Engine problem - suggestions + support needed

[lockeed]

Hey Guys. Here's the story - bear with me !!

Technical info: O-360 A1A 180HP // +/- 80hrs since full overhaul at Lycoming - Yellow tag engine.

Hangar and Ext. Temp -9 deg C (15 deg F)

Went to the hangar today, took off the cowlings and changed the oil + filter for winter (Exon Elite 20W-50). While I was doing misc maintenance on the plane, I pluged the pre-heater pad + my heater for an hour, everything covered under my engine cover laying over the engine bay.

Then I started the engine which started on the first 1/4 turn - All good.

I left the engine idling @ +/- 850RPM for a couple minutes, gradualy leaning... Then 1000rpm fully leaned idle for at least 5 minutes till I started to see the oil temp needle rising. Then I gradualy put full mixture and raised the engine to 1700rpm and did a quick mag check - all good. I left the engine run at 1700rpm for a couple minutes, during which it got up to +/- 75deg. F. on the oil temp gauge. (note that both cowlings were not on the engine while I did the test run so, the engine is much harder to warm up)

Once I had +/- 75 deg. F, I increased the RPMs to 2000, to get the engine somewhat up to normal temperature. Left the engine run at 2000rpm for 2-3 minutes, then back down to 1000RPM lean idle and left it there for a minute. Highest temperature I got on the gauge was aprox 90 deg. F. (again, no cowlings...) All other parameter in Green.

Here's the interesting part. I put full rich, then increased the throttle to get 2000RPM again and the engine hesitated and burped, as if it was missfiring. As I increased the throttle slighly, the engine dropped in RPM as if a "choke" was on and it backfired - then I pulled the throttle to idle and leaved it alone for a second while I gradualy leaned it.

Engine still turned fine on idle. After 30 seconds, full mixture and I increased the throtle to get to 1700RPM to do another mag check, it hesitated a bit but eventualy got up to 1700RPM and stayed there while I checked both mags to make sure. All Good. Once done, I increased the throttle to obtain 2000RPM, again - same thing, hesitation then drop in RPM. I cut the thottle before a backfire could occur this time...

I stopped the engine, did a visual check and inspected for leaks, checked the oil. All good.

Got back in, did pretty much the exact same thing. It hesitated a little bit between 1000 and 1500RPM, but I increased the throttle verry gradualy, I ran it full power and it didn't hesitated this time at higher RPM...

I brought the RPM to 1000RPM, full lean for a minute then pull the mixture off. Than I ran to my computer to write this message!! Joking of course, I had dinner before running to my PC actualy....

Now, what do you guys think might cause this?

While doing test run, I often switched tanks, to try to eliminate variables one by one. I ran with the boost pump on, didn't changed anything. There was no water in the tanks. The tanks vents under the fuselage seam to be free of any debris and I ran a cable into them whitout any obstacles.

One other thing. The very last flight I did was back in mid September. After about an hour of flight, I lined up on the runway in a nearby town for the last leg back home, gave it full throttle, then the engine hesitated and did the exact same symptoms it just did today. It wouldn't take full power. BUT, I had just washed the plane a couple minutes ago and I thought at this point that water must've had acumulated in the carburator housing/bowl or in the air filter, and got sucked in on full power. That day, I cleared the runway and got back to the parking area to check anything I could. After 10-15 minutes laying there with the engine stopped, I tought to myself that the heat coming from the engine would make any remaining water evaporate and dry... After I restarted the engine, it ran fine and got back home safely and without any hesitation from the engine.

A couple things I suspect.

-carburator problem
-missfirering / spark plugs
-fuel filter / fuel system

Let's hear what you guys think!

[sbarger24]

I would try running it up with the mixture pulled out 1/2 inch to an inch, sounds like to me it is running to rich with the mixture all the way in. Maybe I'm over simplifying it we will see what others say.

[Sam Buchanan]

Check the idle mixture, sounds a little lean (would make sense in winter...colder, denser air). Sometimes seasonal tweaking is necessary if temps swing considerably in your local.

[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??

[lockeed]

Originally Posted by DAGO

Did you check your sumps for water??? How is the condition of your fuel caps seals?

Oil Sumps or Fuel sumps? Please clarify. English is a second language for me and sometimes, those terms don't mean the same thing when we use it in a french conversation... Fuel caps have 80hrs, as the plane, they're brand new, but I haven't checked... should I ?

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??

-9 outside and inside - low humidity. Also, the engine did the same thing on takeoff in Sept on a 20deg C sunny day.

[tadsargent]

Your issue is normal, when the Carb is transitioning from
Idle mixture to main meter there is a period when the mixture
Is lean, this happens quickly. The correction is to not jab the throttle, but to smoothly add
It.

[aerhed]

Check throttle shaft for slop. Quick/easy.

[rocketbob]

What's the part # on your carb?

[lockeed]

Originally Posted by tadsargent

Your issue is normal, when the Carb is transitioning from
Idle mixture to main meter there is a period when the mixture
Is lean, this happens quickly. The correction is to not jab the throttle, but to smoothly add
It.

ihh... don't know about that. When I increase the throttle, I always do it gradualy. That's the way I learned to do it, and keep doing it.

Also, when I go from 1000 RPM to 1500rpm - the mixture has been put to rich 5-10 seconds before. I might agree... But when I go from 1500RPM to 2000RPM, the engine has been running full rich for a while, and still hesitate.

[N941WR]

Originally Posted by lockeed

Oil Sumps or Fuel sumps? Please clarify. ...

The "Oil sump" is also known as the "Oil pan" in cars. It is the bottom of the engine where the oil collects.

The "Fuel sump" is can also be called the gascolator, as used in carbureted engines. It can also be any low spot in the fuel system that has a quick drain on it, such as on our wings.