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ma3spa carb

skywagon8a said:
I assume that you have this: http://wiki.ad7zj.net/wiki/images/8...ce_Manual_Models_MA3A_MA3PA_MA3SPA_MA4SPA.pdf
From page 16: "Assure that theaccelerator pump discharge tube is locatedinside the center ring of the venturi"
Service bulletin # MSA-7 dated 10/11/94 covers your situation. There is a kit 666-942 to solve the issue and it appears that your carb has had this kit installed which is the installation of the 47-850 nozzle.
I'm unable to locate the diameter of the jet openings.

If I were you I would pick up the phone and dial:
Click to expand...

Yes, the accelerator discharge tube is located inside the venturi but it really did not make any difference. Don't ask how I know.

Good advice on phoning and I called them. Tech support was very helpful. It seems they start with a .0935" jet in the pepper box nozzle and when they flow test each rebuild, they drill as needed to achieve the "spec" flow. I will be a while before I can measure the existing jet but it follows that a new one will likely be the smallest they would ever expect to use. Since these tubes are about $250 in Canada, I hope to not have to try too many times. Since I also have no cut off rise, the carb guys really recommended that I get a rebuilt carb which should fix all my problems. My thinking is though that there are too many threads that say the new carb owners got was so rich that their motors did not run well. That is exactly where I am at, at full throttle position so don't see the value in doing a new/rebuilt carb.:sad:
 
I just grabbed a caliper to see how big .0935" is and that is a very big jet if he gave me the correct information. Certainly bigger than I was expecting.
 
Am I assuming correctly that you are experimental with a name like zenairdave? If so, why don't you braze or solder the jet closed and redrill it to .0935"? Then just fine tune it until it's correct. Solder may not be correct, but you get the idea.
 
skywagon8a said:
Am I assuming correctly that you are experimental with a name like zenairdave? If so, why don't you braze or solder the jet closed and redrill it to .0935"? Then just fine tune it until it's correct. Solder may not be correct, but you get the idea.
Click to expand...
I am not bound by FAA regs,
I do not have a death wish however.
In principle, making the hole smaller so it can be drilled out is (in principle) an alright idea but trusting that a few thousands of solder is going to stick to the old hole after I drill it out is not something I completely trust.
I will have to decide whether to buy a new nozzle, order a new rebuilt carb or switch to an AERO Injector set up which will also work inverted. :lol:
 
zenairdave said:
I am not bound by FAA regs,
I do not have a death wish however.
In principle, making the hole smaller so it can be drilled out is (in principle) an alright idea but trusting that a few thousands of solder is going to stick to the old hole after I drill it out is not something I completely trust.
I will have to decide whether to buy a new nozzle, order a new rebuilt carb or switch to an AERO Injector set up which will also work inverted. :lol:
Click to expand...

Egg the hole out before soldering. I'm guessing you never hot rodded any cars, bikes, sleds or...........................when you were younger. This is the same carb that came on your grandfathers Farmall when he got back from the war. Simple fix if you can't find new. If nothing else it will tell you what size jet to buy

Glenn
 
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Not to get too technical on jets but the entry and exit angles of the hole also affect flow.That said I would solder it and drill it to what I thought was close then buy the correct jet if it worked out.Another way to plug it is to press a piece of rod into it then drill your hole.Both methods would require drilling oversize first.

Bill
 
If you want adjust carb jet, I would say the first thing you would need is a 4 cylinder egt/cht. Fuel flow and map would be nice also. Go fly the plane and figure out what you have. Now pull the carb and jet. Get a fine drill bit index and figure out what bit fits the nozzle. Take the next bigger bit. Put drill bit in vice and by hand turn nozzle onto bit, once drilled rotate nozzle in reverse to smooth out jet. Put on plane and test. I have a friend that had a buddy that i don't remember the name that did it 18 times!! He would do it again!! What do you have more of time or money!!

Sometimes it is as simple as going to the old guys that have hangers full of stuff including small stock of nozzles that you can trade out!!
DENNY
 
I was thinking about your carb troubles today at work, and I wondered if that carb has the "economiser" feature. It's a air channel that applies a vacuum signal to the float chamber area. In full throttle conditions the float chamber is exposed to ambient atmospheric pressure, and anything other than full throttle, the butterfly valve creates a vacuum signal that reduces atmospheric pressure and therefore flow out the main nozzle.
So in your case, if the hole in the nozzle is to big it would have restricted flow at anything less than full throttle, and at full throttle it would flow like gangbusters.....

Something to think about...
 
Pacerfgoe,
I think that you are thinking about the small Stromberg carburetors. They use back suction for mixture control.
 
Any updates on this issue? I have an O-200A with the same problem. I have installed new carb, cylinders, and checked many things. Still can't get away from too rich at full throttle. I lose about 50 rpm when slowly going to full throttle from 75-80%. I can get the rpm back by leaning mixture.
 
mk.temp said:
Any updates on this issue? I have an O-200A with the same problem. I have installed new carb, cylinders, and checked many things. Still can't get away from too rich at full throttle. I lose about 50 rpm when slowly going to full throttle from 75-80%. I can get the rpm back by leaning mixture.
Click to expand...
In principle, this is an easy tuning problem to fix, in reality, it is not. The internal circuits that come into play at full throttle are too rich. In most carbs, that is simply a matter of changing the Main jet to a smaller size. When the carbs that we are talking about went from the two piece venturi to the one piece, the internal negative pressure changed (suction) which caused the now "famous" rich running conditions at full throttle. So, back to the rich running at full throttle issue. to reduce the main jet size on this carburator requires a new emulsion tube. These are not sold in different sizes for this carburator. Different sizes are made for different carburators if you can figure out what sizes "standard" tubes are. To further compound this, after speaking with the current manufacturer, they test flow each carb and drill the emulsion tube to get the "book" flow. If this is true, there is no way to know what size emulsion tube is in each O-200 carb. All I can say is I think the one in mine needs to be smaller. The tubes were very expensive $200 - $400, I did get the stock size specification but have not taken my carb apart to see what size it is. At this time I have been operating at 85% throttle position for climb out rather than leaning at this critical stage of flight. I have this option because my cub does not really require all 100 ponies to get off the ground.
Of coarse there are other things that can cause rich conditions that must be eliminated before adjusting carburation to solve some other problem. Leaking primer, restricted air filter, leaking carb heat are but a few.
 
zenairdave said:
In principle, this is an easy tuning problem to fix, in reality, it is not. The internal circuits that come into play at full throttle are too rich. In most carbs, that is simply a matter of changing the Main jet to a smaller size. When the carbs that we are talking about went from the two piece venturi to the one piece, the internal negative pressure changed (suction) which caused the now "famous" rich running conditions at full throttle. So, back to the rich running at full throttle issue. to reduce the main jet size on this carburator requires a new emulsion tube. These are not sold in different sizes for this carburator. Different sizes are made for different carburators if you can figure out what sizes "standard" tubes are. To further compound this, after speaking with the current manufacturer, they test flow each carb and drill the emulsion tube to get the "book" flow. If this is true, there is no way to know what size emulsion tube is in each O-200 carb. All I can say is I think the one in mine needs to be smaller. The tubes were very expensive $200 - $400, I did get the stock size specification but have not taken my carb apart to see what size it is. At this time I have been operating at 85% throttle position for climb out rather than leaning at this critical stage of flight. I have this option because my cub does not really require all 100 ponies to get off the ground.
Of coarse there are other things that can cause rich conditions that must be eliminated before adjusting carburation to solve some other problem. Leaking primer, restricted air filter, leaking carb heat are but a few.
Click to expand...

Have you tried flying it without the air filter on?

Glenn
 
Make sure the screws on the float bowl are not coming loose, This will cause it to run rich. It is a rather common problem.
DENNY
 
id really like to have a small study with AFR meter and just give it a go.. lets see just where we really are.. it seems like my 85 hp is really undercarbed at times.. would not be that difficult to bench a couple carbs on a plane in a day with two or 3 guys swapping parts or drilling jets.. id think you could ebay the jet parts and make a spread sheet quick.. same with venturi sizes
 
I have tried disconnecting the primer, also making sure no carb heat is leaking past the flapper. I ran it without the foam air filter element, at part throttle it ran terrible, only improving if I turned carb heat on. It originally had a 10-4894-1 carb factory overhauled in 2001. I replaced it with a MSA factory overhauled 10-4894-1 earlier this year. Both carbs lost rpm at 85% or greater throttle. With the new cylinders I moved the timing from 24 to 28 with little change. It runs pretty good otherwise. The aircraft is a 1965 Champion 7ECA. The air box is smaller than that of a cessna 150, I have thought about installing a 150 air box and testing to see if that helps. I find it hard to believe that all cessna 150's run this way. It is very noticeable on takeoff, has a light stumble right at the last bit of throttle travel. Pulling it back to 85% or so cleans it back up. I have read about the idea that the carb adds extra fuel at full throttle for "cooling", if I thought there was some sort of passage in the carb that provided this extra fuel, I would pound some sort of plug in it and be on my way. I would think this would show up on a flow bench.
 
mk.temp said:
I have tried disconnecting the primer, also making sure no carb heat is leaking past the flapper. I ran it without the foam air filter element, at part throttle it ran terrible, only improving if I turned carb heat on. It originally had a 10-4894-1 carb factory overhauled in 2001. I replaced it with a MSA factory overhauled 10-4894-1 earlier this year. Both carbs lost rpm at 85% or greater throttle. With the new cylinders I moved the timing from 24 to 28 with little change. It runs pretty good otherwise. The aircraft is a 1965 Champion 7ECA. The air box is smaller than that of a cessna 150, I have thought about installing a 150 air box and testing to see if that helps. I find it hard to believe that all cessna 150's run this way. It is very noticeable on takeoff, has a light stumble right at the last bit of throttle travel. Pulling it back to 85% or so cleans it back up. I have read about the idea that the carb adds extra fuel at full throttle for "cooling", if I thought there was some sort of passage in the carb that provided this extra fuel, I would pound some sort of plug in it and be on my way. I would think this would show up on a flow bench.
Click to expand...

Sounds to me that if it runs better with carb heat on or with the filter on that it's running too lean not too rich?

Glenn
 
cubdriver2 said:
Sounds to me that if it runs better with carb heat on or with the filter on that it's running too lean not too rich?

Glenn
Click to expand...

If your climbing and go to full throttle it will drop rpm, if you then lean with the mixture, you get the rpm back.
 
Are you sure it's not an early one-piece venturi? Too rough to be airworthy....IMHO
 
I think your experiencing the conditions I outlined in post #38. The last 1/2" of throttle movement (towards full throttle) allows extra fuel flow for cooling and then you pull it back 1/2" for cruising. My MA-3 SPA has this "back suction economizer system", but not all have it....seems to me like yours does.
If you have Precision Airmotives' PDF on MSA float carb handbook look in section 3 operations Item "F" then have a look at figure 2 to see it.

Google precision airmotives msa handbook
 
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An update to my problems, O-200A in Champion 7ECA, stumbling at WOT / rpm loss. Continued to try many things with no success. Replaced the Brackett air filter with a Donaldson P10-7150 ($98.75). Now, aircraft runs and SOUNDS much, much better. No more stumbling at full throttle. Bigger rpm drop in flight with carb heat, more ground static rpm.
 
mk.temp said:
An update to my problems, O-200A in Champion 7ECA, stumbling at WOT / rpm loss. Continued to try many things with no success. Replaced the Brackett air filter with a Donaldson P10-7150 ($98.75). Now, aircraft runs and SOUNDS much, much better. No more stumbling at full throttle. Bigger rpm drop in flight with carb heat, more ground static rpm.
Click to expand...
Thanks for the update on your solution. I have just been avoiding full throttle position. One of my thoughts is I know my O200 is over propped with a 71-44 which is more likely a good C90 prop. Over propping makes a rich running engine and that maybe I should have a C90 carb on my O200. I have not spent the money to test my theory. I may test your different filter idea.
 
Does anyone ok now where I can find the correct carb for my O-320-A2B. I am getting parts ready for the Kenmore 150HP STC on my PA-12. Any good sources for the purchase would also help.


Sent from my iPhone using SuperCub.Org
 
Does anyone ok now where I can find the correct carb for my O-320-A2B. I am getting parts ready for the Kenmore 150HP STC on my PA-12. Any good sources for the purchase would also help.


Sent from my iPhone using SuperCub.Org mobile app
 
10-3678-32 is the one for the supercub unless you have an early sump. But if I your stc doesn't specify I'm not sure you have to use that one.

Sent from my E6810 using Tapatalk
 
Dont forget to check for a faulty primer. I had that mixture problem on my marvel. No real adjustment, just more of an on/off. Changed primer out and fixed my issue.
 
A follow up to something I have been living with for a while. Too rich of jetting at full throttle, otherwise running fine. After a few years of trying to figure out a feeling that my 0200 was running a little bit rough, I started having left mag drop at run up. OK, new problem I figured. New plugs on the cold cylinder made it better but still not proper. New wires and plugs on bottom, (LH) mag. and still not cleaned up. Slick mag had 600 hrs so off it came and a test mag installed. Problem same. Ugh. Well, back to trouble shooting manual. I knew the plugs were not carboned but were terribly sooty. Well, the only thing I had never tried was the accelerator pump check valve. There is a one way valve that you can access from the bottom and outside of the carb. ( It really only comes into play when you stroke the pump so it can suck fuel from the bowl and then push it past the 'other' accelerator pump check valve. That one is also external and is actually factory set which is supposed to be replaced as an assembly. ) I replaced both and things seemed better after a runup to clear things out. WELL, now the when I advance the throttle, RPM increases all the way to the stop. (It used to drop RPM as I approached full throttle. ) Just thought I would follow up and suggest not to ignore the possibility that the accelerator check valve could be the culprit as I did.
 
It's not unusual to have that check valve flow extra fuel when not needed. Local Old Timer A&P told me he had seen several that were fixed for over rich via replacing. Not sure why they start leaking. Maybe adjustment changes.

Gary
 
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