Refuelling without flooding

[Tim Donald]

I have got a Saito 82 mounted inverted in a Ripmax Bolero.  Initially I had lots of problems as the fuel tank was too high but the incredibly helpful people on here diagnosed the problem and I modified the airframe so that the tank could be lowered to the correct position.  Anyway,  everything is good now but I have an issue that every time I refuel the tank (fill until fuel flows into the tube going to the exhaust) the engine floods.  Does anybody have and suggestions on how to stop this happening?  I can't see the tank (and it's not transparent in any case) so I can't stop fuelling before it overflows.  This is how I've always refilled my 2 strokes without a problem but none of them are mounted inverted.   

[David Davis]

Do you disconnect the overflow pipe from the silencer when filling the tank. If not perhaps the fuel is flowing into the engine from the exhaust valve.

[Nigel R]

Are you filling through the carburetor feed line?

 

[Tim Donald]

No I don't.  This could very well be the problem.  I'm using an electric fuel pump to fill and often some fuel does get into the exhaust (which I then tip out).  It doesn't look like enough fuel to get back into the engine but maybe there is.  I will try disconnecting the overflow pipe for fuelling and see if that makes a difference.  Thank you.

[RottenRow]

As David says. Alternatively, make sure that the exhaust is pointing downwards so that any overflowing fuel runs out and not back towards the engine.

 

Also, do you have the throttle fully closed when you are refilling? If not, try doing that, as it will reduce the flow of fuel into the carb (assuming that the Saito has a twin needle carb).

 

I have several inverted four strokes (no Saitos though) and I fill the tank in the way that you describe. The engines never flood, in fact I have to prime the engines before hand starting.

 

I only use a manual fuel pump though, so have more control over the filling process than might be possible with an electric pump (which only operates at one speed).

 

Brian.

[Tim Donald]

No Nigel,  I've got 3 lines to the tank,  the carb feed,  the exhaust pressure feed / overflow and a line for filling.  I could try filling from the carb feed,  good idea.  Now I think logically about it there are only two ways it could flood,  through the carb or as David has suggested through the exhaust.   I will have a play around.  Thanks!

 

[Tim Donald]

Thanks Brian.  Yes the throttle is fully closed.  I'm wondering if my electric fuel pump is a bit too enthusiastic and more fuel is getting into through the exhaust then I had thought.  Anyway,  got some suggestions to try now so hopefully I can work it out next time.  Thanks.

 

[Cuban8]

Thinking about my own inverted fourstrokes - the overflow fuel into the exhaust tends to run straight out through the silencer opening and would have to go uphill to get into the engine.

Maybe your pump is forcing a small amount past the carb, especially if not closed fully?

If after filling and you get the  flooded condition, does the engine remain clear after 'pulling it through'?

 

[Nigel R]

I make an external loop in the carb line, break the tube and use a plastic snake inner to join them together. Makes an easy point to tap into the carb line for zero cost.

 

Fancier DIY versions of this scheme are possible (see e.g. https://outerzone.co.uk/plan_details.asp?ID=15841 for inspiration)

 

Fuelling widgets are also available commercially of course.

[Engine Doctor]

If its flooding through the car then excess pressure is building up forcing fuel to carb. Check the pressure feed that goes to exhaust for kinks and check the nipple on the exhaust is clear and as said that the exhaust point downward angle  while filling to prevent backflow to engine . Disconnecting the pressure feed while re-fuelling should prevent any issues.

[Jon H]

The tank setup i use on my 360v powered sea fury uses two tanks set up so that one overflows into the other allowing both to fill from one pipe. The result is with one tank full the fuel pump pressurises it for some time while the other tank catches up. This forced fuel into the carb and made a mess in the cowl when it dripped all over the place. My solution was to set a throttle cut that totally closed the carb way past the normal idle position. As my throttle kill is momentary i power up the model, do my normal control checks, hold the throttle kill and then turn the model off before i release the switch. I can then fill without drama, turn everything back on and is job done. 

 

This is a very specific circumstance though and i cant think of any other model i have ever owned where the fuel pump floods the engine through the carb during filling. I flooded a few with fuel in the exhaust (2 stroke in particular) but not through the carb.  

[Jonathan M]

Interesting thread to read.  I've always manually pumped fuel in and later out again - that way I know how many 'turns' is a full tank and how much of that tankful is then used in a typical flight of 𝑥 minutes, which then helps refine the timer so I that I'd use only 3/4 of the fuel normally.  This also allows me to pump fuel in with more care or less depending on the engine configuration, e.g. on my sidewinder Irvine 53 with three tubes coming out the tank overfilling doesn't flood the engine or at least prevents it by safely flooding out the silencer, but on my upright OS 46 with two tubes (no separate filler tube) it does so I've learnt to be more careful.