ma3spa carb
- Thread starter swoeric
- Start date
I have pulled my carb apart and i have found that the jet is free and clear. the mixture shaft seems to be unworn and the carb in general looks fresh and new with one exception. the inside of the carb has soot. there is soot around the jet inside and out. there is soot inside the bowl. the soot looks like black carbon from maybe a fire although no signs of heat.
this gets me to my problem i have mo mixture control other than on / off as i slowly pull the mixture back the engines will suddenly hesitate then die if i continue to pull back.
the engine is a c85 any help would be great
this gets me to my problem i have mo mixture control other than on / off as i slowly pull the mixture back the engines will suddenly hesitate then die if i continue to pull back.
the engine is a c85 any help would be great
cubdriver2
FRIEND
upstate NY
mike mcs repair
Registered User
chugiak AK
intake leak allowing more air in from other places???
It's kind of hard to understand your problem.
It sounds like :
During operation as the Mixture is leaned it drops off instantly.
Normally a correct mixture will have a slight rise before it shuts off.
Have you checked ( & how) did you check Idle Mixture?
As Mike said; a leak in the Induction System will cause Lean Operation.
A Lean Mixture drops right off.
It sounds like :
During operation as the Mixture is leaned it drops off instantly.
Normally a correct mixture will have a slight rise before it shuts off.
Have you checked ( & how) did you check Idle Mixture?
As Mike said; a leak in the Induction System will cause Lean Operation.
A Lean Mixture drops right off.
Hardtailjohn
Registered User
Marion, MT
The "soot" that you're seeing is most likely a hose coming apart on the inside. Had that alot, especially if mogas has been used. I look for about a 50 rpm rise just before the engine dies at idle, when the mixture is eased back very slowly.
JH
JH
the engine does drop off instantly from all rpms and temps. i was able to pull it back some with no effect on a -20 day.
I am unable to lean to achieve a max power or rpm rise.
I have been all over the intake and there are not any leaks. I had one before and it caused a bit of popping. This has been remedied. The primer is located in the #1,2 cylinder heads. the spider is completely blocked off.
The only thing I havent checked would be what my actual jet size is and or should be. In theory I would be safe a bit fat because i could manually lean it out..(I plan on Crank and Pistons soon ).
What is the quickest way for me to find the jet size for a c85, 90, 0200, and 0235 ... good chance they are all the same?
I am unable to lean to achieve a max power or rpm rise.
I have been all over the intake and there are not any leaks. I had one before and it caused a bit of popping. This has been remedied. The primer is located in the #1,2 cylinder heads. the spider is completely blocked off.
The only thing I havent checked would be what my actual jet size is and or should be. In theory I would be safe a bit fat because i could manually lean it out..(I plan on Crank and Pistons soon ).
What is the quickest way for me to find the jet size for a c85, 90, 0200, and 0235 ... good chance they are all the same?
Cub Builder
MEMBER
North Central AR
This sure sounds like a familiar problem. Check those things already previously listed, but also check the part number on your carb against the part number specified for your C-85. Make sure you have the correct venturi and jet for a C-85. If one is running a MA3SPA intended for a larger engine, the jet and venturi are likely the wrong size. That makes the mixture control extremely touchy, which is exactly what you are describing. I saw this problem one other time when a friend tried running a MS3SPA off from a 150 Franklin on his C-90. The symptoms were very much as you describe. I know the carb he was using was good as it came off from my Stinson. The solution was to get a MA3SPA with the correct part number for his C-90.
mike mcs repair
Registered User
chugiak AK
is this a NEW problem??? or has it always been like this since you have had this plane???
since ive had the plane. On the tcrafters site most of them had strombergs without a true mixture control or it was wired off.. i was under the assumption this is what i had and never gave it a second thought...then while chasing an intake leak (bad clamp) and oil tank leak (bad weld) I realized i had a marvel..
Cub Builder
MEMBER
North Central AR
So, what probably happened is that someone found a good buy on a MS carb and put it on there in place of the Stromberg NAS carb. It's likely that it's not the correct one for a C-85. Check the part number on the data tag, then compare it to the part number called out in the Kelly aerospace cross reference chart. The part number you are looking for is a 10-4240. If the part number doesn't match that, you've got the wrong carb. Kelly Aerospace has the engine/carb cross reference chart on line at: <http://www.kellyaerospace.com/fuel_charts/Carburetors/Facet_Marvel_Schebler_Carb.pdf>
Steve Pierce
BENEFACTOR
Graham, TX
Yep I talked to them and ended up using a Stromberg. More differences than just the jet between the O-200 and the C85 Marvel.
I've been thinking about your carb and it's issues. How in the hell does soot get into the float bowl?? The only thing that I could come up with is it must at some point been through a fire caused by the primer on the O-200, or maybe even on your C-85 before you blocked the primer at the spider. It must have smouldered for some time to cause that.
The likely culprit causing your lean condition is the float setting must be very very low. Float setting (fuel level) is critical with these carbs and a low fuel level will need much more suction at the nozzle to get the fuel flowing, compared to a correctly set fuel level. You can check this by first shutting off the fuel supply, then remove the bowl drain plug and then install a nipple that you can slide a clear hose over. Tie the hose up so you can see where the fuel level is compared to the bowl parting line...and then turn on the fuel supply. The fuel level should fill up to about 7/16" down from the parting line for a correctly set fuel level.
I'm not 100% certain, but the only differences between most of these carbs are nozzle sizes, idle tubes, and slight changes to the float level.
The 10-4240 is supposed to have a 47-782 nozzle, and the 10-4894 has a 47-799 nozzle....The venturi, idle tube, float level and pretty much everything else is the same between the two carbs.
The likely culprit causing your lean condition is the float setting must be very very low. Float setting (fuel level) is critical with these carbs and a low fuel level will need much more suction at the nozzle to get the fuel flowing, compared to a correctly set fuel level. You can check this by first shutting off the fuel supply, then remove the bowl drain plug and then install a nipple that you can slide a clear hose over. Tie the hose up so you can see where the fuel level is compared to the bowl parting line...and then turn on the fuel supply. The fuel level should fill up to about 7/16" down from the parting line for a correctly set fuel level.
I'm not 100% certain, but the only differences between most of these carbs are nozzle sizes, idle tubes, and slight changes to the float level.
The 10-4240 is supposed to have a 47-782 nozzle, and the 10-4894 has a 47-799 nozzle....The venturi, idle tube, float level and pretty much everything else is the same between the two carbs.
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Steve Pierce
BENEFACTOR
Graham, TX
We had a carburetor that had been in storage for some time with a black soot in the float blow. Maybe some sort of by-product of fuel over the years?
Cub Builder
MEMBER
North Central AR
Eric, Drop me an email at <jscott.planes@gmail.com>. Sometime this weekend, I'll scan in the exploded view and parts list for these two models of the carb and email you the .pdfs.
Steve Pierce
BENEFACTOR
Graham, TX
So will you modify your existing carburetor to meet the C-85 specs?
After changing all the fuel lines from a J3 tank to the gascolator we still had soft black stuff collecting in the bowl. Turns out it was coming from a steel drain plug in the bottom of the tank. jrh
I just took apart my friends 10-4240 and noted a few things while doing this. I also phoned a Tech at Avstar to find out a few things about the set up of these carbs.
The thing that I noticed first about this carb is the nozzle airbleed is completely removed, and the resulting hole is .119"(other carbs are in the neighborhood of .025-.050") The technician said this is normal for this carb, and will allow lots of air to mix with the fuel thats traveling up the nozzle.
The nozzle is a pepperbox style that goes along with the one piece venturi. Its a 47-852 nozzle with a .087" size jet. This is different than the listed nozzle on the parts break down (47-782). The end of the nozzle at the venturi end is restricted ( down to .128") compared to a regular nozzle, I figure this is so the vacuum pulse pulls air through the pepperbox end and emulsifies the fuel mixture further, rather than just pulling the fuel out of a regular nozzle end and not really mixing as well with air. The Idle tube (229-587 -.055") is the same as your carb, and everything else is pretty much the same between the carbs.
Your original problem of no mixture control (assuming no additional vacuum leaks) must be from either a low fuel level, a loose fuel bowl, or a very lean nozzle jet.
Whats the size of the jet in the end of your current nozzle?....Oh and whats the number on it?
The thing that I noticed first about this carb is the nozzle airbleed is completely removed, and the resulting hole is .119"(other carbs are in the neighborhood of .025-.050") The technician said this is normal for this carb, and will allow lots of air to mix with the fuel thats traveling up the nozzle.
The nozzle is a pepperbox style that goes along with the one piece venturi. Its a 47-852 nozzle with a .087" size jet. This is different than the listed nozzle on the parts break down (47-782). The end of the nozzle at the venturi end is restricted ( down to .128") compared to a regular nozzle, I figure this is so the vacuum pulse pulls air through the pepperbox end and emulsifies the fuel mixture further, rather than just pulling the fuel out of a regular nozzle end and not really mixing as well with air. The Idle tube (229-587 -.055") is the same as your carb, and everything else is pretty much the same between the carbs.
Your original problem of no mixture control (assuming no additional vacuum leaks) must be from either a low fuel level, a loose fuel bowl, or a very lean nozzle jet.
Whats the size of the jet in the end of your current nozzle?....Oh and whats the number on it?
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Does it have a one or two piece venturi? There is an AD to either inspect the two piece at annual, or instal a one piece replacement. Sometimes the one piece is a little troublesome so the solution is to put the two piece back in and inspect it at annual. The problems with the one piece is similar to what you described. If you want, I will swap you out for a stromberg 
zenairdave
Registered User
Ontario
I hate to renew an old thread but this seems like the correct spot for this. I have an O200 with the correct ma3spa carb 10-4894-1 with all the current updates that everyone hates. After fixing other engine problems and getting the float set exactly after a few trys, the carb is working fine up to almost full throttle. Past that setting, the rpm drops a few hundred and the egt's fall off. With significant leaning , the RPM's will come back up so I know it is going rich once all circuits and the main jet are pouring fuel in. I suspect this is just the typical new once piece venture richness but it is possible someone a long time ago drilled the darn mixing tube / main jet out while trying to fix a lean engine.
I would like to decrease the nozzle size but unless I can find what the stock hole size is supposed to be, I cant even determine whether to order a new stock size or try to find a smaller tube with the updated pepper box design. So my question is , anyone know what the stock size hole should be for a 47-850 Nozzle assembly? And part two, how would I find a smaller main jet nozzle if the existing one is stock still?
I would like to decrease the nozzle size but unless I can find what the stock hole size is supposed to be, I cant even determine whether to order a new stock size or try to find a smaller tube with the updated pepper box design. So my question is , anyone know what the stock size hole should be for a 47-850 Nozzle assembly? And part two, how would I find a smaller main jet nozzle if the existing one is stock still?
Sorry I can't help with the sizes, I know how frustrating it is to find any info on this.
If you go to the vansairforce website and search "carb nozzle sizes" there is a partial list of sizes there.
Unfortunately your nozzle size is not on the list, but if you do find out the size could you send a note to "GrayHawk" and get him to add it to the list....
If you go to the vansairforce website and search "carb nozzle sizes" there is a partial list of sizes there.
Unfortunately your nozzle size is not on the list, but if you do find out the size could you send a note to "GrayHawk" and get him to add it to the list....
skywagon8a
MEMBER
SE Mass MA6
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:
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:
