The International Cessna^® 170 Association

I thought I bought a pristine airplane. I am slowly working out the gremlins, but the current one defies logic.
I am getting a lot of sooty exhaust on the left side. I did a compression check, and saw nothing below 73.
4 of 6 top plugs were sooty, but dry, so I don't think it is oil. Oil consumptin is OK for a continental, at about 5 or 6 hours to a quart.
It must be running rich, but why only the left side? I lean until rough at any altitude.
The primer goes to the left side, but no evidence of any leaking.
The clamps on the exhaust stacks appear to be rubbing into the intake elbows, but if they had rubbed through, I would expect leaning, not rich.
Do I have a carb overhaul in my future? What is the carb number, 10-something?
Where to I look to solve the problem?

But, you do have evidence of your primer leaking - the exhaust on that side. Replace your primer o-rings and see what happens.

When you lean and get it rough you are running rough because of the two leaner cylinders. Look for leaks in the intake system to those and then you will be able to lean the whole batch of cylinders more.

Am I correct in assuming that you are using autofuel? Auto fuel unlike avgas, will produce a oily soot on the cowl, inside the stacks and on the plugs. Not sure how much soot your talking about but I too have had that problem.

One other reason I believe the left side is "sootier" than the right is the blast coming off the prop is moving from left to right (port to starboard)and impacting the cowl more on the left than right. This too is the reason for the application of right rudder on rollout. ( I see the flames coming)

What kind of mag drop do you have across left/right during runup? Does the engine run smooth on left and/or right only? If you have more than 100-150 rpm drop (from both mags on) you may have one or more bad or marginal plugs. If you dont have a way to test them, swap them with the right side plugs and see if the problem moves.

JJH55

JJH55 wrote:
One other reason I believe the left side is "sootier" than the right is the blast coming off the prop is moving from left to right (port to starboard)and impacting the cowl more on the left than right. This too is the reason for the application of right rudder on rollout. ( I see the flames coming)

JJH55

Jim, guess you only have bugs on one side - the prop moves them from one side to the other? Come on now, you don't believe the prop influences exhaust stains do you?

Joe, I know you don't like to disturb 78D whilest its snuggly tucked in the hangar with the Barney Blanket and preheat, but have you looked at the exhaust stains on your cowl? Perhaps we need to discuss over a 30 pack and retorque your LG.
JJH55

Jim, I can't believe that you would insinuate that there is a Barney blanket on my airplane. The 30 pack sounds good - I'll call Robert - but we have banged and torqued 78D's gear all we are going to. That big exhaust stain, it will wipe off by the way, is because my primer is leaking. It's not because the prop blows more on one side than the other. Did you leave your car running again today while you are at the office? Folks, if you have ever witnessed someone sitting and telling BIG stories for a few hours, and then stop all of a sudden, look at you and ask "Did you leave your car running?". As you answer no, they jump up real fast with a look on their face like "Gee, my car has been sitting out there for hours running!", it is a look that will put a grin on your face.