[DarrenL]

Hi all,

Typically, the week before the Rally, our carb has come back as "beyond economical repair"

It was fitted to our C90. I have access to the same carb off an O200 - is it likely that they would be jetted the same?

Thanks

Darren

[Rob L]

Probably won't help you here & now, but these carbs have a "core value" for service exchange units, so make sure it doesn't get thrown away.

What model of carb for what engine?

Edit: I see engine as being C90
Edit 2: are you on a permit or CofA?

[DarrenL]

Thanks for the replies - I forget to look in this forum!

Indeed, it's a C90 on a permit. I'd been trying to get it to the Rally but looks like too many issues and it all won't get done in time.

It's a long story, but the carb was removed by a maintenance org. because of rough running at high revs/carb heat and sent off to be checked.

I've discovered the cause of the rough running (cracked exhaust under the carb heat shroud feeding exhaust gases back into the carb), but the people who looked at it sent it back beyond economical repair because it has a 2 piece venturi which it seems is subject to AD 98-01-06. Linky here:

http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgAD.nsf/AOCADSearch/9F87A5E42C10900C86256A410065C0CD?OpenDocument

This states:

"If a two-piece venturi is installed, inspect the carburetor at each annual, 100-hour, or progressive inspection, to determine if the primary venturi is loose or missing. If either of these conditions is found, prior to further flight, repair the carburetor by installing a serviceable two-piece venturi or by installing a one-piece venturi in accordance with Precision Airmotive Service Bulletin (SB) No. MSA-2, Revision 1, dated November 11, 1991, Revision 2, dated December 28, 1993, or Revision 3, dated October 10, 1995. Installing a one-piece venturi constitutes terminating action for the repetitive inspection requirements of this paragraph."

The carb lookers were looking at the work to convert it to a single piece venturi and make the other changes as necessary. This makes it uneconomical apparently!

But the AD seems to suggest that the 2 piece is fine as long as it's inspected annually or every hundred hours.

Am I reading it right? Are the carb people just trying it on? I don't see the need to a new carb?

Thanks!

[Joe Dell]

I'm currently flying with a carb that came straight off an O-200 and onto a C90. No issues to date. The model number is different, which led me to look up the overhaul parts list for both carbs. Identical.

[Rod1]

If it is an SB and there is no MPD associated with it it is not compulsory unless your inspector says so.

Rod1

[aerofurb]

As it is an Airworthiness Directive it is mandatory. I would imagine that the carb overhauler are required to abide by any ADs due on a component when it passes through their organisation for overhaul or repair.

It may well be that the associated Precision Service Bulletin says that a one piece venture must be fitted at any time the carb is tripped down for repair or overhaul (I haven't read the SB).

Often it is no more expensive to buy an overhauled exchange carb for the cost of having your existing carb repaired/overhauled.

I would hazard a guess that the LAA are unlikely to overrule the repairer's view that a one piece venture should fitted at carb strip down.

[DarrenL]

Thanks for the replies. The AD just says that the 2 piece venturi should be checked every 100 hours or annually, whichever is first. If it's loose, it should be replaced with a 1 piece. It's not loose on my carb.

Unfortunately, the maintenance guys have already ordered the carb and I can't cancel it. So I'm going to have to return a perfectly servicable one unless a carb body turns up at the LAA flea market at the weekend of course!

In the meantime, I have access to the carb off an O200, so will give that a try

[cockney steve]

As a semi -literate layman who has had a goodly few years tinkering with carbs, I read the following.

"IF it has a 2-piece venturi, inspect it annually....if it's broken, replace with a good one or convert to a 1-piece venturi...If it ISN'T broken, there's nothing to fix....carry on until the next annual.

As regards wear..... throttle spindle, float pivot /needle /seat. in the case of accellerator pumps, linkage and seal wear.....in the case of constant -vacuum carbs such as SU and Stromberg, the biased-needle designs wear both needle and jets....the Kei Hin copy does not!
You would need hundreds of thousands of gallons of fuel through a jet to cause appreciable wear. OWT's to generate cash from what is , effectively, an everlasting component.

[aerofurb]

The mandatory AD refers in its text to a manufacturer's SB. The manufacturer will (they all do by and large) consider the SB mandatory even if regulating authorities do not count SBs as mandatory.

Maintenance organisations (be it involved in aircraft, engine or component maintenance) have to (enforced by the regulating authority) technically assess SBs and other continuing airworthiness data. It may well be that the applicable repair/overhaul manual demands any carbs being stripped down for inspection/repair/overhaul must have two piece venturis replaced.

Sure, the AD 'only' mandates an annual/100 hr inspection but the carb has gone beyond that by going for inspection/repair/overhaul.

It is unfortunate that in this day of litigation, maintenance organisations have to ensure they make sure that all of their work abides by the law (not interested in partaking of an 'all engineers are crooks and bounders' argument) - and the law as it might be interpreted by a non-expert judge. Aircraft crashes, person dies, spouse offered 'no win/no fee', carb (mag, engine or whatever) found to have not been in compliance with a manufacturer's 'mandatory' SB after work carried out. Difficult one to fight against with a non expert court - 'but it says here - 'mandatory' '.

That's the way it is I'm afraid. I'm not talking car maintenance here as I don't get involved with it, so can't comment. I can comment only on aviation maintenance procedures.