1000J performance curiosity's

ok, i'v decided on the pistons i'm going to run in my kz1000J, i'm going for the 1075cc 12.5:1 compression pistons, and i was wondering if i have to modify my head in any way?

ill be getting a valve job, all but one of my shims are in spec.

and will stock cams do fine for now? anyone know if they will provide enough flow for it to run correctly, and do i have to degree it only if i take the cam gears off the cams, or is this required every time the cam chain comes lose?

it has no air filters, the exhaust is also open, the carbs are jetted too rich as it is now, think it will be fine running on aviation 100?

i need opinions and perfomance tips, i'm on a budget but i can get the gas at a good discount from my employer,i know my way around a small block chevy but i have no clue as to what makes these kz's tick.

so please make some suggestions

i dont reccomend anything over 10.25:1 for an aircooled streetmotor,although i have run more than one 13:1 motor on the street they are tempormental overheating beasts in my experiance.i would suggest taking the extra money you need to blow on expensive race gas and spend it on a good porting job and a good set of cams,youll get more out of it by going that route than you will with higher compression pistons and youll be able to drive it without all the headaches.degreeing the cams is done when assembling a motor with a differant set of cams to get the most out of the combination,if you dont remove the sprockets from the cams after that it shouldnt be a problem.as far as no air filters,thats a big no no unless you want to see all that expensive machine work go down the tubes from dirt eating it up,uncorked headers definately give me a warm feeling when i hear one rumbling by but they kill bottem end torque;)

i was afraid of the overheating issues, could a guy still have it tuned to run on 100 at 10.5:1?

you actually wouldnt need or want to run 100 octane race gas if you have a normal 10.25:1 ratio. unless you are expiriencing detonation, use normal pump gas. if you dont have detonation using a certain octane, going up ONLY hurts power. thats because the higher the octane, the slower it burns, and requires a higher compressionn to ignight it. you make the most power using the LOWEST octane of fuel you can get away with without detonation. its a common thought that "if i put in race gas it will work better" not on normal compression motors, only ones that need it. for example, my uncle runs 114 in his drag vette going all motor, he only runs 116 when he needs it(when hes using nitrous)

i guess i should mention its the actual cranking pressure that you need to worry about,but without making things too complicated id say a 10.25:1 motor with a mild set of cams should be a reasonably safe bet to run on 93 octane pump gas with no major issues;)

I bought a new 1982 GPZ1100 and it was pretty much shot by 1983 but already had 24,000 miles on it so I thought it safe to use a Wisco 10.25-1 kit. I forget what kit it was, somewhere around 1130 I think. Boy did that bike run great after that. Only one small but important problem though, I could only ride it about 5 miles before major detonation would start. Biggest mistake I've ever made using that high compression piston setup and this was back when leaded premium was still everywhere. Sold that bike real quick after that and got my MKII which I will always leave stone stock. Everyone else can run these pistons without problem though, so it's probably just me. I have major problems with detonation on the stock Kawasaki's I still ride with 8 or 9-1 compression.

yeah, if you go wild with cams and porting your 10.25:1 motor may need race gas due to the higher cranking compression. like they say compression ratios are only good for bragging;) example, my zx12r has a compression ratio of 12.2:1, but it runs great on pump gas:evil: :whistle:

Good choice with the 1075 10.25:1 motor for the street IMO.

Street Porting, say 88-90 CFM@10" and a set of either

K410 APE - 470-15 Megacycle - or Web 110 cams will get the job done nicely.

Top off with a Dyno Jet jet kit for the stock CV carbs and spice up the exhaust system with your pipe D'jour and you'll have a nice, quick, fun street ride.

PS - Don't forget to double check your suspension while it's down for the rebuild....steering bearings...fork oil / seals...swing arm bearings, etc.

Larry, Are you aware that the same jet needles are used for a GPz750 Dynajet kit as are used for a KZ1000J Dynajet kit as are used for all the 1100cc BS34 kits? With very different needle jets (main jet holder tubes with different diameter openings), the jet needles seldom work well in any BS series application. It is less expensive and more effective to bump the pilot jet up one size (to #40), leave the stock jet needles alone and put in larger main jets (somewhere between #140 and #145 depending on the application). I have STACKS of Dynajet jet needles that HAD to be removed in order to properly tune customer's BS34s. The rest of your advice is spot on. The 10.25:1 kit offered by APE which includes some street cams and a moderate displacement bump is about as radical as a person would want to get if they were interested in all around performance and reliability. If someone wants a purpose built street racer, there are other options but reliability (mostly the ability to shed heat) suffers. I personally believe that the stock 8.25:1 compression pistons offer sufficient performance for a classic bike and if I wanted MORE performance I would start looking at more modern bikes but can understand why some owners might want more modern performance and the look/feel of a classic Kaw. They should just keep in mind that a new 600cc cr will still smoke most any classic Kaw, no matter what mods are done... unless the owner is really into performance mods (nitrous/turbo, etc).

wiredgeorge wrote:

Larry, Are you aware that the same jet needles are used for a GPz750 Dynajet kit as are used for a KZ1000J Dynajet kit as are used for all the 1100cc BS34 kits? With very different needle jets (main jet holder tubes with different diameter openings), the jet needles seldom work well in any BS series application. It is less expensive and more effective to bump the pilot jet up one size (to #40), leave the stock jet needles alone and put in larger main jets (somewhere between #140 and #145 depending on the application). I have STACKS of Dynajet jet needles that HAD to be removed in order to properly tune customer's BS34s. The rest of your advice is spot on. The 10.25:1 kit offered by APE which includes some street cams and a moderate displacement bump is about as radical as a person would want to get if they were interested in all around performance and reliability. If someone wants a purpose built street racer, there are other options but reliability (mostly the ability to shed heat) suffers. I personally believe that the stock 8.25:1 compression pistons offer sufficient performance for a classic bike and if I wanted MORE performance I would start looking at more modern bikes but can understand why some owners might want more modern performance and the look/feel of a classic Kaw. They should just keep in mind that a new 600cc cr will still smoke most any classic Kaw, no matter what mods are done... unless the owner is really into performance mods (nitrous/turbo, etc).

Big bores,Nitrous and Turbos.oh my:ohmy: :evil:

RonKZ650 wrote:

I bought a new 1982 GPZ1100 and it was pretty much shot by 1983 but already had 24,000 miles on it so I thought it safe to use a Wisco 10.25-1 kit. I forget what kit it was, somewhere around 1130 I think. Boy did that bike run great after that. Only one small but important problem though, I could only ride it about 5 miles before major detonation would start. Biggest mistake I've ever made using that high compression piston setup and this was back when leaded premium was still everywhere. Sold that bike real quick after that and got my MKII which I will always leave stone stock. Everyone else can run these pistons without problem though, so it's probably just me. I have major problems with detonation on the stock Kawasaki's I still ride with 8 or 9-1 compression.

I've been riding mine with 10.25 - 1 pistons for a couple of years and have not had any detonation problems running on premium, (it never occured to me try a lower octane gas).
The only time I'm concerned about overheating is getting stuck in downtown traffic on the hottest days.

themachine wrote:

ok, i'v decided on the pistons i'm going to run in my kz1000J, i'm going for the 1075cc 12.5:1 compression pistons think it will be fine running on aviation 100?
i have no clue as to what makes these kz's tick.
so please make some suggestions

1075/10.25, J head, mild cams and I'd stay away from the Av gas. These close to square motors "72/66" can be made to run quite efficintly. This combination can be made to bump the 10s without too much trouble with alittle practice. The "average street squid" on a 600 anything doesn't run that quick. Just don't try to outrun them on the big end.

Post edited by: modprod, at: 2007/03/02 22:36