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lr172

Well Known Member
I just purchased an O-320-B1A that I am overhauling for my new RV-6 project. The engine was taken out of service in the early 80's and has been sitting indoors for a few decades. Very little corrosion and has all new top end components not yet installed.

This engine has the Marvel MA-4 carb (-12 version) that, according to the engine log, was rebuilt not long before taken out of service. It is tight with no slop and appears in great shape. My issue is how to clean it. If it were an auto carb, I would pull it apart and mechanically clean the small passages. However, rebuild kits are over $250.

I am concerned that there is varnish/deposits from the evaporated gas. Does any one have experience here. Do I have a chance to clean this properly with chemicals? I have considered pulling it apart to clean the jets and small passages and just purchase the gaskets that I need. I could then inspect everything else. My challenge here is that I do not have an overhaul manual or Parts catalog and can't seem to find one.

Does anyone know where I can find these documents?

Thanks for your assistance.

Larry
 
Its likely that the gaskets are dried up particularly the leather accelerator pump seal. A gasket kit is not expensive. I soak stuff like this in Eldorado CT2400 but its over $100/gal. I recommend you disassemble it, clean everything in a solvent tank, then spray and scrub with phosphoric acid then very thoroughly rinse everything. Also clean all passages with some pipe cleaners.

If you can get a hold of the Lycoming service instruction collection there are some paper manuals there.
 
Last edited:
rocketbob said:
Its likely that the gaskets are dried up particularly the leather accelerator pump seal. A gasket kit is not expensive. I soak stuff like this in Eldorado CT2400 but its over $100/gal. I recommend you disassemble it, clean everything in a solvent tank, then spray and scrub with phosphoric acid then very thoroughly rinse everything. Also clean all passages with some pipe cleaners.

If you can get a hold of the Lycoming service instruction collection there are some paper manuals there.
Click to expand...

I thought more about this after posting and I feel the same. I am quite worried about the leather accel pump. I can't imagine it is worth leaving it in there. Where do you find gasket kits? Spruce has all the parts, but no gasket kit. I can get the rebuild kit from Marvel for $250, but it has more than I probably need, given the recent rebuilt. I think that I will only need gaskets and the pump. I found a manual for Avstar MA-4 with same part numbers, so I think this will work for me.

Thanks for the help.

Larry
 
Rocketbob,

While I have your attention maybe I can ask you another question. My carb is a 10-3678-12. This carb was used on various O-320's with the tapered riser sumps. They also used a straight riser and in those cases spec'ed a 10-3678-32 carb. I spoke with Marvel and confirmed the -32 is a richer carb. I am swapping my tapered riser sump for a straight riser sump and wondering whether I need to find a -32 carb.

I did some research on and found a couple of people the used both on a straight riser and got better GPH levels and better overall performance with the -12.

If you are familiar with these applications, I would appreciate your perspective.

Thanks again for your help.

Larry
 
manual

I purchased a cd that has the Marvel service manual for the MA4SPA. Don't know if this is your carb, but I would share the CD if you need it. Randy
 
Some of the models of carbs have several different configurations that make them run richer or leaner. Different jets, diffferent venturi's, etc. The straight riser is going to breathe a little better and you can convert one by setting it up on a mill and bore it out with a boring bar. I imagine you can make your carb work just fine.
 
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