in my yamaha DT shifter times I found out that lower gearings worked the fastest times and the tranny could be used more efectively.

in tigth sprint courses shifting a lot was a waste of time and slowed down too much, we had this very nice street couerse were I only used 1st 2nd and 3rd gears, I used 13T front sprocket and 17T in the rear.

try try and keep triying...

Augusto.

hey RICKRACER....how did that 240 crank,rod and head I sold ya end up working for the rest of the season? I sure am jealous of your setup now!

Augusto, good points there. With the fact that we can now run a 250 in UAS, which could be a bit much, I've speculated that a short-shifted setup w/ the final drive keeping the power in the meat of the midrange (still making stock sudam power, but with 2x the TQ) will result in the smoothest/fastest setup in most dirt conditions.

Hey Javamanic, it worked good, I didn't use the head, it's still in the plastic bag you sent it in, I was already cutting and porting the original one. So far I've turned that motor around 6000 for a few Saturdays on the road course, and it ran good. It's sitting waiting for me to come up with another kart to put it on, so some other family members can use it. I may see if I can find a lower tooth count rear sprocket....23 is as low as QRC goes for the hub that's on there now, but maybe a solid hub/sprocket? I see them all the time for 50mm axles, but not for my 1.25"er.

Check with tractor supply thay have them hub and sprocket

I'll check this weekend, thanks,

yes you should try using less gear changes, in fact of the 3 gears that I used 1st was used only to start the race (we started from a still standing, like F1), 2nd and 3rd were for actual racing, it behaved kind of direct drive and when I needed to come off the turns a bit faster instead of downshifting I just pulled a bit the clutch to let the beast wake up, was very efective, I miss those street races, soo much fun and hundreds of spectators.

Augusto.

Got a bigger air filter on there yesterday, motor's running better now. Been playing a little in the parking lot at the shop, and a little test running on the road over by my friend's shop. I was gonna take it to the drags last night, but it started sprinkling rain. Hopefully I can get it scaled and aligned this week, scare up some tires, and hit the road course next weekend.

post a youtube video

Augusto

Not youtube, but it works, this is at the 1/8 mile dragstrip last weekend:

http://s68.photobucket.com/albums/i...rrent=Race2.flv

http://s68.photobucket.com/albums/i...rrent=Race3.flv

http://s68.photobucket.com/albums/i...rrent=Race4.flv

Gonna try to do some more video in the next couple days or so,

Just last night, I figured out why my gear ratio estimations were off so far. It was really confusing me that the final drive ratios everybody was recommending were so numerically low.
There is a primary ratio involved as well, best I can tell about my motor is that it's 3.0:1, (cranks spinning 3 times for every revolution of the clutch shaft, I had assumed that this was 1:1, ), so the final drive must be divided by 3 to find the total overall gear ratio. I've not been able to hold my kart at WOT long enough to see/feel the actual top speed, but I know it's upwards of 70 mph and still climbing. Apparently, that's due to me turning it 9500 rpms and 5th being O.D. in the trans. My Digatron acts funny with this motor, but it recorded a 9500+ "max rpm" the other evening when testing on the road by my friends shop.

13/23 is a 1.76923:1 final drive ratio, but you have to multiply that times the primary ratio (3:1), to get the actual ratio of "crankshaft to axle" rpms, which makes it 5.30769:1. Knowing this, I see that equal front and rear sprockets would give a 3:1 overall ratio.

So right now, my overall ratio is a 5.30:1, yesterday, I ordered a 15 tooth front sprocket I'll have later today, which will put me at bout 4.50:1. How much lower do I need to go? Tractor Supply does have (basically blank) sprockets, and I think I can make them work for me for a rear, but how much lower do I need to go?

I have had good luck starting with the same ratio as the donor bike, or just a bit lower, just calculate the tire's diameter difference, if you wish I can do the math for you, give me the bike's tire diameter and the f/r sprockets it had.

Augusto.

Looks like the donor bike was 13/49, 3.0 primary ratio, and the tire was 84.18" in circumference. The rear tires I'm running are about 38" in circumference. I just did a 15 tooth front sprocket, which puts me at a 1.5333 final ratio and a 4.59 overall ratio, and it seems to make a pretty sizable difference with just the limited testing I've done, (buzzing the parking lot, ), it seems to want to go more, rather than break the tires loose so easily like it was doing before.

13/49=3.77

( 3.77 x 38 ) / 84.18 = 1.65

with the data you give, you need a 1.65:1 ratio to have the same final ratio of the motorcycle, this would be 14/23

you say you have now 1.53 this should be 15/23 rigth?

I'd say you got it correct now, and maybe lowering the ratio a bit more will make it faster since the kart weigths less than the bike, why don't you try a 16/23 ? I'll bet my money on this.

Augusto.

I ordered a 15 tooth sprocket yesterday, got it and installed it today. I will have to custom make a 16. I'm pretty sure it will be easier to make a smaller rear one. I think the gearing is close enough for it's first outing at the road course, I should be able to hit 100 if need be. Took a little more video today. This is just messin around in the parking lot at the shop, I just put in the new front sprocket, hoping for a little less violent reaction to the gas pedal,

http://i68.photobucket.com/albums/i.../th_Kart086.jpg

http://i68.photobucket.com/albums/i.../th_Kart087.jpg

http://i68.photobucket.com/albums/i.../th_Kart088.jpg

As if you can't tell, this thing is a TON of fun, and could easily be very dangerous.

I know it's been forever since there was an update to this thread, but I've just got too may irons in the fire to keep them all stoked at the same time. :roll: 8)
I finally took the kart to the road course, they sent me an email about an Owner/Operator Appreciation Day. What normally costs $50 for 3 hours, was 4 hours +, for free. All I can say is.....

HOLY SH*T BATMAN!!!!!

It was the 3rd fastest kart there, and only not the fastest by far because of: (1), no front brakes, (2), carb bogging badly at anything over half throttle, and (3), fuel pickup in the wrong place.

No front brakes because I strap-started the kart on July 4th weekend on my (patent pending, once I get the bugs worked out, :mrgreen: )roll-up kart lift, which means throttle partially opened, and in 3rd gear. When it fired, it went to about 6 grand and started vibrating quite a bit, probably from one of the back tires being flat for a while, even though it was aired up when I cranked it. Well, it vibrated off the stand and took off on it's own, turning about 5 or 6 grand in 3rd gear, down the driveway, across the street, and into the neighbor's yard across the street, smashing into a tree. Fortunately, no cars or pedestrians were in the street, and no one was in her front yard. The only damage to the kart was a broken front rotor, and of course, the scar in the tree. Rotor = "Made in Italy, $93 + shipping", :shock: :cry: :cry:

I think the carb problem is just from it sitting up for too long, gonna give it a good cleaning and see what happens with it. After I took the rotor off and set the brake balance bar to all rear and no front brakes, I drove around the neighborhood for about 15 minutes, but there was no place to even think about going full throttle at all, so I didn't know how bad the carb was til I got to the track. :roll: :?

All the high $$ race karts have their fuel pickups going in the top of the tank, with a weighted, swinging pickup that can follow the fuel. Mine is at the right rear of the tank (typical oval track tank), once it gets near half a tank, high G right turns have the fuel pump sucking air til the track straightens out again. Next time out. mine will have a swinging pickup as well, :wink: 8)

The two faster karts were both GREAT running 125 shifter karts, which are supposed to have like 35 hp stock, (99 CR125), and as much as 45~50 when properly modified. My old dinosaur (93) RM250 motor is supposed to be 42 hp stock, with the pipe and K&N filter, let's say...maybe 45. But the other two would pull hard right from the turns and keep shifting, putting 5~10 kart lengths on mine...til it stopped bogging spitting and sputtering, then it would reel em back in almost like they put the brakes on, right on their bumper, even go around em on the outside if it was a long sweeping turn, next tight turn, they'd go by, and the whole thing would start all over again. One person standing on the observation platform said they actually saw it pull the front wheels coming out of the tight left-hander in front of the platform, it felt like it to me as well, but I wasn't sure til they came to me and said so too. That ain't horspower, it's TORQUE, :mrgreen:
All in all, this thing is even more of a BEAST than I thought it would be, and I had some pretty high hopes. I promise to get video next time, there was just no time this time around, I was thrashing on the kart right up till midnight Friday night to get it ready and loaded up for Saturday morning.
I realized I didn't have any pics of the kart with all the bodywork mounted, so here's a few pics I took the other day, 8)

http://i68.photobucket.com/albums/i...t/Kart001-2.jpg

http://i68.photobucket.com/albums/i...t/Kart002-2.jpg

http://i68.photobucket.com/albums/i...t/Kart003-2.jpg

http://i68.photobucket.com/albums/i...t/Kart004-2.jpg

http://i68.photobucket.com/albums/i...t/Kart005-2.jpg

http://i68.photobucket.com/albums/i...t/Kart006-2.jpg

It will probably make one more trip to the track, after I get the brake rotor, carb straightened out, and new fuel pickup done, just to make sure it's all working great. Then I'll blow it all apart, paint, polish and maybe some powder coating. 8) :mrgreen:

FYI, there is a class at Speedway Park kart track in Fruitland Park, that you would fit into, it's a Sat. night track and there is a M/cycle engine class, I'm sure they would welcome you.

it's funny but I was just searching for your thread last night to glean a few tips on mounting and running sometihng like this on the affordable side of karts.