Engine Stumbling real bad on go arounds.

[fishhook]

I had a customer run into a carb acting up, well we figured it was the carb, we overhauled it. Then same issue, chased about 10 other things it could be. Then I said screw it and changed the carb off of another that was known to be good. Problem went away. I figured it must have been something that is overlooked inside the carb. Definately get eyes on the inside of the muffler.

 

[aktango58]

When are you applying carb heat on your approach, what rpm when you do, and when are you taking it off?

One plane I flew really did not like carb heat on much, as it flooded the engine when at idle. Solution was to lean out if you were using lots of carb heat, or keep a few rpm on and remove carb heat a bit above ground to allow the engine to clear itself.

Now, back to the one question: does your plane need carb heat on final? Some cubs do, some don't.

 

[skywagon8a]

Now, back to the one question: does your plane need carb heat on final? Some cubs do, some don't.

Some airplanes do, some airplanes don't. Under some conditions they do, under other conditions they don't. Wait until the day when your engine ices up and you find pulling the carb heat knob doesn't do anything and you don't have enough room to land straight ahead. Then after you mess up your pants getting it around with marginal power safely on the ground.....you find that the carb heat pull wire broke.

Get in the habit of testing it and using it.

 

[isaacdjohnson]

I held the carb heat knob closed on go around and still the same issue. I have not yet adjusted the accelerator pump arm ill try that today. Again thank yall for all the help I really appreciate it?

Isaac

 

[BC12D-4-85]

^^^^I'm not suggesting the pump is set wrong. But there are options for more or less fuel per stroke that you may try.

On carb heat, it's nice to confirm it's working (notable rpm drop from rich mixture) and there's no ice present in flight or prior to takeoff/landing.

But there's also no absolute requirement it be applied continuously unless you suspect carb ice is steadily forming. Lycoming's already heat the upper carb via contact with the hot oil sump which helps. And any leaks around the carb heat box flap tend to warm the carb.

Gary

 

[DENNY]

I understand it is a new rebuild but pay attention to the sides of the fuel bowl for fuel staining. Also grab the air cleaner and give it a shake. A loose fuel bowl will cause it to run rich. If it continues to have issues do a deep dive into the past post on tapered vs straight sump and what carbs work best for each one.
DENNY

 

[isaacdjohnson]

I am so sorry for the late response. I have it working with in acceptable levels now. After changing the carb from a -32 jet to -12, lowing the amount of fuel the booster pump put out and retarding the mags by 2 degrees it seems to be working better. If you jam the throttle it will still stumble however now if you slowly and smoothly apply throttle (like a 3 count) it will operate properly which before it was not doing. Not sure what exactly fixed probably a combination of all of it. Anyways thank yall so much for all the help hopefully it continues to operate correctly.
Isaac

 

[DENNY]

Soooooo, I am not an A&P so take my advice for what you pay for it. Did you have the mag timing advanced at the time of your first post? You should not have to retard stock mag timing to max a Lycoming run properly. If they are slick mags the internal timing should be checked even if they are fresh rebuilds slicks are notorious for having early issues. Some engines require a slow throttle input the 0320 is not normally one of them. From your description I think you still have a issue it has just improved. How many hours on the engine?
DENNY

 

[isaacdjohnson]

Soooooo, I am not an A&P so take my advice for what you pay for it. Did you have the mag timing advanced at the time of your first post? You should not have to retard stock mag timing to max a Lycoming run properly. If they are slick mags the internal timing should be checked even if they are fresh rebuilds slicks are notorious for having early issues. Some engines require a slow throttle input the 0320 is not normally one of them. From your description I think you still have a issue it has just improved. How many hours on the engine?
DENNY

The mag timing was around 26 to 27 degrees which is not all that abnormal for a 0-320 I retarted it back around to 25 which is what the data plate says it should be at. The engine is higher time at around 2400 hours with 500 hours in the cylinders and around 400 on the mags. I haven’t checked the internal time of the mags that is a good idea.

 

[skywagon8a]

The mag timing was around 26 to 27 degrees which is not all that abnormal for a 0-320 I retarded it back around to 25

That is a clue the internal timing has changed.

 

[algonquin]

when I get one of these problems I take a step back and take a good look at the front of the airplane for something that may have been over looked. Then i start going thru the engine : no jumping around period. Start with the air intake, look at things like the diverter valve, is it attached solid in the air box etc, Mirco examine everything. Then fuel , open lines and check the flow rate into a paint mix cup and time the flow, I hope you see where I’m going.
Send the mag out to a mag shop not a local general repair shop. Have the 500 hour inspection done.
ps when checking the fuel tie the tail down and Check flow both ways. Also look in the fuel tank making sure there isn’t something like a rag.
You will find it because it’s mechanical, but jumping around will confuse the inspection and drive you crazy. I wouldn’t fly it until you have an answer. One last thing don’t try to save money just do it what ever it takes.

 

[bob turner]

Probably not relevant, but we started having the same problem on a C-90. Opening the throttle would make it start to quit. Then it would catch up.once it really did quit.

All that started rather abruptly - I had put a temporary wood prop on while they re-pitched the Mac, but during the first two hours with the wood prop all was normal. Then, all of a sudden . . .

I have never rebuilt a Marvel Schebler, preferring the simpler Stromberg, but suggested re-doing the accelerator pump.

Shop took one look at the carb, sent a grand to Spruce, got a rebuilt carb the next day- not only fixed the problem, but got an extra 125 rpm on climb out. Done.

 

[hunt/trapak88]

Haven’t read this whole thing so maybe already checked but had exact issue on a C90 in exact same situation- few turns on mixture knob on carb cured it.

 

[bob turner]

I can see I need an MS overhaul manual. Hope it is as good as the Stromberg Manual. Strombergs don’t have a mixture knob.

 

[skywagon8a]

I can see I need an MS overhaul manual. Hope it is as good as the Stromberg Manual. Strombergs don’t have a mixture knob.

He's talking about the idle mixture. Back suction altitude mixture is optional on the small Strombergs.

 

[BC12D-4-85]

Owner experience: On bench if topped with fuel and activated the accelerator pump should send a stream of fuel to the ceiling. The pump's parts delay the discharge and spread it out over a brief time. If the plunger is worn, the pump chamber not filled properly, or the discharge check valve inhibits flow, the pump can discharge too little fuel. Too little = too lean. But the main discharge nozzle and atomizer assy also affect the mixture, as does the venturi design.

More here: https://www.insightavionics.com/pdf files/MA-4 Carb Manual.pdf

Gary

 

[hunt/trapak88]

Idle mixture correct

 

[bob turner]

A couple turns on the Stromberg idle screw is only really valid if you start from fully closed. Would not have worked on our carb, since it had been doing quite well and then instantaneously started acting up.

I put the metal prop on today - re-pitched from 74-46 all the way down to 74-42. 50 rpm difference, and seems rougher. Pulls about the same as my dirtbag wood prop. Owner seems to think it is better.