650 engine upgrades

Hi all, I have searched the archives and found alot of information on the many enhancments that can be performed on the 650 engine. My question is what is the best bang for the buck to increase power without totally rebuilding the engine (I am not a skilled mechanic)?

I just got a 1977 kz650 c1 parts bike and plan on learning as I go on my first complete dissassembly. I am planning on going with a modern mono-shock rear and a newer front end, and just want a bit more than stock. While I have it appart what can I do that is inexpensive, but will give me a bit more oomph?

Thanks in advance, and as soon as the rain stops, I will post a few before pics...

A little bit of porting in the right places can add some oomph. I had mine done years ago at a shop. They did it on there own during a rebuild. Try to find out the proper areas to shave, it may be something you can do yourself.

If I'm not mistaken, where the rubber boots from the carbs connect to the cylinder head, there's a bit of an edge in the metal that can be removed and smoothed. And then also around the valve guide area. But again, you really need to know where and how much.

Having gone through this twice with my '77 650 in the last 14 months, here's my 2 cents worth. If the bike is still running strong and compression is good leave the guts alone.

Check the valves for clearance and lap them if needed. Soak and clean out the carbs, port the head taking out just enough to give good smooth airflow (remove the casting edges using a variable speed drill and aluminum cutting bit,) hook up the coil wiring modification (from wiredgeorge in the tech section) and throw an inexpensive header pipe on the bike. With the pipe you will have to rejet and kzr members will give you lots of advice for recommended jetting sizes.

The above listed massaging wilth a check of the ignition should help wake up the bike and it will cost you probably ony $350-$500

Cheers-Colin Firth -Ontario Canada

Here's a pic of what the 650 looked like last season...coming soon...

'77 Kz 650 Custom - (Miss July on 2006 Kzr Calendar,) Newest rebuild includes Wiseco 810 kit, Kz750 cams, Kz750 intake valves, 750 GPz springs, Ported head, WG Mikuni 28's, Velocity Stacks, Dyna Ignition and coils, MAC pipe, 14 tooth front sprocket, going back to original '77 Moon Dust Silver. Goal is to have a stock-looking bike that will tighten up any loose dental fillings off the light.

Another thing to consider, might be getting a 750 block and pistons if you can get them cheap, might be a bit rare tho. if they are in good shape it would be a good displacement bump without any costly oversize piston kits. and if you ever do plan on going over sized in the future, the 810 kit would be another jump in power

reborn650 wrote:

port the head taking out just enough to give good smooth airflow (remove the casting edges using a variable speed drill and aluminum cutting bit,)

you wouldnt happen to have any pics of your head after this work would you?

The above listed massaging wilth a check of the ignition should help wake up the bike and it will cost you probably ony $350-$500

You can also look for a KZ750 motor (generally $250-$350) and bolt in an additional 10-11 hp with the capacity for more.

It depends on what you want to do

if the motor is tired or you have a spare you just want to freshen up a good stock rebuild and blueprinting can make quite a differance.these motors are built on a production line,no two ever turn out exactly the same.if you can get away with stock bore with just rings and spend a little money on a good valve job and clean up ports ,just straighten up the rough spots dont try and hog the ports out youll do more damage than good.good springs and a good set of drop in cams.a set of 26s a decent header and an electronic ignition and you should a have a pretty reliable good running little bike that should keep you entertained till you grow into something bigger. goodluck,happy wrenching!

...and a good set of drop in cams...

What would be a good set of drop in cams for a 650?

steell wrote:

You can also look for a KZ750 motor (generally $250-$350) and bolt in an additional 10-11 hp with the capacity for more.

Shouldn't it be badged a 750 then? Better get new sidecover emblems

Has anyone done real world dyno testing when installing headers and such on these bikes? I know the advertising claims, but I am truly curious whether gains are made in the real world or if the powerband is just adjusted.

- Nate >>

mariozappa wrote:

...and a good set of drop in cams...

What would be a good set of drop in cams for a 650?

KZ750 cams are a bit hotter, gpz 750 cams are hotter still (although you dont have the worm gear to drive the tach, so then you need to get an electronic tach) and if you want to $pend a lot, get a set of web cams as they are even better

steell wrote:

You can also look for a KZ750 motor (generally $250-$350) and bolt in an additional 10-11 hp with the capacity for more.

If you do the whole motor swap for a 750, you might as well get the gpz 750 for a bit more "oomph"