Kz650 '76 Historic Race Bike

Nice build. I have similar setup. 700cc Wiseco Kit, Andrews #20 Cams (.350 lift), Martek Ignition, Fork Brace, etc etc.

I can tell you from personal experience that 120 DynoJet Mains (112.5 Mikuni) were 1 size too big for me. I stepped down to the 118 DynoJet (110 Mikuni) and the bike runs way better! Should help with that curve you got. Here is vid and pic for reference, note it was still in breakin so the vid doesn't demonstrate her full capabilities. She has 1000 miles on her now and shes is FAST!

Hey Srgt..... nice bike..... sounds and looks good and I kinda wonder about the 117.5s and 120s being a little too rich too..... got a set of 115s for my 29mms instead of starting off with the 117.5s (which I ran with the stock motor) and already have 112.5s and 110s if the dyno air/fuel ratio shows I need em. Always planned on the #30 Andrews cams .370 lift..... even called them and talked it over way back when..... was always dreaming of the 810 or 831 kit too but got cheap and old and decided on the 700. Anyway hope you post more and stick around.

hi there

nice bike! i ran for 5 seasons a big bored gpz750/ 810 kitted in the italian championship, ending up vice champion in 2015.

with the stock carbs, cams and compression, there's very little you can do to increase hp, and indeed your numbers are nice but not race winning material. the most cost effective change you can do is mill block and head to try to get to at least 10:1 CR, cut deeper valve reliefs if you need more clearance. youll be surprised at what just bumping CR can do. from then on you need to dump some money on cams, porting and carbs. VM26 (actually 27mm ID) off a GS750 are still relatively cheap and will be a big improvment over the stock VM24 carbs you have.

search for my build thread for more info, way too much to list

Thanks for the info, 5 seasons
I've got a plan, sort of, which is coming along. I'm getting a set of cams being welded and ground made now in Queensland. They'll have 0.375" lift, and I have a KZ750 head on the bench, stock but with APE valve springs.
The compression ration now should be 10.25:1 with the Wiseco pistons and 700 kit.
And today I finished some new carbs, VM28SC's of a 75 Z1.
I'll need to do the dyno thing when its all together to get the jetting right.
Getting there and it's great fun, I'm really enjoying it

sounds good, very difficult to find best main jet without a dyno,

you could easily go higher CR, my 810 motor is 12:1, puts down a nice 90 rwhp

my old photos dissapeared, so here you go

Who's doing the cams and what kind of money are they talking ? Don't have the cash right now but am curious. Always dreamed of the .370 lift #30 Andrew's grind but never did.

Gpggle GPZ750 modifications and there is a pretty good article on our small blocks. It and others I've read recommend a .020 or .030 cut on the head to get a true 10.5 to 10.7 ratio and that Weisco pistons are not quite 101/4 to one as they state. I get around 165 psi now and before I was closer too 150-155 (with a slightly scored up one at 145) so its up but not sure if its 3/4s of a point ? I don't know....Hopefully its a true 10 to 1.

Of course this would require degreeing them in with slotted sprockets and (have them cut as they are not sold) but "maybe" its something you should do any way if your looking for that last little bit of power. I didn't want to go this far so I elected to just go with the least amount to clean it up and that turned out to be .004 by APE....... Like those carbs too should make a big diff with the cam. Also wonder if you should try to look for a dyno that reads the fuel air ratio too..... that's half the reason I'll probably still do mine.

Ivan Tighe Cams (Ivan Tighe Engineering) in Queensland, the quote was $520.
Thanks for the reference to the article, I'll check it out. Curious about milling the head, especially as its on the bench now, but I'm not an engine builder or mechanic, I just work this stuff out as I go along. I'm nearly 60 and am still working it out
My dyno guys machine reads fuel/air mixtures, probably the most useful feature.
Z750 head all done...

one dyno tip i can give you is to first find the best main jet that gives max HP at WOT
slide carbs are not precise like CVs or injection and going by AF reading is not really productive.

once you have the best main jet, work down the rev range with the needle height/shape only, using the AF as rough guidance only.

my experience is that best AF will feel flat on track, slide carbs want richer then optimal AF

So the Z1 VM28SC carbs are on, with short stacks and foam RamAir filters over. I had a dyno run to check the jetting and all is well.
I guessed a 122.5 main which turned out to be spot on.
With a 17.5 pilot and needles on 2nd it is lean in the first 50% of throttle which I'll have a look into.
Dyno shows only a few more horsepower, but it seems to be a lot more useable. The power would peak and then drop off quickly with the VM24SS carbs, now it peaks and holds until who know what revs. This means I may save a gear change, or win a drag race to the finish line
Next are the cams which when they come I hope will make a noticeable difference.

Was told I should see a good 4 to 5 hp on the top end with the 29s and a stronger mid range and it feels like it on the old 2 lane black top we have around here anyway ........ yours looks good on the top end bet you can feel it too .... can't wait to see what the cam does for you.... will be watching.

Ok, so the incremental increase continue A break between races, I've been doing things which I was hoping would give incremental increases. This time a KZ750 head, which I cleaned up the intakes, not polished, jus cleaned up, and same KZ750 cams. Also added a Dyna 2000. Dyno run today showed it now a touch lean with a 122.5 main jet, so with limited resources we used a 1.30mm drill to enlarge a set of main jets. Best runs now are 67.5hp, so a bit over a 10% increase, which we are happy with.
I have a set of reground cams on the bench which are the next thing, but as I'll have to check the valve/piston clearances I will try and wait until the end of the season. The quest continues ....



Z650B
Wiseco 700 kit
KZ750 Head and cams
Home made 4 into 1
Dyna 2000 ignition; curve 4, 9500 rpm limiter, 35 degrees advance, B7ES plugs
Z1 carbs, VM28SC with short stacks and foam overs. 1.30mm mains, 17.5 pilot, 1.0 slides, needle 2nd clip
(Sitting on the bench) Custom grind cams, “#253B that is 282 adv, 251@0.50” and .375” cam lift”

Wow... this is real data and very interesting. Following.
I wonder what will happen with the .375 high lift cams.