Rejetting Question

Ive met a lot of friendly, knowlegable guys in here so I dont want to take this question to another forum.

Im dealing with a 77 XS650 and the stock jets are 122.5 Main and 25 pilot. The PO put airpods on the bike and 2 into 1 exhaust. Im not sure what jets he has in it (Im on a business trip and its late and I have some downtime). I was told that moving up to 127.5 main is too small, and 30 pilot is too high.

I bought 127.5 main and 30 pilot at the suggestion of someone who I thought knows what he is talking about. Now there is some doubt.

The bike backfires on deceleration, runs hot and is DEFINITELY running lean.

Do you think a 137.5 Main and 30 pilot jet might cure this issue?

And would some please explain the difference in from a 122 main to a 127,5? Like, how much more fuel is let in with a 127,.5, and how much MORE would a 137.5 let in? Im running really lean

I would think there's an XS650 site where you can get fairly precise guidance on what jets to use with your setup.
From the diagrams at partzilla the 77 XS650D has cv carburetors, so that adds some difficulty to the tuning.

In general you would increase the jets 1 or 2 sizes for each intake & exhaust change and also adjust the jet needles. I don't know if you can raise the jet needles on cv carbs. Comparing the specs at motorcyclespecs.co.za, the 750B is similar to the XS650D. The 650D has 88% of the displacement & 96% of the max power, so the jetting on a similarly modded 750 Twin should be a good guide. The Yamaha has Mikuni BS38 carbs & I'm assuming the Kawasaki has mikunis as well. the spec page just says they're 38mm.

I had a 78 xs650 until recently, the problem you speak of is common to all bikes that use CV carbs mixed with pod filters it just does not work you can fiddle around with jets all day long and you will either get it right at lower or top end running another reason why performance bikes owners change to round slide and flat slide carbs, the very best thing you can do is to get stock air boxes or change carbs to non CV, with the aftermarket exhaust i ran a Delkevic two into one with all supplied baffling (still loud) and did not have to re-jet, but with some exhaust you may have to come up one or two sizes on each pilot and mains, There is always some sort of bun fight going on in the XS 650 sites about this subject and many fart around trying to get their bikes to run with pods and reckon they have it running perfect until you hear it and it runs like a pig. Stock airboxes is the way forward.