engine stalls in very cold weather when throttle advanced briskly

[Guest markfnkl]

I have a J230. The temperature was about -14C today when I went to fly it, and I encountered some problems on which I'd appreciate feedback/suggestions.

 

The Tanis heater had been plugged in overnight. The plane started without

 

problem.

 

However, during mag check I had unusually large drops in both mags, though they

 

would then recover to a normal drop.

 

Most alarming was that when the throttle was advanced rapidly during run-up, the

 

engine would stall. This problem did not occur when the throttle was advanced

 

slowly.

 

The problem persisted even when the oil temp reached 57C. We decided not

 

to fly.

 

Thoughts?

 

 

[jetjr]

Headed for 38 deg C here today so cant really imagine the issue. We are spoilt here for weather.

 

In much milder conditions ~ 0-5 deg C the carb is highly prone to ice up especially when idling. This isnt icing like in the books I think, its to do with cold air freezing fuel as it vapourizes(dribbles) from carby

 

I assume you had carb heat etc

 

In this cold conditions maybe carb heat design isnt warm enough?

 

 

[Guest markfnkl]

Thanks, jetjr. Actually, I wasn't using carb heat: might help and will give it a try. Thanks for the suggestion. 38C is hot, but I'll take it any day over -15C, which is what is forecast for tonight!

 

 

[facthunter]

A CV carb should not stall even if the throttle IS opened quickly ( because the dashpot slide/piston opens only when there is enough vaccuum to lift it). You could have ice or the needle and jet are one of the lean ones. It's most likely ICE. The oil temp won't have much to do with it. The ice could easily form when you are warming up. In cold temperatures there is less atmospheric moisture, but there is always some unless you are in a desert or Polar regions, or at very high altitude.(Unlikely). Nev

 

 

[Jabiru Phil]

Always use carbie heat with revs after mag check for around 15 seconds. If ice is present the revs will pick up when heat is removed.

 

I also use heat just prior to take-off if ice is present (last part of taxi)

 

Phil

 

 

[JabSP6]

Mark

 

I have a 3300 that had a similar thing happen after I had a service done. It was winter and luckily for us the temps rarely get below 10 Degrees C. The motor ran perfectly the day before with the same OAT. We had changed the spark plugs from the Irridium back to standard plugs and every morning after start up the motor used to give a cough when trying to advance the throttle quickly. This would continue for about 5 mins until the engine warmed up. After a week of this I changed the plugs back to Irridium ones and the problem dissappeared. Since then i have found that by monitoring each cylinder head temp and exhaust temp my fuel mixtures were on the lean side. I have richened both the needle jet and the main jet by one size. Motor now starts first time every time no matter what the outside temp and has never given any sign of hesitation. Just something to think about with the spark plugs. I would firstly try carby heat as others have suggested and then look at the carby jetting.

 

Wags

 

 

[Guest markfnkl]

Thanks, FactHunter and JabSP.

 

You both mentioned the jet size, and you may be onto something. In fact, a while back I did have the jet size decreased because I was burning more than the reported normal GPH. My fuel burn did improve significantly, but perhaps it is causing the current problem. By the way, the temperature here as I write this is . . . -26C!![ATTACH]12947.vB[/ATTACH]

 

 

 

[facthunter]

Get rid of those lean setting jet and needle. Jabs don't like lean mixtures. If you have run them for long check leakdown (valve seating). Nev

 

 

[Relfy]

the -26c is chilly but the 'feels like -31f' (-35c) listed at the bottom is downright scary! As FH said, the lean burn jets etc on the jab motor are the cause of a lot of other problems down the track.

 

 

[Modest Pilot]

One thing to keep in mind is that if yopu use carb heat, use it for at least a minute as per ops manual. This avoids the posibility of re- freezing. Just how cold the manifold can get was bought home recently on my mates 180HP J250. It has two Bing Carbs and a large x-over balance tube. The temp up here has been in the 30c range but with 90% humidity. The crossover tube gets no Carb Heat and has been freezing to the touch with frost all over it. (and you know how hot a Jab gets under the engine cowl!)

 

 

[coopjim]

MarkI have a 3300 that had a similar thing happen after I had a service done. It was winter and luckily for us the temps rarely get below 10 Degrees C. The motor ran perfectly the day before with the same OAT. We had changed the spark plugs from the Irridium back to standard plugs and every morning after start up the motor used to give a cough when trying to advance the throttle quickly. This would continue for about 5 mins until the engine warmed up. After a week of this I changed the plugs back to Irridium ones and the problem dissappeared. Since then i have found that by monitoring each cylinder head temp and exhaust temp my fuel mixtures were on the lean side. I have richened both the needle jet and the main jet by one size. Motor now starts first time every time no matter what the outside temp and has never given any sign of hesitation. Just something to think about with the spark plugs. I would firstly try carby heat as others have suggested and then look at the carby jetting.

Wags

I know this is an older post but I'm curious about this topic since I'm having similar problems. I live in the Midwest USA and we're having a hard winter. I have a Lightning with the Jab 3300 in it. I had an oil pan engine preheater installed and cover the cowl so I have no problems with starting but I'm having a very hard time getting the engine to accelerate to full T/O power after run-up, even using carb heat. We installed larger jets (now running 285 needle and 265 main) but continue to have an almost stalling of the engine when applying full power after run-up. I've asked my mechanic to look into the Iridium plugs. Have they continued to be effective? I'm even considering the AeroJector throttle body fuel injector to replace the Bing. I can't find many folks who have tried it other than in the Sonex.

 

Thanks,

 

Jim

 

 

[BlurE]

Let me start by saying I don't know anything about Jabaru engines.

 

In Automotive terms I would suggest the heart of the issue is the mixture reaching the cylinders is too lean. The best explanation I have heard for this is that a significant amount of fuel vapour condensates on the walls of the cold manifolds. Thus the actual mixture reaching the cylinders is much leaner than the carburetor is trying to achieve. To over come this in the old days we used 'choke' to over-richen the mixture (so it didn't matter that some fuel was 'lost') until temperatures stabilised. Kids who have grown up spoilt with EFI and wondering what I am talking about. Warm air may stop icing in the carby, but it may not heat the manifold as quickly.

 

Again, I don't know anything about Jabaru engines. I am just suggesting a mechanism that may explain the issue.

 

 

[facthunter]

It is a thread dredge , but still valid. The choke is used to enrichen the mixture at low engine temps as engines need it to run under those conditions. Not fully vaporising the mixture when everything is cold, is very much a part of it and it what gets to the cylinder as a vapour that is what has to be" burnable" to light the fire. The CV carb on the jab does not have a "choke" in the pure sense but an additional mixing chamber that is set more rich. This only operates when the throttle is closed or nearly so and can cause the symptoms as described. Often aero engines are much more rich at low revs than cars, so they don't stall when the throttle is opened. As a consequence the plugs will tend to soot when taxiing for long distances in some aircraft. Nev

 

 

[Jabiru Phil]

What temperatures are we talking about?

 

You mentioned iridium plugs. We swear by them for cold starting at our club, but doesn't seem to be related to this problem.

 

Being a lay person with only practical experience, I would look at an intake leak.

 

Just my thoughts.

 

Hope you post the result

 

Cheers

 

Phil.

 

 

[coopjim]

There has been lots written and read about possible cause. We're convinced it's a lean mixture problem too. Run-up is fine. The problem comes with the increase to full throttle for T/O. We've increased carb jet sizes, checked carb float levels, tried running it with carb heat on, partial choke, looked for intake leaks, etc. The Folks at Jabiru USA thought it might be turbulent air in the intake side of the carb so they sent us a device to "stabilize" the air flow. Nothing has worked so far. The Iridium plugs are a new angle and we're happy to try it out. It ran fine last Fall but this problem developed with the colder temperatures. We're about to the point where there are no larger jets that's why the partial interest in the AeroJector TBI.

 

Thanks for the thoughts.

 

 

[facthunter]

Check that your dashpot is installed correctly and is closing fully. Nev

 

 

[coopjim]

Check that your dashpot is installed correctly and is closing fully. Nev

What do you mean "dashpot"?

 

 

[John M]

I have a J230. The temperature was about -14C today when I went to fly it, and I encountered some problems on which I'd appreciate feedback/suggestions.The Tanis heater had been plugged in overnight. The plane started without

 

problem.

 

However, during mag check I had unusually large drops in both mags, though they

 

would then recover to a normal drop.

 

Most alarming was that when the throttle was advanced rapidly during run-up, the

 

engine would stall. This problem did not occur when the throttle was advanced

 

slowly.

 

The problem persisted even when the oil temp reached 57C. We decided not

 

to fly.

 

Thoughts?

Mark:

Why do you advance the throttle rapidly?

 

I have been taught ever since I got my private in 1963 that slowly advancing the throttle was much easier on the engine stress due to the gyroscopic and inertia affects of the prop.

 

What was the oil temp when you did the mag checks?

 

Excessive mag drops can be caused by:

 

1. Fowled plugs

 

2. Incorrect spark gap

 

3. Incorrect air/fuel mixture

 

4. Incorrect or bad fuel

 

What do the EGTs show during mag checks?

 

JohnM

 

 

[coopjim]

Thought I'd post an update. A lot has happened but not much result. We replaced the plugs and ignition wires, caps and rotors. Adjusted the valves and we sent the carb to Jabiru for inspection. They found the carb float level low and adjusted it as well as cleaning and inspecting the entire carb. We installed it and still had the same power drop at 2500 rpm. The engine is now in a crate headed to Jabiru USA for evaluation and repair. Fingers crossed it's not a big problem.

 

I'll let you all know when it comes back.

 

 

[bexrbetter]

May I ask what brand spark plugs you guys are using?

 

 

[coopjim]

May I ask what brand spark plugs you guys are using?

NGK iridium

 

 

[coopjim]

May I ask what brand spark plugs you guys are using?

NGK iridium

 

 

[bexrbetter]

So it's a 2 cylinder ..... or more!

 

 

[coopjim]

So it's a 2 cylinder ..... or more!

Yes, two plugs per cylinder. I wanted to be sure I got that right.