Jetting help!

Hello all,been a long while since i been in here(sold my kz) have a question for a friend of mine. The bike is a 1980 kz 1000 and i need to know proper main jet size for it with a open header and pod filters. bike is still running stock jetts and its lean as all hell. Runs ok at low speeds but has that lean pop when rolling fast. Gotta know what size to buy,thanks for any help.

Carbs are 28mm mikunis.

Jetting will depend on whether the accelerator pump assembly is working. Remove #4 pod and manually work the throttle and see if there is a squirt of gas through the #4 pump nozzle into the venturi. If there is, you may want to stay with the #15 pilots and bump main to a #115. If the pump isn't working, you will need #17.5 pilots with the same main jets. Based on all the popping you describe, there is very likely another issue as well... perhaps an air leak.

Post edited by: wiredgeorge, at: 2008/02/21 09:15

The air intake boots are cracked but they dont appear to be deep cracks, is the ok or should they be replaced?

If they're cracked they probably are leaking due to being too hard if not through one of the cracks. Carefully spray some WD40 on the boots without getting it into the carb intake. If the rpm's rise you got a leak. Buy new ones as used ones are a shot in the dark.

Are the pods Emgo's or K&N's?
Do you know what pipe it has and I'm assuming by open you mean no baffle?

15 pilots (stock) and 115 mains might work out OK but it would be nice to know what is in there before recommending another jet size. The mains should be 102.5's if it's an LTD, MKII still stock which were very lean to begin with IMHO. Shafty's had 112.5's stock. How lean is it at idle? Does it pop back through the carbs?

Its a Star open-header but will soon be a Kirker open, no baffle. And the air filters are not k&N's. And it is a chain drive.

Any visible crack in a carb holder and the they should be replaced.

kzmarvo wrote:

Its a Star open-header but will soon be a Kirker open, no baffle. And the air filters are not k&N's. And it is a chain drive.

If it were me, I'd pop a set of 17.5's pilots in and the 115's or 117.5's. You can always try the 15 pilots first but I think you're going to have too large of a transition from 15 pilots to anything larger than the 115 mains when you roll it on and end up with a flat spot in the mid range. Jetting is tweaking after you get in the basic range, there is no spot recommendation on unless you just get lucky. Stock setups are so much easier as you can address the factory lean with no more than 1 or 2 steps in jets. Open baffle 4 to 1's are pretty tricky when trying to jet it for top end (over 6G). Your plugs are going to tell you the most about getting it jetted right unless you have access to a dyno.

If you want the best chance of getting it as close to right as possible be sure everything else is good (valve clearance, compression, spark) and you may have to replace the needles so as to have adjustable clips as a lot of the 1980 and later carbs had fixed needle heights. This will help you tweak the mid range.

I will always be learning carb setup especially on needle jet sizes and performance results. Carb setup for peak performance on any bike with engine, intake or exhaust mods is a learning curve that has no end to it, have fun, drink a beer or six after you get frustrated and try again later! :laugh:

Oh and it goes without saying I guess but be sure to re-balance the carbs after each change you make to be sure it hasn't changed or you're peeing in the wind trying to tweak it!

Why re-sync the carbs after changing jets? Just curious.

wiredgeorge wrote:

Why re-sync the carbs after changing jets? Just curious.

Well I have found that just like year to year they seem to easily come out of balance for no good reason, it wouldn't hurt to do a quick check to be sure nothing got knocked out of adjustment or especially with older boots created a vacuum leak by pulling and reinstalling them. Just good a reassembly practice to get in the habit of IMHO else you might be blaming the new jets when it is a leak or adjustment issue.