racer_2828
Member
On a big bore Yamaha with the 54mm piston in it running alky what would be the desired Tillotson carb of choice? Also what pipe would you run on a 1/5 mile oval with this combination?
Open Yamaha carb
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alvin l nunley
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I have no idea on the carburetor, but lots of ideas on the pipe. If it was me, I would be in touch with RLV. You'll need to know the exhaust port opening in degrees in order to get real accurate information. If you know at what RPM the engine reaches peak torque, even better.
With that big piston, have you considered adding counterweight to the crankshaft? It's a big help. Even a stock Yamaha benefits from increased counterweight, so I'm sure your engine will be doubly better with extra counterweight.
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
Jon Brogden
Member
Blake , I think the HL380 would be the way to go in a Tilly for a 54 mm setup, I've converted a lot of 360A's to alky also for KT's but the big bore should handle the 86cfm or so of the 380. The intake tract will have to be optimized for the 380 with the alloy manifold and phenolic bored to 1.125 and since this is an open the port has been opened up some also to match the phenolic. Find a gas one to convert or be prepared to plug some holes in the alky 380 though because it was designed for an open flathead and is has an idle circuit too rich for a Yami. Al when the extra weight was added to the KT crank in a cheating situation, was it 180 degrees from the rod ? I always assumed it was two plugs 90 degrees from the rod to make the crank weigh more without changing the original balance ratio that Yamaha used. If your balancing for a heavier piston , then 180 degrees from the rod is appropriate. If your using the Burris piston you can get by with not counterbalancing, it's just not that much heavier, but the Aussie, Strike piston that's another story. If your building for the States , no reason to use anything other than the Burris big bore piston. Jon
alvin l nunley
Site Supporter
I know it's a fact that more counterweight in a stock KT crankshaft improves performance of the KT 100. If it improves the stock performance, if you add a heavier piston, you may have to add even more weight.
What I have seen done is both cheeks with two weights each. I don't have the spacing numbers.
Weighting of crankshafts is something that has been done, to the best of my knowledge, since 1985. Jeff Nelson, Of Invader karts, was disqualified at the enduro nationals for having counter weighted crankshafts in his dual kart. The engines were built by somebody in Ohio and I don't think Jeff had any knowledge of it.
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
Jon Brogden
Member
Al, two weights in each half, one at 3 o'clock one at 9 o'clock, with the rod at 12 o'clock would make sense, that position should affect the original counterbalance ratio the least. So when building an open the hot setup should be that added weight plus the extra weight of the big bore piston added at 6 o'clock, to stay with the clock face reference to add some more to the overall weight of the crank. That's something I'm gonna have to try, it should help a high compression motor even more than a stocker. Jon