Appreciate all your help @Ed_H. That’s the plan unless I find out that the Tilly carb doesn’t require it.
Never ran the tillotson carb on these motors myself but given that they are self pumping and that action is part of how they meter fuel there should be no need for a retun.
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I’m going to spring for the Tillotson. Thanks again @Ed_H.
Solved!
Appreciate the assists from @Ed_H and @Bai7200.
The issue we were having was caused by the lack of a fuel return line with the Dellorto carburetor. We ran that before in my son’s older chassis which already had a third fitting on the fuel tank, but didn’t think we needed to tap a third fitting on the newer Tony fuel tank. At high load, the motor was asking for a lot of fuel, but the lack of a return line was creating a bottleneck in the carb. Excess fuel had nowhere to go, resulting in a rich condition, smoke out of the exhaust, low head temp, and the motor holding back dramatically on the top end.
Swapped the old Dellorto carburetor out for the new Tillotson, which doesn’t require a return line. It has an internal fuel pump, so we ditched the old fuel pump that was paired with the Dellorto. Still have a bit of tuning to do with the needles, but I’ve got it at a decent baseline and it’s running really well now.
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