Fuel pump

[Richard Acland]

Is there any way of retro fitting a fuel delivery pump to supply fuel to an SC 70 four stroke.

[Robin Colbourne]

Hi Richard, would a Perry Pump do the job? These rely on vibration from the engine to pump the fuel.  You probably want the VP-20.

[Engine Doctor]

Give Weston UK a call . I sèm to remember that they used to sell a pump that worked on crankcase pressure pulse.

[Richard Acland]

Thanks for the replies. I will check them out.

[J D 8 - Moderator]

Crankcase pulse pressure worked pump will not work with a 4 stroke engine. The only bit of pressure in the crankcase is some bypass from the piston/liner.

  A 2 stroke uses crankcase pressure to send fuel/air up the ports to the combustion chamber.

[jeff2wings]

You can use crankcase pressure on four-stroke and irc Brian Winch explained in his column how,basically most pumps use the + and - pressure pulses in the crankcase on a two stroke as it draws in a fresh charge and the pumps it into the cylinder, this obviously is not the same process in a four-stroke but the action is still the same in that the crankcase volume increases and decreases with every stroke, thereupon producing +and- pulses which requires the vent,it's not just there to let the oil out! So in oder to use a pump Brian suggested using a second crankcase vent with a one way valve to admit air on the up stroke and provide a positive pulse on the down stroke for the pump or directly to the tank, in effect the same as using timed pressure on a two stroke. 

[Richard Acland]

No one seems to stock Perry pumps in this country. Spoke to Weston UK and they dont do fuel pumps. I will keep searching.

[jeff2wings]

So in direct reply to the op then the Perry pump suggested by  Robin would fit the bill,it sorted out a problem for a club mate a long time ago with a very early saito that had the carb mounted directly to the head Lazer style in a vintage model, red zephyr I think, the tank being a lot lower it would only run 1/2 a 4oz tank but the pump ment it would use all the tank.

Brian's suggested system may have been more about directly pressurising a tank directly for a smoke oil tank,four-stroke engines have a much better fuel draw the there 2 stroke equivalents 

 

Edited August 8 by jeff2wings
Forgot picture

[Engine Doctor]

14 hours ago, Richard Acland said:

Is there any way of retro fitting a fuel delivery pump to supply fuel to an SC 70 four stroke.

If all else fails fit a YS FS . They are all pumped. A 63 mk1 or two is a more powerful than a SC or OS 70. Only draw back is they do like a drop of 20% nitro.

[Dave Brooks]

Have you tried Just Engines for Perry pumps? I got one from them about 18 months ago. 2stroke and 4stroke versions available.

[Robin Colbourne]

6 minutes ago, Dave Brooks said:

Have you tried Just Engines for Perry pumps? I got one from them about 18 months ago. 2stroke and 4stroke versions available.

I just looked there Dave.  The website shows out of stock on all the Perry glow pumps.

[Robin Colbourne]

Taking a lateral thinking approach, the objective is to provide a constant pressure fuel supply.  Control line pilots achieve this using a pressure filled silicone baby pacifier (teat) filled with fuel.  Maybe a balloon pressurising the tank, or a battery driven pump would do the job.  Otherwise by a Perry Pump from Ebay when one comes up in the UK.

Edited August 8 by Robin Colbourne

[jeff2wings]

An idea Jim Walker came up with some 70 years ago,l would be interested to know way a need for a pump inthe first place?

A YS pump system although designed for 2 stroke operation  

 

 

[Paul De Tourtoulon]

6 minutes ago, jeff2wings said:

,l would be interested to know way a need for a pump inthe first place

Finally, someone asking why.😇

[Richard Acland]

The reason I want to try a pump is because a few years ago I built   a Stolp Starlet. The engine is mounted sidewinder fashion. The tank sits quite a way back but is on a level with the engine. It was fitted with an OS 70fs. I set this engine up on my test rig and it ran well with a nice idle, however when I fitted it to the model although it would reach peak RPM and was OK mid range it would start to hunt and then cut out when it came to idle.  I bought new fuel fitted a new plug and it was still the same. I removed it put on my test rig and it ran perfectly. I had a spare SC 70 fs so decided to fit that   Same result, would not idle. I decided it must be that the tank is too far back and that a pump might help. Also since building this model it has only flown once and I would like to get it going again

[Paul De Tourtoulon]

So why not move the tank ?.

[Richard Acland]

It would require major surgery. If I was to start cutting it about I might just convert it to electric although that would go against my religeon. I I like to have something oily and noisy up front.

Edited August 8 by Richard Acland

[john stones 1 - Moderator]

That's a nice model, do it justice, commit to surgery and move the tank forwards.

[Richard Acland]

Maybe when I have finished my current build I will take it in hand and put it under the knife. It will keep me occupied when the nights draw in.

[Jason Channing]

20 hours ago, J D 8 - Moderator said:

Crankcase pulse pressure worked pump will not work with a 4 stroke engine. The only bit of pressure in the crankcase is some bypass from the piston/liner.

  A 2 stroke uses crankcase pressure to send fuel/air up the ports to the combustion chamber.

I dont think you know your engines and pumps too well as thats how Perry pumps work. Even the YS pumps external or built in use crankcase pressure. In the past Ive used Perry pumps  on a four stroke no issues .

[J D 8 - Moderator]

              Was just having a grey moment. Have done lots with engines, not just model ones but larger stuff as well. 

[Robin Colbourne]

Would a small header tank near the engine do the job?

[Braddock, VC]

Richard, if you have a mechanical bent it's fairly straight forward to modify a two stroke petrol pump from a portable petrol power tool to suit a 4 stroke.

I have used this on several 4 strokes, particularly lasers and it sorts all repeat ALL the issues out.

As guidance ignore what the self appointed experts say unless they have actually tried it.

The procedure is along these lines.

Remove the pump/carburettor from the petrol engine.You will see an orifice on the flanged face that sits against the crankcase. A short piece of brass tube 3mm od needs to be placed in this hole and secured with epoxy. NOT the main inlet tract btw.

ALL the jets MUST be screwed tightly closed.

you now have two inlets the 3mm brass one is to be connected to the exhaust pressure nipple of the 4 stroke - be prepared to replace this silicon tube regularly, the other inlet connects to your tank.

Now you have to drill and tap a hole into the inlet fuel side of the carb and fit and seal a nipple there, this goes to the fuel feed on your engine.

Secure the pump/carb to the firewall and connect up your pipes.

What effectively happens is the engine carb draws fuel when the engine is on the inlet stroke and the carb float and needle valve close it off so it doesn't leak.

I used this on several lasers and also on a big Italian 25cc two stroke glow where the tank was over 300 mm away from the firewall. It worked on that giving it a decent idle.

You may find, as I found, that lasers will tick over reliably at around 1600 rpm.

I can't give you any more detail as IIRC I did this over 20 years ago, in fact the pump is still on one of my planes. and my mate's 25cc one still has one fitted as well.

I gave up modelling some years ago. At that time I had a friend with a lawnmower business and used pump/carbs were free. As you don't use the jets that little unreliability issue is sidetracked.

This solution is cheap in both cash and time so rather than spending hours looking for something like a perry pump that probably won't work unless you spend hours setting it up this little gem relies on hydrostatics and works from the get go with a modicum of needle twiddling. Of course some experts will try and explain it's about as difficult to do as building the great wall of china.

I always found that negative waves seemed to rule on this forum.

[J D 8 - Moderator]

1 hour ago, Robin Colbourne said:

Would a small header tank near the engine do the job?

 Chicken hopper system as commonly used in Control line models in days gone by. Probably still used by some.

[Andy Stephenson]

JD8, can you explain how the engine can still draw fuel from the main tank up to the header without suffering all the problems of fuel draw from a remote tank. It seems that you still have to overcome this to fill the header tank.