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Keihin jetting


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I just bought a 1989 banshee from someone who had it jetted for 7,000 feet(I’m at sea level) I need to rejet it, when I looked at what jets it had, the main jet was 210 and the pilot jet was 32. Everything I have been looking up say around 300 main jet and 27.5 pilot jet. When I call a couple of my local atv shops, they say 300 seems a bit high. It has vforce 4 reeds, no air box and upgraded fatty pipes. What do you guys think I should jet it at?

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1 hour ago, IsaacL said:

I’d say start out by throwing a new set of plugs in it and run it wide up the road to see what color the plug shows. You want it to be a Caramel looking color. 

Ok. I understand that lighter is lean and darker is rich. So if it is lean do I got higher main jet or lower? Vice verse for rich?

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3 hours ago, 375hp banshees said:

Main is: higher the # = bigger hole= richer afr

 

... and 300 &27.5's a good start, might want to go higher than 300 & lean out if needed= safer

& there's more to it than wot & look ...search plug chop

Does the throttle have to be all the way open or just a consistent amount of open? I don’t think I have enough space to get it all the way open around where I live. Also, could I just use cheap spark plugs for the testing or do they have to be some ngk ones

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13 hours ago, Matthew crosthwaite said:

Does the throttle have to be all the way open or just a consistent amount of open? I don’t think I have enough space to get it all the way open around where I live. Also, could I just use cheap spark plugs for the testing or do they have to be some ngk ones

Get the ngk or whatever you’re going to actually run in it. It’s only a few dollar difference most likely. But I’ll give you a step by step of what to do. 
1)warm up your bike so it won’t blow up when you do the test lol

2) remove the old plugs and put in the new ones and do NOT start it. 
3) take your banshee to a place where you can open it up and run full throttle.

4) As soon as you’re ready, start the bike and go. Full throttle through every gear(obviously don’t push it to the point where you’re worried it might blow up). When you reach full throttle in 6th gear, pull in the clutch and shut it off. Coast to a stop. Take the spark plugs out and put the old ones back in. Keep in mind which plug went to which cylinder for jetting reasons.

5)look down the spark plug lobe and look for a coffee or caramel color. Or to make it easier cut the threads off the plug to see it better

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17 minutes ago, IsaacL said:

Get the ngk or whatever you’re going to actually run in it. It’s only a few dollar difference most likely. But I’ll give you a step by step of what to do. 
1)warm up your bike so it won’t blow up when you do the test lol

2) remove the old plugs and put in the new ones and do NOT start it. 
3) take your banshee to a place where you can open it up and run full throttle.

4) As soon as you’re ready, start the bike and go. Full throttle through every gear(obviously don’t push it to the point where you’re worried it might blow up). When you reach full throttle in 6th gear, pull in the clutch and shut it off. Coast to a stop. Take the spark plugs out and put the old ones back in. Keep in mind which plug went to which cylinder for jetting reasons.

5)look down the spark plug lobe and look for a coffee or caramel color. Or to make it easier cut the threads off the plug to see it better

Cool thanks. I might have to take it out somewhere because there won’t be enough space where I’m at.

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31 minutes ago, Matthew crosthwaite said:

Cool thanks. I might have to take it out somewhere because there won’t be enough space where I’m at.

Yea it’s tough to find room to do it sometimes. You could also to a 1-3 pull and when you get in the top of third gear hold the brake slightly to give it resistance and go about 40 yards like that. 

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1 hour ago, Matthew crosthwaite said:

Cool thanks. I might have to take it out somewhere because there won’t be enough space where I’m at.

You really need to get the bike warm enough to get color on the plugs. I would also start at 300 main and 27.5 pilot. Get it into 4-5th gear if possible. Get it good and warm. You want the plug strap to be cardboard colored.

 

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9 minutes ago, locogato11283 said:

Also, just FYI.. Those are Mikuni jetting numbers. Keihin is 45, 48, 50 pilot.. 155, 158, 160 main..

I assume you have OEM Mikuni on it?

Oh thank god you said that because I have keihin carbs. No wonder why everyone was saying 300 but my shops around me were saying like 190. So what would be good for a keihin?

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3 minutes ago, Matthew crosthwaite said:

Oh thank god you said that because I have keihin carbs. No wonder why everyone was saying 300 but my shops around me were saying like 190. So what would be good for a keihin?

If they really are Keihin carbs, you should be somewhere around 165 main and 50 pilot. Those numbers (210/32) before don't even make sense really.

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2 hours ago, Matthew crosthwaite said:

Oh thank god you said that because I have keihin carbs. No wonder why everyone was saying 300 but my shops around me were saying like 190. So what would be good for a keihin?

Start with 160 and that should be rich I’d think. It’ll give you a good start at least. My 34mm Keihin carbs have 155’s but I think I’m going to drop to  a 152 and check that as well

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