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When I first got the bike I bought a Pamco kit, with mechanical advance, coil and plugs. The plugs are NGK iridium BPR7EIX. These only have 91 miles on them.

Wideband oxygen sensors provide a stable fuel mixture reading for someone to use for tuning purposes. They report the exact air to fuel ratio left after combustion.

@5twins I did the same thing with Super Lube synthetic grease, I use it on orings mainly. The entire kit I used from Mikesxs was wrong but the short needle was not doing me any favors. I think the only thing okay with the kit was the bowl gasket....haha. I'm sure I will need to tinker with it...

I decided to put it back together with Z-4 needle jets, 4N8 needles, 127.5 Main and 45 Pilot. It's runs as it should, strong all the way up to 100mph. No more bog in 5th gear after half throttle. I probably need to replace the diaphrams for a smoother transitions. Thanks everyone for the help!

Last week I determined the jetting and other brass used in my 1974 carbs were a weird mix of random pieces. I found the needle jets were Z-4 Mikuni instead of the Z-6 it should be. Would leaving the new style, longer Z-6 impede performance? It does put the nozzle tip higher in the throat of...

I went ahead and ordered all the stock size jets and needles from Yamahaxs650.com. I'm not sure if I can, but it looks like I can shorten the long Z-6 needle jet, so I ordered a couple of them. Fingers crossed it works and hopefully I get the shipment next week.

I wonder if I could shorten the long Z-6 needle jet to match the length needed for the 74-75 carb? Then I could get the correct needle and jets to go with the short z-6.

Honestly, I have no idea. The carbs original to the bike were badly corroded, but I had set from another 74. I did not swap the needle jet, those do show age to them, and both carbs have the Z-4 in them. Where should I go from here? Is there a combination of available parts I should try...

Hello everyone! Long time lurker and searcher but I'm coming up with more questions than answers. My 74 has what seem to be the correct BS38 carburetors. I think I used a MikesXS rebuild kit 10+ years ago and must have swapped our most of the brass unfortunately. I had a situation were the...