Carburetor Main Jet-Pilot Jet-Needle

I have a 1980 KZ 1000 LTD I purchased about a month ago from EBay, and has come from California. When I received it I could start it but would only run with the choke on and even then really bad. I have pulled off and rebuilt the carbs. Had the stock jetting, Pilot Jet 15, Main Jet 102.5, and I would guess the stock needle. Bike is mostly stock but does have a Kerker 4-1 header, I replaced the stock air cleaner with a K&N (In the factory air box) have added a pair of Accel coils and wires, voltage was low to the coils (10-10.5v) so I repaired and cleaned some of the wiring as well as build the 12v relay from WG. The other variable is I am in Albuquerque NM and we are at 5000 ft.

While rebuilding the carbs the kit came with 102.5 as well as 105 main jets, I installed the 105. I have adjusted the carbs as well as sync’ed them. Now that it is running and I have a starting point now I can start looking at proper jetting.

While running between idle and about 2800-3000 rpm the bike surges and is hard to ride, especially trying to start from a dead stop. This condition does improve after it has warmed up, but that really seems like quite a while. Once I get past 3000 rpm well hang on, it runs really strong. I ran it up to about 90 mph but chose to not go any faster till I make sure there are no more surprises. The first road test was late evening air was cool. The following day I went for another ride, and most any speed as long as I was just cruising at a steady speed the bike would surge sometimes pretty bad. I could roll the throttle open and would pull really strong, just problem while at a steady speed, while this was happening it was getting pretty hot out. By the time I was going back home the air temp had dropped, and was getting ready to rain, bike no longer was surging.

My conclusion is that I need to fatten up the Pilot Jet by 1 step which I believe is 17, and maybe go 2 steps on the Main Jet. Plan on ordering 2 or 3 different size sets so I can go more if needed. My question however is the needle. The manual I am using lists the needle number as 5CN29, and the drawing breakdown indicates 3 possible needles, 5CN08, 5DL31, & 5CN07. The 3 listed doesn’t include the one that is listed as what came from the factory. I know that some carbs come with adjustable needles, and I have read people are shimming the existing needle higher to richen the carb up between idle and 1/2 throttle. Would I need to shim this or be better off with a different needle, and if so how much shim or which of the 3 different needles?

Sorry that the post is so long but I wanted to include all the necessary information.

Thank You
Jim Smith

jms3257 wrote: I have a 1980 KZ 1000 LTD I purchased about a month ago from EBay, and has come from California. When I received it I could start it but would only run with the choke on and even then really bad. I have pulled off and rebuilt the carbs. Had the stock jetting, Pilot Jet 15, Main Jet 102.5, and I would guess the stock needle. Bike is mostly stock but does have a Kerker 4-1 header, I replaced the stock air cleaner with a K&N (In the factory air box) have added a pair of Accel coils and wires, voltage was low to the coils (10-10.5v) so I repaired and cleaned some of the wiring as well as build the 12v relay from WG. The other variable is I am in Albuquerque NM and we are at 5000 ft.

While rebuilding the carbs the kit came with 102.5 as well as 105 main jets, I installed the 105. I have adjusted the carbs as well as sync’ed them. Now that it is running and I have a starting point now I can start looking at proper jetting.

While running between idle and about 2800-3000 rpm the bike surges and is hard to ride, especially trying to start from a dead stop. This condition does improve after it has warmed up, but that really seems like quite a while. Once I get past 3000 rpm well hang on, it runs really strong. I ran it up to about 90 mph but chose to not go any faster till I make sure there are no more surprises. The first road test was late evening air was cool. The following day I went for another ride, and most any speed as long as I was just cruising at a steady speed the bike would surge sometimes pretty bad. I could roll the throttle open and would pull really strong, just problem while at a steady speed, while this was happening it was getting pretty hot out. By the time I was going back home the air temp had dropped, and was getting ready to rain, bike no longer was surging.

My conclusion is that I need to fatten up the Pilot Jet by 1 step which I believe is 17, and maybe go 2 steps on the Main Jet. Plan on ordering 2 or 3 different size sets so I can go more if needed. My question however is the needle. The manual I am using lists the needle number as 5CN29, and the drawing breakdown indicates 3 possible needles, 5CN08, 5DL31, & 5CN07. The 3 listed doesn’t include the one that is listed as what came from the factory. I know that some carbs come with adjustable needles, and I have read people are shimming the existing needle higher to richen the carb up between idle and 1/2 throttle. Would I need to shim this or be better off with a different needle, and if so how much shim or which of the 3 different needles?

Sorry that the post is so long but I wanted to include all the necessary information.

Thank You
Jim Smith

Next test opportunity after starting and the engine is still warming up, slightly crack the choke and see if the engine accelerates smoother, if it does now you know you need richer pilots. The small bit of raw fuel from the choke is fooling the engine into thinking it has richer pilots. You might also be able to richen up the air screws. You want to maintain an air screw adjustment of about 1.5 turns out. If your engine runs better less than 1 turn, or more than 2 turns you need to make the approiate pilot jet change.

That is how I determined I need a richer Pilot Jet, when I pull the choke on it smoothes out. Kinda hard to ride down the road playing with the choke.

Jim: