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S2A Tuning
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Author:  Goodwrench [ Thu Aug 04, 2022 10:44 am ]
Post subject:  S2A Tuning
Hi all,

I recently purchased a 73 S2A for a winter project and after going through the oil system and the carbs, I'm putting a few miles on it to see how it runs before I start disassembly for restoration. The carbs are to spec with the exception of the needle jets. The resource site calls for 220#0- 2/4. The needle jets in my carbs are stamped 214 O2. The engine pulls strong up to 6K then drops off. I'm wondering if the Needle Jets are the issue. Would the 214 stamp vs 220 mean they run leaner?

Jet needles are 4EJ4. Clip is set at #3 from top.
Main Jets are 85R
Pilot Jets are 25

Air box and filter are stock and filter is clean.

Carbs were thoroughly cleaned.

Exhaust is stock. Baffles have not yet been removed and checked (could be an issue I guess).

Thanks for any input.!
Author:  Jim [ Thu Aug 04, 2022 10:54 am ]
Post subject:  Re: S2A Tuning
I'm not up on needle and needle jet designations, but there should be information about that on the resource site. The needle circuit doesn't do much at wide open throttle though, as shown here: http://kawatriple.com/carb/mikunicircuit.html That diagram does point out that the primary choke is important at WOT, and I don't know if your non-stock needle jets have a different choke size.

Are your 85R main jets genuine Mikuni, with the Mikuni logo stamped on them?

It's definitely possible your exhaust system is clogged as you were mentioning.
Author:  Goodwrench [ Thu Aug 04, 2022 11:09 am ]
Post subject:  Re: S2A Tuning
Thanks for the quick reply Jim! :thumbup:

Yes the mains (and all jets) have the Mikuni stamp.

I'll keep playing with it and if anyone has three Mikuni 220#0-2/4 Needle Jets please PM me.
Author:  Jim [ Thu Aug 04, 2022 11:19 am ]
Post subject:  Re: S2A Tuning
I'd check for clogged exhaust pipes next, since the needle circuit isn't going to limit wide-open performance.
Author:  mraxl [ Thu Aug 04, 2022 12:37 pm ]
Post subject:  Re: S2A Tuning
After setting for a while it may be needed to try to run it full on for an extended period to clear crankcase residue.... especially if you are noticing excessive smoke when opening it up. Removing baffles may help clear running issues but clean & replace with new packing.
I doubt needle jets are your problem and finding new stock jets will be near impossible.
Author:  Goodwrench [ Thu Aug 04, 2022 1:49 pm ]
Post subject:  Re: S2A Tuning
Thanks gents.
I'll get those baffles out and see if it makes a difference.
Author:  Jim [ Thu Aug 04, 2022 2:00 pm ]
Post subject:  Re: S2A Tuning
It may not run great without them, but with them cleaned, repacked and installed it will if that was the problem.
Author:  Goodwrench [ Fri Aug 05, 2022 12:31 pm ]
Post subject:  Re: S2A Tuning
Attachment:
DSCN5156.JPG
The baffles were my problem. The LH baffle was missing the retention bolt and the end rod was bent so I assumed that it was stuck and someone else gave up on it. Sure enough it was locked up solid. I don't have a slide hammer so I crafted up an Appalachian baffle puller out of stuff from my junk drawer. I put just enough pressure on the end rod to stress it without bending it further. Then I started and revved the engine. The tension on the baffle released, so I tightened the puller and revved the engine. This process broke the baffle free after 5 or 6 rev / tightening cycles. The other two baffles came out without too much difficulty. I haven't cleaned the baffles yet but on the test ride the dead spot after 6K is gone. It will pull in the front wheel up in second gear and I'm confident I have the issue sorted.
Author:  Goodwrench [ Fri Aug 05, 2022 12:32 pm ]
Post subject:  Re: S2A Tuning
#2
Author:  Goodwrench [ Fri Aug 05, 2022 12:33 pm ]
Post subject:  Re: S2A Tuning
#3
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