Another Stromberg NA-S3A1 Question

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robmorgan
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Another Stromberg NA-S3A1 Question

Post by robmorgan » Sun Mar 17, 2013 19:02

I have a Chief with a a-65 modified to 75hp. I have a Stromberg NA-S3A1 carb. The problem I am having is that going to higher RPM the engine blows black smoke as if it is too rich. It runs fine at idle and runs good after it gets to the higher RPM but it hesitates quite a bit (along with the black smoke).

I pulled the plugs and found them to be VERY dirty (black). I looked had the carb looked at and did a bunch of research on line about them and the mechanic and i decided the float must be off. While we were working on it also replaced the Needle and seat (could not believe how expensive they were). The float was set (no changes needed) and we re-installed. I am still getting the black smoke as well as a small leak while the engine is running. After looking at it the leak is coming from the throat of the carb.

Does anyone have any idea why i am getting the black smoke and why it only leaks when running? I found a guy who can rebuild it but he wants way too much money.

Great Forum and thanks for all the great reading!

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joea
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Re: Another Stromberg NA-S3A1 Question

Post by joea » Mon Mar 18, 2013 10:13

Rob,

My first guess is that your needle and seat are not shutting off the fuel and its over-flowing, thus causing a rich mixture.

Any idea what type of needle and seat and are you running car gas in your plane?

BTW, welcome on board!

Joe a

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Re: Another Stromberg NA-S3A1 Question

Post by robmorgan » Mon Mar 18, 2013 10:50

Just replaced with a new metal needle and seat. I currently have a mixture of 100ll and Ethanol free MoGas.

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hangerash
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Re: Another Stromberg NA-S3A1 Question

Post by hangerash » Mon Mar 18, 2013 11:01

Rob,

JoeA made some good points. Is it a Delran needle (if so did you add the weight to the float?)
Was the needle lapped to the seat when installed?
Are you using auto gas and not the Delran needle?

Richard
Richard

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Re: Another Stromberg NA-S3A1 Question

Post by MikeB » Mon Mar 18, 2013 13:08

If I remember correctly there is a procedure for setting the float level using a column of fuel to simulate the 'head of pressure' in the fuel system. I remember Dave Johnson had a posting some time ago about it. Even though I've rebuilt all kinds of carbs for tractors and trucks I send my aircraft carbs to Bolduc in Blaine Minnesota. Not cheap but they always come back fixed properly. If you have raw gas running down the throat when the engine is running I think you've located the source of the black smoke. While the Strombergs are a simple updraft carbureator it appears they're fussy with the settings.

Mike

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Re: Another Stromberg NA-S3A1 Question

Post by MikeB » Mon Mar 18, 2013 14:08

http://www.joea.com/phpBB2/viewtopic.ph ... 5&start=90

This should be Dave Johnson's posting regarding the carbureator rebuild...you have to go down several posts to pick it up.

Hope this helps!

Mike

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Re: Another Stromberg NA-S3A1 Question

Post by robmorgan » Mon Mar 18, 2013 22:35

Is it a Delran needle (if so did you add the weight to the float?)
No, it is a metal needle. OEM style. No weight added.

Was the needle lapped to the seat when installed?
No, but that is a great idea. It was not leaking before and still blowing smoke. Really seams like it it running too rich but i am stumped. Its warm here in south Texas but not HOT yet. Field elevation is only 600 ft. I checked to make sure it had the correct jet in it and it does.

Are you using auto gas and not the Delran needle?
From time to time when i can get the ethanol free auto gas i use it. I also use a lot of 100LL. probably about a 50/50 mix in the tank now.

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hammmike
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Re: Another Stromberg NA-S3A1 Question

Post by hammmike » Wed Mar 20, 2013 17:53

My primer was bad and it was sucking extra gas when running. I verified it by plugging primer hole in intake with proper size plug and running it around the strip once. Some thing to look at. Plugs cleaned right up .Mike

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Re: Another Stromberg NA-S3A1 Question

Post by robmorgan » Wed Mar 20, 2013 18:35

That is an excellent point! We checked to make sure the primer was working but only that it was shooting gas in not if it was sucking when it wasnt supposed to.... I will check it out.

Thanks Again!

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Re: Another Stromberg NA-S3A1 Question

Post by robmorgan » Mon Apr 01, 2013 01:08

Well, I figured that I don't see too many resolutions to problems posted on many forums and thought i would share what the solution was here. I finally sent the carb off to someone who knew the carbs pretty well (not the $850 guy, who is great but too expensive). Apparently what had happened is that one of the ports had somehow got clogged with some "fuzzy" stuff. No word on what the fuzzy stuff was but what it was doing was not allowing the pressure to equalize and creating a high pressure in the fuel bowl (explanation that i got). I should have it back tomorrow and will put it back on the plane and see what happens.

Thanks to all the chimed in!!!

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