Carb problem on full rich take off?

I could use some input here. Sunday on take off roll full power and full rich, I got about 100 ft off runway in steep climb when the engine went real rough and low power. An observer said he saw some white smoke briefly. I had lowered nose and reduced throttle and mix back some. Pump was on. Tanks were near empty with about 4 gal a side. I have 0-360 lycoming new from Van's with 140 hours tach with trouble free flights. In fact I flew 400 miles Sat with no issues. Temp outside mid 80s. Then yesterday after looking for any issues under cowl I fuels up with 109ll and tried again. Same thing! The engine runs fine if I lean back 1/4 or more on take off but never had to before from my 1000 ft msl runway.
Carb hasn't been tinkered with either but I did remove left mag to have internal timing checked by mag shop. After reinstall, the engine starts much easier and was running quite well for last 6 or 7 flights. I have been adjusting the idle mixture but nothing else with carb. Rechecked mag external timing and mag sync and looks fine. Not sure what has happened. Like I said, the two flights the day prior were just fine on take off and cruise.
What would cause white smoke? Water? Feels rich though.
Any input appreciated. I'm guessing I'll need to remove carb and have inspected. It's only got 140 hours on it though.
Thanks!

Have you confirmed the air intake is clear of any obstructions? Have you sumped your fuel tanks? Did the plane sit outside the night before? Just thinking out loud here.

Good luck,
Bill

Tough to say why it is has changed, but your symptoms and tests point to a mixture that is too rich. Was the engine heat soaked prior to T/O? Boiling fuel in the bowl can reduce the bouyancy of the float and allow the fuel level to increase, causing a rich condition. In this case, the rich condition should subside shortly after T/O, as cool fuel reaches the bowl. Do you have past experience with this engine in hot weather?

Debris in the needle/seat interface can also allow the bowl to over-fill, but you would be richer than normal in all power settings (requiring additional leaning via mixture knob). You can also have a failing float that is alllowing the bowl to fill too high (Marvel has really struggled to get this right). The carb's inherent mixture control is VERY sensitive to the fuel level in the bowl and anything that changes it will alter that mixture. Higher is richer, lower is leaner.

Does your fuel pressure spike? Higher pressures (usually above 7 or 8) can over-run the needle/seat and raise the level.

The excess smoke was proabably grey and is common in over-rich condition. It is more black than gray, but it would be hard to see that from several hundred yards away. I would assume this smoke was due to the over-rich condition, given all of the other data. There is no way to get enough water in these engines to produce visible white smoke. That much water in your fuel would not allow you to recover via leaning.

Larry

First thing I would do is inspect the carb. float.

If you have a float that is beginning to sink because it is partially filled with fuel (metal or hollow plastic) or becoming fuel saturated, it will raise the fuel level in the float bowl and cause an excessively rich mixture.

Carb float SB complied with?

Bill,

This thread might have some relevant info:

http://www.vansairforce.com/community/showthread.php?t=32931&page=3

Rob S.

Thanks to all so far. Let me try to answer some of the questions.
The engine, mags, carb all new. First flight April 2015. No issues with engine performance in flight or take off ever. Starting up became difficult and do I had the mag looked at. Worked fine after re install. Plane was not left outside. Flight just a couple hours prior was uneventful. Never had this happen before. It has now happened 3 times on take off. St 5000 feet I tried to move to rich and that was a no go. It has been quite warm lately but first flight yesterday was only 70 degrees and take off was an issue until I leaned it.
Sounds like everyone thinks I should have carb serviced?

Carb

The "axle" that the float rotates on is a very sloppy fit. (by design??) There have been issues with the float rubbing on the carb body. During installation the float should be gently pushed to the side in both directions and moved up and down to check clearance between the edge of the float and the body.
I personally don't trust any of the plastic floats. I have a legal PNA metal float.

Kato's 8 said:

Thanks to all so far. Let me try to answer some of the questions.
The engine, mags, carb all new. First flight April 2015. No issues with engine performance in flight or take off ever. Starting up became difficult and do I had the mag looked at. Worked fine after re install. Plane was not left outside. Flight just a couple hours prior was uneventful. Never had this happen before. It has now happened 3 times on take off. St 5000 feet I tried to move to rich and that was a no go. It has been quite warm lately but first flight yesterday was only 70 degrees and take off was an issue until I leaned it.
Sounds like everyone thinks I should have carb serviced?

Click to expand...

Something is likely going on in the carb. There are some things you could do yourself. However, if not comfortable with that I don't see a choice other than to send the carb in for service. If it were me, I would separate the carb (4 screws and may need a $4.00 gasket for re-assembly). You could check for blockage in the needle/seat, bad floats, mis-adjusted floats or cracks. Seperating the carb is pretty straight forward and I would encourage you to research first. If you can't find the problem, you can then send it in.

If your comfortable making more flights, I would want to know if this problem is limited to take-off or if consistently rich in cruise as well. This will help you troubleshoot the problem. You can compare the full rich EGTs you are getting now to what you were getting before, assuming you can't tell if your red knob is further back than it used to be.

Larry

Larry

Carb

Before removing the carb and sending to a shop or taking it apart: Check that the screws holding the top and bottom halves together are tight. Remove the air filter to inspect condition. Look inside carb throat from the bottom for anything loose, broken or obstructing.

Don Broussard

RV 9. Rebuild in Progress

Than you for response. I'll look at it again and then think about splitting to check for blockage etc. then if needed, send for service.
Thanks!

Just wanted to thank all for the help and to let you know I found the problem right away. I had installed a doubler on the emergency air intake door mounting ring. It was about an inch long and 1/2 inch wide. Iused it for two pop rivits that were loose and had wallered out the hole in the fiberglass. Well I found it laying loose in the filter bowl below the carb! Not sure why it came loose but it did and was probably just laying there undisturbed at lowere throttle settings. When I advanced the throttle the last Inch or so is when it would stumble and that was probably because the carb was sucking that double up and blocking something.. Not Good!! So I removed it and put the filter back in place and test run with tail tied down to max power. No Issue now! Im darn lucky that that piece didnt get sucked up into the engine and even more Lucky I didnt put the airplane in the trees.
Now Ill be fixing that door assembly In a way nothing will come loose again.
Whew!

Kato's 8 said:

Just wanted to thank all for the help and to let you know I found the problem right away. I had installed a doubler on the emergency air intake door mounting ring. It was about an inch long and 1/2 inch wide. Iused it for two pop rivits that were loose and had wallered out the hole in the fiberglass. Well I found it laying loose in the filter bowl below the carb! Not sure why it came loose but it did and was probably just laying there undisturbed at lowere throttle settings. When I advanced the throttle the last Inch or so is when it would stumble and that was probably because the carb was sucking that double up and blocking something.. Not Good!! So I removed it and put the filter back in place and test run with tail tied down to max power. No Issue now! Im darn lucky that that piece didnt get sucked up into the engine and even more Lucky I didnt put the airplane in the trees.
Now Ill be fixing that door assembly In a way nothing will come loose again.
Whew!

Click to expand...

If you suck a plate up against the carb opening it acts as a choke plate, forcing a rich mixture. Glad you found it before damage to yourself or your plane. Don was dead on to look for simple stuff first. Occams' Razor (often the simplest answer is the correct one) proven again.

Larry

Summer is here...

I flew Saturday with the temps in the mid. 90's and had to lean a lot to get power due to density Alt. Only got 1900 static at full rich!