I am a bit reluctant to ask this question, but it is so weird that I can't think of a cause. Basically I have a friend that has been flying stunt for more years than I care to think. He is an expert at F2b, only advancing years restrict his scores. So he is no fool at setting up engines for stunt.

 

Did he ever change fuel for a fresh and clean mix ?.
Does he mixes  and filters his own fuel ,because tiny little Castor oil parafin flakes.
Maybe the Methanol barrel has been soaked to much moisture/water over the month/years.
Could be a water/moisture prob.(in low percentage) which causes overheating and flame outs.
Just my thoughts.

Peter

Excess varnish can cause a similar symptom in some engines, but 4 at the same time is odd.

Phil

Kinda what Peter said.  I'd be looking for what he's doing that's different from previous years and/or from other folks, and what's common to all the planes.

If his electrics start cutting out after two minutes this coming year, I'd suggest a ritual involving a pagan shrine, a chicken, and a sharp knife.

 

Randy Cuberly

Does he have the tanks plumbed properly? Maybe the feed and vent lines got switched.

Hi Andrew,
                  if your friend is only getting a constant two minutes 'out' of 4 completely different setups then look for what constantly puts those two minutes 'into' them.

Does he use a common syringe to fill the tanks? Is it being filled with only enough for a two minute flight by mistake?

Brett, that is the really odd thing, the engines ran perfectly normally, neither rich nor lean, they simply cut as though someone had turned an "off" switch. The only obvious connection between these recalcitrant engines is, I assume, the fuel. Fresh fuel from the same manufacturer was used as a first stab at the problem and when that didn't do any good another brand was tried. They were all 5% nitro and 22 to 25% oil (half and half castor / synthetic).
  The chances of 4 separate engines having unconnected problems which gave the same symptoms is remote in the extreme and yet if the problem stems from the same source, what could it be?
 

  I have had individual engines do that from time to time, one particular engine would do it over and over even on the test stand. The only solution I ever found was the fuel. Byron fuel, in particular, was like a magic cure-all, that was the only fuel it would run on.

     Brett

Thanks Everyone,
  A lot of interesting suggestions there. No I don't know if the same syringe is used on all 4 models and again, I don't know if there is a senior moment about using too small a syringe which is only good for 2 minutes or so. Come to think this may well be a reason! After the engine quits and the plane lands , you can restart the engines no problem. Now can I remember if the plane was refuelled before the restart? no I can't so let me ask the question. I think that something like this must be the answer, otherwise it is too weird to contemplate!

Andrew.

Thanks for that info Brett, I will get back to him and ask the appropriate questions, I really would like to find out what is going on. Maybe I can make him an offer for his stunt engines, someone has to get something out of this odd situation!

Thanks,

Andrew.

Andrew,
I understand this is a frustrating problem, I think the common thread is the fuel. I assume that these ships were flown before and didn't have this problem. Sometime you can get a batch of fuel that is contaminated with something that causes all kinds of issues. You didn't mention what brand of fuel he is using. I think it is worth trying some SIG 5% or the Byron helicopter 5 or 10%. These are know high quality brands and would eliminate one possible issue. Also, if these engines have some time on them have him remove the plug and turn the engine through the compression stroke to check for excess tightness (if an ABC should be a little pinch near the top of the stroke). If it is very tight there may be some varnish that needs to be removed (it seems unlikely that the four of them all have the same amount of varnish). Last clean out the needle valve spraybar. Keep us posted.

Best,       DennisT

Hello Everyone.
The problem has been found, there is a huge amount of very strange goo in the silencers. It isn't the usual sort of rubbish one gets, but some very odd bubbly looking stuff. This has been restricting flow no doubt. Now how did it get there? Well my theory is that the engines were not put away properly for the winter.
  My friend's usual technique is a bit idiosyncratic. He first puts in a good amount of air tool oil and works this around the engine. he then puts a small amount of fuel in the tank and lets the engine run until fuel is exhausted. He then works in another good dose of air tool oil and that is it. Quite why he does it this way. I have not got a clue. He is over 80 and has always done it this way, with excellent results.
  My theory is that he put in something else rather than air tool oil. This has reacted with the normal castor goo in the silencer and the witches brew bubbled up, giving a restriction in the silencer. Once it is cleaned out, then the engine run returned to normal. If I am correct, then I don't have a clue what it was that he put in the engines. There is a fair selections of bottles and cans in his workshop and it could have been any one of them, in a senior moment. I am surprised that the engines would restart easily after the two minute run, but then there was no rush to get airborne so maybe they cooled sufficiently to restart? Still a few queries as to the why and how, but the problem has been nailed.
  Oh yes I checked engines and bearings and there appeared to be no damage to anything, so he looks to have got away with it!
Thanks for all the helpful suggestions, I was somewhat reluctant to post this one because it was a "how long is a piece of string question" and wasn't sufficiently defined! Oh by the way The glow plugs are new Enya 3s, the original plugs were tried and they were not very good. They dropped substantial revs when the glow lead was removed and a trial flight with one of them produced a bit of a faltering engine run. So maybe the liquid X didn't do a lot for the plug. Probably a case of a poisoned element too? Strange that the "two minute" flights appeared to be normal. The plug problem wasn't noticed at the time and that is strange too. Maybe we were not as attentive as we should have been.

Regards,

Andrew.

Hello Steve,
I think you either misread what I wrote or maybe I wasn't too clear in my explanation. The problem was that the mufflers were obstructed with some sort of bubble infested goo! I have no idea what it was or indeed how it got there. My mooted explanation was just that .......mooted ! I have never seen anything like it in nigh on 60 years of power modelling. At least there is a common explanation for the strange behaviour of several engines quitting after a few laps. Quite what the messy goo is and where it came from is still an unanswered query!

Regards,

Andrew.

Thanks for the advice Steve,
Sounds pretty good to me. Unfortunately my pal has gone electric and seems there is no way back for him! So another one lost to LiPos. No chance with me, I have enough real engines to last the rest of my life! No way is the march of electric powered planes going to claim me as a victim. I like oily, smelly planes!

Regards,

Andrew.

This made me think of a friend of mine.  He is an outstanding pilot and always gets very good engine runs.  Near the end of a flying season, his #1 model started to experience engine run gremlins.  Not consistent!  After all the *usual* changes, a strange phenomenon showed up.  He always runs muffler pressure and the pressure nipple on the muffler was clogged almost solid.  He reamed it open and the great engine runs returned!  I would have probably never thought of that...........

BIG Bear
RNMM/AMM