Rejetting for 76 KZ900

I have had my 1976 KZ900 for 10 years now and last summer had to make a few mods due to original parts deteriorating. Had to remove the original 4 into 4 exhaust and replaced with a Mac 4 into 2 system and installed pod filters. Since then it is harder to start off the line and almost dies at about 1800 RPM in first gear, then goes great after that. I have been told that pod filters and aftermarket exhaust means carbs need to be rejetted to fix the problem I am having.

What I am looking for is some advice as to what to try for jet sizes. The main jets are stock 110 and I know the pilot jets are stock but not sure what size they are. I currently have the carbs all apart for an overhaul as they started to leak some fuel. So any advice someone may have would be a great start for me.

sean5775 wrote:

I have had my 1976 KZ900 for 10 years now and last summer had to make a few mods due to original parts deteriorating. Had to remove the original 4 into 4 exhaust and replaced with a Mac 4 into 2 system and installed pod filters. Since then it is harder to start off the line and almost dies at about 1800 RPM in first gear, then goes great after that. I have been told that pod filters and aftermarket exhaust means carbs need to be rejetted to fix the problem I am having.

What I am looking for is some advice as to what to try for jet sizes. The main jets are stock 110 and I know the pilot jets are stock but not sure what size they are. I currently have the carbs all apart for an overhaul as they started to leak some fuel. So any advice someone may have would be a great start for me.

I just rejetted for MAC 2-1 on my 750 twin. Stock main works best on mine, sounds the same for you if it runs strong at higher RPM and throttle opening. I'd put the stock jet in and see if it runs good.

On mine, when I went one size up on the main it hesitated and bogged a bit when I was accelerating full throttle above about 4K. Jets are cheap, you might want to buy some mains to try for stock and +1 size since that will almost surely be the right range for you.

Mine also ran very lean at low RPM (1K - 2k) and had a bad hesitation trying to accelerate. I had to go from a 45 pilot up to a 50, and I went two slots richer on the needles (move the clip DOWN the needle not up).

Mine runs perfect now.

I have found the needle clip position has the big effect for throttle response off line. You might try dropping your clip two slots and see if it hits for you.

You will know the right pilot jet when the idle "sweet spot" on the mixture screw is maybe 2 or 2.5 turns out from bottomed. Also, I found a good test of the pilot jet is to accelerate as slowly as possible in first gear through the range of about 1k to 2500 RPM. On my carbs, that zone is mainly fed by the "pilot bypass" system in the carb so it is basically defined by the pilot jet and the mixture screw doesn't affect it much.

If it misses and pulls weakly in the low range at very light throttle, the jet is probably too lean. If it is strong but surges, that was too rich. The right pilot jet lets me slowly accelerate through that zone perfectly smoothly.

Hope that helps.

Forgot to add: as always, checking the spark plug color is a good way to see if you are lean or rich. A golden tan is perfect, white is too lean, and sooty black is usually from running too rich.

Post edited by: bountyhunter, at: 2008/03/05 12:50

I know it is running too rich since the plugs are always fouled. Last year I went through 5 sets of plugs and trying to adjust the carbs did not improve anything.
The bike will accelerate smoothly when gradually accelerating. It has a slight hesitation at 1500-2000 RPM when accelerating quickly from a stop. Otherwise it runs strong. The only thing that was suggested to me last year that helped was wrapping tape around the pod filters so that not so much air could get through. That stopped the low end hesitation, but made the high RPM range seem like it was struggling for power at such times like climbing large hills on the highway it lost lots of power when before I could gain speed up the biggest of hills.

I just plan to take this one on a few longer trips this year and am hoping to try and get it running as best as possible. Before the aftermarket exhaust and pod filters it always ran great through all RPM ranges.

I will try some of the suggestions but one answer tells me in a way that smaller jets is the answer but the other says that 1 size larger is probably a start. But jets are cheap and I can try a few out and see what happens.

I will know more when I get my carb gaskets hopefully tommorrow and get the carbs back on the bike so I can test the jets. Any other suggestions would be appreciated.

I know it is running too rich since the plugs are always fouled. Last year I went through 5 sets of plugs and trying to adjust the carbs did not improve anything.
The bike will accelerate smoothly when gradually accelerating. It has a slight hesitation at 1500-2000 RPM when accelerating quickly from a stop. Otherwise it runs strong. The only thing that was suggested to me last year that helped was wrapping tape around the pod filters so that not so much air could get through. That stopped the low end hesitation, but made the high RPM range seem like it was struggling for power at such times like climbing large hills on the highway it lost lots of power when before I could gain speed up the biggest of hills.

That might be why I keep seeing the old pros saying that pods are the Spawn of Satan. You might want to try the stock airbox.

I know it is running too rich since the plugs are always fouled. /////It has a slight hesitation at 1500-2000 RPM when accelerating quickly from a stop.

I can tell you what that meant on mine: I was putting in too big of a pilot jet to try to compensate for the needles being too lean. YMMV. I went two slots rich on the needles and back down to +2 rich on the pilot.

If I could put the stock airbox back in I sure would. But its in horrible shape, all cracked up and way beyond repair. I put it back in for a few years the first time I had troubles with pod filters. I had it all glued up to keep it together but its long seen its day. It was that way when I bought this bike 10 years ago. Only new parts for the airbox that are available anywhere are the ducts but I need everything. I don't like the pod filters mainly because when I get caught riding in the rain the moisture gets in there and it runs horrible, but unfortunately I have no choice but to run pod filters until I may get lucky enough to find a good used airbox. As a matter of fact I could buy the correct ducts and build an airbox which may solve my problems since I do not want pod filters.

sean5775 wrote:

I may get lucky enough to find a good used airbox. As a matter of fact I could buy the correct ducts and build an airbox which may solve my problems since I do not want pod filters.

You can find good used parts at then sites where Ksaki bikes are being parted out (dismantled). I can't access the links from this home AOL computer, but they exist. Do a google search and you will find them. I found all the parts for a 1979 KZ750 from a head to cams to an alternator, coil, strater and the prices are usually dirt cheap compared to new cost.

With an air box, I would think that you could find one.

Last I knew Z1 Enterprises had "NEW" Old style airboxes.
www.z1enterprises.com/detail.aspx?ID=2670

The airbox on Z1 enterprises is for a Z1 and not a KZ900 and I already tried that and it will not fit. They are almost impossible to find. Could have got one once for $600 which was too much I thought, but if I had my time back I would buy it.
I know the coils are good, they were just replaced with Dyna Coils when I did the electronic ignition, which did not change how it ran. The timing is set right, I verified that many times before and after the electronic ignition was installed. I know the float levels are right on, the carbs are properly synchronized.

Anyways I should have my new carb gaskets tommorrow so I will put it back on the bike and try it out. I have a few different jets to try.

sean5775 wrote:

The airbox on Z1 enterprises is for a Z1 and not a KZ900 and I already tried that and it will not fit. They are almost impossible to find. Could have got one once for $600 which was too much I thought, but if I had my time back I would buy it.
I know the coils are good, they were just replaced with Dyna Coils when I did the electronic ignition, which did not change how it ran. The timing is set right, I verified that many times before and after the electronic ignition was installed. I know the float levels are right on, the carbs are properly synchronized.

Anyways I should have my new carb gaskets tommorrow so I will put it back on the bike and try it out. I have a few different jets to try.

I googled "KZ900 air box" and the first post up had a used airbox for $190.

kz900.com/a.html

I'll wager you could find more.

:woohoo: Hey Link to ebay for stock air box starts at 25.00. cgi.ebay.com/ebaymotors/KAWASAKI-KZ900-Z...ash=item150225314954
And any chance you have the right upper exhaust pipe for sale.:dry: thanks Bob/moneypit rke8985@netzero.com