gx200clone + TAV2 only 4700rpm?

[DCProductions]

Hey guys,

I'm running a gx200 clone modified as follows:
18lb valve springs
#90 Jet
high flow intake
high flow exhaust
18cc cylinder head
no governor (obviously)

My TAV2 is stock except that I occasionally run yellow springs in the driver. Even then my kart tops out at about 4700 downhill.

Now, this is a yard kart so it could be ground or air resistance. Still, I would think I could at least hit 5000 to 5200. The engine revs (without load) well beyond 6000, which I don't like to do cause I don't have an aluminum flywheel yet. TAV2 that's holding the engine back?

 

[Doc Sprocket]

How are you measuring RPM?

 

[DCProductions]

I've got a tach from a skidoo (I think). It's really just for any 1-2 cylinder engine 2-4 stroke. It wraps around the spark plug wire and reads the pulse. I know that it's working reasonably well because my torque converter is supposed to engage at 2100 (I think) and that's what the tach reads when it does engage.

 

[anderkart]

Hey DC, you might just be fighting a gearing problem here but we'll need more info to tell:

How many teeth are on your jackshaft output gear and axle sprocket, and also how tall are your rear tires? It'd also help us to know the approx. weight of the kart and driver?

If you have any pics of the kart post-em up, we might notice some other potential issues.

Also its a bad idea to free-rev these ungoverned industrial engines whether they have a racing flywheel or not. An engine like yours that might survive just fine at 7000rpm under a load/driving the kart could easily blow while free-spinning at 5000rpm. Lots of karters have learned this lesson the hard way.

 

[Doc Sprocket]

My thoughts exactly, on all counts.

 

[DCProductions]

Right now I've got an 11/54 tooth ratio 41 chain and the TC goes into 0.9/1 overdrive which puts me at 10/54. My tires are 15 inch ribbed tires. As far as the weight I don't think my kart weighs more than 200 lbs since two guys can easily lift it into my truck. I weigh 155 so I'd say complete weight is 320-350.
I heard that a flywheel exploding isn't too bad. It's something like, oh I don't know, a grenade going off. That's not so bad right?
That's actually one of the things that worries me most. There are a lot of safety parts that I'm missing from my engine. I want to upgrade so bad but safety first. I'm kind of glad that the engine doesn't rev too high under load or something bad might have happened.

Not the best picture but it's all I had on my phone. Pretty ratty but I'm cleaning it up.

 

[devino246]

Right now I've got an 11/54 tooth ratio 41 chain and the TC goes into 0.9/1 overdrive which puts me at 10/54. My tires are 15 inch ribbed tires. As far as the weight I don't think my kart weighs more than 200 lbs since two guys can easily lift it into my truck. I weigh 155 so I'd say complete weight is 320-350.
I heard that a flywheel exploding isn't too bad. It's something like, oh I don't know, a grenade going off. That's not so bad right?
That's actually one of the things that worries me most. There are a lot of safety parts that I'm missing from my engine. I want to upgrade so bad but safety first. I'm kind of glad that the engine doesn't rev too high under load or something bad might have happened.

Not the best picture but it's all I had on my phone. Pretty ratty but I'm cleaning it up.

The whole "flywheel exploding" thing is more or less a myth. The part that you do have to worry about is your connecting rod breaking, which is entirely possible. IMO, the only part you need that you dont already have is an ARC Billet connecting rod. Theyre like $60 or something like that. BTW, it not high revs under a load that you need to worry about, its without a load that you should worry about. Just dont rev it without one anymore.

 

[Doc Sprocket]

Okay, so with the 11/54, we get a reduction ratio of 4.9:1. With The CVT in high/OD mode, we get 4.41:1. Perhaps engine braking is responsible for it's refusal to go much faster downhill. FYI, I'm getting 47.56 MPH at 4700RPM for you.
I suspect that a lower ratio would allow your engine to spin faster, but there's a few things to consider.
How is performance? Does it seem acceptable in the acceleration department? Lowering the gear ratio might give you more oomph at take-off, and it might allow the engine to spin faster in the top end. However- right now, it would seem that it's self-limiting at a safe enough RPM- Are you willing to accept that?

 

[DCProductions]

Glad to hear that the flywheel shouldn't explode! I almost got scared into buying one, though it would be a nice upgrade. Also, I will not be free revving the engine now- thanks again. BTW, any opinions on the long rod (non-stroker) 3.323 I think. AGK and NR both offer it for the same price as the regular.

As far as performance goes I have great acceleration (fastest kart in my "go kart gang"). I used a gps speedometer to get a max speed of 55mph so I don't know if the torque converter is going beyond 0.9/1. Not too sure about that top speed though; all I know is that it's WAY faster than stock. And yes, this speed is acceptable. I don't think it would be safer to go much faster.
The reason I want a faster engine is so I can gear it down (like you said toy story) and get more power with the same speed.

Note: The TC seems to shift early. I have put the driven on 3 and used the stronger driver springs but still shifts fast.

 

[Doc Sprocket]

I completely understand why you'd want to gear it down. But if you're reasonably happy with the performance, it may be best left alone. I don't necessarily think your flywheel will detonate, but the truth of the matter is that something will fail sooner or later. It may not be spectacular, but broken is broken.

As for speed, I'd believe the GPS as long as you have a long enough stretch to let it read for 20 second or more. It could well be that you're going that fast. Maybe the CVT is going beyond .9:1, maybe your tires are actually larger than 15". Wouldn't surprise me, tires are often NOT the marked size.

I once got mad at my Comet 40 and drilled a new hole for even MORE spring tension in the driven...

 

[DCProductions]

To the drill press!

Oh wait...
I'm stuck in a dorm...
with no power tools...

 

[Doc Sprocket]

Ugh... A fate worse than death!

 

[devino246]

Ugh... A fate worse than death!

maybe your tires are actually larger than 15". Wouldn't surprise me, tires are often NOT the marked size.

Id be willing to bet that low speed tires like the ones on a kart, expand a little at high speeds, altering the ratio and increasing speed. If the tires are actually 15.5, and expand .5" at top speed(making 16" tires), that would put him at around 51mph.

 

[DCProductions]

My buddy got some trailer tires for his kart. 16x5.3-8 I think. Those won't expand but are they any good for kart tires?

 

[Doc Sprocket]

For general purpose goofing off, probably okay. Don't expect too much in gravel, sand, or mud. If you do use them, you might do well to lower your gear ratio an equal amount.

 

[DCProductions]

Yeah we haven't been fairing too well in mud- just kind of point it where you want to go on dry ground, floor it, and hope you make it through. BTW, thinking about going to 16" rear tires (turf tread- little more offroad grip). Should I keep the same gear ratio or go to a 60 tooth?

Nobody on the ARC long rods?

 

[Doc Sprocket]

Sorry, I don't have any info on the rods.

With the tire sizes, you're looking at a theoretical diameter increase of 1". I say theoretical because I have found that tires almost never match published specs.
Best bet- try the tires. If you've lost too much grunt, then gear down.

 

[anderkart]

Nobody on the ARC long rods?

You'll find lots of good info searching/posting in the Honda and clone forums here: http://karting.4cycle.com/forumdisplay.php?f=71

 

[DCProductions]

Ok thanks guys. I think that's about all I need for now. Can't really test anything out but look forward to having some pics and maybe video in the future.

 

[Doc Sprocket]

http://arcracing.blogspot.com/2008/02/using-long-rod-in-ohv-kart-engine.html

Check that out re: the rods. I stumbled upon it after following a link to a different topic.