I have having a very hard time diagnosing an issue that I'm having on a 0-200 on a C150. Engine runs very nicely up to 2400 RPM, but the final inch of throttle push and it starts sputtering, surging, and not sounding good at all. Pull the throttle back and it runs nice and smooth. Leave the throttle in and pull the mic mixture out just the right amount and it runs smooth as glass and 2600RPM. But pull the mixture out just a bit too far and it will shut down. First instinct is a fuel problem. Clean and inspect gascolator. Take primer line off and cap, problem persists. Tear the carb apart and sure enough its had mogas sitting in it and looks terrible. Old non-vented nozzle as well. So installed a new carb. Problem improves slightly, but mostly still there. Intake looks good, no blockages. Mags have a fresh 500hr inspection. Plugs all test good and resistance is within limits. Compressions are all good. Engine is high time, around 2000hrs SMOH but things look good internally.
What am I overlooking? Am I over complicating it? It has the continental tech rep, a local engine shop, a couple good old AMEs, and I quite stumped. Open to any ideas.
Thanks in advance.
David

Try another carb. I realize 2 bad carbs is highly unlikely but its possible. Carb just seems the most likely considerI guess what you have described.

A couple more ideas, check for air filter/intake blockage, check carb heat valve for full closure and seal material condition.

theamherst wrote:A couple more ideas, check for air filter/intake blockage, check carb heat valve for full closure and seal material condition.

Checked both of these. It all looks good.

G44 wrote:Try another carb. I realize 2 bad carbs is highly unlikely but its possible. Carb just seems the most likely considerI guess what you have described.

I agree that this is my best bet right now. All rhe symptoms point to excess fuel at full throttle. I wish I had another 150 in the shop with a known working carb that I could swap out quick. Should be getting one in in the next couple days and that will be my first step. If it was an intake blockage it should smooth out when leaned, but I don't think it would make full RPM then. I did check the intake and it is all clear. I should clarify, rhe plane ran great this spring, then sat for a couple months this summer and is now running this way.

This might be a stretch, but have you verified the fuel flow rate at the supply hose upstream the carb? Or course carb would be number one suspect, but what happens if the new carb is fine and the fuel supply demand at WFO isn't being met?

A friend of mine recently had his Pacer tanks expos d and he decided to replace his hoses. There were pieces of wood and what looked like plywood veneer in the tank port. Ya never know.

One time I took off from a friend's farm strip after a visit in a cub with an O-200 and the engine started sputtering at about 100 ft AGL. I pulled on carb heat, it helped a little but it was still cutting out bad.

I was over a big pasture so I started pulling back power to land and the engine smoothed out. Hmm. I increased power and it was ok, back to climbing. But full power was messy and so I backed it off to where it was smooth and limped home.

Turns out it was a bad spark plug. I know you said you checked them all for proper resistance but maybe just swap em and try.

Zzz wrote:This might be a stretch, but have you verified the fuel flow rate at the supply hose upstream the carb? Or course carb would be number one suspect, but what happens if the new carb is fine and the fuel supply demand at WFO isn't being met?

A friend of mine recently had his Pacer tanks expos d and he decided to replace his hoses. There were pieces of wood and what looked like plywood veneer in the tank port. Ya never know.

One time I took off from a friend's farm strip after a visit in a cub with an O-200 and the engine started sputtering at about 100 ft AGL. I pulled on carb heat, it helped a little but it was still cutting out bad.

I was over a big pasture so I started pulling back power to land and the engine smoothed out. Hmm. I increased power and it was ok, back to climbing. But full power was messy and so I backed it off to where it was smooth and limped home.

Turns out it was a bad spark plug. I know you said you checked them all for proper resistance but maybe just swap em and try.

If it was a fuel supply issue, leaning would make it worse not better wouldn't it?
The plugs are something I've been thinking as well. Good idea and relatively cheap to swap out and try.
Thanks.

A1Skinner wrote:If it was a fuel supply issue, leaning would make it worse not better wouldn't it?
The plugs are something I've been thinking as well. Good idea and relatively cheap to swap out and try.
Thanks.

Oh, sorry, I missed that 2600 was your full RPM and leaning improved it. That is suspicious.

Zzz wrote:

A1Skinner wrote:If it was a fuel supply issue, leaning would make it worse not better wouldn't it?
The plugs are something I've been thinking as well. Good idea and relatively cheap to swap out and try.
Thanks.

Oh, sorry, I missed that 2600 was your full RPM and leaning improved it. That is suspicious.

Ya, its smooth to 2400, then turns rough, and leaning smooths it out to make it pull full rpm. If I leave it leaned where its smooth up top, its rough on acceleration at the bottom because its to lean. It's a real stumper.

David,

When I lost engine power on takeoff and just landed straight ahead in a 0-320 172 it was blockage. The pipeline mechanic had replaced a leaking tank with a used one. Dead mouse in used tank lost all hair which impacted the nipple screen in the carb. When you changed carb that would take care of that possibility but what Zane was talking about might cause some full flow blockage.

Is there any way its pulling fuel through the primer?

Hozer wrote:Is there any way its pulling fuel through the primer?

I disconnected and capped the primer line at the firewall which should have negated this. I am going to cap it at the inlet to the engine just to double check, but I don't think its going to change anything.

contactflying wrote:David,

When I lost engine power on takeoff and just landed straight ahead in a 0-320 172 it was blockage. The pipeline mechanic had replaced a leaking tank with a used one. Dead mouse in used tank lost all hair which impacted the nipple screen in the carb. When you changed carb that would take care of that possibility but what Zane was talking about might cause some full flow blockage.

This would add up if leaning the engine didnt smooth it put and make it run at a higher RPM. It would make the problem worse, not better.

Was the problem there before the mag inspection? I hope you didn't get a bad carb, but I also wouldn't be surprised. I've never had that issue with a plane, but took 3 tries to get a good rebuilt carb for a 6 cylinder chevy once...

Hozer wrote:Was the problem there before the mag inspection? I hope you didn't get a bad carb, but I also wouldn't be surprised. I've never had that issue with a plane, but took 3 tries to get a good rebuilt carb for a 6 cylinder chevy once...

I did the mag inspection trying to get rid of the problem. I hope its not a bad carb, but in really leaning that way right now...

Had almost the same symptoms in an Ercoupe with a C-85 many years ago. Turning on carb heat helped quite a bit but not completely, also leaning helped but not completely. It turned out to be a partially blocked fuel line to the carb, caused by an improperly installed end on the fuel line. Scary thing was the fuel line had been replaced a few weeks earlier and had flown fine for about 25 hours.

Dale Moul wrote:Had almost the same symptoms in an Ercoupe with a C-85 many years ago. Turning on carb heat helped quite a bit but not completely, also leaning helped but not completely. It turned out to be a partially blocked fuel line to the carb, caused by an improperly installed end on the fuel line. Scary thing was the fuel line had been replaced a few weeks earlier and had flown fine for about 25 hours.

Ok. I will check it out for sure. The fact that leaning it out made it ran at full RPM had me sure it was an over fuelling condition, not a partial blockage. Gotta love trouble shooting eh? Haha.
Thanks.

Have you drained the tanks and tried different fuel? If not I’d definitely do that and, as others have said, swap plugs. Good luck

You mentioned bad auto gas in the old carb, you might try to rig a completely separate tank, something like an outboard motor tank, filled with fresh av gas and see what you get. That way you eliminate the entire fuel system up to the carb. Just be real careful about the possibility of fire.

Update. Change the fuel line from the gas orator to the carb as the inside of the old line was in poor condition. Drained and flushed the tanks, put fresh avgas in. Lots if flow coming out of the line when draining into a bucket. Fpybd one cylinder that was slowly dying and replaced it with a serviceable one. New spark plugs installed. Still doing the same thing.

I've also recieved more information about the initial incident. It ran great on takeoff for about 4 minutes then had a power loss, which is what I'm dealing with now. This information was given to me at a later date by the PIC. He came out to fill out the journey log as TC has been after him due to the incident. The fact that it was running good at takeoff power for 4 minutes before having a power loss adds more confusion. I'm starting to wonder if it's not an internal engine issue. Thoughts?