M20C Carburetor Problems - Overhaul or New

[rubixcube2k3]

So I just got the bad news today that my carburetor needs to be overhauled/replaced. The issue arose after I noticed a 500RPM Drop when pulling carb heat on runup. Getting a little personal with the plane, we found that the bowl bolts are loose and the vibration has shaken the mating surfaces and bolt threads to beyond a level  of reasonable comfort for simply tightening and replacing the gasket.

  Looking at my logs It's been less than 300 Hours since it was last overhauled by a shop in OK.  Is this kind of wear normal? What are you carbed guys/gals seeing in terms of carb maintence? The PN on my carb is 10-4164-1

I've looked at the AV Star carbs that are replacement for my old Precision/Marvel Schebler, but I'm not sure the extra cost is justified. They look pretty spiffy, but they're around twice the cost for a factory new carb.  Can anyone give me any advice from a similar situation? Do I have other options here?

 

I've been advised that changing out my fuel lines and oil cooler lines is necessary too (all dated 2nd Quarter of 1974 and stiff as a rock).

Abe L. Harper, Jr

[jetdriven]

Abe, you just can't get a break. Didn't your machine just come out of Maxwell's shop?

 

[rubixcube2k3]

Yep....Early December.  6hrs of flight later and here we are again...

They didn't have a reason to look at the carb bowl bolts, but from what Teledyne is saying here, this problem has been going on for well over a year or two. I can recall when I first noticed the RPM Drop back in October. If you want to see how loose it is, I can shoot you the video I shot yesterday when they called me to come look at it.

I don't know how bad other people's luck is, but mine is making me wonder if I'm living right. I've gotten prices from $800 to $2000 for carbs....This annual was 1/4 of what my first was, but that still wasn't exactly cheap.

Oh, Did I mention that my new (installed Dec 2010) Oil Cooler has a broken flange and it has to go back to Pacific Oil Coolers for Overhaul....

I have to laugh to keep from crying...

Abe

[garytex]

All the suppliers and overhaulers I learned about years ago for Marvel Shebler carbs are gone.  Sorry, I was going to try to point you in the right dirrection.  But the lesson, which was that there are good and bad parts manufacturers and overhaulers seems to be the same.  500 hrs on a carb is insane.  They last for years.  Find someone who knows good from bad from indifferent, and get the good parts and overhauls.  I had to suffer through the sqame kind of bullshirt you are because I was using a bad overhauller who also used crappy parts.  Find someone who knows the difference, and follow their advise.   

[garytex]

The parts that I have seen variances in are the one piece venturi which is much harder to manufacture than the old 2 piece, and the jet.  Precision used to make a multi hole jet that atomized better.  I checked what I believe is their website, and could only find injected stuff.  

I just remembered that I have their old from 1996 phone #.  Here it is for what it's worth  425-353-8181.  Maybe they are still cranking, and still good.  Their one piece venturi looked much better than the original and then replacement ones that I got on an OH'd Carb from Consolidated Fuels, and the combo of their jet and multi hole venturi gave me 75 rpm static on a MA4 SPA equipped O-300, which was huge on takeoff and climb on my underpowered C 170.  I believe that better atomization is what evened out and lowered EGTs, as fewer unburnt drops of fuel were entering the muffler and burning there.  I want to repeat the caveat that things change with these parts over time, and there is something approaching art in fabricating venturis, as I (imperfectly) understand it.    

Good luck

Gary