Jetting issue

I think the jetting is off on my 1977 Kz650. It currently has a Kerker 4-into-1 running open baffle, and pod filters. It's been fouling spark plugs pretty fast which leads me to believe it's a rich condition, but I would think it would run lean with those modifications. It runs alright and doesn't really smoke or anything but when I twist the throttle really fast it will cut out and start to die. When I'm high in the rpm range it seems to pull as it should but I've also been told it pops flames when I let off. I also live at about 4800 feet if that has any effect on it. I was reading that 117.5 main jets might make it run better, and the ones I found online look like they will thread in, but they are a lot shorter than the factory mains. Is that what people run when they re-jet? Thanks ahead of time for the advice and the bike is for sale if anyone is interested!

Pics of the plugs? When was the last time the valves were adjusted?
Steve

Here's one of the plugs that I changed out recently. I doubt the valves have ever had an adjustment. It has 7500 original miles on it and I've been planning to do that soon.

First thing I'd do is get a baffle for the pipe. Open pipes are annoying as hell to everyone within earshot of your noise.

Second thing is check the fuel level in the carbs using the clear tube method. Your service manual should have details. The over rich condition could be related to leaking float needles and not due to the jetting.

Are you sure that the plugs are not getting oil fouled because of dried out valve stem seals?

That's where I was going next. Beat me to it. :whistle:
Steve

Not only is it annoying, like Nessism said, you are killing your low and mid range power. Put the baffle in and get a factory air box and filter on it. Then, AFTER you check valve clearance you can go for jetting. Be aware that there is more to jetting than just throwing in main jets. With a factory service manual, a lot of patence, and the help of the good people on this forum tou can have a great running bike.
Jerry

Pulling the baffle kills the top end. Doesn't do much good anywhere else ether. Loud does not mean ponies.
Steve

Used to run 4 or 5 buddy's bikes in our home made 1/4 .... 1/3 and 1/2 mile blacktop...... we got really good at leaving at a 5,000 rpm roll on and was super consistent with the results.Never lost against 3 750 Honda's (one a 16 valve), a 750 Suzuki, 700 Knight hawk, 750 V Honda etc even got a 79 Yamaha 11100 till he tuned it up (well ok the Hawk got me by a bike in the 1/3 but not in the 1/4 but I out weighed him by 90 lbs and his 6th speed trans got me)........

Had the header and open air box installed and the jetting done when we started (30lbs knocked off too gas tank near empty even near drained it a few times ) so I don't have the improvement there but I can tell you removing the baffle didn't do a thing ..... it ran as close to exactly the same as I could tell ....tryed 3 or 4 times..... advancing the timing 2, 4 and 7 degree's same result, Dyna S and coils too although it probably started better...... even going from a 16 tooth to a 15 tooth front resulted in the same felt so much stronger but nope same 2 to 5 bike win. Even tryed a full dose of (Nitro power additive from performance labs) snake oil rip off. :laugh: :blush: