Flooded O-320 with MA-4SPA 10-5217

[bryanflood]

Hi, need some advice from the experts. I have an RV-9A with an O-320
and a MA-4SPA P/N 10-5217. I checked the fuel pressure and it is
normally between 5 to 5.5 psi. About 9 months ago I installed a
rebuild kit in the carb. This included a new float needle valve and
seat but not a new float. I set everything by the book and it worked
great for about 100 hours until this weekend. The plane was
impossible to start, it was flooded, couldn't figure out why. Then
found that the gas level in the bowl was at or above the carb split
line. Took it all apart inspected the needle and seat under a 10
power scope, still looked good. The float is metal and I cannot see
any evidence it contains any fluid. However even after making sure
everything is set correctly I was able to comfirm that that fuel was
being allowed into the bowl until the float was completely
submereged and then just barely stopped, this seems odd b/c the seat
and needle are really too new to fail and the float is dry. The float seat combonation was set to the correct height, so it became "solid" at the correct float setting, it's jsut that it took more pressure on the seat to fully shut off the fuel. The float part number is 30-766 with a date of 3 90. Can floats fail in some other way? or should I just try to throw another needle and seat at it? The whole thing seems odd to me.

Thanks for the help,

Bryan

[WilburD2]

Bryan, if the float is still sound, (dry) then it might be something simple like dirt and/or varnish build up on the float pivot arm and holding the float down (open). Hit it with a good cleaner once or twice and see if it changes anything.

[videobobk]

First, your problem and mine may be very different, but I had similar less than a year ago on the same setup. Replaced the needle/seat, then the float. Nothing except a big waste of money. My mechanical fuel pump had decided to increase it's output pressure from time to time. Never did figure out why, and five A&P's told me it couldn't happen, but replacing the FP did the trick. I would look very closely at the FP and at fuel pressure in general. Also, and I don't know if this could be a factor, but when fuel is warm, it expands, is less dense and might not exert as much upward pressure on the float valve. I don't know where you are, but I'll bet it is warm there.

Bob Kelly

[bryanflood]

So, here are some things I probably should have mentioned before. I have seen the bowl overflow both on the engine driven pump and on the electrical pump. Most of my testing however has been on the electrical pump. I tested the fuel pressure for the electrical pump and it was dead stable at 5 psi, a buddy who was also there said he saw 5.5 psi briefly, but I never did. I also thought the float was sticking in the bowl, so I suspended the top half of the carb in a large glass bowl with the float completely free and turned on the fuel. The fuel level went up until the float was almost completely submereged, like 99 to 100% and then the fuel level seemed to stop or slow to an undetectable level. So the problem is not likely to be that the float is sticking in the bowl.

I have not cleaned the float, maybe varnish buildup has made it too heavy or sticky on the pin as WilburD2 suggests, although it certainly seems to be free. I will give this a try today.

Thanks for all the suggestions...

Bryan

[Mark Burns]

Bryan,

After replacing the float bowl on my MA4-5 (why is another story) I noticed the float was rubbing the side of the bowl

There is not much room in there at all, at least on the 4-5's.

What I would do is with the carb dry of fuel I would pick it up and rotate it to the left all the way around until it was upside down. I could hear the float flopping over. When I did the same thing to the right the sound was very different so I was pretty sure the float was rubbing the bowl. I smeared a light coating of grease on the bowl and sure enough it rubbed off on the float. i just had to "tweak" (bend) it a little to clear. The hinge pin allows the float to have quite a bit of lateral play. This can also be "tweaked".

If the float is "catching" on the bowl it will stay down a liitle too long and flood. With the engine running it will be less likely to catch I would think due to the engine vibration.

Just something to check.

One more thing. Confirm that your seat part number is the correct one.
If the seat has too large of a hole the float cannot hold back the pressure like it should. Simple "hydraulics"

Mark

[Bob Martin]

Check that the main valve "clip" is seated correctly too.
The clip that connects the floats to the main valve.
the hinge pin runs thru it for it to seat properly.
The clip can be pushed forward ahead of the hinge pin and look correct but it will not let the valve "seat" correctly.....
Ask me how I know.....
Good Luck.

[bryanflood]

Mark - Any idea how big of a hole the seat should have? Yesterday I confirmed that the "quick kit" I used 9 months ago was the correct kit... but that doesn't mean the hole in the seat is correct. Great idea something I have not checked.

Bob - Looking at the service manual the figure on page 9 and figure 13 show the clip in front of the float arms or another way to look at it is between the float arms. But then figure 10 of the service manual shows the clip behind the arm of the float in front of the hinge pin. I'm not sure how to get the clip to go around or behind the hinge pin b/c the float bracket that holds the hinge pin and the float travel stop are in the way. We very carefully made sure that the clip did not contact any area that would casue the float to hang. I'm probably missing something in your response... could you explain it again to me. I really hope this is my problem, would love it to be an easy fix. BTW- My clip is behind the flaot arms in front of the hinge pin and bracket, like in figure 10. You know, sort of off to the side pointing right and slightly aft.

[Bob Martin]

Bob - Looking at the service manual the figure on page 9 and figure 13 show the clip in front of the float arms or another way to look at it is between the float arms. But then figure 10 of the service manual shows the clip behind the arm of the float in front of the hinge pin. I'm not sure how to get the clip to go around or behind the hinge pin b/c the float bracket that holds the hinge pin and the float travel stop are in the way. We very carefully made sure that the clip did not contact any area that would casue the float to hang. I'm probably missing something in your response... could you explain it again to me. I really hope this is my problem, would love it to be an easy fix. BTW- My clip is behind the flaot arms in front of the hinge pin and bracket, like in figure 10. You know, sort of off to the side pointing right and slightly aft.[/quote]

First off, mine is a MA4-5 for my 0-360, so not sure exactly how your 0-320 carb looks. I don't have the parts manual at home here either. But I'm trying in attach a picture for you to see my part.
The SS clip that connects the floats to the valve hinges on the same pin the floats do. You can push the clip farther forward, towards the bowl and it will work but not correctly. It would let the valve seat 100%....sometimes, so it gives the illusion it is working. But it isn't. I hope the picture helps explain this. The picture shows the clip installed correctly.
[IMG][/IMG]

[Mark Burns]

Originally Posted by bryanflood

Mark - Any idea how big of a hole the seat should have? Yesterday I confirmed that the "quick kit" I used 9 months ago was the correct kit... but that doesn't mean the hole in the seat is correct. Great idea something I have not checked.

Bryan,

Sorry, But I don't know the answer to this question. Maybe a call to Precision will get you the answer. I've never called them so I don't know how helpful they are.

Precision Airmotive phone: 360-651-8282

Mark

[bryanflood]

Yeah, my clip is made of bent wire, different than yours. Great picture though, wish people could always send pictures it makes things so easy. Nobody seems to have pictures of the inside of the carb (probably not a big suprise).

Thanks for the help.

Bryan