Fuel syphoning into carb

[Mark Barker]

I've got a new Spot On 50 L with a 4-stroke ASP 70. I can't lower the tank any more which means it is too high and it putting the glow fuel straight into the carb. I have heard of Perry Pumps, but I believe that if I just pump it it could make it worse without a regulator. I have seen a Perry Pump with a regulator, but the spec said it was meant to be for a 2-stroke. Any ideas?

[GrahamWh]

Is the ASP inverted? If so, you could raise the carb by changing it to horizontal.

[Mark a]

You could try a longer fuel feed pipe and loop it above carb level it may help.

Mark.

[Mark Barker]

Thanks for the ideas.

ASP is inverted and I've already cut the cowling. I really want to stick with it!

I was going to use a longer tube and loop it to see if that would help, but I've just read on a different site to try using a uniflow tank system. I'd never heard of it. It uses 2 clunks. One clunk goes to the carb and the other to the muffler, with a one way valve so no fuel goes into the exhaust. As soon as you've filled up, block the air inlet. Completely new to me, but it might just work as it's meant to stop the syphoning effect. Unfortunately, the centre of the tank is more than 1 1/4" higher than the carb. It's an ARTF. I'm surprised the tank is in such a daft position, but I can't lower it.

Many thanks for your help. I'll come back if it works.

[Don Fry]

I have a artf P40, same problem, as the makers assumed the motor if a 4 stroke would be sidewinder, when the cowl is plenty deep enough to hide the motor/silencer inverted, the downside is the tank position comes in too high, about 2 inches. The feed loop on mine runs to near the top of the cowl, then down to the engine. It works fine, fuel it, open the throttle, apply starter to draw fuel, apply glow power and away it goes, no problems. And it is simple and cheap. KISS principle applies.

[Martin Whybrow]

The Perry pump won't work as the VP type pump, the only one that works with a 4 stroke, doesn't incorporate a regulator; you'll need to add a regulator, either a Cline or an Ironbay regulator, and a pressure feed to the tank to ensure you still get fuel flow when the tank's lower than the engine in flight.

I'm not sure about the uniflow system, the descriptions I've seen for it defy physics and I can't see how it would work.

[cymaz]

+1 for looping the tube over the top. No cost solution to the problem if it works.

[Mark Barker]

Thanks again for all the input. I looked for a Cline regulator and an Ironbay. Don't think they sell them in UK, I've seen them on an American site. That would do the job. I think I'll try a big loop as suggested and also use the uniflow system to see if that works. I have seen a regulator for a 2-stroke running from crank case pressure. All sounds very complex. They shouldn't sell ARTF planes clearly showing in the manual a 4-stroke inverted without mentioning you may need a regulator. Very frustrating. Once again, thanks for all your input. I'll let you know how I get on.

[Martin Whybrow]

Posted by Mark Barker on 02/11/2014 22:39:31:

Thanks again for all the input. I looked for a Cline regulator and an Ironbay. Don't think they sell them in UK, I've seen them on an American site. That would do the job. I think I'll try a big loop as suggested and also use the uniflow system to see if that works. I have seen a regulator for a 2-stroke running from crank case pressure. All sounds very complex. They shouldn't sell ARTF planes clearly showing in the manual a 4-stroke inverted without mentioning you may need a regulator. Very frustrating. Once again, thanks for all your input. I'll let you know how I get on.

Weston sell the Ironbay regulator, but it isn't cheap! To be fair to the manufacturers, some 4 strokes have the carb on a long manifold which puts the spraybar close to crankshaft height, so inverted operation isn't an issue.

[Mark Barker]

Thanks Martin for the info.

If the loop and uniflow don't work, I'll go to Weston and get the regulator.

[Cuban8]

I'm surprised that this is such a problem. When I've come across a similar issue, arranging the model to be in a slightly nose up attitude when starting will prevent excess fuel from draining into the carb. Keep the throttle closed until ready to start..........open and prime...........reduce to 1/4 open, glow on and away you go!

One way valves, fuel pipe loops, Perry Pumps, magic fuel tanks? .........KISS.

ASPs four strokes are not fussy about tank height anyway (I've used them for years) so once the motor's running and tuned correctly, I doubt if you'll have a problem.

Edited By Cuban8 on 03/11/2014 08:03:59

[Engine Doctor]

Hi type carb extension into the search panel for a previous thread. I fitted this mod to an sc 52 some years ago and it worked brilliantly. The engine in the. Pics is a saito and is just used as a demo. The model was a proto type corsair with a glass fuz that had had a tank platform fitted at the upper half of the fuz . the engine was fitted inverted so as to hide the head from sicking out of the top. This mod raises the carb to the height you want and stops all the flooding issues.

[stu knowles]

If it is just a question of stopping the fuel running out when the engine stopped, just stopping off the fill & vent pipes will stop leakage. No air in - no fuel out.

[Tony Richardson]

Hi Mark try this **LINK** it may give you the answers you are looking for.

[Mark Barker]

You are right cuban 8, the ASP four stroke will work with a high tank. The excess fuel from the siphoning effect goes out the exhaust. But it performed so much better on the bench when the tank was in the right position. If Possible I would like to get the same performance in the plane.

re. Engine doctor, raising the carb would completely eliminate the problem. I will look into carb extension in the search panel.

re. Tony link very interesting

one of the problems with the siphoning effect. If you adjust the mixture to take in consideration the siphoning effect, when the plane is inverted for a prolonged period. The fuel would no longer be siphoning into the carb and the engine would not perform the same.I can get it to start ok. It just doesn't perform as it should. I will consider all the inputs and I'm sure, whether I move the carb, or use a regulator I'm sure it be ok. I will post the results once I've worked on the plane

.Many thanks

[Cuban8]

Go for the extension - good idea & it's the simplest solution providing you can find a suitable size. Valves and pumps may just lead to more problems, I've been down that route in an effort to solve a similar issue in the past.

Good luck.

[Mark Barker]

Well, here it is - sometimes, the simplest things are best!

At my club there are a couple of guys who do not use a pressurised system with 4-strokes (air tube going to the exhaust) or with a high tank. A very successful way is by adjusting the mixture, especially idle jet, as 4-strokes seem to naturally suck in the fuel. I was all prepared today to try the uniflow system. It wasn't too successful, but I didn't spend too much time trying to adjust it. I then tried traditional pipework and just disconnected the pipe from the exhaust which pressurises it. With careful tuning, although it doesn't make sense, it seemed to work fantastically! As there was an awful cross wind today, I didn't fly, but all the ground tests were fantastic. I look forward to good weather for my maiden flight.

Once again, thanks for all the input. It is helpful to consider different options.

Mark