KZ650 Bore Kit need Cams?

Im in with others hear thinking that going to maybe a set of 28mm, or 26mm stock carbs would fix your low end issues. You will loose some top end as the smaller carbs will restrict flow but your bigger cams and bigger bore should still make more top end than a stock motor. If your looking for drivability and some stop light to stop light runs. Stay with what you have and drop the 29’s. Put them to sleep and store them. 

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That is a early clutch cover, kicker hole is using a block off plug or cap. The later motors with no kick starter have a cast boss but no hole. The 750's are flat where the kick start hole would be.




 

It also has a later style points cover with upper / lower case letters, so checking the serial number of the engine to make sure of the year makes sense to me.  Ed

Im here for the dymags and bitchin rear suspension!
Since this bike clearly has had some real money thrown at it I would check if the head has been hogged out for a race application. If the ports and valves are huge no amount of cams/carbs/tuning will get it to run right at part throttle. have you measured the in/ex ports? what size valves? Another thing to consider is compression may be even higher than 10.5/1 if the head was decked.

hardrockminer post=863916I think 29 mm carbs are a bit oversize for that engine.  They probably don't get enough air flow to run properly.  The original 24 mm should be OK but might struggle a bit at the top end.  A set of 26mm off a '76 KZ900 would solve that issue if you ride that fast.

At the higher compression with stock cams you should not have detonation problems but I would use high test gas instead of the stock recommendation of regular.

The VM29 smooth bores flow 75CFM per carb mouth. When the VM29's were introduced they were listed for use by the KZ650 (race motor)

A stock KZ650 head flows 59 CFM, stock 750 head flows 69 CFM, stock GPZ750 head flows 74 CFM.

You can easily attain 74 CFM on a 650 head with stock valves by porting it to about a stage 2 level (I have the flow chart to prove it) Put bigger valves in and its up around 85 CFM or more (depending on how aggressive you get)

Welcome to the KZR Forum SFlesch.  Bunch of good folks here to help.  I really like the paint scheme and as others have commented the parts that have come with your find.  
I have a 77 KZ 650 B1 model.  If yours is an early one like mine, Mine is mostly stock except for suspension.  If I can provide some feedback just let me know.  Looking forward to seeing your new to you KZ up and running.  Please keep us posted.  

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The previous owner who built the bike said it was very rough at low RPM. He said he was constantly playing around with the carbs to try and get it to run better, but never found the right setup. Do you think that could be attributed to too large of cams (0.41" lift) or too large of carbs (29mm)? I'm open to using the high performance parts but want it to be drivable around town. I bought the bike with the engine disassembled as he planned to replace the valve guides, so I am that deep into it anyways. 

Appreciate the advice, as this is all new territory to me! 

 

On my personal 650 street bike I am running 831cc engine with 10:1 compression, big valve ported 650 head (86 CFM) .400" lift WebCam camshafts. I have tried every carb from stock VM24 to VM26, TM33 flat slides, and RS34 flat slides. It runs different with every carb combination. With the smaller carbs it rips off the line but does not pull at higher RPMs which is fine if you want to reduce speeding tickets. Its a drag race monster with the 33/34's. Fuel economy sucks with the flat slides as I have to run a big pilot jet. If I had some 29 smooth bores I would probably be running those.



 

I'm with the "carbs are the problem" crowd, 29 mm smoothbores aren't the easiest carbs to tune, I'd be looking for a set of 26mm Mikuni's off a KZ1000, or you could use a set of BS34's off the GPZ750's, a lot of people don't like them,  but set up well they are a very good carb. I definitely wouldn't be changing the cam, your problem is on the fueling side, remember, 29 smoothbores are essentially a race carb and are designed to work in the higher rev range, I've seen a lot of people struggle setting the smoothbores up on a road bike, I had a set for my bike {GPZ750} but sold them in favor of Mikuni BS34's with a jet kit.  

PS, that's a very nice looking 650, I like everything but those clubman handlebars, a low set of superbike bars would be perfect...

Welcome 

CVK32 Keihim carbs off early Ninja 600 and zr7/s as well can work.
Need the ZR7 manifolds and air box boots (if using an air box).

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hardrockminer post=863916I think 29 mm carbs are a bit oversize for that engine.  They probably don't get enough air flow to run properly.  The original 24 mm should be OK but might struggle a bit at the top end.  A set of 26mm off a '76 KZ900 would solve that issue if you ride that fast.

At the higher compression with stock cams you should not have detonation problems but I would use high test gas instead of the stock recommendation of regular.

The VM29 smooth bores flow 75CFM per carb mouth. When the VM29's were introduced they were listed for use by the KZ650 (race motor)

A stock KZ650 head flows 59 CFM, stock 750 head flows 69 CFM, stock GPZ750 head flows 74 CFM.

You can easily attain 74 CFM on a 650 head with stock valves by porting it to about a stage 2 level (I have the flow chart to prove it) Put bigger valves in and its up around 85 CFM or more (depending on how aggressive you get)

That's good information that I was not aware of but....the current problem is not the top end, but rather the low end.  Carbs have to operate over a wide range of engine power and must be designed to provide the correct fuel/air mixture across that range.  

The information provided was quite general and I tried to provide a general answer.  No mention of porting.  Only the new volume and compression.  I would add that I'm not an engine specialist by any means but I am a mechanical engineer with good knowledge of how the engine components should function as a unit.
 

As 750 R1 mentioned, the VM29s were designed as racing carbs, and as such, they can be really fiddly at low throttle openings and lower rpm. Lumpy cams and large ports can exacerbate the problem by providing less than optimal vacuum signals. Once they get past the pilot circuit, they are excellent. On the street, a set of Keihin CVK or CRS would be great choices for smooth operation across the board. You will likely have to play around with jetting a bit, but there is plenty of help here, and the good jet companies will also offer their knowledge to help you get it sorted. Dynojet, Ivan’s, and 6Sigma have extensive experience with a wide variety of engine and carburetor combinations, so you will not have to start from scratch or go it alone.
clearly, the previuos owner spent a great deal of time and money on high quality mods. When you get it dialed in, you are going to have a really nice hot rod.

This is for the original poster in regards to the smooth bore carbs.
The throttle valves (slides) are very different in those carbs than the standard set for round slide carbs that were originally equipped (VM24)

Below is a exploded view showing the 29 smooth bore slide #29 and jet block #6 :

 

The slide is hollow almost all the way to the top, the jet block is removable and is bolted on from the float bowl side. It is hard to see that the jet block is removable when assembled, it looks like it is machined into the carb body as its throat. The main issue with this design is low throttle tuning because of turbulence, see below :

 

This is a standard round slide carb cross section where the slide has a "bottom" and below is a cross section of a VM29/33 smooth bore carb :

 

You can see how the mixture goes up into the slide causing turbulence, this turbulence reduces as the slide is lifted up into the jet block, there is zero turbulence at full throttle.

This is the low throttle issue smooth bore carbs have to overcome with careful throttle manipulation and precise jetting.

Note : These sections are not exact, they were taken from another source to make a point.


 

The attached photo (taken from the Kawasaki carburetor mechanical training manual) shows the influence of the different fuel systems at various throttle levels in a typical Mikuni carburetor.  One can see that at low throttle it's the pilot system that provides fuel for efficient engine operation.  The various humps and bumps show how difficult it is to provide fuel over the entire operating range.  If high end performance is needed a carburetor that is too small will not deliver enough fuel to optimize engine power.  Conversely at low carburetor performance one that's too big will cause performance issues.  Ideal performance occurs with an air/fuel mixture ratio of about 15 to 1, with a slightly richer ratio at low speed and a higher ratio at high speed. 

Optimal carburetor performance depends not only on the carburetors but also on engine characteristics.  For example, if the intake manifold is too small then larger carbs won't help much.  There was another thread where the question was asked about blocking the air vent ports.  The answer is a definite no because carburetor performance depends on the difference between lower pressure in the carb throat and higher pressure in the bowl to drive fuel up the main or pilot jets into the throat.  The air pressure in the throat depends on the velocity of the air passing through.  The faster it goes means the lower the pressure in the throat, which means more gas being pushed up the jets into the air stream.  The physics behind carburetor design is very simple but the actual design requires consideration of every other part of the combustion system from air intake to exhaust.