No cut-off...

[Roger Dyke]

Hi All,

 

I have two Irvine engines. A red 61 mk2 and a red 46 mk3.

 

Both engines in their models work really well.

 

My problem is cut-off. From tick-over at about 2500 RPM or so, I operate the cut-off switch and the revs immediately drop to probably a couple of hundred RPM and stay that way for about a minute before stopping altogether. Both engines are the same. I have checked the carb barrels and they are completely closed. The carbs are new so it's not wear.

 

Any ideas?

 

Roger

[Cuban8]

If you were to put your finger over the carb intake to block it totally when the barrels are closed , does the engine stop cleanly then?

[J D 8 - Moderator]

Double check the "completely closed" if there's a pin space can keep going. A couple of % more on cut off movement will likely sort.

[Brian Cooper]

Air is getting through somewhere. 

The "O" rings don't last forever. . . One which is often overlooked is the one on the needle valve. 

[Paul De Tourtoulon]

I have a 'Marine' one with the perry carb, ( yes in a plane )even completely closed it will run forever, I stop it the old way, throw a rag into the prop.

[Cuban8]

Yes, it's not going to take much of an airleak to cause a problem - had this before. Usually caused by wear in the carb somewhere, but as they are new items maybe a fitting issue? What carbs are they? Genuine replacements or something else? Seems odd that both engines are playing up in the same manner - suggests a very close look at the carbs needed. Perhaps a drop of fuel over the carb might give away a tell tale leak.

Unlikely to be an airleak elsewhere seeing as both engines are acting up the same way - had an engine with a similar issue ages ago caused by a tiny leak at the backplate. Just enough to cause a problem with the residual fuel in the engine and bypassing the carb.

Sad to say some carbs of the budget engines aren't of the best quality.

Edited December 13, 2024 by Cuban8

[Roger Dyke]

Cuban8: I never thought of the obvious, putting my finger over the air intake. I'll try that and thanks for the tip.

 

J D 8 -Moderator, Brian and Paul: Both carbs are genuine 'Irvine Jetstream' and new. Also at cut-off the the barrels are fully closed against the spiral end stop. As far as I can see (with a small torch) there is no sign of a gap between the barrol hole and the body.

 

The problem must be staring me in the face as I have been running glow engines for years and never had this problem before.

[J D 8 - Moderator]

  On the Jetstream carb if you turn the screw [ one driver pointed at ] in pic it adjusts how far the barrel closes affecting both air and fuel intake at the slow end. Half a turn will likely result in a stop. Later Jetstreams do not have this screw in which case your slow running may be set too rich.

 To stop a still running engine better than finger over venturi [close to prop]  or chucking a rag at it is to just pinch the fuel pipe shut.

 P.S. Engine in pic is a car Irvine 20 converted for air use.

[Roger Dyke]

The Jetstream carbs that I have do not have the throttle-stop screw as indicated.

 

The slow running screw setting is ideally balanced for good transition pickup.

 

The feed pipe to the carb is shielded by the fuselage side so is a little difficult to get to.

 

Apologies for the negative answers as I'm sure I'm missing something here. I am going to remove the carb to do some leakage tests on it.

 

It is a rule of the club that I'm in, that we have a means of remotely killing the engine (hence the original query).  

[J D 8 - Moderator]

 Quite under stand, most clubs require engine kill, my club does. 

Those carb needle valve O rings can go hard over time and getting exact fitting replacements difficult.

 The old trick of a bit of fuel tube between needle and carb body to stop air getting in works well, may be worth a try.

[Andy Stephenson]

Replacement O rings are available from Modelfixings...

https://www.modelfixings.co.uk/o_rings.htm

It's the top one in the list.

[Roger Dyke]

As mentioned earlier, the two carbs are new and the 'O' rings look and feel perfect. I have removed one of the carbs and attatched a length of fuel pipe to it (main needle open three turns). I have opened the slow running needle a couple of turns and placed the carb under water. I then blew as hard as I could down the fuel tube with the barrel closed -- No tiny air bubbles whatsoever. There definitely doesn't seem to be any leaks. A bit of a puzzle this.

 

Thanks for the link to Modelfixings.

[Engine Doctor]

Ive found Irvine engines front bearing often leak fuel out running fast and this changes to sucking air in at low speed. Swap front bearngs to rubber sealed bearings with the inner seal removed. 

Check the other sugestions first to eliminate all other possible air leaks.

[Roger Dyke]

I’ll bear that one in mind as a last resort as the engines are a little tricky to remove.

 

I haven’t seen any evidence of fuel leakage from the front bearings up to now.

[Cuban8]

16 hours ago, Engine Doctor said:

Ive found Irvine engines front bearing often leak fuel out running fast and this changes to sucking air in at low speed. Swap front bearngs to rubber sealed bearings with the inner seal removed. 

Check the other sugestions first to eliminate all other possible air leaks.

Maybe pack some heavy grease between the prop driver and front bearing to create a temporary 'seal' to see if it makes a difference?

[PatMc]

I had the same problem with 3 out of 4 Irvines before I went the quiet, clean route with my power models.  Safe way to stop the engine is to apply the unpowered starter to it.  Worked every time for me 

[Roger Dyke]

Cuban8 and PatMc,

 

Many thanks for the tips. Our club rules say that we have to have a method of killing the throttle both in flight and on the ground, hence the question.

 

I now have a few things to try at the next opportunity.

[Roger Dyke]

Cuban8: A question you asked earlier. Having now verified that there are no leaks on the carb "O" rings or joints, I've also tried your tip of putting my finger over the air intake with the barrel fully closed. --- No difference whatsoever, still continues to tick over at a couple of hundred RPM's for about a minute.

[Martin Harris - Moderator]

I’ve had the same problem with Irvines despite the front bearing being a rubber sealed type.  I discovered that the air leak was due to movement between the bearing and the crankcase. The cure was to assemble with Loctite Bearing Seal.  

[Roger Dyke]

Hi Martin,

 

Thanks for that. I would have never have thought of that. I suppose it's a strip down and new bearings then. It seems such a shame as the engines run pefectly.

[Engine Doctor]

It seems odd that a British engine made in england from a long heritage of performance engines would have a basic fault of a sloppy front bearing fit ,  originals had made in England cast into case an later ones had mzde in Japan. Even more strange when they were bought out or farmed out to OS and still had the same issues. Is it just my suspicious mind or would OS continue the faulty manufacturs so that more people would buy the OS equivalent and the competition would die out ?

[J D 8 - Moderator]

As a long time user of Irvine engines [70's]  I steer clear of those "made in Japan" "assembled perhaps" They are not the same as those Made in England.

[Paul De Tourtoulon]

2 minutes ago, J D 8 - Moderator said:

As a long time user of Irvine engines [70's]  I steer clear of those "made in Japan" "assembled perhaps" They are not the same as those Made in England.

My one a .53 lost its chrome in probably less than 2 hours running.

[Andy Stephenson]

36 minutes ago, Paul De Tourtoulon said:

My one a .53 lost its chrome in probably less than 2 hours running.

If it was an OS made one, it probably had a nickel plated liner which were notorious for that happening.

[Konrad]

Designed air leak.

 

This was something that we the customers asked for. That is some kept complaining that there was oil/fuel spitting out of the front bearing. So to quiet the complaints manufactures added a low pressure port. This was to allow the  low pressure under the carb at idle to suck the fuel that had gotten past the front crankcase seal to be drawn back into the engine. 

 

Originally this was done with a drilled passage. But this cost time and ran the risk of broken drill bits. Later it was found that broaching a grove with the boring bar was much more friendly to the manufacturing process.

 

As to nickel there is little wrong with properly applied electroless nickel plating. OS tried a few short cuts that ruined her reputation. 

Now nickel never could compete with the performance of real chrome plating. But for the general sport engine properly applied electroless nickel plating was more than adequate.

 

Friends don't let friends fly nickel,

Konrad