I do have a question about this inaccurate chart - what is being referred to as “Straight Dia”?

My Honda Shadow 750 uses a pair of 34mm Mikuni CV carbs.  It has the convoluted stock air box and overly-complicated air intake tubes.  The rear baffles on the dual exhaust have been removed.

The prior owner removed the exhaust baffles and there is evidence that someone has been in the carbs.  I suspect cleaning only and not rejetting.  I haven’t dived in yet to investigate, but I need to get in there and do something to eliminate a lean “dead spot” right off idle up to about 1/8th throttle position.

I’ve adjusted the air/fuel mix screws about 1 turn richer and it helps, but the issues still isn’t 100% cured.

Everyone knows this is a bit of trial and error, but dealing with dual carbs that are wedged in the “V” and have to be synchronized isn’t something I want to do multiple times.  The carbs must be removed to do any tinkering.

Stock jetting is front cylinder 40/105, rear is 40/108.  A carb tuning/jet selling website suggests 40/108 front, 40/110 rear with 1 shim (washer) on each needle.  This set-up is prescribed for slightly modified exhaust (part baffles removed) and a stock air intake system and filter.

The next prescription from the calculator is for lightly modified exhaust AND air intake.  It bumps the primaries up to 42 and mains to 110 front and 112 rear with a shim on each needle.

To me, the shims on the needles are going to having the most impact on eliminating the lean condition just off idle and during transition.  In a way, this is akin to shimming the needle on the Savage CV carb to reduce afterfire on deceleration.

Sorry for the long post.  I’m getting to my other question.

I’m about 3.5 turns out on the air/fuel mix screws.  Assuming I find a pair of stock 40 primary jets in the carbs, I’m inclined to go up to 42s (as recommended when exhaust AND intake have been slightly modified).  The shims on the needles are definitely getting installed.  WOT is good.  No real evidence of running too lean up top.  But could it be better?  I’m debating the 108/110 vs 110/112 change.

Please don’t tell me to do “1 mod at a time”.  I can go up on the primary jets from 40 to 42 without an issue - just dial back the air/fuel mix screw to something more reasonable  like1.5-2.0 turns out.  The shims seem to be the fix addressing the lean condition.  What to do with the main jets?

Interested in thoughts, but don’t tell me to do 1 mod at a time.  LOL.  (I’m not overly concerned about mpg.)

Somebody (one of you gurus) tell me to go 42/110 front, 42/112 rear with a shim on each needle.  And if I create a rich condition at WOT, just deal with it and the lower mpg.  Note: using WOT isn’t how I normally ride, but some extra oomph is always welcome!  Maybe the 108/110 mains is my happy medium and compromise.

Gary, your chart definitely makes more sense and agrees with how I think about it.  And the fractions are in the right order!

Any thoughts on my dial-in tuning approach?

Thanks Gary.  Compression is good.  I bought the bike last July with 2600 miles (bike is a 2006 mint condition).  I've added about 1700 miles and at about 4300 total.  Bike is just now getting broken in.  

I'm thinking with the 42s, I should only need to be 1.5-2.0 turns out.  Totally agree about the mid range riding 80%.  It's unnerving to have this lean condition where it's at in transition.

That's what I said about adding a shim/washer - raise the needle.  That's really the main fix as I see it.  The 42s are mostly because I'm turned out 3.5 with the 40s.  Between raising the needles and going up to 42s, my transition should correct.

Thanks Dave.  Yup!  Exactly!  I have to consciously think about it because the Honda has a pair of CV carbs and my S40 has a VM36 (ala Lancer carb swap).  Once you get it backwards and go the wrong way a couple times, it becomes obvious.  lol.

I could probably get away with 4 turns out on the 40 primary jets and get some more improvement, but that’s too many turns out, and then I’d be worried about the screws vibrating out.  Plus, it’s not the best fix for my lean transition issue.  If I wanted to do 1 mod at a time, I’d raise the needles with a shim/washer.  I think that alone would resolve it and I could probably keep the 40s and go with a more normal 2.5 turns out.  Service manual calls for 2.375 turns out as the initial setting and then do the idle drop procedure to dial-in the final adjustment.  Most of the guys on the HondaShadow forum that have tinkered with their stock bike after a carb rebuild or just wanting to tinker have landed about 2.75 turns out with the stock set-up.  None of them are at less than 2.5 turns out (obviously a little lean out of the factory to please the smog gods).

Hey Mike.  Thanks for the clarification of the "straight dia".  I was wondering if that was referring to the non-tapered top of the needle.

I think I may have thrown you off with my talk about the VM36 slide carb.  I'm talking about the CV carbs in my Honda.  So vacuum/piston diaphragm in the Honda CV carbs.  No pics to share.

Thanks for the validation on the larger primaries and raising the needles with shims/washers.  The washers i have are almost 1mm think.  Should do the trick and correct this annoying and nerve racking lean spot.

It's mostly just a feel that I need to go up 1-2 sizes on the main jets.  I don't do much WOT, but when I do it "sounds" like it might be a tad lean.  Then maybe it's supposed to sound that way.  With partial baffles removed, I think I can go up a size on the main jets.