Topic: Best bang for buck performance mods?

[Dunk]

What are the bestr bang for the buck performance modifications for a CB750 (mine is a '72). Right now I'm pretty happy with the bikes performance, but I have a few issues I'd like to fix. Namely breaking up above 6500 RPM and missed shifts at high RPM. When I run it up to redline in first or second and shift quick it'll 90% of the time go to neutral/false neutral. I will probably rebuild the engine and trans this winter and am thinking what performance mods would be worthwhile to do while the motor is out and apart. Obviously porting the head is on the top of my list for bang for the buck. What else is there that I can do though? As far as cost effective upgrades? Anything expensive that's worth doign while it's apart? Just trying to plan ahead so I know how much I need to save and what I ought to research before the winter.

My buddy rides a Shadow VT1100 so I'd like to be able to hang with him better than I can now. When he nails it I gotta kick it down two gears and rev the piss outta my CB750 to stay with him.

[eldar]

Well there is no one thing you can do. But if you can put together a few mods that will work together.

Canuck, you must be mis-reading. Doing the head is one of the BEST things to do to these bikes. Anyt type of mod starts here. Contact mreick and ask him about it. It will cost some bucks but will be worth it. Without a headjob, any other mod you make will be worth very little. He will ask a few questions about what you want to do and then give his advice. 

From there the Dyna-s or if you have the bucks, 2000, is the way to go. The S on its own is a HUGE improvment over points. Some might try to tell you otherwise but just ask yourself, "why do they NOT use points anymore?" Because there is better out there.

From there you can either stop of continue on. You can get a new and somewhat hotter cam and 836 kit or you can stop. You will have gained some HP just from the head and dyna but it really comes out with 836 and a hot cam.

Stock hp is around 50, there are some members here who have taken their engines to about 100. Just remember, it is the total sum of the work that you do, not just one thing.  Also remember though that everything in you bike must be done properly so you do not have any failures.

[vames]

um...all good advice above....but if by "breaking above 6500 RPM" you mean reving higher than 6500 RPM, then something is wrong with your bike and fixing it could be your best performance mod ever.

examine your carbs (stock air box and exhaust? - need different jets or needle position? synched?)

timing, etc.....the list of things to check is in many places on this forum.

[eldar]

Well if he is set on doing mods, then it is worthless to bother fixing his break up issue as any changes he makes will be out the window anyways, unless he is waiting till winter to do it that is.

[TwoTired]

My buddy rides a Shadow VT1100 so I'd like to be able to hang with him better than I can now. When he nails it I gotta kick it down two gears and rev the piss outta my CB750 to stay with him.

There is no substitue for displacement in the throttle twist arena.  Small engines make horsepower with RPM.  I usually run the smaller 550 and if I need to scoot, it goes down two or three gears to make it happen.
These SOHC4 engines take RPM with aplomb.  However, if yours is "breaking up above 6500", there is a maintenence or configuration problem you should address.  Possibly there has been an air filtration or exhaust change since it left the factory and the carb adjustments haven't been made to compensate correctly for the corresponding change to engine breathing characteristics.  If so, a bit of carb tuning after a full tuneup, should get your eager engine well into the red band.  Learning to read the spark plug deposits can help determine what areas of carb tuning to address.  We can help if you post focused and well lighted pictures of the plugs, including the porcelain deep into the plug.

Do not expect large power gains from a Dyna ignition unit. And, if someone says there is, ask for the dyno or time slip numbers to prove it.  The Dyna doesn't make power, it circumvents the slow degradation in timing accuracy the points incurr over long usages times.  If you want to pay to jump off the cliff as others have, at least it won't hurt anything.  But, if you want bang for the buck where bang is more horsepower, put your money elsewhere.

Cheers,

[paulages]

Do not expect large power gains from a Dyna ignition unit. And, if someone says there is, ask for the dyno or time slip numbers to prove it.  The Dyna doesn't make power, it circumvents the slow degradation in timing accuracy the points incurr over long usages times.  If you want to pay to jump off the cliff as others have, at least it won't hurt anything.  But, if you want bang for the buck where bang is more horsepower, put your money elsewhere.

agreed--the only thing you'll get out of a dyna ignition is consistency (which i appreciate).

[eldar]

Funny how you put it as jumping off a cliff when the dyna has been proven as being better than stock. Funny how I do not see many people running points on anything but the stock engine and when they switch, they see an improvement. But you will never know it unless you do it I suppose.

Don't get me wrong, points are ok but fact is they are just not as good as a dyna or any other electronic ignition system, stock points are not as good as hondaman's unit either.  If you need proof, look at ANY of todays engines or even MOST engines in the 80s. You will find NO new engine that runs on points. What more proof do you need. I know manufactures' like to mess with things but not ignition and even to go past that, there are NO aftermarket HI-PO kits that use points.

If a person wants to stay bone stock, hey good for them but at the same time, maybe they shouldn't be subtly insulting those who switch.

[dusterdude]

dayum!

[eldar]

Yeah when stock it is still an improvement but the big bonus comes when you juice things up in your engine.

[mlinder]

If I may make a suggestion, according to your other thread, it's running crappy.
Your points plate and #$%* need to be fixed or replaced, you have wonkey timing. Go ahead and replace it with a DynaS. No reason not to, really. Best 120 bucks I've spent on my bike so far.
After that, just get your bike running properly.
You said you are running  aftermarket pipes and Pods.
Get your jetting right (which you can't do until you fix your timing issue, adjust your valves, and timing chain.)
You may find that, once you fix this, you'll find that 6k and up will have plenty of power for you.
My 69K0 has some pretty scary acceleration from about 4.5k on, but once it hits that 6.5 to 7k range, it really gets moving.
As it stand, your current issues won't even let you get your bike in it's power range.
Make performance decisions AFTER you get it up to it's real performance envelope.

[firecracker]

I've been told the easiest way to make your bike faster is to remove excess weight...

...as in, lose a few pounds, lard@ss!

I think I'd rather work on the engine...

 

[jonbuoy]

What are the bestr bang for the buck performance modifications for a CB750 (mine is a '72). Right now I'm pretty happy with the bikes performance, but I have a few issues I'd like to fix. Namely breaking up above 6500 RPM and missed shifts at high RPM. When I run it up to redline in first or second and shift quick it'll 90% of the time go to neutral/false neutral. I will probably rebuild the engine and trans this winter and am thinking what performance mods would be worthwhile to do while the motor is out and apart. Obviously porting the head is on the top of my list for bang for the buck. What else is there that I can do though? As far as cost effective upgrades? Anything expensive that's worth doign while it's apart? Just trying to plan ahead so I know how much I need to save and what I ought to research before the winter.

My buddy rides a Shadow VT1100 so I'd like to be able to hang with him better than I can now. When he nails it I gotta kick it down two gears and rev the piss outta my CB750 to stay with him.

Try keeping the upwards pressure on the gear shifter till you've let the clutch out (if not doing so already) if youre picking a false neutral 1st-2nd

[333]

What many have said here is true.  Your bike should pull smoothly to redline.  You should read your sparkplugs and see if the jetting is right.  If you are running pods and an aftermarket exhaust, it's gotta be off.  You may have another ignition problem.  In addition to all that's been suggested, check the spark plug caps and their connection to the wires.  They "screw" onto the wires and there may be corrosion there.

And at the risk of starting another oil war, consider a changing the type of oil you use.  I have used Honda HP4 w/ Moly for 20+ years in a 550, a 750, and currently a 350Fwith no problems.  In fact, I always noticed a smoother transmission when changing over to this oil.  No more missed shifts, no false neutrals.  Some will say the moly oils can't be used with our era of bikes.  Honda says otherwise..  When HP4 first came out(moly version only), Honda issued a bulliten , listing amoung others virtually all street bikes from 69 on.  The exceptions were the automatics and anything with a centrifugal clutch.  It won't fix a bent shift fork, but it may solve your shifting issue

[MRieck]

The HP4 is a great product. I use both the 20/50 and 10/40 in my CB, Yamaha and Hayabusa. As a side note...I have noticed no difference between the the HP's with Moly or without.

[VitaminCB550]

Why hasn't anyone said exhaust, intake, jetting first? 

[MRieck]

I'll tell you what.....do a leak down test on the engine first and see what kind of shape it is in. Something with 12 or 15% leak isn't going to do crap unless you pump TNT into it.