>>All the carburated planes I have flown called for having the electric fuel pump on during engine start.
Mine doesn’t. O360 A1D. It calls for fuel pump on till fuel pressure is on. Then off for the start.
The reason to use the electric pump before startup on a low wing carbureted plane is to fill the float bowl to make up for evaporation during the period during which the engine was stopped. If the carburetor float valve were to stick, the fuel pump will not build pressure and fuel will overflow from the carb. At that point you would not want to start the engine. If all is well the fuel pump will build pressure in the line after the float valve closes, and from that point on it makes no difference to starting whether the electric pump is on – its deadheading against the closed float valve.
Arne wrote:
All the carburated planes I have flown called for having the electric fuel pump on during engine start. None of the injected planes.
It’s not a “recipe” if it’s in the POH.
Yes, that’s right of course. Mine (PA-28-161) says that. But it doesn’t mention when to turn it off. I (and others) have always taken this mean “on until fuel pressure, then off”, not “on during cranking”. Obviously if a person abandons the aircraft in a hurry, they might omit to turn off the pump or master…
In a frequently flown (and maintained) plane there’s no excuse for fuel ‘evaporating’ from the float chamber, and if it is neccessary to run the pump then it might be indicative of something else. Despite that, I do check this and fuel pressure always appears immediately, so no refilling of the carburettor. (In contrast, the Series One Land Rover does need to 5-10 secs of fuel pump to fill the leaky old carb almost every time)..
The pump is not mentioned again in the POH until pre take-off, when it is to be ‘On’ again. Not neccessary if it’s meant to be left on all the time!
Anyway, none of this should detract from the dangers of throttle pumping, which is not in the POH and WILL lead to fuel running out of the cowling!
On most of the checklist I find for the PA-28 at the aeroclubs in Sweden is that you have the pump on during engine start and then shut it off before you start taxi. I am not saying it is right or wrong but it is the most common practice here I think.
Fly310 wrote:
On most of the checklist I find for the PA-28 at the aeroclubs in Sweden is that you have the pump on during engine start and then shut it off before you start taxi. I am not saying it is right or wrong but it is the most common practice here I think.
Agree.
Fly310 wrote:
On most of the checklist I find for the PA-28 at the aeroclubs in Sweden is that you have the pump on during engine start and then shut it off before you start taxi. I am not saying it is right or wrong but it is the most common practice here I think.
Same in our checklists in Switzerland.
Aveling wrote:
The pump is not mentioned again in the POH until pre take-off, when it is to be ‘On’ again. Not neccessary if it’s meant to be left on all the time!
That is not an argument. Checking an item that is supposed to have been set before again at pre take-off makes sense and I’ve seen it in several checklists.
I turn the electric pump off before starting the engine, having listened to and watched its on/off operation and fuel line pressure rise without the engine running. As noted above its not doing anything useful once you have a couple of psi fuel pressure on the gauge. After turning the electric pump off but before starting the engine any decrease of fuel pressure can be noted, generally that results from a slightly leaky float valve. Then after startup with the electric pump still off, you can watch for degradation in fuel pressure as you taxi that would due to a faulty mechanical pump. With all that done, before runup and takeoff with both pumps now running you have done a basic check of the carb float/valve and both pumps independently.
I operate a Robin DR400/180 and the POH states “Throttle…carry out 2 or 3 injections, then 1/4 travel forward”. We do not have a primer, so pumping the throttle (injections) is what we do. We have had starting problems in the past, and then the tendency is to pump more, but with properly serviced mags, it starts after two blades.
In the POH for my PA28-181 it is definitely fuel pump on for start. However I ignore that and this is what I do
I had 3 months with progressively worse starting problems and it transpired it was my mags had issues. The last IRAN was under the previous ownership as part of my pre-buy requirements.. Let’s just say that “inspection” wan’t done very well. I ended up putting two brand new mags on as the old ones were not worth rebuilding.
During those 4 months I was having to pump the throttle etc which I now realise is a bit of a dodgy path to go down.
