Tillotson HL style Carb Help

Wingit

Wingit

Member
The class my daughter is running requires this style carb. Can you tell me what those two adjustments do? And when to adjust them? We have always run flat slides so this thing is the moon to me.



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Needle closest to motor is the 'low side' and controls the mixture from idle to 1/3-1/2 throttle. Other needle is 'high side' and controls mid-top rpm. Are you running a 2 stroke or 4 stroke engine?
 
It seems odd to mandate a tilly in a clone 4 stroke class. Do you have to run gas or alky? which HR Tilly?
 
Depending on who built the carb. I’d start with screwing both needles in until they just do seat. Then back them out 1-1/2 turns each. You’ll need a CHT or EGT on your mychron to properly tune. The low side needle, nearest the manifold, is what you’ll fiddle with when you first hit the gas. The other is the high side adjustment for upper RPM adjustment. You have to adjust it under load. If you don’t have a Dyno that means on the track. Fire it up in the grid roll on the track and floor it. If it dies open the low side. Keep doing that until it goes when you floor it. Once it’s taking full throttle off idle run it and watch you temp. You want you CHT at least 325 and under 425. If you can’t get heat in the engine, close the high side some. Once you get it to run in the upper 300’s you need to recheck off idle and tweak again. Honestly I don’t have a lot of experience on OHV’s but I do with flatheads. Usually Tillotsons are set up a little differently between the two. For reference, I usually end up about 2-3/4 out on the low side and about 3/4 turn out on the high side on a flathead. I set my idle about 500 RPM under my clutch stall. Some folks say you can’t idle a Tilly, I’ve never built a carb that wouldn’t idle and I’ve built close to a thousand if not more. One thing you don’t want to do is let it sit and idle for extended amounts of time. Don’t be the first guy to light up in the grid.
 
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Flip the carb over and see what model number is stamped into it, Tillotson made numerous different models of their carb, each designed specifically for a particular engine combo. It is highly advisable to not put an unknown carb on your engine, if its too small you can easily lean out the engine and possibly burn it down, also if its too big, you can easily wash down the cylinder wall and starve the rod bearing and wrist pin of lubrication which always ends up in terminal destruction of the bottom end/shortblock of the engine.

Typically the best Tillotson for a mild modified small block 4 stroke kart engine is the HL 304 WX, when its properly prepared for the fuel your using, big difference between one prepared for gas and one prepared for alky…hope this helps…dr
 
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