Recommendations to overhaul Marvel carburetor

[correamoon]

The three things I remember that cause mild roughness in these engines are:

1) The clocking of the propeller, mentioned before

2) Loose intake manifold hoses or elbows. A small leak in an intake connection will cause that cylinder to run lean.

3) Broken flow divider in the sump just above the carburetor. The newer sumps have this part cast in as part of the sump and have no problems. The older ones were made out of sheet steel and riveted (this may not be the right word, but the fastener is similar to those attaching the data plate) and had a tendency to crack and fall out or get sucked up higher into the intake system, causing uneven mixture distribution. Check the third post in this thread for photos. Edit: Sorry George, I missed your post on this possibility before I posted. At least now there's a link to the photos...)

Hi Miles

Thanks for your suggestions point 1&2 were checked and changed the manifold rubbers just in case point 3 is something new to check I will order a new carb soon, I contacted Marvel to be sure about the right part number and got a quick response and also an interesting information, anybody knows why the carburettor model changed?

Answer by Marvel

"The Type Certificate Data Sheet for the C-145-2 engine states that the
eligible carburetor is Continental Motors part number 530490. This would
represent MSA's part number 10-3237. The 10-3237 carburetor has been
replaced by the 10-4895-1 carburetor.

[correamoon]

[...
You bring an interesting point as my carb temperature indicator shows low temperatures too often...and I respect them and use carb heat all the time even immediately after take off, according two very experience pilots/mechanics my temperature indicator could be working wrong but on the ground before flight is showing the right ambient temperature...is anything that can be wrong in the carburettor that can be creating more ice than it should?....

A lower temp than ambient during engine operation is quite normal. The method to use a carb temp gauge is to avoid carb throat temps below abotu 35 degrees F (5C). The vaporizing fuel refrigerates the carb throat and freezing temps may cause humidity to freeze and reduce air flow. It is highly unlikely you need carb heat at full throttle climb after takeoff.

I also had an occasional rough engine about ten years ago which was traced to leaking oil seals in my magnetos. It was intermittent and virtually impossible to duplicate. Slight oily-ness inside the points cavity ws cured with new seals and no more problem.

I highly believe that the problem is something small like your past problem with the mag oil seals and after try all possible trouble shootings looks like the only way to go is to overhaul the main components I will go first for the carb and then the mags thanks for the support!

[GAHorn]

In my experience the mags are more maintenance intensive than the carb....and probably easier to accomplish locally. Just FYI.

[ghostflyer]

The carb has a number of changes over the years which included a one piece Venturi and a different float material plus a float retaining spring was changed also . I normally try and buy new and send the core back . The 2 piece venturi must go as they break up ,plus they are made of a magnesium alloy.

[correamoon]

In my experience the mags are more maintenance intensive than the carb....and probably easier to accomplish locally. Just FYI.

Thanks, today the mechanic told me that my flow divider is the latest cast type and in good shape...so I can discard that too...frustrating problem...well let's send the mags and harness for overhaul and if problem still there next a new carb...

[blueldr]

It was a good many years ago that they came out wirh the change to the one piece venturi in the carburetor, A rough running engine was a common result after the change and there was a number of advised corrections. I remember that the company (in Seattle) that made my venturi sent me a new part, a brass tube with a number of small holes of various sizes and locations to replace a like unit in my carburetor. It looked so much like what I already had that I borrowed a friends set of pin gages and checked the hole sizes and locations. It was identical, but I chanced it anyway, only to no avail.
You must consider how much screwing around with carburetor removal, dis assembly , re assembly, re installation, and re test flying this crap required. It wa a real pain in the ass and all to no avail. The engine simply ran ROUGH.
I went through this process almost two months and then finally said the hell with it. I again pulled everything apart, put the old two piece venturi in again along with the other original parts and left the "V" I had stamped in the data plate. (How would you erase a stamped in "V"??) The engine ran fine again and I flew it until I pulled it to install theTCM IO-360 engine.

[correamoon]

It was a good many years ago that they came out wirh the change to the one piece venturi in the carburetor, A rough running engine was a common result after the change and there was a number of advised corrections. I remember that the company (in Seattle) that made my venturi sent me a new part, a brass tube with a number of small holes of various sizes and locations to replace a like unit in my carburetor. It looked so much like what I already had that I borrowed a friends set of pin gages and checked the hole sizes and locations. It was identical, but I chanced it anyway, only to no avail.
You must consider how much screwing around with carburetor removal, dis assembly , re assembly, re installation, and re test flying this crap required. It wa a real pain in the ass and all to no avail. The engine simply ran ROUGH.
I went through this process almost two months and then finally said the hell with it. I again pulled everything apart, put the old two piece venturi in again along with the other original parts and left the "V" I had stamped in the data plate. (How would you erase a stamped in "V"??) The engine ran fine again and I flew it until I pulled it to install theTCM IO-360 engine.

Thanks for the comment and I know another pilot that had the same experience, an interesting fact is that Ly Con overhauled my carb at the end of 97 and the single Venturi AD is from beginning of 98 but looks like Ly Con knew this was coming as they installed the single Venturi and proper fuel nozzle...thanks.

[sfarringer]

When I first bought my 170 in 2004, my mechanic said he could fix my slightly rough engine, if I found a 2 piece venturi and old style fuel nozzle.

He was right.......

I can't imagine ever sending in my carburetor and letting them discard the old parts that work great.

Wasn't an intermittent though, so I doubt if it is your problem.

[correamoon]

When I first bought my 170 in 2004, my mechanic said he could fix my slightly rough engine, if I found a 2 piece venturi and old style fuel nozzle.

He was right.......

I can't imagine ever sending in my carburetor and letting them discard the old parts that work great.

Wasn't an intermittent though, so I doubt if it is your problem.

Well yesterday I discovered something interesting the serial number of my carburettor doesn't matchs the one Marvel told me should be installed I wonder if my airplane has the wrong carburettor as previous owner told me always ran rich???

Emailed Marvel with this new information waiting for their answer.

My serial number is
Carburetor
model: MA3SPA
part number: 10-4439-1
s/n S-5-8206
overhauled 1996

What Marvel told me
The Type Certificate Data Sheet for the C-145-2 engine states that the
eligible carburetor is Continental Motors part number 530490. This would
represent MSA's part number 10-3237. The 10-3237 carburetor has been
replaced by the 10-4895-1 carburetor.

[sfarringer]

10-3237 was superceded by 10-4439
10-4439 was superceded by 10-4895
10-4895 was superceded by 10-4895-1

Any of these are acceptable carbs for the C170

[GAHorn]

You don't mean serial number...you mean model number.
And since you're overhauling...get the latest version 10-4895-1. (While the diff's may be minor you might as well get the correct part.)
PS-what bluEldr posted is correct: the single piece venturi has a reputation as one that doesn't run quite as smooth as the two-piece...but it's the one stipulated biy the AD note if you wish to avoid repetitive inspections. PN's are superceded for a reason and it's generally best to get the superceded part.

[correamoon]

You don't mean serial number...you mean model number.
And since you're overhauling...get the latest version 10-4895-1. (While the diff's may be minor you might as well get the correct part.)
PS-what bluEldr posted is correct: the single piece venturi has a reputation as one that doesn't run quite as smooth as the two-piece...but it's the one stipulated biy the AD note if you wish to avoid repetitive inspections. PN's are superceded for a reason and it's generally best to get the superceded part.

There is no way I can know how the engine ran before the one Venturi piece I bought the airplane from the grandchild of the owner at the moment of the overhaul but looks they didn't care about have the engine perfectly smooth while I do so maybe the one piece Venturi is the culprit on this (at least one of the Livermore C170 residents had the same problem and went back to two pieces Venturi) I will buy the latest model carburettor and cross fingers.

Thanks
Leo

[correamoon]

You don't mean serial number...you mean model number.
And since you're overhauling...get the latest version 10-4895-1. (While the diff's may be minor you might as well get the correct part.)
PS-what bluEldr posted is correct: the single piece venturi has a reputation as one that doesn't run quite as smooth as the two-piece...but it's the one stipulated biy the AD note if you wish to avoid repetitive inspections. PN's are superceded for a reason and it's generally best to get the superceded part.

There is no way I can know how the engine ran before the one Venturi piece I bought the airplane from the grandchild of the owner at the moment of the overhaul but looks they didn't care about have the engine perfectly smooth while I do so maybe the one piece Venturi is the culprit on this (at least one of the Livermore C170 residents had the same problem and went back to two pieces Venturi) I will buy the latest model carburettor and cross fingers.

Thanks
Leo

I can only say good things about Marvel, great support answering all my questions, here goes the latest answer my engine is 145-2 and looks like my carb is better for the O300...maybe something is there...

"The 10-4439-1 carburetor is another, though less common, eligible carburetor for the O-300 series engine. The 10-4439-1 carburetor has also been replaced by the 10-4895-1 carburetor.

The 10-4439-1 is an eligible core for full core credit."

[GAHorn]

The C145/O300 differences are largely nomenclature. (Contenental switched from identifying engines by max horsepower to identifying by arrangement & displacement. The O300 largely is the C145 called by it's new name.) The carb folks likely have no knowledge of the actual differences, nor will the actual differences likely have anything to do with the carb model. In fact, it' unlikely the current Marvel folks can state the actual differences in their mentioned model numbers, particularly which differences are significant for C145 vs O300. For that reason, and for the fact that your engine is running "rough" intermittently and not continuously, the implication that a C145 should have an earlier carb model is not likely the culprit. The latest TCM manual for BOTH engines specifies the 10-4895-1 carb.

(The largest differences which might be instrumental are INsignificant, namely: Change in cam lift/timing and material of construction (cast iron vs steel cam) and lifters (steel vs cast iron) which change the relationship between manifold pressure vs RPM at low power and torque at high RPM. The fact is... your C145 has likely been overhauled more than once in it's lifetime and if so, and if the current Service Bulletins were followed, your C145 probably has the later cam and lifters.)

So, even if your C145 had a later carb with an early cam, the fact that the roughness is intermittent and not repeatable at a particular torque curve point makes the carb model question unlikely as a cause.

[correamoon]

The only good thing about this problem is all the things I am learning is like an intensive (expensive) training about the engine of the C170 thanks again.