Topic: StrongPerf CB550 bike, CB650 Engine, KZ650 62mm pistons. Planning thread.

[turboguzzi]

I would tend to think that if you do raise the block by 1.5mm the cam tensioner would still take it. Sure do slot the cam wheel and degree the cam if you do so. make a dry test with some 1.5 spacers first.

On the other hand, have a look at the sectioned piston posted by speedyracer (second page )
http://forums.sohc4.net/index.php?topic=19200.0

 and you'll see that they usually have quite a lot of meat to remove. I did on my pistons a 6mmX1.2mm chamfer on the edge and had no problems whatsoever. this was pretty much the recomendation in the gentleman's express story

"Shortening" the rods your way sounds scary to me. powroll used to shorten them by heating them up and compressing with a press for their XL125 stroker kits. sounds bizare too....

Take the ally plate and the original base gasket to a signage company that uses a pantograph mill and they should do it in a jiffy by copying

Cheers
TG 

[StrongPerf]

I would tend to think that if you do raise the block by 1.5mm the cam tensioner would still take it. Sure do slot the cam wheel and degree the cam if you do so. make a dry test with some 1.5 spacers first.

On the other hand, have a look at the sectioned piston posted by speedyracer (second page )
http://forums.sohc4.net/index.php?topic=19200.0

 and you'll see that they usually have quite a lot of meat to remove. I did on my pistons a 6mmX1.2mm chamfer on the edge and had no problems whatsoever. this was pretty much the recomendation in the gentleman's express story

"Shortening" the rods your way sounds scary to me. powroll used to shorten them by heating them up and compressing with a press for their XL125 stroker kits. sounds bizare too....

Take the ally plate and the original base gasket to a signage company that uses a pantograph mill and they should do it in a jiffy by copying

Cheers
TG 

Great thread you linked me too. Those pistons have so much extra meat... I'm only talking 5 or 10 thou on the rod shortening not 60. Not my way either, just possible if I had too. I'd have to see what kind of meat on the small end for offset bushing. Neither of these are my preferred choice, just stating possiblities. I was wondering just how much I could move the jug out and get away with the tensioner. I'll do just like you said and check it. I think that would be the easiest and best method but wouldn't mind taking some off the pistons. That would help lighten them up and make it easier on the rod bolts. Thanks for the input. You guys are way ahead of me, I don't even have a motor yet. Planning is fun though!!!

[StrongPerf]

Piston's and rods are mine. $32 shipped. Let the fun begin.

I'll be motor shoping after the holidays. My local motorcycle wrecking yard quoted me $200 for the 650 motor. He will let me make compression checks, etc. to make sure it's good. If it isn't good when I get it running he will swap me for what ever other good one he has. I think that's a pretty fair deal. You guys think this is an ok deal?

Now I need to figure out what year I wan't. Like what head and carb's etc. I'm sure you guys can help with that right?

I guess I should re-name this thread to an engine planning thread...

[MRieck]

You will get a massive torque increase but probably not the power output you expect as the CB650 valves are smaller than KZ650 valves (from memory)
 As machining isn't a problem, I found it better to fly cut the cylinder head to a 7~10 degree angle out to the new bore size, it gets close to intake valve seat, but, if done correctly, unshrouds it very well and increases flow on short side of intake (forget which angle, and the special cutter I made is 4,500 miles away)
PJ

There is a commercially available tool to flycut chambers. I did it to my 750 head. You index it off the cylinders. It also provides a "wedge" squish area(for larger pistons that lack a flat squish area.....like the KZ650 piston) as well as the unshrouding PJ talks about.

[StrongPerf]

You will get a massive torque increase but probably not the power output you expect as the CB650 valves are smaller than KZ650 valves (from memory)
 As machining isn't a problem, I found it better to fly cut the cylinder head to a 7~10 degree angle out to the new bore size, it gets close to intake valve seat, but, if done correctly, unshrouds it very well and increases flow on short side of intake (forget which angle, and the special cutter I made is 4,500 miles away)
PJ

There is a commercially available tool to flycut chambers. I did it to my 750 head. You index it off the cylinders. It also provides a "wedge" squish area(for larger pistons that lack a flat squish area.....like the KZ650 piston) as well as the unshrouding PJ talks about.

I'd love to know more about this. When the time comes I'll get in touch with you and get more info. Thanks!

[754]

is the angle of the tool between 7 and 10 degrees??.. it would be easy to make.

I assume the piston angle should match??

[StrongPerf]

So I'm getting ready to pick out a motor. I understand the 79/80 pd carb/head combo vs. the 81/82 cv carb head combo.

I'm guessing the CV carbs work better and are bigger right? Especially for this modded 672...

I'm guessing that one style isn't bigger or longer than the other and either will fit my frame ok...

This would tell me the CV set up is the way to go. I'm also concerned about finding parts like jets, needles and such for the CV's. I know there are lots of parts avail for the older carbs due to the popularity of the CB750 but what about the CV's?

Would you guys go with the CV's or the older style?

Thanks for your input and have a nice weekend! Catch your responses Monday...

[paulages]

i'd go with the PD intakes if i were you. 750 carbs mate right up to the manifolds, which gives you more options for jetting, etc.

[cafe75-550]

I will temper my opinion by saying I've personally never run a set of the CV's but...

Stay away from the CV's!!

The early 650 CV's are not the best designed carburetor, and few performance parts are available for them. Not the easiest to work on either, based on what I have seen on this forum. And if I remember, they're only 26mm, which is larger than the 550 carbs, but the same as the earlier 650 carbs.

I would go with the earlier '79/80 head, and then run CB750 carbs as the earlier heads have the same spacing as the 750's. This gives you 28 mm carbs and plenty of available parts for tuning...

[bill440cars]

       Just "Happened" onto this one and gotta say that I'm quite intrigued by it and ANY discussion of this nature! Always interested in hearing about what you can do by swapping in some different parts and all! I've also been told that the earlier 650 head and carbs (79'-80') were considered to be better.

                               Later on, Bill  

[StrongPerf]

Ok guys. I'll fully take your advise and go with the earlier PD carbs and the earlier motor. Now to get the motor...

I can get the carbs from my local wrecking yard for a very fair price with a guarantee. What year model 750 carbs am I looking for?

Thanks

I got the pistons this weekend. #4 has a pinched rings. I hope I can get the rings out and true up the lands without much problems. I'm sure I can get it right. The rods look really good. I didn't have time to measure them but I will sometime this week.

[paulages]

Ok guys. I'll fully take your advise and go with the earlier PD carbs and the earlier motor. Now to get the motor...

I can get the carbs from my local wrecking yard for a very fair price with a guarantee. What year model 750 carbs am I looking for?

Thanks

I got the pistons this weekend. #4 has a pinched rings. I hope I can get the rings out and true up the lands without much problems. I'm sure I can get it right. The rods look really good. I didn't have time to measure them but I will sometime this week.

any of them will work, but the earlier (pre-'77) ones are easier to tune and find parts for. the PD series carbs have accelerator pumps though, which you might prefer.

[StrongPerf]

Thanks Paul. Let me see if I understand this. Pre-77 are easier to tune and find parts for

any of them will work, but the earlier (pre-'77) ones are easier to tune and find parts for. the PD series carbs have accelerator pumps though, which you might prefer.
[/quote]

Thanks Paul. Do I understand this right? Pre-77 are easier to tune and find parts for but do not have accelerator pumps? Post-77 have accelerator pumps and work better but are harder to tune and find parts for? Are the post-77 called PD series or are they both?

Thanks

[paulages]

post '77 550, 650, and 750 carbs are all of the PD series, the 550 being the only ones without accelerator pumps. i'm not aware of any performance advantage of the late ones, other than the lack of wheeze when you grab too quick a handful. sure feels nice to have that when you want it. i'm probably going with the early ones on my project though, as i want the ability to tune, with mine being so far from stock.

[StrongPerf]

post '77 550, 650, and 750 carbs are all of the PD series, the 550 being the only ones without accelerator pumps. i'm not aware of any performance advantage of the late ones, other than the lack of wheeze when you grab too quick a handful. sure feels nice to have that when you want it. i'm probably going with the early ones on my project though, as i want the ability to tune, with mine being so far from stock.

Sounds like I want the accelerator pump but mine will be far from stock and I want to tune too. Are the jets/slow jets and such different between them? I noticed a couple of guys tune the later model carbs (Ed) but if generally the earlier carbs are easier to tune that's what I'll go with... Sorry to bug. Am I getting this right?

I will ready up on the versions and get smart about it...

[StrongPerf]

The early ones have the rubber caps on the top, the later (accel pump) carbs have 2 bolts covers. I like the accelerator pump carbs better.
 DG

Thanks

In your opinion are the accelerator pump version just as easy to tune?

[StrongPerf]

In your opinion are the accelerator pump version just as easy to tune?

 Fine tuning any carbs can be a bugger. I like the later carbs because the needles are easier to get to (you dont have to seperate the carbs), and the accel pump can be slightly adjusted. The later carbs also have a high idle ramp that opens the throttle slide when the choke is on and are less fussy when the choke is applied making cold starts easier.
   The pilot jets arent as plentiful, but can be drilled out (when done carefully and at VERY small increments). The main jets are available.
   DG

Thanks for the info DG. From your explination, I understand the only thing better in tuning about the non-accelerator pump carbs are that slow jets are available. This isn't an overwhelming advantage because the slow jets can be drilled in th accelerator pump carbs which are better in all other cases...

Either will work with the early heads, right? Ok so I buy the early motor (not CV style) and keep an eye out for some carbs!

Sounds like a plan.

[StrongPerf]

With this project I will custom make some headers tuned for this particular combination. I am quite experienced in this and will share the formulas and info along the way.

Probably after the holidays I'll post up formulas for calculating pistion speed and load, valve sizes, optimum intake dia and length, exhaust pri dia and length and collector diameter and length.

Thanks for all the help so far guys!

[StrongPerf]

New Engine building thread. Gentleman's Express style. Help appreciated. Thanks

http://forums.sohc4.net/index.php?topic=44678.new;topicseen#new