I have a new to me 172 with a 0-360 A1A and fly it off a 3200 elevation runway. On takeoff it seems to be rich engine not smooth. As soon as I pull the mixture out some it clears right up. If I use carb heat on landing engine runs ruff and stumbles. I also noticed that when I prime the engine for start the first stroke there is no resistance the second stroke there is. There used to be resistance on first and second stroke. Can a bad primer cause a rich condition?

Short answer is yes, a bad primer can cause a rich condition. Same as leaving your primer unlocked and out slightly can cause a rich condition.

Several things can cause a engine to run rich. First thing I would do is check to see if the float bowl on the carb is loose or if you find fuel stains on the sides of the bowl. With the fuel on disconnect the primer line at the engine and see if is leaking past the primer in the cabin. In straight and level flight at 2400 RPM see how much EGT rise you get before your first cylinder hits peak. At full rich you should have 150 degrees below peak EGT on any cylinder. RPM drop with carb heat should be 100 -150 degrees. Also do a in light mag check at 2400 RPM. A 4 cylinder EGT/CHT is very useful when trying to figure out problems like this one. DENNY

Thanks Guys I will get it checked out I was suspicious primer was faulty as there was always resistance for about 3/4 of first stroke now there’s none. No engine monitor it’s on my list to get done this winter.

Also when you get things squared away, Lycomings like to have quite a bit of fuel to start but then like to run lean. Lean to max RPM regardless of DA makes them run happier.

My ame took a look and did a few circuits with her and came to this conclusion…the CS prop is fluctuating 100 rpm on takeoff and when doing touch and goes the weird oscillation was the Goodyears spinning down so tapping the brakes fixed that. Maybe time to get the Governor rebuilt he figures everything fuel wise is ok. That Mt prop does pull when doing a full power run up for setting mixture it will drag the tires on pavement.

David K wrote:My ame took a look and did a few circuits with her and came to this conclusion…the CS prop is fluctuating 100 rpm on takeoff and when doing touch and goes the weird oscillation was the Goodyears spinning down so tapping the brakes fixed that. Maybe time to get the Governor rebuilt he figures everything fuel wise is ok. That Mt prop does pull when doing a full power run up for setting mixture it will drag the tires on pavement.

Composite props. If your Governor is even slightly inclined to “hunt” any composite prop will surge more than a metal prop. It has to do with the mass of the prop.

If it’s mild it won’t hurt anything, just an annoyance, but if it’s pretty noticeable, it’s likely a good idea to have the Governor rebuilt.

MTV

Yes going to look for a exchange or new. Was quoted rebuild will take up to three weeks and don’t want to be sitting for that long.

There are about 4 different common carbs that can be installed on the O-360-A1A, all of which have different nozzles. In some airplanes like the FG Cardinals and Mooney, you need as much fuel as you can get to run just because otherwise the #3 cylinder will get way to hot on climbout. I recommend you start with the engine monitor, and try to solve the other issues once you know how hot you're cylinders are getting.

I would like to install a engine monitor but my 172D model has limited clearance behind the tachometer and manifold pressure gauge where the cgr30 will go because of the arm that ties the yokes together.