Why does my engine run differently than most others? – General purpose aviation news

RV-4 vans.

Q: I risk to see if I can get an answer to my engine problem for my Van’s RV-4. It looks like this: I have a Lycoming O-320-E3D (L 46580-27A), a Marvel Schebler carb MA4-SPA 10-5009 and a Slick 4370/4371 magnetos. I had a rough idle at 600-700 rpm and turned around Wang Aircraft Forum for help.

One guy said I had an induction leak. It had the same engine, and at 600 rpm its MAP was 10-11 and I had 14. I started chasing leaks and I did almost everything:

  • Float change (SB-2)
  • A new throttle shaft and bushing are installed.
  • Tried another MA4-SPA carburetor with a green label
  • Adjusted the fuel level in the carburetor
  • Checked the resistance of the spark plug
  • Checked the ignition cables with a high voltage test box
  • Checked the electronic gap of the magnet
  • One coil of the magnet has been replaced
  • Tested magneto in the shop of aviation mechanics
  • The compression test result is 79/79/79/79
  • Checked all the usual things like induction gaskets, hoses, etc.

All this came to nothing.

The engine does not run poorly at 700 rpm, but the MAP is the same and the inclination of 1000 rpm before idling does not give the usual increase of 50 rpm before shutdown. This indicates that the engine is already running on poor, but I tried to install the idle mixture screw from 1 turn to 5 rpm and there are no changes. When checking the magnet at 1700 rpm I have a drop of 60-80 rpm.

I was helped by two different aircraft mechanics and they nodded. Don’t understand this.

What about my engine, so it doesn’t work like most other engines? Did I notice something? Specialist consultation is required.

Hans Strale, Stockholm, Sweden

Lycoming Lycoming O-320-E3D engine.

A: Hans, I have no doubt that you have worked hard to find your problem, but perhaps I can suggest a few more things that can help solve your problem.

I have to agree with the person who said you have an induction leak, but now you have to find it. By the way, the card number he gave you is correct.

Did you take some soapy water and use a brush to paint all the inlet pipes on both the flange and the oil map when the engine was idling?

If there is a leak, you will notice that where there is a leak, it boils.

Of course, you need to be very careful, making sure that the parking brake is on and the wheels are lined.

I assume you have previously checked all the intake gaskets for fuel stains that may indicate a gasket leak?

I would also very carefully inspect the inlet pipes where they are attached with a rubber hose between the inlet pipe and the oil pan. Old or damaged hoses in this area can be the cause of the problem.

I also suggest you remove all the inlet pipes, including the rubber hoses on the oil pan, and carefully inspect the steel tube that is inserted into the pan for leaks. Over time, these tubes can weaken, which will also lead to induction leakage.

If you find that any of these pipes are weakened, they can be re-killed with a special tool.

If there were no problems in this area, I would reinstall everything using all the new gaskets, etc.

I also recommend you remove and lock the complete primer system. The primer line may be cracked, which may cause induction leakage. When you remove the primer nozzle (s) from the cylinders, you need to plug the holes in the cylinders with a 1/8 x 27-inch head screw.

Be careful here. Use some thread grease and do not tighten this cap, which could cause the cylinder to crack in this port.

Honestly, at this point Hans, I can’t think of anything else to check out, so I’ll leave that to you. I am sure you will find and fix the problem.

https://generalaviationnews.com/2022/02/20/why-is-my-engine-running-differently-than-most-others/ Why does my engine run differently than most others? – General purpose aviation news

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