Walbro Carb with 3 Hole Can

[jhannah]

We run a PRD RK100 in Jr. Sprint Enduro with the 3 hole can. Any hints on carb adjustment? Is it the same as other cans, pipes? We can only get about 12000 rpm out of it, and it seems to be very rich, to the point of flooding out.

In Briggs Jr we ran rich on purpose with the intake restrictor, but I don't know the dynamics of this setup.

Thanks

[Jimmy Moore]

Set the fulcrum arm height at .035" below the carb body and set the pop off at 10 psi. Set the high speed needle at 1/4 turn open and set the low at 2 turns open and tune from there. If it still runs rich then come in on both needles at the same time. Move the high needle a bar width at a time and move the low needle 1/8 turn at a time and you'll soon find out where the range is. Some use a carb trigger to close off the high jet at top end where there's alot of vacuum and fuel flow but, you can usually set it at a 1/8 turn minimum on the high and 1 1/2 minimum on the low and run there if your temps look good.

[Roger Miller]

As for your peak RPMs, you need to look at your gearing. For tracks that need ratios in the 5:1 - 6:1 range, a 3-hole can and that kind of load will hold down what you can achieve for peak RPMs.

Sprinting at around 7:1 - 8:1 helps the motor not load down and allows higher RPMs.

We have raced both Sprints and Road Race with cans and the gearing is way different, carb tuning is important, and, peak RPMs are different.

I don't claim to be an expert...

[jhannah]

We are racing ar Summit Point, over 3000 foot straight, and a nice down hill into turn 5. The mychron data shows peak RPM about 2/3 down the straight. The gearing doesn't seem to matter much on the straight, we tried 17X79 thru 17X85, and only changed rpm a couple of hundred. WE are still on a major learning curve on gears and clutch (SMC axle).