[josh martin]

I figure that this has been sold, but if not, how much for everything? (Engine, pipe, silencer, carb, mount, airbox, etc.)

[josh martin]

Stunningly, kart recovered today. Rusty and filthy but complete other than mychron. Sold through local flea market. Gonna start with the scotchbrite and wd40 tomorrow.

[josh martin]

Fought a very similar sounding problem for a long time. Solution: Dellorto fuel pump with no return line. Has an internal 0.5 psig bypass. Problem was created by excessive return volume, w or w/o 200 main jet in the return.

[josh martin]

The entire process is ridiculous. Who mandates a change involving their own product line with insufficient inventory? Our one rotax driver will miss the first two events of the season, and all they can tell us is how far behind they are. I don’t care. You dictate the change, be prepared to support it.

[josh martin]

Jay,

To be clear, the $2000 was spent on clutches for two different karts, not that that makes it much better. There were two issues going on:
1) The engine builder was supplying inaccurate dyno curves causing us to set the stall speeds way too high, and
2) Our home track is short (4/10ths) and very technical, so you are constantly in and out of the clutch, resulting in abnormally fast wear. There was no viable solution to this other than the 3-disc, which has been bullet-proof comparitively.

Thinking logically, I’m sure if the track was a bit more wide open with fewer drastic rpm changes that the two disc would be fine. Still wouldn’t run the wet clutches in sprint racing. They do have a lot more parasitic drag.

Josh Martin

[josh martin]

Walt,

We are using the patriot three disc. Great clutch. In order to accurately set the stall speed, you will need a torque curve for your engine (from a dyno). The clutch stall should be set 400 to 800 rpm below the torque peak. Lacking a torque curve, if you are using an sr-y pipe, the stall should be nominally set at 7600rpm. If you are in an open pipe class, the stall may vary from 9000 to 10600 rpm, depending on the pipe (we are at 10600 with a tsow pipe). Hope this helps.

Josh Martin

[josh martin]

Tom,

In our experience, the only reasonable clutch to use for sprint racing on a kt100 is a patriot 3 disc. If your class weight is over 300 lbs, the two disc wont live. The wet clutches are great for road racing, but has far too much drag for a sprint track. After destroying $2000 worth of two disc clutches last year, then getting 6+ events out of the three disc clutches before friction disc replacement, I’d have to say the patriot three disc is the way to go.

Josh Martin

[josh martin]

Brian,

Don’t know what others will say, but I’m happy to tell you what works for me:

1) Both outer bearing collars pointed outboard – maintains axle (and handling) symmetry

2) Check out sharkshifters 4 o-ring exhaust outlet. Works really well

3) My j-arm is equally close. If all else is assembled correctly, no problem

4) Again, try shark’s mount. Fits well enough im not even familiar with the problem.

Best of luck,
Josh Martin

[josh martin]

Rob,
If you are willing to do some road racing (in sprint style karts or lay-downs) KART’s series runs 5 races anually in Kansas and one in Hastings, NE. Additionally, there is a sprint track in Kansas City that may be reasonably accessible to you.

Josh Martin

[josh martin]

People have, so please tread lightly on that subject. As for the track, it isn’t nearly as scary as it looks. Its a blast to race, has a 3100 foot 120 mph piston sticking straightaway, and is set in a beautiful state park. Come join us for the two races scheduled there this year. You’ll be glad you did.

[josh martin]

We generally run 3-5 psig higher pressure at road racing tracks than we do at sprint tracks. This increase has nothing to do with rolling resistance, but is a product of making sure that the bead stays seated on the rim. If the pressure is too low, the bead will unseat even with beadlocks.

[josh martin]

I do not think that Eric’s last point was really off topic. For those of us in the middle of the country (we are based in Oklahoma), there are not a lot of nationally recognized race options in which we can participate. Given that two of the three events are under a day’s drive away, this effectively produces a regional series with national exposure for us. Given that they are using SKUSA rules for stock moto, and our goal is to ultimately participate in pro tour events, it allows us a more accessible opportunity to practice our racecraft under the same set of regulations. Seems like a better way to gain experience than driving a thousand miles. Will we participate in the Vegas event? Probably not. Time and money won’t allow both that and Supernats, but it doesn’t mean we won’t support the other two. I am enthusiastic about another series. In response to the concern about the dilution of events, that may happen in Vegas, but with the inclusion of Rotax in the US Open,its more likely that it will simply service a different set of participants. As for the Dallas and Grand Junction events,my bet is that there will be an entire set of participants that no one knew existed but who have been waiting for a taste of higher profile racing closer to home. More accessibility means more participation, and I think that is what we all hope for our sport.

[josh martin]

Water temp 130 F. Max egt 1280 (and I mean max. 1300+ and the piston becomes one with the cylinder). Egt should be measured 10cm from the exhaust side of the piston. Get the CR125 jetting app that is avaiable. It is great for sprint tracks, and more or less dead-on (Keihen carbs only, mind you). Add 15 to 20 sizes to the app’s main jet for road racing. If the engine revs to max rpm on the stand at wot and doesnt go blahhhh, its too lean. Never go more than 5 hours on a piston and ring. All of this learned by me the hard way.

[josh martin]

Based on experiencing a very similar sounding problem on a 125 shifter, check your fuel pickup in the tank. If the hose on the pickup has become stiff with age, this will cause fuel starvation in or coming out of corners, as the pickup cannot adequately follow the sloshing fuel. Additionally, I have found that the square dellorto pumps perform far more reliably than any of the mikunis. Others may disagree, but since changing to the dellorto pump, I went from a mess with it every race scenario to a much more pleasant mess with it never situation.

[josh martin]

Freddy is one the money with the upper end rebuild advice. While you are at it, check the shaft seals on the crank and for cracks in the carburetor boot. While the crown of the piston looks like the engine has been running rich, the damage to the skirt and pitting on the piston surface look like damage from being run too lean. Leaking crank seals and/or a cracked carb boot can cause this and make proper jetting impossible. Burned one down for exactly these reasons with similar looking damage.

[josh martin]

No carbon fiber or magnesium at all. Would’ve bought steel hubs if we could get them. The karts were so light we couldnt make weight with our light drivers without resorting to frowned-upon ballast methods.

[josh martin]

My personal opinion is that stock honda is, in reality, less expensive after buy-in than kt-100 (we spent 4x as much keeping the kt’s in clutches as all the maintenance total on the stock honda), but that’s just my opinion. If you want to talk about forward thinking organizers, however,it is my opinion that our local club president, Ron Pattison, of the Tulsa Kart Club, has one of the best local plans for two-stroke.

For most of 2014 and the upcoming 2015 season, the Tulsa Kart Club has and will be running what can be described as an “adult-2-stroke-up-125cc” class. Its a run-what-brung class that includes kt-100, TaG, Rotax, stock and mod shifter, KZ, and whatever else you show up with. If there is a referencable nationally sactioned weight, we use that. If not, the competitors agree on a weight. If it doesn’t result in competitive racing, we change the weight. If you are a novice and you don’t make weight, that’s ok.

Ron’s policies have resulted in a TaG class with 2 entries at the beginning of the season growing to an open class of 12 entries for the season closer. We all had fun and some beers aftetwards. Something to think about, at least locally.

[josh martin]

Our team has been fighting the weight problem from the opposite direction, but as a result, I may have some helpful advice here. We are using Praga Tacho chassis’, and have had a very difficult time getting some of our drivers to make weight. This is not a shameless pitch for a brand, just something for which I happen to have definitive data. Our kt100 kart weighs in at 147lbs, the leopard at 158, and the stock honda at 200. This leaves about 200 lbs for the driver in kt100 and TaG and 185 in the stock honda. Im sure other manufacturers offer similar chassis weights as well.

[josh martin]

Our team is relatively new to the sport above a local level, but the decision has been made to move almost entirely to stock honda and more or less abanbon TaG and Yamaha. While the buy-in on the stock hondas is considerably higher, so is the reliabilty. Maintenance costs are lower (22 races this season on 2 pistons and the same clutch) and multiple sanctioning bodies seem to agree what comprises a “stock honda”. While we might have to change an airbox or silencer series to series, at least we can run the same powerplant. This decision should help end the disappointment associated with finding out that $20k worth of engines purchased one season are not only not legal for the following season but also essentially worthless on the used market. Shifters all around for 2015!

[josh martin]

For what its worth, i use the cr125 jetting app regularly. I find it to be highly accurate for sprint track racing, but have discovered (the hard way) that its suggested jettings are way too lean for big road-race circuits. It is still useful, as long as you understand its limitations. For large road-race tracks, i have found you need to add nearly 20 jet sizes (if it says 178, you need about a 198), otherwise a 100 mph piston stick is in your future. That being said, it is dead-on for about any size sprint track.

[Author]

Posts