I was asked why I didnlt have a filter on my plane engine and I told my friend I was told not to. Is this correct? And is it normal for fuel to be blowing out of the intake hole? If you can help let me have it.

G'day Mate,
I personally don't use a fuel filter in any of my planes, BUT, I do use a very efficient filter in my fuel can, in my flight box, so the fuel is filtered before it gets to the tank in the plane.
I have never had a problem, with dirt in my fuel tanks.
I find that filters are more trouble than they are worth, most of them can leak, & case tuning problems.
And lately I have noticed guys using filters on their muffler pressure lines, I find this practice ludicrous, in the extreme.
If bits of junk are coming out of the engine, & going back into the tank, then you have big problems inside your engine.
just my 2cents worth.

My engine runs great but fuel seams to be coming out of the air intake hole when runing. Is this normal?

You're absolutely sure it's coming out of the actual intake? No pinhole near the carb nipple or anything? Some engines are like that, it has to do with port timing. As long as there are no leaks in the fuel line or the needle valve, and the engine runs fine, there's not much to do about it except live with it. I'm assuming that what you're referring to is not a fuel filter but an air filter for the carb. They're good for keeping dirt and grass out, but they won't help to keep the fuel in if your engine is one of those that likes to spit out the intake.

Err... Are you talking about an air filter or fuel filter?

This is a shot in the dark but, the engine is running forwards... right?

Bill

Yea. The airfilter. It's an SK enging. I'm not sure about any hole. I'll have to check. If I'm a little slow we're on dial up and it's not good. I do get fuel splater on the canopy. It is nice to be getting advice from experiance. Thanks

It is running forwards. As your looking at the plane from in front the prop is spinning ccw.

You are absolutely correct about fuel spraying out the intake on some engines, it's normal for them. I use an air filter to help keep the plane clean:
http://www3.towerhobbies.com/cgi-bin...&I=LX9160&P=ML

There are coarse and fine filters. I find the coarse does the job.

You can also take a bit of discarded panty hose material and affix it to the intake with one of those small rubber bands that are used for dental braces.

G'day

Like Alan, I have not used filters on my engines (and I have had lots of them) for more than 30 years. I just make sure that the fuel that goes into the tank is clean and does not contain moisture. A filter either inside my fuel bottle or after the fuel pump does the filtering for me. To keep the moisture out, keep your fuel in sealed containers and if you can, avoid opening them when the weather is humid or rainy. If you find you can't get your engine to idle reliably, always try some fresh fuel before changing settings or reaching for a new plug.

As for fuel coming back out of the carby air inlet, the only engines that I have seen that did this were Super Tigre G15 high performance glow engines which had a huge air intake and they would spit a bit back if they were tuned rich. (It is usually best to tune your engine a little rich (about 1 quarter to 1 half turn back from max revs as that way it will last longer and you are less likely to have "dead stick" landings. Remember, as your tank empties, there is a slight drop in fuel pressure and if you have tuned too lean, the engine may stop or worse, overheat. Are you sure the fuel is coming out the carby air intake? Some engines throw a little out the front bearing (not really normal to do so) and you will always get some mist of unburnt fuel/oil mixture coming out the exhaust which will splatter all over your plane. Some mufflers leak so that some fuel comes out the joins of the muffler as well but usually not very much.

But ... and this is really the important bit ... if it is running well and performing well, not stopping in flight and has plenty of power, then I would not be too worried. My Saito 72 four stroke in my big lazy Kadet Senior leaves a nice white vapor trail as it snails through the sky. (Well it is not very fast and it leaves a trail like a snail.) So does my Saito 100 in my Four Star 60. I get worried if I can't see at least a bit of a trail from my engines when they are at or near to full power.

All the best. Have fun and keep flying.

It doesn't make any difference what the fuel is. The idea is to remove debris from the fuel before it clogs up the engine's fuel system. I filter the fuel coming out of my fuel cans and also have a fuel filter between the model's fuel tank and the engine.

CR

I use the BruLine fine air filter on my engines because I figure the couple of dollars for the filter is cheaper than a piston/liner set . It also stops fuel spitting back out the carb so the outside stays cleaner too. Some engines can leak fuel quite badly from the front bearing but this tends to get spread all over the model, not just behind the carb.

And no two engines are alike, you may have a little slop in the crankcase and it is letting pressure back through and out the carb. The crankshaft is actally a valve, it rotates to open and close so the fit between it and the case is important. You may want to disassemble and inspect it to be sure it didn't swallow some rocks and ruin the seal.

Thanks for all the advice, I have a little work to do. The engine runs great and has plenty of power as my nephew showed us. I have flown the plane a number of times but I never dreamed it would do what he did with it. And I would like to keep it that way so I'm off to buy filters and I will be checking the motor out. Again thanks.

What size SK engine is yours? A SK 50 doesnt spit much fuel from carb(even inverted).Check your HSN o rings,carb inlet nipple red gasket,or muffler gasket.Probably those are the source of residue.

It is a SK .50. I'll do that. Thanks.

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Virtually all two-stroke model glow engines spit a little bit of fuel out of the carburetor while running normally. Some folks use a venturi extender (pipe that raises the air opening away from the needle valve spray bar) or an air filter to capture the errant fuel and to let it be ingested by the engine. It saves making a mess on the model, however, many times, the air filter will reduce performance a bit. Not so the venturi extension.


Ed Cregger


***There are also fuel filters. That is what some of the folks responded to, thinking that you were referring to fuel filters. Like some of them, I filter my fuel several times on the ground and do not fly a fuel filter around in my model. Do whatever makes you happiest.

I've heard that a venturi extension can often improve performance, is this true or have the old wives been at it again?

As far as an air filter degrading performance; this is true, but clean it after every flying session! That will keep any performance loss to a minimum.

As usual in life, it depends. <G>

As you may know, not only are our glow two-stroke engines affected by exhaust tract resonance, but they can also be manipulated via intake tract resonance as well. Doing so, either in the exhaust or in the intake tracts will also tend to narrow the engine's performance band in the process. Gordon Jenning's "Two-Stroke Tuner's Handbook" explained the nuts and bolts of these phenomena. I am sure that there are many other books of equal value available these days.


Ed Cregger

G'day I can think of three examples of the use of "ram tubes" on the inlet of carbys. Racing car engines often used them, Saito's larger engines such as the 120 use them and the blokes that fly old timers use very long ones on their Texaco engines to make sure that no fuel escapes the inlet venturi. The OS 60 "open rocker" four strokes are fitted with simple control line type venturis that can be up to 4 inches long with a simple Cox TD spray bar at about the half way point. These engines are tuned to run very slowly (just above idle) on very large props so that they are very economical on fuel. Actually there is a forth that I just thought of. The new OS 110 Alpha series four stroke uses one as well.
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Check the o-ring on your high speed needle. My SK50 leaked from there and was a real pain to tune and shut down. I ordered a new HS needle and o-ring and problem solved.

Simply put if you have a longer intake runner on a 4 stroke engine it improves the power at low rpms whil becoming a restriction at higher rpms. 2 stroke engines have very different internal charge dynamics so it may not be true for them. 2 strke glow engines will probably see better low speed power from the bypass ports being modified .