TOPIC:

i picked up an 81 kz 440 that sat for a few years i cleand the carbs, put in new plugs and changed the oil. the advancer was froze up so i clead it up good. its running straight pipes with pod filters on intake so i re jetted but bike wont go over 4000rpm and runs rough but onlt under a load. any ideas?

Sounds like it's still lean, does it have the blunt needles or the tapered ones? What do the plugs look like? How many steps up did you go on the main and idle jets? Needle clip position? Idle mixture screw?

Bone head,
CV carbs + pods + short straight pipes = nearly impossible to tune for smooth running. Depending on where the pipes are cut, you may have a reversion wave pushing the air / fuel mixture back into the carbs at that rpm.
There are several discussion threads on this forum started buy guys who did the same thing, I do not recall a single one that got their bike to run as well as stock.

the valves in the 440 go out of spec very quickly. make sure that isn't part of your problem. if you don't want an air box going with mikuni VM carbs would be much easier. takes no time at all to get them running right.The CV carbs that come with the 440 are so finicky if they haven't been taken care of they can be very expensive/ time consuming to get running correctly even with the stock set up. it's been a year and I'm still tinkering with mine with the air box and all but the VM carb worked good day 1. just a suggestion.
if your dead set on the CV carbs make sure all the rubber in the carbs is good for start. leaking o rings inside the carbs will cause all sorts of problems. check your diaphragms very carefully to make sure they are in good condition as the pod filters will make them more sensitive to external air properties. How do your carb holders look? are they original? The CV carbs can have all sorts of issues with no back pressure. Try stuffing some steel wool in the exhaust to see if there is a major improvement. I know I have seen a few people on here that have mentioned having to do that to fix a bike that had its pipes cut by the PO. if you get a chance throw up a picture of what your working with. most the time I know I'm just scrolling through looking for bike porn
I will also second TexasKZ, I haven't been around as long but I have not seen those carbs work better than stock with that setup.

Straight pipes are dumb. Get some mufflers.

They work on tractors and old HD's'
Steve

punisher11b wrote: . . . going with mikuni VM carbs would be much easier. takes no time at all to get them running right.The CV carbs that come with the 440 are so finicky if they haven't been taken care of they can be very expensive/ time consuming to get running correctly even with the stock set up. it's been a year and I'm still tinkering with mine with the air box and all but the VM carb worked good day 1. just a suggestion. . . .

Sounds like a good idea to replace the KZ400/440 stock CV carbs with VM manual slide carbs, especially when the stock air box is unavailable for whatever reason, as the VM's are better at accommodating pod filters than are the CV's.

Wondering which model's VM carbs would be an acceptable choice for fitting as replacements for the stock CV carbs on the KZ400/450? (Thinking ebay possibilities).

Good Fortune!

Patton wrote:

punisher11b wrote: . . . going with mikuni VM carbs would be much easier. takes no time at all to get them running right.The CV carbs that come with the 440 are so finicky if they haven't been taken care of they can be very expensive/ time consuming to get running correctly even with the stock set up. it's been a year and I'm still tinkering with mine with the air box and all but the VM carb worked good day 1. just a suggestion. . . .

Sounds like a good idea to replace the KZ400/440 stock CV carbs with VM manual slide carbs, especially when the stock air box is unavailable for whatever reason, as the VM's are better at accommodating pod filters than are the CV's.

Wondering which model's VM carbs would be an acceptable choice for fitting as replacements for the stock CV carbs on the KZ400/450? (Thinking ebay possibilities).

Good Fortune!

I know the VM 34 carbs fit directly into the 440 carb holders. this is where I got mine. fairly reasonable.
www.amazon.com/Mikuni-Carburetor-Lever-V...uminum/dp/B000GV8QAO

VM 34 seems kinda big considering that the 900/1000s seem to rock pretty well with carbs in the 26-29 range.

Was thinking in terms of maybe something more like 22mm or 24mm from one of the the smaller fours, or perhaps even the 26mm carbs from KZ900.

Seems like 34mm manual slide would be too much carb for KZ400/440, but I have no experience with using any other carbs on the KZ400/440 other than the stock CV carbs.

For example -- using rough figures -- the KZ1000 has four 250cc cylinders, with each 250cc cylinder receiving air/fuel mixture from a 26mm manual slide carb.
It's okay to fit 29mm smoothbore (manual slide) carbs to a KZ1000, but 33mm smoothbores are usually too much carb for a KZ1000 (i.e., a 33mm manual slide carb for each 250cc cylinder).

In comparison, each 200cc or 220cc cylinder on a KZ400/440 would be receiving air/fuel mixture from a 34mm manual slide carb.

At least that's my [possibly screwed-up] thinking at the moment.

Good Fortune!

probably way big, I agree. I only know that the aperture is the same as the stock CV carbs and that it will fit right into the carb holder. although probably still work a lot better with pods and strait pipes than the CV carbs will

My understanding about VM manual slide bore size is that the "signal" strength (force of draw through the bore, being volume and speed of air being sucked through the bore during the cylinder's intake stroke) is critical to getting the air/fuel mixture into the combustion chamber during the intake stroke.

At low rpm, such as idle, the signal strength is enhanced by configuration of the slide cutaway design and by having to move through the narrowed bore opening due to lowered position of the slide.

When the carb bore is too large, the signal is weakened because the same suction being supplied from the intake stroke is pulling through a larger opening (i.e., the larger bore).

A common example of coping with a too weak signal at idle rpm or low rpm is when a 29mm smoothbore is readily tuneable at lower throttle slide positions, but a 33mm smoothbore on the same engine proves difficult to tune at lower throttle positions due to an insufficient signal in the larger 33mm bore.

Good Fortune!