the hi-needle in the Tillotson HU carb of a 6800 doesn't seem to produce a change in operation. In the prior life of this eBay saw, the pison was seized to the point of self-destruction, so pop-off metering may be the cause. I replaced the crank seals, and I rebuilt the carb with the Tilly rebuild kit, which unlike the Dolmar/Makita rebuild kit does not include a new metering spring. Now I'm trying to check the valve seat and pop-off setting.
In some prior threads, Glens has pointed to this site: http://www.aerocorsair.com/id28.htm, which is oriented toward rebuilding larger carbs for small personal aircraft. It recommends setting the pop-off pressure in the 10-12 psi range for larger carbs. (Higher pop-off limiting fuel flow at wide open throttle (?-possibly due to inability of fuel pump to push sufficient high side fluid pressures due to higher vapor pressures of some fuels-?), and the starvation at the jets then causing lean siezure during flight, and possible death of the pilot.)
In their service manuals, Dolmar/Makita *imply a *max pop-off pressure of 0.5 bar, or about 7.5 psi, but I can't tell if they are talking about testing the crankcase seals or the metering valve pop-off setting. That's all I've found re numeric values. Does anyone know if the Tilly/Stihl/Other rebuild manuals, have any numeric specs for testing carb pop-off?
What would be the pop-off for the Tilly HU & HS chainsaw carbs? (A search on "pop-off" yields some discussions on testing, but doesn't indicate the range of desired numeric values.)
In some prior threads, Glens has pointed to this site: http://www.aerocorsair.com/id28.htm, which is oriented toward rebuilding larger carbs for small personal aircraft. It recommends setting the pop-off pressure in the 10-12 psi range for larger carbs. (Higher pop-off limiting fuel flow at wide open throttle (?-possibly due to inability of fuel pump to push sufficient high side fluid pressures due to higher vapor pressures of some fuels-?), and the starvation at the jets then causing lean siezure during flight, and possible death of the pilot.)
In their service manuals, Dolmar/Makita *imply a *max pop-off pressure of 0.5 bar, or about 7.5 psi, but I can't tell if they are talking about testing the crankcase seals or the metering valve pop-off setting. That's all I've found re numeric values. Does anyone know if the Tilly/Stihl/Other rebuild manuals, have any numeric specs for testing carb pop-off?
What would be the pop-off for the Tilly HU & HS chainsaw carbs? (A search on "pop-off" yields some discussions on testing, but doesn't indicate the range of desired numeric values.)