Stromberg NAS3A1 metering jets for a C90

So in typical fashion I started yesterday to remedy an oil leak, and before I got to the test run I had bled the brakes, removed the airbox for hole elongation remedy and removed the carb for the typical needle/seat small leak that has grown into a large leak. Snowball effect.

Just opened up the carb, and see that the main metering jet appears to be stamped a #48. I need to get a number drill to check this, but was this the original size? I thought it was as listed below but SB-m49-17 also suggests that these are the newer sizes?

My understanding is that these are the jet sizes?
A series 1-1/4" #49
C75 1-5/16" #46
C85 1-3/8" #45
C90 1-3/8" #44

SB-M49-17 states that the cam is changed to the latest design (#531076) to address the back pressure of the standard muffled exhaust, then in addition to valve spring replacement, the jets should be changed to a #44 main and a #55 bleed. It does not state what the previously used jets should be.

So, I have a 788 cam in the C90-8F, and straight exhaust. Without back pressure concerns, and the "second generation" camshaft, what main jet and bleed air sizes are correct?

(800 hrs on the engine, runs good but myself and others have mentioned that it doesn't "sound" like it spins up to WOT as compared to others. WOT RPM is a touch low for a C90, which could be attributed to the 7146 prop, but other info suggests that prop is fine. Plugs look pretty good, typ. carbon deposits, although #2 (RF) plugs were rich compared to the rest, suggesting potentially a cam/valve issue, but this is first I've seen them so I need to track this for awhile)

Quick update, as I hadn't found this info earlier.

Seems my carb is stamped as #A-18033A-3, which has few references online. What I did find on Bob Kachergius's site has it listed as appropriate for a Cont. A-65, A-75, and A-80. Didn't know there was an 80, but anyone know the difference to any of those listed for a C-90?

TCDS shows Bendix-Stromberg NA-S3A1(CMI/TCM P/N 530625, 530726,531126, 530846, 531157) , which seems close to Bob's list.

Thanks,
Peter

Dunno if he specifically addresses this, but here's a link to Harry Fenton's page of misc Continental 4-banger info and tips.

http://www.bowersflybaby.com/tech/fenton.htm

Harry's page has a ton of good info, and while I've read over it numerous times it does not address the specific jet sizes.
Mine is operational and back in use, but I think I'll keep an eye out for a C90 carb that falls within the six type numbers for a C90.

Pb


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Farmboy said:

Harry's page has a ton of good info, and while I've read over it numerous times it does not address the specific jet sizes.
Mine is operational and back in use, but I think I'll keep an eye out for a C90 carb that falls within the six type numbers for a C90.

Pb


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Click to expand...

10-4252-2

cruiser said:

10-4252-2

Click to expand...

Lol. Or, there is that option.

Thanks Jim.
pb

Too many of these carbs have been converted to another model and never had the data plate changed.

Revised my thinking slightly while talking to the folks on the j3 forum. Trying to find the proper jets (44/55) to test. The one installed is stamped a 48 unless it was drilled oversize.

Spruce has a "C85" jet but doesn't say what size it is. Could get one and drill it.


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Pete, Is the engine still running? Don't over analyze it just go burn more gas than Glenn does and all will be good.

Lol, I've considered that a few times Douten.
It's always been just a touch short on rpm, and looking at props also forced a look at other variables that would affect rpm. As the typical Stromberg leak had increased this spring, it was time for a needle and seat anyhow.
Once opened of course you look at everything, and while the goal is to narrow down the right prop size to harness the power, one must ensure the best power/rpm is there to begin with.
If I test a 44 jet and get more rpm, then we know it's not the prop limiting rpm. If rpm doesn't change, then fuel flow is probably just fine.

Edit : My static-WOT level flight rpm range appears on the face to be lower than typical. I will be testing another prop soon, with documented performance on a current C90, so we can get additional baselines.


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Are there mixture controls on the strombergs?

No sir.

Farmboy said:

No sir.

Click to expand...

That's pretty lame... I'd be hunting a new jet, too.

Well it's really not much of a blanket issue CamTom. Properly setup the Strombergs will work quite good, as evidenced by the number still flying. I just happen to have one that I'm suspect of, and it works well in its parameters. I just think it's parameters should be larger. [emoji848]


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Somebody didn't put an intake manifold (spider) from an A65 on it did they? jrh

It doesn't appear so, no step in the spider, straight throat.


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