XS 750: A Tale of Carb Rejetting Woes


1979 XS 750
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Hi everyone,

I wanted to make this post for my fellow XS 750 owners. Although seemingly few and far between on the internet (R.I.P. Yamaha Triples.org), I want to make this post as an overview of the modifications I made to the intake and exhaust on my bike.

Intake Filters: Uni Pro pod filters (54mm O.D., 74mm Length)
  • I decided to rip off the stock airbox partially because I'm an idiot and wanted it to look cool, and also because the previous owner had destroyed the OEM filter.
  • The first thing I noticed about the pod filters is that they really don't like staying on the carb intakes. If you screw them on too tight, they slip off. When oiling your filters try your best to not get any on the rubber, it makes it super slippery and even harder to get on the intakes.
Exhaust: Delkevic 3-1 Stainless Exhaust
  • The exhaust was more of a necessary modification, as the previous owner hollowed out the stock exhaust making it unbearably loud.
  • Installation was very straightforward, however one of the bolts on the muffler mounting bracket is hard to get in without having a very low-profile allen wrench.

Rejetting: 137.5 Main jet (130 stock), 47.5 Pilot jet (42.5 stock). Needle not adjusted.
  • My model XS750 is 1979, but on the older Mikuni carbs the jets are much larger, this sizing won't apply for you.
  • After making these mods, my bike refused to start. I checked the diaphragms and floats, everything seemed fine. Turned out it was a clogged passageway in the float bowl that controls fuel on choke.
  • Runs great, makes it all the way through the rev range. You'll have to mess around with your mixture screws to get it perfect.

These mods were fairly smooth sailing even for a newbie like me, but I figured I would still share the little knowledge I have after getting so much help from y'all on these forums.
Sounds like you have the short pods with the rubber end caps? If so, they don't flow much better than stock. I know because we put them on a local guy's 650 and didn't need to re-jet at all. A better choice is the 4" long all foam filters. They flow through the ends as well as the sides .....

Uni Pod.jpg

Also, for oiling these black foam filters, you don't want to use the specialty foam filter oil, it's too thick and can clog them. Instead, just use a simple 50-50 mix of gas and motor oil. I bought a bottle of the cheap Walmart brand straight 30wt. especially for this .....