WHAT TYPE OF CARBURETOR?

[dacker]

I am trying to research what type of carburetor is required on my A model. I have an O-300A. My Marvel Schebler is the MA 3SPA 10-2850. I have the Marvel Schebler manual and have looked at a couple of other places and can't seem to find any reference to that number. I saw on one chart that the required carburetor is the 10-4895 for the O-300A,B, and C. The TCDS doesn't seem to address this and I don't have my Continental manual at home with me (if that would even help).
I am getting ready to do an engine rebuild and would like to replace the carburetor as well, and want to make sure that I use the right one.
Any ideas?
David

[blueldr]

Contact El Reno. they have a chart that lists all the Marvel Schebler applications and specifications. Price unknown.

[GAHorn]

The TCM Ovhl manual lists the carb as TCM PN 628945 (which is superceded now to 633029 according to Cessna). This same carb also has a Marvel-Schebler PN 10-4439. El Reno lists 3 carbs for the C145/O300: PN 10-4439-1, 10-4895-1, and 10-3237-1, all of which have exactly the same individual internal part nos. in all the overhaul kits.
I have looked throughout the listings and find no application for a 10-2850. (Closest thing I could find is a 10-2848 which fits a C-125 engine, but I do not know if that has any relationship to the carb you have.)
MA 3 SPA carbs in various configurations were fitted to all kinds of engines including Lycomings, Franklins, Rangers, and the list goes on. Each of those has a different part no.
FYI--Spruce sells the 10-4439 for $529 exchange ($400 core.) Precision and Consolodated are the two most popular overhaul facilities. Consolodated has the better reputation. 334-286-8551

[dacker]

Thanks for the info. You are right about the listed overhaul parts for the MA3SPA carburetors. I had to replace the accelerator plunger and couldn't find my model in the overhaul manual in order to find the part numbers. We (me and my mechanic) finally realized that all of the different models of the MA3SPA carburetors had the same part numbers listed (at least for the parts we were looking at).
My engine came off of a '56 C172, maybe that is the reason for the different carburetor. By the way, the carburetor does have aviation stamped on it, so I feel fairly confident that it wasn't one that was left over from somebody's tractor, but it certainly could have come from some strange airplane in an undocumented swap. From what I understand Marvel Scheblers are/were used on any number of different types of equipment including tractors!
David

[zero.one.victor]

My overhauler got me an exchange carb 4 years ago, it's a 10-4896-1.
The carb came from Precision Airmotive in Marysville Washington. I think they're a major source of MS carbs. Don't have their number handy but I believe they advertise in TAP.

Eric

[dacker]

I called Hatfield's, he was full of information...off the top of his head he said that my carburetor was a Precision carburetor; Precision bought out some of the Marvel Schebler carburetor models but not all. He told me this off the top of his head so I am not sure if he recognized the numbers or just assumed. Anyway. I think I will be buying one of the previously posted models from Spruce, Aviall, or someone else. I just hope that I can get credit for my core, it should be worth around $400.

On another note, I was looking at the Precision website, they have an explanation for new, rebuilt, and overhauled. (You experienced guys already know this). New being self explanatory, rebuilt being rebuilt to OEM original specifications with some used components being retained, and overhauled being rebuilt with components (some new, some used), meeting specified performance specifications.

I thought this was interesting.
David

[GAHorn]

I called Bobby down at Hatfields, and the bad news is that Albert (their carb specialist) has had a stroke, and they are not doing carbs right now. Their experience (and the rumors I've heard over the years) confirms that Precision does not perform as well as they should, and they recommend Consolodated Fuel Systems. 334-286-8551 for overhauls, etc.

[lowNslow]

I've heard of Precision and Consolodated, but I notice Chief Aircraft offers carbs from American Fuel Systems and Kelly Aerospace. Anybody have any experience with the last two. Spruce still seems to have the best price.

[GAHorn]

Kelly Aerospace and Consolodated are the same company. (Kelly is parent.)

[FredM]

I had a carb overhauled by Kelly Aerospace. I was attempting to fix a stubborn engine problem. Low static rpm. Pretty much everything else had been eliminated. I sent them my carbeurator because they were the last company to overhaul it. when I got it back I still had the low rpm problem plus a very bad fuel leak. I sent it back to them again and was told they couldn't find anything wrong with it. I told them I was not going to accept the same carb back unless they found something wrong with it.
of course they didn't have any other carbs to send me. After questioning them about their test bench I found out they mount their carbs horizontally. When I suggested they tilt it since my carb is on a taildragger they finally found the leak TWO MONTHS LATER and they didn't reinburse me for the extra shipping I had to pay. I still suspect the carb as the cause of the low rpm but haven't been able to find anyone to loan me a serviceable carb to confirm it.

[Dave Clark]

Hey Fred, what makes you think the carb is at fault? Does it lean properly, IOW will it run rich then seem to lean out normally? Other than someone installing the wrong venturie I can't think of anything that would cause low RPM.

It's always good to remind the shop that it 's for a taildragger. Especially the old Strombergs for the (A65-C85 engines)

[FredM]

Nothing particular makes me think it is the carb. It's just that I have eliminated everything else I can think of except the carb. I needed new plugs and ignition harness anyway, that was first changed. swapped mags with another set. No stuck valves, compressions are all between 74-78 on all cylinders. I did find some worn rocker arms, tips had been reground too many times causing excessive valve lash. I replaced all lifters and used oversize pushrods as required. Still have the same problem.

[blueldr]

Fred M
You seem to be plagued with low static rpm. Have you ever had the rpm you are looking for on this airplane? By that, I mean is the airplane new to you? Maybe you have a fat prop. Too much pitch for the rpm you're looking for. It is not uncommon to find props that have beem repitched but were not restamped with the new pitch. One of the airplanes that I have now had low static rpm and it was stamped 53 but measured out at 56. Sombody wanted more cruise speed and tweaked it up but didn't re-stamp it. Is this a possibility on your airplane?

[pdb]

Dear Gabby:

After all this exciting talk of carbs, a friend of mine looked under her skirt discovered that she has a 170B with a MA3-SPA Carb Part #10-2848. This externally identical to the 8-4439 which TCM says should be used but I think it was designed for the 125hp Cont. and likely is a bit diffferent internally.

This has been in the plane for a decade and it has worked perfectly, flawlessly, but her mechanic says it is time to think about overhauling as a little wear can be seen and she is not getting any younger.

Should she reveal her secret to the mechanic immediately and order a new carb. She keeps muttering, "If it ain't broke...." but her insurance agent and the forces against aviation might not be so understanding.

What's this poor old girl supposed to do and how soon should she do it?


Confused

[zero.one.victor]

I don't have any suggestion on the time frame but maybe the different part number carb wouldn't make any difference as far as trading it in for an OH'd unit? An MA3-SPA core is an MA3-SPA core, eh? Seems to work that way sometimes with mags--sometimes the ones you turn in don't even have to have the same number of plug wires as the new ones!

Eric