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Mikuni vs Dyno Jet

  • Thread starter Thread starter lhanscom
  • Start date Start date
L

lhanscom

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Are Mikuni and Dyno Jet main jet size numbers the same? I have a Dyno jet kit in my carbs right now, and need to go up a size in the mains, so I'll probably end up getting mikuni jets instead. The jets in it right now are 130's and I'm thinking 132.5's are what I need. Also, the way I've diagnosed this is that, at highway speeds holding constant throttle, it surges. I'm right to think this is the mains right?
 
Could be needle heighth as well. Mikuni mains will work with the Dynojet kits.
 
Would the needle be involved when doing 75mph, and around 5800rpm? I was thinking it would be all on the mains. Thanks for your help.
 
You're still on the needles at that point and the size of the mains shouldn't have that great an influence. The mains take over at about 3/4 throttle. There is some overlap but at 5,800 you're on the needles. Most upper rpm problems are from too rich of a mixture.
 
Very good, how much would you raise the needles? Full notch, half notch?
 
The only way to know for sure which way to go is with a plug reading. You may actually need to drop them. Go a half at a time. I know it's a pain to keep pulling the carbs but that is what you go through to get the jetting as good as it can be.
 
Well at least I have the weekend to tinker with it, although the nice weather is going away again for a while, got all the way up to 50. Thanks alot for the info, and by the way, the pipe sounds great.
 
From my experience,if you can feel surging at 75 mph,I would try a full notch richer. Surging usually means you're beyond a 1/2 step from perfect. I have seen bikes that are running pretty good at that speed,and have no noticable surging,but when you take a plug read,they are still a light gray. It is always better to error a bit on the rich side. KK.
 
Dynojet and mikuni numbers are not the same. 138 in a dynojet would probably be 115 in Mikuni.
 
Yep! Surging usually means too lean. Raise the needles a full notch and see how she reponds.
 
It's been a while since I ran the stock carbs with the Dynojet kit and I don't have them anymore. But, I believe the Dynojet mains were 116's and when I switched to Mikuni mains I was running either 125's or 130's.
 
Thanks for all the info, I raised the needles 1 notch, figuring if I went too far I could just go back half notch. Anyway, it's too cold to go for a ride, so I can't tell if the surging bit is gone, but now when I crack the throttle and raise the rpms to 4000 or so and hold it, it sounds like it wants to back fire. It doesn't actually make a big explosion, just a bunch of little pops, making it sound kinda crackley. Also, I looked at my plugs, but unfortunatly, the last 20 mi of my ride is back roads, and I wasn't experienceing surging there. So my plugs didn't look too bad. Thoughts???
 
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