Engine problem - suggestions + support needed

[rvbuilder2002]

Originally Posted by Mike S

Symptoms sound like possible carb ice, but you said it is -9C. outside, so I am wondering if there is even enough moisture in the air to cause carb ice??

Considering how new the engine is and that it was apparently operating fine the last time you flew it, I'm with Mike.... Carb. Ice.

Now that you have ground run and leak checked it, I suggest you put the cowl back on and try it again.

[lockeed]

I drainned the tanks from the drain under both wings. But I haven't drained the gascolator - didn't tought about it. I have experience with car mechanic, but items like the gascolator are new to me.

See picture to make sure we're talking about the same thing.

[lockeed]

Originally Posted by aerhed

Check throttle shaft for slop. Quick/easy.

Are you talking about the push/pull cable?

[DanBaier]

With carburetor operations, it is not unusual for the engine to stumble in the range of 1200-1500 RPM. What is happening is that the idle circuit is closing off and the venturi is picking up. In that transition range is where the stumble occurs.

The stumble may not be related to other things going on in the engine. Also, if you get hesitation from 1500-2000 RPM, it is probably not due to the transition.

You could have carburetor icing, water in the fuel, a leaking primer line, bad magneto timing, etc.

Because you had something similar in September, if it were me, I might start by putting the plane into a warm hangar to melt any ice that formed in the fuel tanks. Then, I would drain avgas to be sure there was no water in the fuel, and be sure the magneto timing was correct. The thought being to get ideal fuel supply and ignition to see what happens then.

Check PM

Dan

[lockeed]

Originally Posted by rocketbob

What's the part # on your carb?

Carburator: Marvel/Schebler
Part # 10-3878
model: MA-4-5
Serial: G 51 9231

Overhauled at the same time as the engine.

[john.schwaner]

(note that both cowlings were not on the engine while I did the test run so, the engine is much harder to warm up)


--cylinder barrel overheating and piston scuffing concern--

At high power settings without cowling the cylinder barrels are not adequately cooled. In a demonstration test-cell test we did years ago on a O-320 the engine ran fine at idle and up to mid power range for a short duration test run.

When attempting to go to full power smoke was seen coming from the cylinder barrel paint within 1 minute. When we removed the cylinder we had severe piston scuffing.

CHT and oil temperature had not responded and in fact may have never gotten above red-line as they do not measure cylinder barrel temperatures.

Test was done at about 70 degrees ambient. Although I have no cold weather experience (California guy), I would be careful about cold temperatures due to the large temperature differences.

At one time Ram Aircraft was selling (or attempting to sell) a portable engine shroud for running engines on the airplane with the upper cowling removed. Would make a nice group project.

[harleyl]

The arrows in the picture you sent are pointing at the gascolator. You should check for water in the gascolator every time you fly along with your fuel tank sumps. Do this after every refueling, also.

[Dave62]

Possible intake hose leak. These are the hoses that connect the carb area to the cylinder intake area. They will cause a very lean transition and very rough spot along with the burps you diescibe.
Dave62 (Swift Driver)

[aerhed]

Not push-pull cable. Throttle shaft in carburetor. Throttle plate (butterfly) is attached to throttle shaft about an inch & a half below the oil sump (pan?). When shaft & bushings are worn they suck air and can exhibit the symptoms you describe. Your engine is low-time Lyc rebuilt, but you didn't specify carburetor time. Open throttle 2/3-3/4 travel. Grab throttle arm (what cable attaches to) and wiggle. Do the same on other end of shaft. Noticeable play means air suckage. Takes only seconds to eliminate this as a possibility.

[Walt]

Originally Posted by john.schwaner

(note that both cowlings were not on the engine while I did the test run so, the engine is much harder to warm up)


--cylinder barrel overheating and piston scuffing concern--

At high power settings without cowling the cylinder barrels are not adequately cooled. In a demonstration test-cell test we did years ago on a O-320 the engine ran fine at idle and up to mid power range for a short duration test run.

When attempting to go to full power smoke was seen coming from the cylinder barrel paint within 1 minute. When we removed the cylinder we had severe piston scuffing.

CHT and oil temperature had not responded and in fact may have never gotten above red-line as they do not measure cylinder barrel temperatures.

Test was done at about 70 degrees ambient. Although I have no cold weather experience (California guy), I would be careful about cold temperatures due to the large temperature differences.

At one time Ram Aircraft was selling (or attempting to sell) a portable engine shroud for running engines on the airplane with the upper cowling removed. Would make a nice group project.

Good point John, and I totally agree, high/full power engine runs on the ground should be kept as short as practical and used only to verify proper engine operation. Maybe 10-15 secs max with cool down between runs.