I have noticed that the engine in my buggy (SH .21 in a Swift) appears to be very sensitive to fuel line (tank) pressure.
If I tune for mid-tank pressure, the engine gets on the pipe and head temperature can be controlled around 240F, but with the same HSN setting at full tank it is too rich to get on the pipe and with a nearly empty tank temperatures shoot to over 280F due to the lean mixure caused by the drop in pressure.
The venturi design on the carb doesn't look too great, I'm guessing that at WOT there is not enough depression to suck the fuel out of the HSN jet and the engine is really relying on tank pressure to force enough fuel through. When fuel tank/line pressure drops off as the tank nears empty it starts to run too weak and overheats.
At first I thought I had an air leak so I rebuilt the engine. I used ultra-copper RTV to seal the carb neck and back-plate and sealed the LSN threads with PTFE tape. The engine starts and idles OK but the air/fuel mixture is still varying greatly from full-tank to empty-tank.
Is there anyway I can make fuel line pressure more consistent as the tank empties without resorting to a new/different carburettor?
A pressure regulator between the tank and the carb would be ideal but due to the low pressures involved I doubt that an effective one could be made or bought without major expense.
Does tuned-pipe length and/or the position of the pressure pipe tapping on the tuned-pipe have any influence on the pressure in the fuel tank as it empties?
If I tune for mid-tank pressure, the engine gets on the pipe and head temperature can be controlled around 240F, but with the same HSN setting at full tank it is too rich to get on the pipe and with a nearly empty tank temperatures shoot to over 280F due to the lean mixure caused by the drop in pressure.
The venturi design on the carb doesn't look too great, I'm guessing that at WOT there is not enough depression to suck the fuel out of the HSN jet and the engine is really relying on tank pressure to force enough fuel through. When fuel tank/line pressure drops off as the tank nears empty it starts to run too weak and overheats.
At first I thought I had an air leak so I rebuilt the engine. I used ultra-copper RTV to seal the carb neck and back-plate and sealed the LSN threads with PTFE tape. The engine starts and idles OK but the air/fuel mixture is still varying greatly from full-tank to empty-tank.
Is there anyway I can make fuel line pressure more consistent as the tank empties without resorting to a new/different carburettor?
A pressure regulator between the tank and the carb would be ideal but due to the low pressures involved I doubt that an effective one could be made or bought without major expense.
Does tuned-pipe length and/or the position of the pressure pipe tapping on the tuned-pipe have any influence on the pressure in the fuel tank as it empties?