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Jet size help gs750 w/k&n filters

  • Thread starter Thread starter dlanes
  • Start date Start date
D

dlanes

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I got the pod style k&n filters today and after I installed them the bike seems to bogs with more than 1/4 throttle. I think I need bigger jets now, but I just put in 120 mikuni jets for the emigo pods and 4 to 1 exhaust which worked out great. What kind of jets would you recommend? Do you think I need 130 main jets now? It also makes a deeper sound while excellerating with noticable power loss. K&N part number is RC-2454.
 
If you're at close to sea level, or around there (no more than 5-6K feet above) Id recommend around 125 to 127.5 mains, STOCK pilot, and the needle clip at the second slot from the bottom. That should be a good starting point, and you'll need to fine tune from there.
 
The cycle shop I got my jets they only come in increments of 5. So should I shoot for 130s? I keep the needle in stock position for the emgos and it worked great.
 
No. 130 is too rich. You need to be using GENUINE MIKUNI Jets btw... off brand jets are not to be used. They are generally NOT accurately measured, and you have no idea what they REALLY are size wise. You can get REAL mikuni jets from Z1, for acouple bucks each. you will likely need to pick up 125s AND 127.5s, as either may be right, depending. Unless of course you dont mind waiting for the right ones to show up if you only order one size and they dont work. Main jet size is of UTMOST importance. One size too rich or too lean, and the bike will run like hell at some point in the throttle positions. Get the right jets, Mikuni jets will come in "half" sizes (2.5, ie 127.5) and listen to the good people on here, and you'll get that sucker tuned in nice. Dont, and you'll have a crappy running bike, and be frustrated by it. :D You will NEED TO MOVE THE NEEDLE for pod filters. Emgo filters are crap, and the reason not moving the needle worked is because they werent flowing worth a shyte. Pod filters introduce more air at a more rapid pace than the airbox. As such, fuel needs to be introduced at a more rapid pace. Moving the needle clip DOWN on the needle actually moves the needle itself UP in the needle jet. So when you turn the throttle, the tapper is thinner than before at any given point, and allows more fuel past the needle. This is why on the CV type carbs, the STOCK fat, slow tappered needles simply do not work.

If you DONT move the needle, the bike will continue to stumble at about 1/2 throttle, untill you get passed the needle and into the needle main transition. If your Main is right, the bike will take off like a rocket there. But, since MOST people spend more time in the pilot and pilot/needle transition than anything else, i suggest you get the needle set right. On the VM carbs, you will need the right main, and then need to work from the pilot circuit up. On those carbs, unlike the CV type, the pilot is its own independent circuit and is metered by the fuel screw and air screw. The fuel screw is the one on the BOTTOM of each carb. The air screw is the one on the side. Id suggest setting the fuel screw at .75-1 turn out from lightly seated. The air screw start with about 1.5 or so turns out. Do plug chops to see how this set up is working. The pilot circuit is only used from about 0-1/8 turn of throttle or so. From there, the needle comes into play. Since this is where you "cruise", you'll need to sort that out. Oh, FLOAT LEVEL is very important as well. Assure that your floats are at 26mm, or that can have an effect on the leaning or richening of ALL of the circuits...and you'll be chasing ghosts.
 
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The jets I got were mikuni, but they didn't offer them in 2.5 increments. I'll get some 125/127.5 from z1.
 
dlanes said:
The jets I got were mikuni, but they didn't offer them in 2.5 increments. I'll get some 125/127.5 from z1.
Click to expand...


Make sure you get the correct jets there are several types and many of them will fit but they will not work properly.

My '77 GS750B had the same set-up as you're running and I ran 120 main jets and upped the needles one notch. After that it was a matter of adjusting the idle mixture screws. I was in Arizona and the elevation at home was 1200'.
 
Yah, I think I just need to readjust the carbs, cuz I put the emgo pods back on and still bogs. Before it was running very well, better than my friends zr6 rocket :P
 
Dont forget to check the float heights.Too low and the carbs will not got enough fuel.
 
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