You can get a basic healthy increase without headwork or rods.
RC used to sell the 30-30 SUPER SAVER Claimed 30 % power increase and 30% decrease in fuel consumption. (IMO your results could vary)
Kit had; 10:1 cast 836cc pistons, RC240 cam (exchange), 4-1 black exhaust.
RC developed this kit to provide you with most effiecient motor possible.
I think this is a very good start. Making everything at once might give the wallet a chock.
BUT, it depends on the milage of the engine.
Maybe time for new internal chains + tensioners? You can check the slack from below. Remove the cover for oil pump. (Drain all oil first).
The measure between the cover surface for gasket relative inner plate of the tensioner holding the rubber wheel, today old and hard. Max is 70mm. (I read somewhere that new chains + tensioner measure 65mm)
Then new cam chain, a heavy duty version and adjustable sprocket for correct adjustment of the cam.
About pistions, the cheapest ebay pistons for $110US is not actual when you want more torque. This is LOW compression with NO dome at all. They write that where they sell the kit. look like OEM, just 65mm instead of 61mm.
The cheap kit I found is probably a good bang for the buck.
A hotter cam need better springs that is a rather cheap investment.
Clutch kit might be something too.
Below my thoughts about CB750 engine repair/ upgrade based on my experience and what I need to do now.
Check at dynoman and cycle exchange where they have nice parts. I'm sure other have too.
- 836cc 10.5 kit + cylinder job to 65mm. Grind the surfaces of cylinder and head. Flat and no scratches.
- Check that valves, seats, valve guides are OK. Maybe enough to grind the valves/seats with manual tool by yourself.
- Cam like WebCam 41/41A, Cycle exchange CX-1/2. DP295 if you need to go further with head job.
- Heavy duty valve springs are not expensive.
- APE Heavy duty cylinder studs for correct torque, no leak.
*** Here must the entire engine to be opened where you need to invest what needed like bad/damaged bearings. ***
Check the bearing close to the final shaft. Old engines had smaller bearing, newer wider double ball bearing. Not expensive when it's a std size of bearing.
- Heavy duty cam chain with new tensioner parts + adjustable sprocket (possible to open the holes in OEM sprocket)
You can replace cam chain without open the crank. Cut the old and buy new chain with Master Link - Tsubaki - BF05M if you buy Tsubaki BF05M 94 Link. - Primary chains with tensioner if not replaced earlier.
- Clutch kit (can be replaced later whith engine in frame). Complete kit for $150 at mentioned sites. Be aware of the alu clutch lifter plate when taking the clutch apart and on again. 4 screws must be untightened just a little on each screw step by step (all at the same time if possible. If not it will brake and increase the cost. You need a tool to remove the clutch, Cycle exchange has. Hammer and screwdriver will destroy the nut You need to tighten it with controlled tourqe.
- Use correct sealer when assemble the crank halves.
I used the blue Hylomar last time and my friend was right, it will leak. Dynoman and cycleexhange have the correct stuff. I used Hemetite Golden some years before which worked well too. DO not use excessive amount of sealer and silicone! Only a very thin layer on each halve, nothing to be squeesed out when tighten, it will block the important oil supplies of head, cam and block the oil pump grid. That will initiate another repair. Maybe an old owner has made that mistake? You will see when open the engine, bad cam bearing surfaces.
- All gaskets and rubber sealings will cost some too.
- New ignition maybe? There are electronic ones as Dyna S, PAMCO for about $120-150. These use OEM coils.
I have very bad experinces of OEM Points.
I heard from the very beginning that CB750 eats point parts. I replaced it every year, "Ignition points, condensers and back plate assembly". I had to drive my bike in France on the highway for at least 50km with one broken contact breaker to find a motorcycle work shop. Ran on 2 cylinders only while gasoline could destroy the lubrication of the other 2 dead cylinders. This thanks to a new complete point set, that broke after only 4000km. Bakelite broken on one of the ignition breaker. The part that has contact with the lobe open/closing the breaker
Sweden-Spain, way back in France I got the problem. Important to have a complete set extra.
- New paint for the engine crank?
- 4-1? There are some Yoshi replicas for $300-500. The chepest from CB750 cafe , the pricier in stainless steel from motogpwerks or Lossa enginering.
I'm sure that both dynoman and cycle exchange can make a nice kit for you. They have experience and have all goodies.
- Next step is not expensive is a lighter alternator when the crank is opened. Engine will answer quicker.
You will soon understand that this is very fun and will go for lighter crank with better rods for heavy compression ratio, hotter cams.
When you take the engine apart. Put the parts in plastic bags and mark everything from where it belongs, which cylinder, valves etc.. Important to put it back the same way again, all parts on head must be mounted in exact same way later.
