Help needed

[Birgir]

Hi

I have an ASP S21A engine in my Mini Super and need some help adjusting it. Although the model is over 40 years old the engine has just had between 10 and 20 flights so it is just about finished the run in period.

The engine is very easy to start but when throttle is fully opened the rev goes up and down without me moving the stick. In the following video you can hear how it sounds.

.

The question is, what could be the cause?

1. To lean mixture

2. To rich mixture

3. Wrong glow plug

4. Vibration foaming the fuel, leading to air in the fuel hose

5. Another cause…

Any thoughts and ideas appreciated

B

(BEB: proof reading is also appreciated)

Edited By Birgir on 25/01/2015 11:33:56

[bert baker]

Hmm I think I would check for induction air leak .

I.e.. where the carb fits the case is there a seal and does it seal, also the carb fixing screws can be another place where air gets in. if it is the sliding cotter pin it may still leak.

Does it have a tank filter on split clunk pipe in the tank

[GrahamWh]

Could be vibration causing an air leak into the carb - new o ring on the mixture needle?

Edited By GrahamWh on 25/01/2015 13:22:30

[cymaz]

Also check that the ratchet spring on the high speed needle is not loose. Blow all the fuel lines and jets through.

Check all the pipe work from the clunk to the carb mm by mm. Could be just a tiniest hole in the clunk pipe, or anywhere along the fuel pipe. Also check the pressure side as well. And the tank bung seal. Just be very methodical.

Hope you get it fixed

Edited By cymaz on 25/01/2015 15:25:08

Edited By cymaz on 25/01/2015 15:26:21

[Engine Doctor]

Hi Birgir. Check all of the above and also check the tank pipes. You say the model is over 40 years old , Are the tank and fittings the same age ? If they are old then check the pipes for corrosion especially if they are brass. If they look black then they are probably corroded by Nitro in your fuel.

[Birgir]

Thank you all for good ideas.

It looks that everyone agree on that the problem is most likely due to “false” air in the system somewhere, i.e. from the tank to the engine cylinder. So I will work from that theory.

Whereas the engine and tank are closed in a balsa cowl and difficult to access it is important to give this a good deal of thought before any decision is made

Let’s play some Sherlock Holmes.

Theory: Air is drawn in to the system at an unknown place

Facts:

1. The system can be divided in to two parts, A, being the engine, B, being pipes and hoses leading from tank to carburettor.

2. Air bubbles have been seen in the fuel line from tank to carburettor at high speed. (New knowledge)

3. Engine is new but some part of fuel line and the tank are a few decades old.

From those three facts we have reason to believe that it is more likely that the problem is in system B. rather than system A.

Tests

1. Does system B hold pressure for a period of time? This can be tested by closing tubes leading to muffler, engine and fill cap. Blow a little air into the system and see if it can hold pressure.

2. Does system B hold vacuum for a period of time? This can be tested by closing tubes leading to muffler, engine and fill cap. Suck a little air out of the system and see if it can hold vacuum.

I’ve already done test 1. and 2. and the system holds pressure and vacuum for at least 1 minute. So I conclude that the system B as a whole is air tide.

Fact 2 does although point to some malfunction in system B

New theory:

The hose inside the tank is leaking.

How possible is that? If the top of the hose where it connects to the nipple going out of the tank leaks, is it possible that he engine can suck some air out of the tank into the fuel line. Remember that there is some pressure in the tank from the muffler.

I would welcome any ideas on that before I start tearing my model apart.

B.

[cymaz]

The join between the pipe and the brass tube edge is a good place to start a pin hole. Put the tank under pressure sealing off all the ends of the pipes. Place it under water and watch for bubbles.

I think putting everything under a vacuum would close off the leaks by drawing the walls in together.

[bert baker]

Try it with tank half full. is it exhaust gasses aerating the fuel.

If the clunk pipe has a hole in it, you will see no ill effect if running a full tank as leak will be submerged in fuel

Edited By bert baker on 27/01/2015 17:21:58

[ken anderson.]

hello b..renew all the plumbing and try a new plug and fuel or different fuel and depending how long the engine has been standing it may need a couple of runs to return to normal-ie-it may have congealed oil inside need's burning off.

ken Anderson............... ne...1 congealed dept.

[Birgir]

Thank you all

I favour the Bert Baker test and will do that.
It will determine if the last theory is true or false

I’ll let you know how it turns out

B.

[Peter Miller]

I know that the model is old but this does prove once again my firm rule. "If you can't get access you will definitely need to."

Access to everything is vital. This is something that I learned on full size aircraft and always apply to my models

IT could even be the clunk blanking itself off against the end of the tank.

I bet that in the end you will HAVE toget the tank out

[Birgir]

Yes, Peter, I've met Murphy once or twice

[Peter Miller]

Allow me to present Miller's First Law.

Nothing "simple" ever is.

[Graham Bowers]

I too believe it is probably a fuel system issue but before doing surgery I'd be tempted to do an engine test by strapping a new fuel tank to the side of the model and use new fuel tube, thus eliminating the old fuel system.

Graham

[kc]

Graham's idea is a good one but note he said " to the side" which means at the correct height!

Peter is also right -at some time you will need to get the tank out. It is probably fuel pipe deterioration so will need tank removal sooner or later. You should be able to remove a tank but it may mean removing a servo. Consider taking a scalpel to the balsa and cutting an access hatch, maybe underneath. Drastic but could be quicker.   Also beware that the nicad will need replacing if it's old and this may mean an access hatch is needed.  Also check carefully for black wire corrosion on nicad leads and switch etc.

But what about that engine? Old ASP engines were known to often have needle valves that leaked. Is that an old engine or fairly new? Leaky needle valves were a poor fit in the threads or the rubber O ring was poor. A simple cure was a few turns of PTFE tape ( as used by plumbers) on the threads making a tighter fit.

Edited By kc on 28/01/2015 14:02:43

Edited By kc on 28/01/2015 14:05:14

[Steve Hargreaves - Moderator]

I think the engine is pretty new kc.....Birgir talks about it just about being run in....

[extra slim]

Guy at our field had exact same engine, similar issues, turned out to be the needle O ring was "crushed" and not seated properly, kind of rushed in. Reseated and it is a lovely little motor. Might be that,

[Birgir]

Hi

I‘m still waiting for an opportunity to perform the Baker-test, i.e. checking if the problem still exist if the clunk pipe is fully submerged in fuel. Because the test needs to be performed outside I must wait for suitable weather, and it can be a long wait around here.

While waiting I’m forced to spend time on my next building project.

B.

[Don Fry]

At 40 years old, if the tank pipe work is not leaking it soon will be if the model is now in use, replace the lot and then have a look at the moter if that hasn't fixed the problem. Does not matter how difficult it is to get at the tank, it has to be done,or as God made little apples the next problem will be when airborne. Ask me how I know.

[Don Fry]

PS. and while your at it replace the switch if it that old, also check battery leads and capacity very carefully and if in sought throw it out.

[Don Fry]

Spell Checkers!, for sought read doubt.

[ken anderson.]

birgir-where do you live-north pole?

ken Anderson..ne...1 ..... north pole dept.

[Birgir]

Hi Ken

In Iceland

B.

[bert baker]

Cool send me some burgers and a cheese cake please

Do look for black wire corrosion on all the radio gear, renew the switch as previously suggested, it ain't worth not doing.

I found it out the hard way, a £5.00 switch or a £50.00 rebuild, yep I'm fifty quid down.

Edited By bert baker on 22/02/2015 17:49:11

[kc]

I wonder if Birgir understands Bert's sense of humour? It made me laugh because I know what a particular supermarket is famous for. If necessary we will explain......