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Any reason not to just replace this old MA-3A carb?

lndwarrior

Well Known Member
The engine is an o-235-C1, the carb is the MA-3A without the accelerator pump. I have been flying this for 6 years.

Four months ago the engine developed idle problems. Rough running, engine dying. I spent a bunch of time going through the entire fuel system. Put new filters in, checked all the screens and lines, checked for intake leaks, etc. I spent a quite a bit of time adjusting the mixture/idle setting on the carb and it seemed to solve the problem.

Today, on take-off with my hand holding the throttle in, the rpm did not reach normal takeoff rpm, and then the rpm started dropping even though I was still holding the throttle in.

I pulled into the runup area, leaned it out and did a high rpm run for 30 seconds or a little longer. The mag drop was in specs. Also, these Bendix mags were bought brand new and installed a year ago.

Did 4 more high speed taxi tests and could not achieve take-off power. I came away feeling this plane is trying to tell me something, maybe for some time. I also decided I was not flying it again until I have the carb inspected or replaced.

I have no history at all on this carburetor. No idea the number of hours or if/when it was last over-hauled. It came with the used engine.

At this point I am pulling it. My only question is to try an IRAN - or just buy a new/overhauled carb?

I am clearly leaning towards a overhauled/rebuilt one from AS.

This carb is clearly an older one but I'm just wondering if there is any reason to IRAN this one rather than buy a newer rebuilt/overhauled one?

To be clear I am not trying to save $500 or whatever between a possible IRAN and a rebuilt/overhauled unit. Plus the inherent delays in an IRAN process, when I can just order a rebuilt/oh'd unit today.

I vaguely recall in some cases "the old ones were better than the new ones" but have no idea of this relates to my carb at all. This is the crux of why I am asking the question.

Any valid reason to have this old one rebuilt rather than buy a newer overhauled/rebuilt unit, if money is not a consideration?
 

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I assume you did steps to rule out carb ice?
If so, with no shown improvement, I'd go for an overhauled unit.
I'd also look at the other usual items like plugs, mag timing (or overhaul if close to 500hrs), filters, etc. while waiting for the carb.
 
Sure it's not a sticky valve?

Good you looked for intake leaks, although that wouldn't explain the inability to reach TO power.
 
I assume you did steps to rule out carb ice?
If so, with no shown improvement, I'd go for an overhauled unit.
I'd also look at the other usual items like plugs, mag timing (or overhaul if close to 500hrs), filters, etc. while waiting for the carb.

All of your suggestions were checked at the condition inspection 3 months ago, including mag timing.

The temp at the time was 85 degrees with the RH around 24%. I don't think it was carb ice.
 
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Sure it's not a sticky valve?

Good you looked for intake leaks, although that wouldn't explain the inability to reach TO power.

So I'm no expert on this but here's what I know.

At my recent condition inspection I borescope all the cylinders. All valve seats, stems and guides looked surprisingly clean.

Since the inspection I have probably only flown about 15 hours.

Also, I have had no problems with morning sickness. The engine starts right up and runs smooth.

However, I did not think to check EGTs when this was happening today.
 
Take the S/N of the carb and see if there are any AD's or Service Bulletins. Some of the very old carbs have AD's for various things like the floats.
Then see if Aircraft Spruce or some other supplier has a rebuild kit available. You should be able to find a service manual for the carb to do a simple tear apart type inspection. If that doesn't seem feasible to do your own rebuild/inspection, then send it out to a specialty company. There are some specialty tools required for some parts of the rebuild (like pressing out the venturi), but you probably won't need these for the basic stuff that you would be replacing. A specialty company would also be able to do the flow testing to return it to service. A quick google search shows rebuild kits are available and so are rebuilt units, so it should be fairly quick to just have your original unit overhauled.
 
Long time a&p your time is valuable. Special tools are required. And have you ever overhauled a carb. Not as ez as one would expect. Allso did you check the butterfly valve and shaft for play? Worn shaft can cause all sorts of problems.
Personally I would just use the one you have as a core. Get an rebuilt unit and be done with it. Less problems and gives you piece of mind.

RD
 
Long time a&p your time is valuable. Special tools are required. And have you ever overhauled a carb. Not as ez as one would expect. Allso did you check the butterfly valve and shaft for play? Worn shaft can cause all sorts of problems.
Personally I would just use the one you have as a core. Get an rebuilt unit and be done with it. Less problems and gives you piece of mind.

RD
Yep, this is what I'm going to do.

Thx!
 
I Have An Overhauled MA-3SPA

Brought it home with me in helping clear out a deceased friend's Zenith project. It needs a new home. I have the 8130-6, owners book, etc. Contact me if interested.

John Siebold
2082833917
[email protected]
 
I went thru 3 carb shops trying to AD/update and get my old MA-4SPA working right and they never did. After spending north of $1500 in those 3 attempts (not to mention the time suck) I finally just bought a factory reman. Runs perfect now. YMMV but I wish I had just gone reman to start, **** I could've bought new!

-Fitz
 
We just went through the same decision making process on our Comanche. The previous owner was very adamant about the carburetor being "a good one" and we had a reputable shop take a look at rebuilding it.

After inspection and all the items they could see wrong with it, their recommendation was strongly in favor of abandoning it as a core and getting a rebuilt unit, which we did.
 
What about Avstar carbs?

It seems they may be cheaper for a new carb, but don't quote me on that, I only searched for a replacement for my o320-D1A. I didn't even know avstar existed until somebody recently sold one here.

The carb I "think" is their replacement for my Marvel is $1208 new, and they will take the marvel core.
 
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