Where to have my stromberg NA-SB rebuilt

[N63045]

I think I need to have my carb rebuilt.

Here are the symptoms. Significant mag drop on runup, ususally left. I mean like 600 rpm last time.

One day I did a runup and it was fine, I had just cleaned the plugs. Taxi to the active and have to hold 8 minutes for landing traffic. I goose it a few time in an attempt to keep it from loading up. When cleared for takeoff I put the throttle forward and it starts coughing, spitting etc and develops about half power. Lower plugs are loaded up with fuel.

It looks like the carb is running way too rich. I assume there is a lean/rich adjustment on the carb. An A&P told me that the range of that adjustment is small and that I need to have the carb rebuilt but he does not know where to have it done.

So, all that to get to this question:

Does anyone know where I can have my Stromberg NA-SB rebuilt well for a good price? I know that uni tech will rebuild it for $975 and they probably do an excellent job, but that seems pricey.

Thanks,

Tony

[3Dreaming]

Re: Where to have my stromberg NA-SB rebuilt

You could always try http://thestrombergspecialist.com/ . He will be just as pricey, and he will tell you he is the best. One other thing to check is the primer. If it is not in and locked or leaking it can cause the same issue you are having.

[N63045]

Re: Where to have my stromberg NA-SB rebuilt

Dreaming, I actually just talked to Bob at the strombergspecialist aka uni tech. He told me about the primer issue as well as the possibility that a clogged air filter would cause that problem. I will test the primer first. Thanks for the info.

[M Towsley]

Re: Where to have my stromberg NA-SB rebuilt

Tony,

Bob in Chicago is very expensive. His whole spiel is about how he has obtained FAA approval to lower part of the float bowl to obtain full float movement. Any good carb rebuild shop should check this as it is part of the specs for the carb. I used KPS Airmotive for mine several years ago. They did a great job at a reasonable price and it has run perfect ever since, (knock on wood). Another friend used them right after I got my carb back and his runs great, too. Link: www.kpsairmotive.com

PS, there is a lot of info on this forum about carb problems. The search bar in the upper right-hand part of the page is a great tool to use.

[M Jones]

Re: Where to have my stromberg NA-SB rebuilt

I've had two of them repaired/rebuilt, as well as some other work done, by Aircraft Systems in Rockford, IL. http://acs-rfd.com/

Mine may not have needed as much work, but the price for the last one a little over a year ago was a third of what you've found. I would call them up.

[M Towsley]

Re: Where to have my stromberg NA-SB rebuilt

Hey Mike,

Glad you mentioned that one, I thought there was one at Poplar Grove but now I remember you mentioning Aircraft Systems, (in Rockford), before.

[N63045]

Re: Where to have my stromberg NA-SB rebuilt

I appreciate the info you guys have provided. I thought $975 was a bit steep for a carb rebuild and I will check on the places you guys recommended. If it costs about the same money, I might want to add a mixture control. Although my home airport is at sea level, I like the ability to lean and burn off build up on the plugs if necessary during a run up. I found a place to buy a Marvel carb with mixture control for about the same money as having Bob rebuild my Stromberg.

BTW, Bob was very helpful in advising me about trouble shooting to make sure it was not a primer problem before I rebuild the carb.

I used the search box here and found some info before I posted. I did not see any recent recommendations of a current carb rebuild shop.

Once again, thanks to all of you for the info.

[M Jones]

Re: Where to have my stromberg NA-SB rebuilt

Hi Marty. Yes, they're pro's, and just really good people too.

Good luck with getting things sorted out Tony. A couple of years ago I had problems with some water in the system that ended up in carburetor bowl in my '39. Different than what you're having in that everything was OK on run-up, but when the tail raised, it would also cough and sputter, then stop! A little disconcerting, but plenty of grass still ahead anyway...

[N63045]

Re: Where to have my stromberg NA-SB rebuilt

I called Aircraft Systems in Rockford. They want $850 for a "standard" rebuild on a Stromberg !!! You can buy a rebuilt MS with mixture control for $781 from Aircraft Spruce....but the core charge is $600 --or $300 if you use a stromberg core.

[M Towsley]

Re: Where to have my stromberg NA-SB rebuilt

Tony,

The mixture on a Stromberg carb for these engines does not operate like a regular mixture. Do some searching on the forum for more info. You cannot lean it on the ground like a regular mixture, it will just stop the engine as you advance the throttle. It is not effective until about 5000 feet.

Give KPS a call, I am curious as to what they want. I cannot remember what I paid several years ago but it was no where near that amount.

[Hank Jarrett]

Re: Where to have my stromberg NA-SB rebuilt

These might give you a little help.

Hank

[Hank Jarrett]

Re: Where to have my stromberg NA-SB rebuilt

Can't get one to attach. Sorry for the length pasted into the text.

Hank

Stromberg NA-S3A Idle Mixture Setting
The Stromberg NA-S3A series carburetors incorporate a back suction mixture control. This control is only
effective at higher power settings and therefore cannot be used to adjust the idle mixture. The following
procedure may be used to adjust the idle mixture. Use normal caution when working around a running
engine, especially with respect to proximity to the prop.
1. Run the engine until normal operating temperatures are reached.
2. Adjust idle speed stop screw to desired idle speed plus 25 RPM. If this is not obtainable, adjust to
minimum speed possible.
3. Adjust idle mixture screw in or out as necessary to maximize RPM at the current throttle setting.
4. Repeat steps 2 and 3 until idle speed is at the desired speed plus 25 RPM and no further RPM
increase can be obtained by adjusting the idle mixture screw.
5. Enrich mixture by turning the idle mixture screw counterclockwise until the idle speed decreases
25 RPM to the desired idle speed.

OVERHAUL INSTRUCTIONS FOR STROMBERG NA-S2 AND NA-S3 AIRCRAFT CARBURETORS
Introduction
The Stromberg NA-S2 and NA-S3 carburetors are designed to meet the exacting requirements of small two, three, and four cylinder aircraft engines, such as are used in small airplanes. The principles of operation as described in these instructions are quite similar to those used in all Stromberg aircraft and motor car carburetors. The specification or setting in the carburetor is the result of a great deal of test work conducted by the engine and carburetor manufacturers in the laboratory and in flight, and should not be changed unless it is absolutely certain that a change necessary to meet unusual operating conditions.
Installation
The carburetor should be so mounted on the engine that the float chamber is at the side of the throttle barrel, preferably with the fuel inlet to the rear. Wit the carburetor in this position, the throttle control lever, which is adjustable to any radial position, is at the right side of the carburetor as viewed from the rear of the engine. The fuel inlet is 1/4" pipe tap connection located at the back near the bottom of the main body if the carburetor is installed as above. When the fuel level is set at the factory, a pressure of on-half pound per square inch at the carburetor is used. As these carburetors will undoubtedly be used on engines having a gravity feed system, it is recommended that the tanks be located so that the minimum head of fuel on the carburetor inlet is twenty-four (24) inches under all normal conditions of flight.
Starting
As the carburetor is not equipped with a primer, the following procedure is recommended for starting. With the throttle closed the engine should be turned over two or three times before the ignition is turned on. This will draw fuel up through the idle system and if the ignition is turned on the engine will start on the next turn over. As soon as the engine starts to fire, it is usually necessary to open the throttle slightly to keep the engine running and to warm it up sufficiently for normal operation.
Adjustment
The main metering jet used in the carburetor is of the fixed orifice type, and its size as well as the remainder of the carburetor specifications has been determined by test work as previously mentioned, so that no adjustment for cruising and full throttle speeds is required. An idle adjustment is provided to take care of slight production variations in the carburetors and engines. A small knurled screw near the edge of the butterfly valve, on the throttle valve body, may be adjusted to control the richness of the misture at idling speeds. Turning this screw in a clockwise direction closes off the passage leading to the upper idle discharge hole and leans out the idle misture. Turning in the opposite direction, of course, gives a richer misture. A throttle stop is provided on the throttle shaft next to the throttle control lever, which should be adjusted to obtain the desired idling speed. Both the throttle stop and the idle adjustment should be with the engine not to obtain the proper idling speed and smooth operation.
Servicing
Once the carburetor is properly installed and the idle adjustment made, very little attention is required in service. A fuel strainer is provided near the fuel inlet of the carburetor, and may be removed by the removal of the large hexagon head plug on the side of the float chamber. A small square head plug is provided as a drain in the bottom of the carburetor. The strainer and drain plug should be removed frequently to get rid of any dirt or water which may have accumulated in the strainer chamber of the float chamber. The entire carburetor should also be inspected to see that all parts are tight and properly safetied.
DESCRIPTION & FUNCTIONING OF CARBURETOR
Float Mechanism
A conventional hinge type of float mechanism located in a float chamber having ample fuel capacity to operate in all ordinary maneuvers in used. This float mechanism is adjusted at the factory to obtain the proper fuel level, and requires no adjustment in service unless it is necessary after a long period of service to install new parts. For information concerning the proper level see the section of these instructions pertaining to "Overhaul."
Main Metering System
The metering system used in the carburetor is of the plain tube type with an air bleed to the main discharge nozzle. The main discharge nozzle is located at the center of the venturi and is screwed into a boss projecting into the air intake. The main air bleeder is screwed into the air bleed arm which is held in place by the main discharge nozzle. The actual metering of the fuel is accomplished by the main metering jet which is assembled in the bottom of the float chamber in a channel through which the gas flows to the main discharge nozzle. The size of the main metering jet affects the fuel consumption at all speeds approximately 1000 RPM to full throttle speed.
Idling System
Inasmuch as the main metering system will not function at a very low air flow (low engine speed), an idling system is provided. This consists of an idle tube with an idle metering orifice in the bottom and several air bleed holes in the wall, an idle air bleed, and two holes in the throttle barrel, which act as idle discharge nozzles. A needle valve type of adjustment is provided on the upper discharge nozzle, which regulates adjustment is provided on the upper discharge nozzle, which regulates the quality of the idle mixture. Fuel for the idle system is taken from the quality of the idle mixture. Fuel for the idle system is taken from the annular space around the main discharge nozzle, passes through the idle metering jet and mixes with the air from the idle bleed located in the main body behind the venturi. The air enters the tube through the bleed holes and the mixture then passes out of the upper or lower idle discharge hole. The relative quantities passing through the upper and lower idle hole depends upon the position of the throttle. At extreme idle, all the fuel passes through the lower hole. The idle system operates up to an engine speed of approximately 900 to 1000 RPM.
OVERHAUL
Disassembly
The carburetor should be disassembled for cleaning and inspection each time the engine is given an overhaul. After the carburetor has been removed from the engine and the hot spot and air intake or heater taken off, the halves of the carburetor may be separated by removal of the filister head screws at the parting surface. The venturi is held in the lower half by a hexagon head screw.
Remove the set screw which holds the float fulcrum pin in place and the plug at the side of the carburetor, which will permit the removal of the float fulcrum pin. The float and the float needle valve will then come out and it will be possible to remove the main metering jet which is located below the float. Remove the idle tube which is screwed into the main body. If there is any indication of dirt or foreign matter in the float chamber, it is advisable to remove the main discharge nozzle. The removal of the above parts will permit a thorough inspection and cleaning of the carburetor, and unless replacements are necessary, further disassembly is not recommended.
Inspection and Cleaning
The bodies and all parts should be thoroughly cleaned in gasoline, and all passages blown out with an air hose.
The float needle valve and seat should be inspected for wear and if the needle valve is badly grooved, both parts should be replaced. The needle valve is made of stainless steel and the seat of naval brass so that under ordinary service conditions these parts should last for many hundreds of hours. Check the main metering jet and float needle seat to make sure that they are tight. It is important that the throttle valve fits the barrel tightly when in the closed position and that the lower edge be flush with the top of the lower idle hole.
Reassembly
All headless screws below the fuel level should be assembled with shellac, being careful not to get any on the end of the plug where it will come off and be carried by the fuel into one of the metering orifices. Headless screw plugs above the fuel level and all other threaded parts screwed into the bodies should have a compound of graphite and caster oil put on the threads.
The float level on these carburetors should be 13/32" below the parting surface and is dependent upon the thickness of the gasket under the needle valve seat. The level should be checked under the same conditions encountered in service as regards the fuel used and the fuel pressure or head at the carburetor. The levels are set at the factory with a pressure at the carburetor of one-half pound per sq. Inch, (19" gasoline at .710), and this recommended for setting the levels in the field. If, after fitting new parts, the level is not correct, remove the needle valve seat and put in thicker gaskets to lower the level and thinner gaskets to raise it. One-sixty-fourth inch change in gasket thickness will change the level approximately 5/64".

[Robert Lees]

Re: Where to have my stromberg NA-SB rebuilt

<snip> A couple of years ago I had problems with some water in the system that ended up in carburetor bowl in my '39. Different than what you're having in that everything was OK on run-up, but when the tail raised, it would also cough and sputter, then stop! A little disconcerting, but plenty of grass still ahead anyway...

Here's my video of exactly that problem in exactly that aeroplane in July 2012! Easterly runway at Dacy; it caught me by surprise (as these things tend to do) and I'm glad I backtracked the whole length before take-off on this occasion! Subsequent flights that day were uneventful.

Link: https://www.youtube.com/watch?v=hYckrzxlclE

Rob

[M Towsley]

Re: Where to have my stromberg NA-SB rebuilt

Hank,

I have torn down, set the float height, and reassembled these carburetors. All under an A&P/IA's observation, (who hadn't a clue how to do it). If you don't have the right tool, which is a large machined piece to remove and adjust the float seat, instructions on how to do it are not going to help. You also need to have a perfectly level base to work off of and a piece you can set the carb into, for the carbs protruding studs, that is also perfectly level to even start the procedure. Not to mention all the gaskets to set seat height. It can take several days to make sure there are no leaks through the needle and seat, and that is if he even has the right needle and seat. It is such a PITA that I decided to have KPS do mine after having my engine stop of final one day. (It had a blocked idle port). KPS got it right the first time.

The pictures below are a tool I had made out of a Craftsman socket adapter. You cannot use a screwdriver to remove the seat, it can easily be damaged.

[N63045]

Re: Where to have my stromberg NA-SB rebuilt

Hank, Thanks for posting that great info on the Stromberg.

Marty, I understand about the Stromberg mixture system. If I stay with Stromberg I will stay with the B model without mixture control. If I go to the Marvel S, I will probably go with the mixture control.