Air bubble of doom in gascolator!

[canav8]

Gary, capping it will isolate it. Rather easy to do. Since I have had experience with this already, it is not necessary for me to do that. 4bravowhiskey says he has already had a problem in UTAH. Im not sure how much of a problem you need to get you to consider not flying it other then you let all of us know after the statistics come out. Sometimes I do not understand pilots reasoning. At least you are on here telling everybody including the FAA what you are doing. SMH

[lowNslow]

Doug, I think I agree with Gary on this one. If it is the primer as you suggest (and your probably right) it certainly should not be a problem to isolate the primer system to confirm.

[4BravoWhiskey]

Apparently nobody is reading my posts. HOW DO I START THE PLANE IF IT NEEDS PRIMER TO START??

[lowNslow]

Pump the throttle WHILE cranking the engine.

[4BravoWhiskey]

As I've said multiple times, that does not work. The carb does not have an accelerator pump.

[canav8]

4bravo Whisky, you can start the plane by setting it at low idle and shutting the engine down with the mag switch leaving it full rich. It should start with pumping the throttle to allow air to get into the chamber allowing a stoechemetric ratio to attain lightoff.

[4BravoWhiskey]

That's a good idea, I'll try that. And will do more ground tests with camera on it. I did install that fuel line bypassing the fuel flow sensor, and so far so good... but may not have enough run time yet to know.

[johneeb]

Jack,
Pretty unusual to have a carburetor without an accelerator pump, which explains why some of us are interested in the carburetor number (or a go-pro video of it).

From the for what it is worth (nothing) department, at one time there was a modification to the fuel system vent, above the cockpit, being made to install a check valve at the opening of the vent. Do you have that modification? This is pretty far fetched but if you did have the check valve in the vent line and it was stuck closed and the vented fuel cap was plugged up you could be drawing a vacuum in the fuel system which would get stronger as you burned fuel away.

[canav8]

Doug, I think I agree with Gary on this one. If it is the primer as you suggest (and your probably right) it certainly should not be a problem to isolate the primer system to confirm.

Karl, First in my experience the primer I was working with had worn O-rings and the walls of the primer were galled. In the case fuel would leak out when the O-rings were extended or primer out thereby allowing fuel to leak out. It would not do this if the O-rings were in good shape. So after I replaced the primer, the problem with the air in the gascolator went away and the engine ran fine.
Now, in 4BravoWhiskys case, I would trouble shoot 3 areas.
First, I would look at the glass to make sure there was no chips at the top of the gascolator where the gasket is.
Second, I would replace the gaskets in the gascolator with known new gaskets.
Third, I would inspect the primer line for a hairline crack near the B-nut. As Gary suggested, capping the primer line will remove any further troubleshooting upstream of the gascolator to the primer unless the problem was fixed. I didnt suggest this because the OP said he has done all this.
If there was a leak in the fuel line between the gascolator and the carb you would see evidence of fuel leaks.
So now, all I was trying to do by my posting was get 4BravoWhiskey to stop flying his plane till he has gotten this fixed. He is part of our community and I do not care to read about another statistic. If he is an A&P then he should understand that a mechanic doesn't know everything and that which he does not know should seek out instruction before he touches it. He comes on here seeking that knowledge but am concerned because he continues to fly it after having trouble in UTAH. How much trouble does he need before he says thats enough and I wont fly it till its fixed. The FAA reads this site. Someone knowingly flying around an airplane with a known problem is asking for trouble. I am asking him to stop. Kindest regards, Doug Mueller

[canav8]

That's a good idea, I'll try that. And will do more ground tests with camera on it. I did install that fuel line bypassing the fuel flow sensor, and so far so good... but may not have enough run time yet to know.

The inline fuel sensor have been know to leak but not afford an air bubble to go up stream during full power engine operations. I highly doubt you will find a problem there.

[4BravoWhiskey]

Doug I truly appreciate your concern. I have been talking to two A&P's both of whom are highly experienced and know this plane well, and neither has recommended that I stop flying it. But to monitor it closely with each troubleshooting step, and I can even monitor it in flight. So I've followed their advice but, but yes I'm the PIC and responsible for making the call regarding safety. I'll just do a lot more ground tests next next and see if I can possibly reproduce it and then hopefully stop it by isolating the primer.

John, I have looked for the one-way check valve at the fuel vent and it is not there.

I'll check on the carb model number tomorrow.

[canav8]

Doug I truly appreciate your concern. I have been talking to two A&P's both of whom are highly experienced and know this plane well, and neither has recommended that I stop flying it. But to monitor it closely with each troubleshooting step, and I can even monitor it in flight. So I've followed their advice but, but yes I'm the PIC and responsible for making the call regarding safety. I'll just do a lot more ground tests next next and see if I can possibly reproduce it and then hopefully stop it by isolating the primer.

John, I have looked for the one-way check valve at the fuel vent and it is not there.

I'll check on the carb model number tomorrow.

Im glad. Not sure anything from the carb to the gascolator will allow air to entrain in the gascolator during engine operation. unless there was a blocked fuel vent but then I would suspect troublesome engine operation not the smooth operation in your videos.

[canav8]

4BravoWhiskey, im pointing out the obvious here but if you had 2 qualified mechanics who knew your aircraft, you would not be seeking help on,this forum board. I will stand down, you have said your piece and I as well. I would love to know though if one of those qualified mechanics signed off your annual. Best of luck in finding your problem.

[lowNslow]

As I've said multiple times, that does not work. The carb does not have an accelerator pump.

I don't know of any carb certified for the C145/O300 that doesn't have an accelerator pump.

[blueldr]

Karl,
I'm with you on that one. I do not know of the part numbered carburetors that are legal on the O-300, but I don't remember ever seeing one without an accelleratot pump. That's why I asked the question about the carburetor part number.I find it kind of hard to believe that a Marvel Schebler carburetor without an accellator pump would be legal after always seeing them with such a pump.
As a matter of fact,I find it hard to to figure why a carburetor like that would have been used on an airplane that is likely to require relatively frequent power adjustments in anything other cruise flight. It sounds more like something that would be used on an industrial engine that runs at a constant load and speed such as a generator or an irrigation pump.

Gahorn,
With you being "de''man", What is your take on this subject ?