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Carb Overhaul Issue

RFSchaller

Well Known Member
I recently sent my carbs out for overhaul to a well known western USA repair center. When they came back my engine was extremely hard to start. Today I removed them and disassembled them. I found the shop had swapped the starter circuit (aka choke) modules to the opposite carburetors. When I swapped them back the engine kicked right over like it used to. FYI the symptoms were really long cranking to start and about 10% increase in cruise fuel flow.

I don't want to identify the shop because it's probably an isolated event and I don't want to get into a pointless legal battle with them. Suffice it to say don't trust any shop will get it right.
 
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regarding carb overhaul in general...
How many hours were on the carbs?
Did they send the old parts back and if so was there obvious wear?
How difficult was the synchronization after overhaul?
Thanks in advance,

I have 400hrs on mine and they have never been overhauled or even disassembled and inspected but continue to run well so I'm reluctant to mess with something that appears to be working well.
 
I've rebuilt two sets of 912 carbs due to ethanol and can see where the choke modules could be swapped by a novice as they are actually marked "L" for right and "R" for left-if I remember correctly. It's been a few years. Good to hear you found the problem.
 
I had 580 hours on the carbs when they went out for overhaul. The only parts they replaced were the O-rings, diaphragms and floats. The floats were within the 7g limit so I had them returned to use as spares.

The carbs did synch when I reinstalled them with the modules on the wrong carb bodies. It just started really hard and used more gas.

I marked the carb domes with an R and L when I removed them, and I noticed the domes had been switched when I got them back. That was my first clue things might not be correct. I notice the ROAN learning video suggests working on the carbs one at a time to prevent swapping parts.
 
I have 400hrs on mine and they have never been overhauled or even disassembled and inspected but continue to run well so I'm reluctant to mess with something that appears to be working well.

At the very least I think I would drop the float bowls to look for debris and also weigh the floats as part of annual condition inspection.
 
At the very least I think I would drop the float bowls to look for debris and also weigh the floats as part of annual condition inspection.

I do that, just not complete disassembly.
Thanks for the response, I think I'll wait another hundred hours before overhaul.
 
My 2 cents

I too just went through a profession ( which means $$) carb/s overhaul as I was at the 200 hour inspection interval but next year I would be at the 5 year rubber replacement interval.

After discussion my situation with the shop I decided to do the overhaul early. Received the carbs back and all looked good and the parts replaced were also returned. Everything looked fine and believe me it was tough to "fix something that wasn't broken."

The only thing needing attention was the plastic bushing on the control arm of one carb where the spring rides.

FYI I maintained the control arms in the same position prior to removal and when reinstalled the carbs were still in sync.
 
I took my 12 on a 3 hour cross country today, and I am happy to say it started easily and is back to burning 4.5 GPH in cruise at 5100 RPm. I'll be doing future carb work myself.
 
In my experience, the carbs are not hard to work on. But, because some of the parts are aluminum alloy and some are brass, they are easily damaged. Also, you will need to modify a screwdriver to be a perfect fit for the threaded alloy needle retainer (it has an unusually wide slot). The needle retainer is held in with loctite and the part into which it is screwed should be warmed to soften the loctite prior to removal. Otherwise, without a perfect fitting screwdriver and warm loctite, the screwdriver slot will distort or shear and the part will be nearly impossible to remove.

My comments here are based on my personal experience and are provided for your interest, only. They are not intended to substitute for the expertise necessary to maintain an airworthy airplane. You get that.
 
I do get that

But just for the reasons you mentioned my choice was to have my carb work done at a shop. Those "trick and tips" could be done by someone who does carb maintenance regularly. Other than an annual float weigh-in I may not do anything to the carbs for two or years, and it would be like starting over for me.
 
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