XS750 carb tuning

[blakemcelroy2000]

Hey all. Anybody had any luck with tuning the stock ‘79 XS750 carbs in conjunction with V stacks and super chopped exhaust? I was able to get the bike to idle and run fairly well, but upon acceleration, it still has a pretty massive “flat spot” at about 2500-3000 rpm. Would I be better off finding a set of later triumph flatsides? Or are varying tapered needles readily available for this sort of application. Thanks!

 

[650Skull]

Welcome Blake. A few guys on here with XS750/850's.

These old bike's, XS650's/750's and the Suzuki GS's don't perform the best without factory air-boxes, especially in conjunction with chopped headers. Very hard to Tune CV carbs this way, and best is to have at least Uni-filters and long pipes with some sort of Baffle. Preferably a muffler.

Don't think changing needle will help. On our 650's, (with CV's), it is the jets that need to be changed or the clip position on the adjustable needles in conjunction with jet changes. Carbs are set up with the needle and Needle jet a a pair and the jets complementing them from the factory. Changing a needle will throw the whole sequence out and you would be starting from scratch and guess work from there.

search feature will bring up threads that may help.
https://www.xs650.com/search/806553/?q=XS750&o=relevance

I have started to put together some XS750,850 info starting from post #10
https://www.xs650.com/threads/xs650...workshop-manuals-and-other-information.30569/

Bottom of Post #1 is a Carb Guide PDF that is the holy grail to tuning our CV Carbs for the XS650. same principle will apply to your XS750 CV's
https://www.xs650.com/threads/tentative-carb-id-layout.43392/

 

[750triples]

Hey all. Anybody had any luck with tuning the stock ‘79 XS750 carbs in conjunction with V stacks and super chopped exhaust? I was able to get the bike to idle and run fairly well, but upon acceleration, it still has a pretty massive “flat spot” at about 2500-3000 rpm. Would I be better off finding a set of later triumph flatsides? Or are varying tapered needles readily available for this sort of application. Thanks!

If you're running Velocity stacks and new headers you'll most definitely need a rejet. I have my 750 one up on the main and pilot jets, running Uni filters and a much more free-flowing exhaust than stock. Since you've got the same year as me you should have the same set of carbs, but I would double-check because the earlier years used much bigger jets.