View Full Version : jet size for an 81 kz650 with pod filters???

08-14-2009, 7:53 PM
what would be a good jet size for my 81 kz650 i've got uni pod filters on it and i live in colorado so its higher altitude. i dont know anything about deciding what jet size. so if any of you know all about that shit, please give me some help ha

08-14-2009, 8:03 PM
someone had suggested to me either 100 or 102.5

does that sound right?

08-14-2009, 11:20 PM
i mentioned this in the thread about that doods 88 suzuki pipes and his rejetting question. How about a rejett tech thread!? someone should do it

08-14-2009, 11:30 PM
fuck thatd be amazing. how do you even calculate jett size??? carbs are too damn confusing haha

08-15-2009, 5:09 AM
What size jets are in there now?

08-15-2009, 9:40 AM
Don’t forget the idle mixture screw, idle jets, and needle position. Oh and synchronize them every time you change stuff out.

Most people who mess with carbs do it wrong. The stock airbox is almost always faster with 20-50% better fuel economy.

If you must have pods, take it to a shop with a dyno and get it done right.

As far as altitude, the higher you go, thinner the air. This enriches the mixture. To correct for this you must lean the fuel metering (jets, needle position) put pods on and it leans the mixture (more air).

So you may not need much I'd start with the needle position (this is your mid range or 2/4-3/4 throttle) Move the needle up in the slide. If it has an adjustable clip move it down, if it doesn’t, put a thin washer under the clip. I say start here because it’s free and you will use this part of the power band most. Next play with the idle mixture screw and then last the main jet to clean things up. You may only need to go up a few sizes. They typically jump in increments of two. So if you have 98 main the next size will be 100, 102, 104 and so on.

Go read up on a how a carb functions and you will have a better idea of what you need to do.

08-15-2009, 11:59 AM
awesome post man,thanks a lot.

08-26-2009, 2:48 PM
yeah something about it would be awesome i found a step by step tech tip on cleaning them but not jetting

08-26-2009, 5:11 PM
don't change anything, just ride it, let it spit and pop, it'll probably last til you get tired of it. then.....ebay

08-26-2009, 8:30 PM
don't change anything, just ride it, let it spit and pop, it'll probably last til you get tired of it. then.....ebay

Yea, run it lean and blow a hole in the top of the piston... rookie.

08-26-2009, 9:07 PM
I agree with EIGHT[If you must have pods, take it to a shop with a dyno and get it done right.}I did and would have never got them right on my own{Believe me i tried many times.} .I asked a lot of people that swore by their combo of jets and shimmed needles but i found out every pod and pipe has a little different air flow. It will cost some but what good is a bike that dont run right. As an example their were two guys that have close to the same set up as mine and are very happy with 75 primary and 110 secondary .[Stock was 68,s and 75,s}After i took mine to the shop they figured it would take 107,s and 110,s. and had to shim the needles 30,000th.Thats a big difference.Hope all works out well.

08-26-2009, 9:30 PM
Yea, run it lean and blow a hole in the top of the piston... rookie.

haha exactly what i was afraid of doing!

08-26-2009, 9:32 PM
i've shimmed the needles and its already running a thousand times better. but i'm pretty sure i've got a vaccum leak from the old rubber that the carbs mount on. its dried out as hell. so hopefully once i replace that shit it will run even better

08-26-2009, 10:29 PM
Spray some carb start on the intake manifolds while the bike is running. If the engine bogs or speeds up you have a leak.

08-27-2009, 12:58 AM
i just replaced my intake rubbers on my 650. It runs a thousand times better, but I still need to get it dialed in

08-27-2009, 12:34 PM
did you ever pull the plugs? how'd they look? how long has that bike lived in CO?

The pods could effect the mixture as much as the jets.

08-27-2009, 2:03 PM
Justin - I just found a good write up explaining how to dial in the mixture screws. This is of course once it's jetted properly.

Set all pilot screws to 1 and 3/4 turns out. This is a lean setting, but at least we know where we are starting.
Start the bike and set the idle at about 1,500 till it warms up enough that the fan kicks on.
Reset the idle down to about 800 rpm.
With someone watching the tachometer, SLOWLY unscrew the pilot needle on #1 carb till the idle climbs and stabilizes, then go another 1/8 to 1/4 turn.
Reset the idle back to 800 rpm and set the pilot screw on carb #2.
Drop the idle back to 800 rpm then repeat this process with carbs 3 and 4.

Now, you have the pilot circuits set correctly and the needles have been dropped.

Take the bike out and ride it. There should be no flat spots when you roll the throttle open. It should be very crisp (a little throttle change gives you a corresponding power change).

If there are flat spots or the bike seems to hesitate, raise the needles 1/2 a clip when you get home. If there are no flat spots and the throttle is crsip, you are good to go.

When you roll off the throttle, there should be no more than the occasional pop if any at all. If it is popping badly, then open the pilot circuits an additional 1/8 - 1/4 turn. Stop there.

If the engine is a little 'mushy' (not crisp) after dropping the needles a full notch, then drop them another 1/2 notch. When it is getting the fuel air mix it likes, it will be very crisp with no flat spots. The perfect setting is to lean it till you get a flat spot, then raise the needles 1/2 clip.

I just did this to mine and throttle response is so much better.