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Mikuni vs Dynojet

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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The main jet that I took out had 122.5 printed on it, and the one I put in was a dynojet 130. Did I put in a smaller jet than what I had and does anyone know approximately what size 122.5 would be in a dynojet?

Also what does moving the needle clip do, as in which way adds fuel and which way reduces it?
 
Lowering the clip richens the mixture by raising the needle. That's where the taper on the needle comes into play. As the throttle is opened the needle goes up which allows more fuel to be pulled into the air flow. As the needle goes down the taper widens which closes off more of the needle jet hole. Lean the mixture out by raising the clip and that lowers the needle.
 
I know a 138DJ is very close to a 130 Mikuni. So a 130DJ would be very close to a 122.5 Mikuni. There are comparison charts on the web if you look. There was one at this site recently but the sizes did'nt go down that low. Maybe doing a search here will turn it up?
 
robinjo said:
KEITH KRAUSE said:
I know a 138DJ is very close to a 130 Mikuni. So a 130DJ would be very close to a 122.5 Mikuni. There are comparison charts on the web if you look. There was one at this site recently but the sizes did'nt go down that low. Maybe doing a search here will turn it up?
Click to expand...

This one? http://www.vmaxoutlaw.com/tech/dyno-mikuni.htm
Click to expand...
Yeah. That's the one that does'nt go down low enough in this case.
Just looking at the chart quickly, it seems to me there's probably a mathematical formula to determine matches.
 
looking closer at that chart, it also says it is a size comparison. But it says they flow differently because mikuni's are chamfered, does this mean that if the 122.5 is close to 130 in size would it possibly flow like a 134 or is the difference in flow only very slight?
 
Bike is running mostly smoothly again. I put the 122.5's in and lowered the clip one notch. There is a significant difference in the 122.5's and 130DJ's. It doesn't get almost any power below 2-2.5k rpms. Could this be due to out of sync carbs, or wrong fuel mixture screws? It also pops on decel.

I remember also someone suggested a while back to switch spark plugs to either colder or hotter to fix popping... Anyone have this experience or remember?
 
booboo13 said:
looking closer at that chart, it also says it is a size comparison. But it says they flow differently because mikuni's are chamfered, does this mean that if the 122.5 is close to 130 in size would it possibly flow like a 134 or is the difference in flow only very slight?
Click to expand...
The DJ's are determined by the size of the hole. 1.3mm is a 130.
Mikuni's are determined by the cc's of fuel that will pass through in 1 minute. A 130 DJ is very close to a 122.5 Mikuni. Neither jet will flow like a 134.
In my opinion, if you now notice a significant change (based on your latest post) it's not because of the main jet swap. It's most likely moving the needle or poor carb synch or ?
 
I'm guessing I need to still get a 134 at least and put the needle back up to #3. This will probably solve all problems, don't you think? But at least its rideable =]
 
The mains are not causing your popping and I doubt the 2,000-2,500 rpm loss of power. The mains take over at 3/4 throttle and above. Decel' popping and low rpm problems are generally pilot circuit problems, but the jet needle can have an "overlap" effect at lower rpm's.
You have to test at different throttle positions and take plug reads to get an idea of what each jet circuit is doing.
 
before I changed the jet needle the low end was essentially good so that's why I think putting it back and going with an even higher main will be what I need to do.
 
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