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

[unclebilly]

By the way, your problem is gearing. I just went through this on my brother's kart. These engines make power in the top end but don't offer much bottom end. You need to gear it lower to take advantage of the power in the higher revs.

[1990C4S]

O2 sensor and a voltmeter...

[cabmandone]

Okay! So I put a new plug in and drove it across the field about 1/8 mile for a warm up. Ran WOT on the way back. There's no lean stumble when opening it up which would seem to indicate the idle circuit is good but the plug looks like it's lean.

[cabmandone]

Originally Posted by unclebilly

By the way, your problem is gearing. I just went through this on my brother's kart. These engines make power in the top end but don't offer much bottom end. You need to gear it lower to take advantage of the power in the higher revs.

Yep. According to the engine chart I posted, it's making 9 hp at 4000 RPM. My problem is, I don't think I'm getting to the 4000 rpm range. I'm still waiting for my friend to bring me his digital tach so I can pop it on and compare to what mine is showing. On the WOT run my tach indicated I wasn't getting over 3250 running across the field. Regretfully I live on a small 2 lane hwy so I don't want to put it out on the road on a Friday (State Hwy Patrol runs it more often on the weekend) so I'm going to drive through a field about 1/2 mile to 1 mile country road and have at it! I'm going to bring some tools and play around. My "neighbors" will probably think I have lost it. At this point I'm not sure if they wouldn't be right.

[cabmandone]

Originally Posted by 1990C4S

O2 sensor and a voltmeter...

You say that... but now I'm wishing I had bought a handheld AFR rather than my mounted unit in my 911. I could have clipped it to the exhaust and checked AFR's... dang it!

[Scott Douglas]

Can you fatten the main circuit easily?
If so, I'd fatten until you know it's too fat then lean a little bit from that.

FWIW, my 912 would pull redline but had a 'reluctance to accelerate' in top gear. Dyno test showed it was leaning out at the top end. Fattened it ran like a scalded dog with a real push in the back effect.

[cabmandone]

Originally Posted by Scott Douglas

Can you fatten the main circuit easily?
If so, I'd fatten until you know it's too fat then lean a little bit from that.

FWIW, my 912 would pull redline but had a 'reluctance to accelerate' in top gear. Dyno test showed it was leaning out at the top end. Fattened it ran like a scalded dog with a real push in the back effect.

That's the trouble with this type of carb, in order to go richer on the main, I have to drill it. There is no adjustment screw for the main jet. I can however add some on the idle side which will make it richer throughout. I'm going to start there but my concern is I'll get too rich on the idle side which will affect my low end response.

[LEAKYSEALS951]

At very least you could fatten the idle side to diagnose the high end issue, understanding idle will suck during testing, and if it turns out the high end leaning is the culprit, go back and drill it, then lean the idle back to where it was.

Go do this right now- quickly! before it gets dark!!

[cabmandone]

Originally Posted by LEAKYSEALS951

At very least you could fatten the idle side to diagnose the high end issue, understanding idle will suck during testing, and if it turns out the high end leaning is the culprit, go back and drill it, then lean the idle back to where it was.

Go do this right now- quickly! before it gets dark!!

I gave the idle screw 1/4 turn out and went after the main. I'm at a #57 bit at this point which I think is a .0430 bit. Still no more RPM's
Plug doesn't look bad. I'm gonna hit it tomorrow morning again!

[asphaltgambler]

The answer is shorter / higher numerically final drive ratio. What ever is the easiest to do - which is chain/ sprocket side of things. Trying either 1 tooth less on small drive sprocket - or add 4 teeth on the large driven sprocket.

[asphaltgambler]

Further, even with more power and or reducing weight - the final drive remains too tall to do what you want.

[cabmandone]

Originally Posted by asphaltgambler

The answer is shorter / higher numerically final drive ratio. What ever is the easiest to do - which is chain/ sprocket side of things. Trying either 1 tooth less on small drive sprocket - or add 4 teeth on the large driven sprocket.

Here's where I get lost. As stated this uses a Comet series 40 driver pulley. It goes back to a Driven pulley on a jackshaft that also has a 12 tooth sprocket. From there a chain connects to a sprocket on another jackshaft that has a 24 tooth sprocket. On that same jackshaft there is an 18 tooth sprocket which then goes to the axle which is a 60 tooth sprocket. So where do I start putting the sprockets?? I'd like to simplify things but regretfully I think in order to do so I'd have to get rid of my reverse gearbox and I don't really want to lose reverse as I do take this thing down inside a woods and it's nice to be able to back away from a mess I got myself into or almost got myself into.

[nota]

robin is a very good golf cart motor but not a go-cart racer
I don't think there is a lot of hop up stuff for it

the honda clone [china] single 390 or 420 has a fair bit of up grades out there
or go nuts with a built 460cc version
they start with a big tork and hp advantage before the ad on's
and some claim way over 25 hp with cams springs forged rods ect
that is the hot single in golf cart hop ups
and not a lot bigger or heaver then the robin

the next is the B&S V twins because of lawnmower racing
there are lots of stuff to make power with them

[HardDrive]

Holy schit does that look fun. Folks that live in the country get to do things us us urban critters don't.

[nota]

that plug don't have much gap !
a bit bigger spark [gap] mite help the hi-end

[cabmandone]

Originally Posted by nota

that plug don't have much gap !
a bit bigger spark [gap] mite help the hi-end

I shot in the middle of the recommended range. I think the range was .24 to .28 so I went .26. I now have a collection of plugs from doing runs, making adjustments, checking the burn and then dropping in a clean plug for verification. I think I'll gap one over the high end a bit and see if it makes a difference.

[cabmandone]

Originally Posted by nota

robin is a very good golf cart motor but not a go-cart racer
I don't think there is a lot of hop up stuff for it

the honda clone [china] single 390 or 420 has a fair bit of up grades out there
or go nuts with a built 460cc version
they start with a big tork and hp advantage before the ad on's
and some claim way over 25 hp with cams springs forged rods ect
that is the hot single in golf cart hop ups
and not a lot bigger or heaver then the robin

the next is the B&S V twins because of lawnmower racing
there are lots of stuff to make power with them

I might have to swallow my pride and take my brother up on the 18 hp. horizontal shaft Briggs he took off a mower. I just can't help but feel like there's something in gearing that I'm trying to overcome. I'm thinking of going down 3 inches on tire width from an eleven to an eight and going with more of a turf tire as this isn't really a mudder. I would think that would reduce rolling friction somewhat considerably by getting rid of 6 inches overall of tire. Not to mention it might help the thing fit in the back of my truck!

[DanielDudley]

Originally Posted by cabmando

There is a very noticeable difference in how the engine winds from no load to load. It's like I'm hitting a wall and it won't build more RPM. I'm thinking gearing has a lot to do with it.

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.

[cabmandone]

Originally Posted by DanielDudley

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.

[javadog]

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.