Any Go Kart Gurus here? I have a need for more speed but can't get more!

[cabmandone]

Originally Posted by asphaltgambler

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

[asphaltgambler]

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.

[LakeCleElum]

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...

[cabmandone]

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!

[911SauCy]

Originally Posted by cabmando

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.

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

[ckelly78z]

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.

[asphaltgambler]

Originally Posted by ckelly78z

. 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' ^^

[flipper35]

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?

[asphaltgambler]

^^^^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.

[cabmandone]

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.

[cabmandone]

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.

[911boost]

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

[flipper35]

Originally Posted by asphaltgambler

^^^^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.

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.

[cabmandone]

Originally Posted by flipper35

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.

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.

Originally Posted by flipper35

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.

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?

[cabmandone]

Originally Posted by BSiple

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

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

[ckelly78z]

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.

[cabmandone]

Originally Posted by ckelly78z

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

[LakeCleElum]

Cab: You seem to like to tinker. I say just find an old motorcycle for cheap that someone has parked out behind a shed.

Use the engine to repower. Ideally, an aircooled 250 to 450 single or twin with electric start. Fab up engine mounts and shift linkage. You could have a simple drive system of one chain and your choice of sprockets to go with a 5 speed trans........Might have to add a fuel pump?.....The sky is the limit...

[cabmandone]

Yeah... I like to play around with stuff a bit. I was talking with my brother about this thing and his suggestion was to go out and get a job to eat up this free time I have. Us self employed people apparently have too much time on our hands ??

[911boost]

I hear you Cab, we camp a lot and the "thought" was the XP1000 would be safer with the roll bar and seat belts than the 4 wheelers we have been riding for years.

Of course that picture was from its maiden voyage out to play in the snow a few years ago. It has been upgraded, broken parts replaced, and been a lot of fun. I use it hunting as well, we strap a couple spoon cases in the back to go deeper into the back country.