New rider, think bike is running rich... how do I?

Hello all,

I just bought my first bike, a 1979 KZ 650C. It's in awesome condition but I'm having a problem... I tightened up the brackets on my carbs but now it seems when I hit higher speeds and pull down on the throttle my bike feels like it's bogging down and experiences resistence, then if I let off the throttle a little it'll start taking off and picking up speed.

So i'm guessing that I'm running rich! I've also had a few problems while idling with the same issue and in lower gears when trying to accelerate rapidly.

If I am running rich, what's the best thing to do to make an adjustment and how much of an adjustment should I make? I don't have an airbox, the previous owner removed it and added some nice pod filters.

Thanks!

Adidas120mi wrote:

Hello all,

I just bought my first bike, a 1979 KZ 650C. It's in awesome condition but I'm having a problem... I tightened up the brackets on my carbs but now it seems when I hit higher speeds and pull down on the throttle my bike feels like it's bogging down and experiences resistence, then if I let off the throttle a little it'll start taking off and picking up speed.



Thanks!

This is a sine of too lean not rich.

I a gree with Otakar, since the stock air box was removed in favor of pod's. It is now running lean because it is getting alot more air. I would pull the carb's and see what jets you have in there. It is probally safe to say the previous owner never re jetted.

Is there a way for me to make an adjustment without needing to rejet the carbs?

If you don't want to get into the rejetting dance, you can always replace the airbox. Ed

i think re-jetting is much simpler, if he doesn't have everything for the airbox, also cheaper.

I don't want to put a lot of money into the whole thing since it runs pretty well, I was hoping I would be able to solve the problem by adjusting the airflow screws.

The screws only affect the throttle in the first 10-15% of opening. To rejet will cost you about $25 if you don't have the jets.

I guess I expected it to cost more than that... Does anyone know what size jets I SHOULD have?

Okay... so I'm looking at this diagram and trying to figure out which jet I'm supposed to be looking at, and how do I figure out what size they are and what size they should be to accommodate the air filters? I appreciate everyone's input in helping me figure all of this out.

Here is the link to the diagram: www.mikuni.com/pdf/vmmanual.pdf

otakar wrote:

Adidas120mi wrote:

Hello all,

I just bought my first bike, a 1979 KZ 650C. It's in awesome condition but I'm having a problem... I tightened up the brackets on my carbs but now it seems when I hit higher speeds and pull down on the throttle my bike feels like it's bogging down and experiences resistence, then if I let off the throttle a little it'll start taking off and picking up speed.



Thanks!

This is a sine of too lean not rich.

And here's why:

I don't have an airbox, the previous owner removed it and added some nice pod filters.

Rejetting and dialing in can be a real time sucker, I have not done it on a 650. My wild blind guess would be +2 sizes up on the main jets and maybe +1 on the pilots.

Once you pull the float boles off the carbs, they will be evident. They will took like a brass flathead screw with a hole unit, roughly in the center of the unit at the lowest part of the float bole. There will be a # stamped in it something like 107.5 ot 97.5 or something like that what ever # it is go two sizes larger for the pod filters one size larger for a aftermarket exhaust if you are running one. Just unscrew them and screw in the new ons. you should not have to mess with the pilots at all.