bike runs bad at full throttle... what's wrong????

I have a 1975 z1 that I just rebuild recently, I had 1974 carbs on the bike about 2 weeks ago and the bike ran perfect.... But then I put on the correct 1975 carbs and the bike runs like crap now.... I rebuild the 1975 carbs, they were carb dipped and all the passages were blown out with compressed air, I put all the jetting to stock since I have original air box and original exhaust on the bike... When you first fire up the bike it sounds great, it revs up nice and idles nice. But once you give the bike more than 1/2 throttle on the road it bogges downs and loses power, can anyone tell me what part of the carb will effect this problem and what can I check for to correct the problem on these carbs...

Have you synced them?

do you have a new battery.....

battery going bad will produce that same thing


aside form that ...can you nurse them up to speed...can you upshift and get the bike running along....or is when you dump the throttle form like half speed....


also you may really have 76 kz900 and not a z1...unless the carbs look the same as the early ones they are going to be 26mm kz900 carbs

oh and pictures posted,when switching parts and naming models and parts, help folks not type answers that could be avoided in a simple picture

bike,carbs,new carbs....pictures

Fuel level in the float bowls, must be set correctly. This effects the entire carb operation. Also if all the stock jets are installed for that set of carbs on your model bike, did you also set the needle clip position to stock (usually middle notch)?

Del_Herring... Have you synced them?

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Yes I did sinc them

do you have a new battery.....

Battery is good shows 12.9 volts

aside form that ...can you nurse them up to speed...can you upshift and get the bike running along....or is when you dump the throttle form like half speed....

I can't get the bike up to speed it realy won't go faster than 50mph, it really boges down and just sounds like you put a sock in the exhaust pipes, serious power loss, but I can drive below 3000rpms fairly comfortably.

trianglelaguna... also you may really have 76 kz900 and not a z1...unless the carbs look the same as the early ones they are going to be 26mm kz900 carbs

They are definetaly 1975 carbs, and the bike is definetaly a 1975 bike, I did have the 1974 28mm carbs on the bike, and it ran perfectly, the 1975 carbs are also 28mm carbs

Motor Head... Fuel level in the float bowls, must be set correctly. This effects the entire carb operation. Also if all the stock jets are installed for that set of carbs on your model bike, did you also set the needle clip position to stock (usually middle notch)?

Will recheck the floats today, but the jetting is definetally correct double check it on the book and online information and it checks out all ok, I checked the main jet size, secondary jet size, needle clip hight, the correct amount of turns on the air jet, and I even check the part number on the carb slides, it all checks out, and is all correct.....

Not really sure on what to do next on this....

good answers....when my bike wont run above 3000 i always need a battery..it can read right and have a bad cell...

other than that i'm stumped....good luck

gosh ...do you still have the other carbs....something must be blocked...high speed jet....type thingy...

3/4 throttle Is Jet needle

full throttle is main jet

I had a flat spot on mine from 3/4 to full.....went up one on jet needle and up 2 on main jet sizes....bike came around and pulled strong with no adverse effects....my setup is very different but this corrected mine.

Are those New Jets, Mikuni? Old jets could have been drilled out. What Jets were in the 74 carbs that ran good, and what jets are in these carbs?
Main jet sizes would be the same I would think, unless the Air Jet in the Airhorn/ Belmouth is smaller. Needle and Needle Jet might be different, and work together.
Have you pulled the plugs to see if it looks either lean or rich?
Did you make any other changes when you Installed the different carbs? Ignition? Did it sit for a while, maybe the ignition Advancer is stuck? Condenser fail?
To help rule out other issues, putting back to the other set up as before would rule out or confirm other issues.

I had a similar problem with a 1981 KZ1000CSR. Try romping up the street and when it starts to run badly, pull the choke and see if it gets better for a second. This will rule out anything else but the carbs. The carbs on the CSR i was working on had lots of crud all over the little screens that filter the gas going through the need/seat valves inside all 4 carbs. It was filling the carbs enough to run good and go up the street but once you hit about 5000RPM it started to sputter really bad like it had a rev limiter or something and the fuel flow couldn't keep up with fuel consumption. After i cleaned up the seats i couldnt keep the front end on the ground

Kitten Tooth wrote: I had a similar problem with a 1981 KZ1000CSR. Try romping up the street and when it starts to run badly, pull the choke and see if it gets better for a second. This will rule out anything else but the carbs. The carbs on the CSR i was working on had lots of crud all over the little screens that filter the gas going through the need/seat valves inside all 4 carbs. It was filling the carbs enough to run good and go up the street but once you hit about 5000RPM it started to sputter really bad like it had a rev limiter or something and the fuel flow couldn't keep up with fuel consumption. After i cleaned up the seats i couldnt keep the front end on the ground

Good post right there KT.