'm running about 20. I'd go higher but these tires are pretty well cracked (yeah... I need new ones).