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).

I'm going to try playing around with the spring pressure on the driven (larger) pulley. I think if I can keep it from opening as soon as it does that I might be able to give it a bit more go out of the hole. Not sure if I'm thinking right there or not though.

Looking more at gearing, the belt drive system according to the manufacturer is 1:1 at high speed and 2.43:1 at low speed. Coming from the same jackshaft the driven pulley (larger) is on, I go into a 12 tooth sprocket which then goes back to a 24 tooth (2:1) on the rear jackshaft. From there I have the 18 tooth that goes down to the 60 tooth (3.33:1)
I'm wondering if I wouldn't be best off to go up in tooth count on the sprocket with the driven (larger) pulley thereby increasing the rpm at the rear jackshaft? It's actually the easiest of the bunch to change.
I can play with the engine and carb but the gearing is where I go off the rails. I'm thinking in terms of this thing hitting a wall out in a field and not building RPM. My goal is to be able to go faster where I'll be driving the most which is in the dirt. My problem is that I also don't know what the maximum RPM for the forward/reverse gearbox is. I'm thinking there has to be a reason they went 2:1 on from the driven back to the rear jackshaft.

Yes ^^ if you go back to my previous post, most likely the easiest way to address this is to add 4 more teeth on the axle / driven sprocket ( the last chain drive ) or go down 1 tooth on the smaller drive sprocket

I think I'll give it a shot. Not much to lose as the sprockets don't cost that much IF I can find one that bolts onto the gearbox the way this sprocket bolts on. If not, I'll have to look into changing the axle sprocket. My only concern with changing that sprocket is the clearance I have to the lower cover.

Here's a picture of the sprocket on the planetary


http://forums.pelicanparts.com/uploa...1508769199.jpg

My guess is those sprockets are 'off the shelf' from some supplier - you may have to get creative with 1 that's 'close' to your fitment.

I've had custom sprockets made for vintage motorcycles I've worked on where, as in your situation, were too tall for what I was wanted. They were surprisingly cheap. If you can't find a bolt on solution, Google 'custom sprockets'.

Know that the material of 'off the shelf' sprockets are hardened. So if you buy 1 ready to go and need to do some additional machining, it can be done be only by an experienced machinists.

Cab - Good luck. You know more about clutching than I gave you credit for. I understand what you say about alignment. It's different than a snowmobile.

BUT, I still say your belt looks too loose and that can cause your issue. Even with belt right, maybe clutches need service? UR on the right track about a spring in your secondary. If I can bore you with a quick story from 20 years ago:

I bought snowmobile from a widow....Seems like great shape, but from day one, it would always bog when taking off. Sometimes if taking off uphill, I'd have to lift the rear with one hand and crank the throttle with the other. Get the track really spinning, drop it an go.

Can't tell you how many times I was thru the carbs adjusting float level and jetting...After screwing around most of the winter: New belt and rebuild the clutch. Ran like new.....

Just an idea...

Bob,
I can't get over how loose that belt is either but I have shown it to the Kart place I bought it and they said that's "normal" for this type of system. The other thing is, with a tighter belt I actually had more slippage. I could hear the belt slipping when I was climbing a hill, that is now gone.

I have gone over this in my head to a point where I'm thinking I'm just going to add more power. I can change the gearing to accommodate the lower HP, lower torque engine OR after looking more into it, I can go with the Honda GX390 13 hp engine which to my surprise produces about 7 hp and 26.5 pounds of torque at 2500 rpm where my current produces about 5hp and 18.75 pounds of torque. On the top end at 3600 rpm the Honda produces about 12 hp and 22.5 pounds of torque where my current at 4000 produces 9 hp and about 16 pounds of torque. I know the HP gains aren't huge but the torque is a definite improvement and torque is where the work gets done. I think with the Honda engine I should be able to overcome the gearing a bit more and for $100 I figure if it doesn't work I can always get my money back or close to it if I sold the engine. There aren't many other options I have that I can say the same thing for.

I knew I should have jumped on that engine. It sold! :mad:

If you're going to do it...swing for the fences, 13hp is nothing.

Find a trashed Honda CRF450R dirt-bike, pre 2009 (with carburetor), Pull entire motor/trans out, configure a jack-shaft, shift lever with hand clutch...45hp w 6 speeds.

THEN you'll have a good time

When I used to race alcohol Karts on a buddy's oval backyard track, I geared the motor to run the RPM that I wanted at the end of the short straightaway. My Briggs Raptor 5HP with a few mods was actually more like 8-9 HP, and it seemed to run really sweet at 5200 RPM. For every 2 teeth I added (from a 58 tooth to a 60 tooth for example) on the axle, I gained 200 RPM. This worked because I was limited by the size of the track, and not trying to gain more top speed, just trying to get better lap times.

The ideal gearing is a 6 to 1 ratio which represents a 12 tooth sprocket, with a 72 tooth axle sprocket for starting out quickly while still having some top speed. I ran a 12 tooth sprocket and a 60 tooth axle sprocket to get less off the line power, and more high end response.

I never dealt with a third sprocket on a jackshaft, so my reccomendation is to experiment with gearing, or rear tire size (taller for more top speed). You can also add some PSI of air to the tire to get a larger circumference which will take the Kart a few inches farther for every rotation of the tires at the same motor RPM.

^^ If you add more air it does effectively increase circumference but that makes the overall gearing higher, making it 'taller' ^^

With that type of belt driven system shouldn't it be at 4200rpm at WOT no matter what speed in mph you are going? Unless it has weak springs letting the weights close up the gap too soon?

^^^^My guess is no ..........as peak torque always occurs below maximum HP/ RPM's. Also total gearing should be short enough that maximum speed is just past max RPM's / power.

So I found this online calculator and discovered that my final ratio is 6.67

Gear Ratio Calculator for Jackshaft Setup

I put 12 at the engine (driven pulley) then 24, 18,16 and hit calculate... BAM! 6.67 final ratio.

As for flipper's question, I'm thinking of it along the lines of driving my truck empty versus pulling a trailer. More weight and rolling friction means my truck has to downshift into 3 or 2 to keep the speed I want to travel. Now in the case of my truck, my HP is built in the higher RPM range as is torque. On my cart only one holds true. At 4000 RPM I'm generating 9 hp but I lost about 6 pounds of torque. This is what really has me interested in finding a Honda GX390 engine. The HP and torque at 3600 is still considerably better than my HP and torque at 4000 on the EX27. I'm thinking the Honda will have the power and torque to overcome the gearing or if nothing else it'll be able to get to its rated 3600 RPM with the current gearing.

Here's a link to the drive system operating https://youtu.be/0PS5_14SizU

I'm thinking more about the belt and some saying it's too loose. If the belt was too loose or too long in this case, I would think that barring the belt slipping I'd be able to build more RPM because the driven would never get pulled to full open and achieve the 1:1 ratio. I think if anything my driven is opening too soon keeping me out of my maximum torque range.

Just step up to a big boy toy..... :)


http://forums.pelicanparts.com/uploa...1508958338.jpg

But, with a continuously variable transmission like his that is driven by springs and weights the engine should be turning the same rpm at WOT regardless of road speed. That's how the snow mobile ones used to work. That is why I was wondering if the springs were weak it allows the weights to move prematurely or the torque cam spring in the secondary is weak allowing it to open up to quick as well.

Think of your electronically controlled CVT in a car when you put your foot down. It keep the engine at a specific rpm as you accelerate. This should be the same as it isn't a conventional centrifugal clutch that just engages or disengages. Unless I am looking at it wrong.

https://s.hswstatic.com/gif/snowmobile-12.gif

This is what gets me. The Kart can't overcome the added resistance/friction when driving off road. In the grass or a field, I get to maybe 3300 rpm and hit a wall where it won't go above that point. On the road I can build to about 4200 rpm.

The clutch engages at about 1600-1800 rpm which I think is right for the springs and weights in the clutch. I could up the driver springs so it engages at 2800 rpm but if I'm playing around down inside the woods, I don't think It will build enough speed to keep it above 2800 when I climb the hill on the way out. If the driven spring was weak it would put me into 1:1 ratio too quickly which is why I put a bit more spring tension on the driven to try to keep it in the higher torque range longer but that didn't seem to do much.
For fun I think I'm going to get a shorter belt and see if it makes a difference. Right now my belt is sized for a center to center distance of 8-5/8" which is what I have. I can buy a belt that is right for 8-3/16 center to center. It might be worth a try?

Those things are AWESOME... but I don't ride near enough to justify having one of those. For me this is just a toy to make getting tree stands setup. I just want to be able to get to the tree stands faster



http://forums.pelicanparts.com/uploa...1508965911.jpg

I keep seeing the older Honda 250cc Odyeseys for sale locally and would love to get one, but just don't have the area to tear up like I would need, to ride one properly.

I have seen a couple of those on CL as well. People seem to be asking what I consider crazy money for those things.

See what I mean? https://columbus.craigslist.org/snw/d/honda-odyssey-fl350/6341124329.html