Running Rich?

[btbell]

I was flying this past weekend and found the engine running rough at idle in the afternoon. It was a really warm and humid afternoon (density altitude 2200ft). When I raised the RPMs, the roughness went away and the engine ran normally. Today the same thing happened at 1500ft density atlitude.

I suspect I am running rich due to the conditions and the carb needs the idle mixture adjusted. Does anyone else have this problem? Can this be adjusted by the owner or does an A&P need to do it? If it can be done by the owner, how does it get done? It looks like there is a black thumbscrew on the back of the carb that may be an adjustment screw?

Any help would be greatly appreciated! Are there any photos out there?

[jgerard]

check out the sacramento sky ranch website for some great info regarding engines

http://www.sacskyranch.com/eng37.htm

Jason
N43643

[lktiller]

I had the same thing, even to the point of the engine going dead on short final.
Checked the plugs and they were sooty black.
Then I realized I had left the primer unlocked!!!!

[btbell]

Thanks for the responses so far. Jason I checked out the website (great site!). One of the sections said:

"1. Mixture to rich or lean. If mixture is too lean the engine stumbles on power application. Lean engine if mixture is too rich. Engine will smooth out and pick up rpm as it is leaned. After mixture is set, re-adjust idle speed. A rich mixture may backfire (more technically, inlet charge combustion). Rich idle, black smoke, and fuel dripping out carburetor is a sign that the fuel level in the float bowl is too high or fuel pressure to the carburetor is too high. Possibly the carburetor float is sinking."

This pretty much describes what has been happening. I had black smoke on Sat and I have had fuel dripping from the carb (engine off and gas on) for a while but everyone I have talked to said it was not a problem. It drips at a pretty good rate at times. Anybody thoughts on this?

[Robert Lees]

We had a situation of black smoke at idle (too rich). A clean-out of the idle jets found some debris, removal solved the problem.

Rob

[M Jones]

-----"1. Mixture to rich or lean. If mixture is too lean the engine stumbles on power application. -------

I've had this problem, but only at takeoff, when the air temp gets down around freezing. Someone suggested keeping carb heat on untill it smoothes out, which helps. That seems to confirm the above remark, as the application of carb heat increases the richness.

[jgerard]

Since I have the non air filter style air intake I was warned about bugs and debris clogging up the carburetor which can lead to the symptoms you're having. When I park the plane I leave the carb heat on which closes off the air intake and keeps the larger bugs from crawling up into the carb.

There is some info floating around the web about what causes stromberg carbs to leak fuel when sitting. I think it was on the Fly-Baby website.

Jason
N43643

http://www.bowersflybaby.com/tech/engines.htm

[btbell]

Definitely rich but not the problem

I pulled the plugs today and they are definitely fouled but that is not the only problem. When I ran her today, she did not develop her normal power as I advanced the throttle. Following someone's advice on the forum, I pulled the prop backwards to find 3 pulls with resistance and 1 without resistance (should have done this first). Confirmed with a compression check that the #2 cylinder has no compression. The A&P suspected the exhaust valve may be hung up, pulled the rocker cover and tapped the valves. It did not help the problem. He still thinks it is a bad valve so I am spending tomorrow morning pulling #2 under his supervision to see what we can find. He said we will probably have to send out the cylinder to a cylinder shop but hopefully we will find the problem and will be able to fix it. Thanks to everyone for their suggestions and help. I will definietly have to lean her a bit once she is back in the air.

If anyone else has had an experience like this, please feel free to share and maybe I could learn a few new things from your experiences also.

Thanks!

[jgerard]

if you send your cylinder out for repair see if they can re-swage the pushrod tube to the cylinder head to keep it from leaking.

Jason
N43643

[alwaysoar]

running rich

Was the cylinder pressurized when you tapped on the exhaust valve? I had a low cylinder and knocked off a lot of carbon with a rubber mallet while the cylinder was pressurized. I would try that before you pull the cylinder which is a pain in the neck requiring dropping the exhaust which depending on your dexterity first requires removing the intakes. If you do this, then check your screen after you've run it and you will see the carbon.

The end of my story is that same cylinder eventually had to come off revealing end play in the rod that showed when it came off a badly scored crank.

Ed@BTV VT
TF 527

[btbell]

Ed,

The cylinder was pressurized when we tapped on it. I will keep the screen in mind. Hopefully it is not anything too major. I will let the group know what we find tomorrow.

Thanks again for everyone's help!! Please keep any other thoughts coming.

[Victor Gisclair]

crank

Ron
Captjon Has one that is yellow tag. give him a
call