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Please Help with CPI's and Jetting


NugShee

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Ok guys I really need your help. I cant seem to get it right and need to know some of your opinions. I have a stock banshee with CPI inframes, shaved head with 19cc domes, 2 into 1 K&N Kit, Stock reeds, Bored 20 over, and I use 3 gallons 110 octane leaded with 2 gallons pump gas mixed at 40:1. I started out with 340 main Jet and a 27.5 Pilot Jet and it bogged real bad on the top end. I went down to 320 mains and still boggs bad on the top end. I am afraid of going to lean and blowing it up. can someone please tell me what to do? Am I running the wrong sized Jets or do I need to do something different? Thanks alot for any advice you may have.

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your first mistake is mixing your 110 gas with pump gas that wont fix the bog but mixing your gas just ruins the 110. 110 is leaded and the pump gas is unleaded you should not mix it. What your mix on oil? And what do your plugs look like?

Edited by bansheeboy2004
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Thanks for the help guys. Well I cant do a plug test since it wont go but half throttle. Once I get to my midrange it only bogs and wont go any faster. The K&N did not look over oiled. It is oiled from the factory and the outerwears werent sticking to it or anything. I have been told by the shop that the needle should remain in the stock middle position. Also thought I should add that the carbs are in synk and I was running with the air fuel screw from 1 to 2 turns out. I will try maybe just running strait 110 octane thru it when it gets running but I dont think thats my problem right now. Oh, and I am using redline oil for my mix. Should I go down to 310 main Jets or maybe even 300. What should I do? Thanks again guys, Mike

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If you are wet & black on your plugs with 340 mains Than i would jet down.unti it starts to run at wot open throttle. try 320 test ride if better but not great try 310 than 300 you will find the right main just becareful and watch the plugs.

 

what is your compression Psi at.

changeing your octane level will not help your bog.

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If it's just a flat bog, sounds like it's lean. If you had it too rich, then when it hit half throttle or so, it'd sputter and potentially foul if you kept pushing it. That doesn't seem to be the case here. Try a 380 and see what shee does. It's possible you may have an air leak causing it to run leaner than it should.

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Thanks guys, When I shut it down there is black unburnt gas on the silencer. When it bogs starting at half throttle it doesnt even try to open up or anything. I have heard that CPI's work diferently then most pipes as you go the opisite direction with the Jets. Also It doesnt smoke at all unless just sitting idel when warming up. So I have tried 340 and then 320, you think maybe I am going the wrong direction and should try 360 or maybe 380?

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Well, it sounds like your possibly lean. If I'm confused, and it does get confusing, and I'm unsure if I'm lean or rich, then I'll go up and get it too rich and back it off. Make sense? Like I said, I don't think you should be that high, so maybe there's an air leak, but it does sound lean to me.

 

Also, my machine is not too rich, in fact, I'd like to put a little more fuel to it, and I have black oil/fuel on the silencers, always do and always will I suppose. In fact, I have to be careful lifting the rear or I'll get an oil ring on each pant leg. :confused: But I like it, am I weird for that? :unsure:

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I don't have CPI's but my brother inlaw has them and we ended up with 290's for hot weather and 300's for cooler weather like 50to 70 degrees.

This is at about 2400 elev.

 

300's would make it fall on it's face in 100 degree weather , even with clamp-on filters.

But then again all bikes are a little different , so check your plugs.

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Its basically like a clamp on Filter. You remove the airbox completely and the air filter goes into a "Y" which then bolts onto the carbs. Ok so what Im thinking is that I will Grab a set of 360's and a set of 300's and 310's I will try the 360's first and if it gets worse I will go to the 310 and then possibly the 300's. Now I need to find out if the 27.5 Pilot Jets are right or not. It seems to start and run good at low RPM's but Im not sure if the main jets come in to play at all at low RPM. Anyway, Ill get the Main dialed in first and then worry about the Pilot Jets. Thanks again for all your help guys. Ill let you know what I end up with.

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Ill get the Main dialed in first and then worry about the Pilot Jets. Thanks again for all your help guys. Ill let you know what I end up with.

Yep. Start with the main jets. Once they're set, then adjust your needle in to where it feels good, then get the pilot situated. Get it idling and starting good.

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