Topic: 78 CB750F Turbo, post build review

[scartail]

Way to go!!! Awesome project man.

[andy750]

Way to go!!! Awesome project man.

+1! Looking forward to see how this turns out. Great work!

good luck
Andy

[Flying J]

All i can say is WOW! im not really even sure how all that works but it is very impressive.

[Bamboozler]

Thanks everyone. If there's anything you may be unclear about post a question.  If not I, someone should be able to answer it, and if not it can be investigated.  As I've said before the project has been a blast and I'm sad its completed; onto the next!  I think turbocharging/supercharging is such a cool way to pull serous power out of a motor.  I think its cool to literally have the ability to destroy your motor with too much power by a simple turn of a knob on the boost controller; thats power!    

After I post on the fuel side of things I'll paste the tuning details from the other boosted thread to tie in how it runs and things I've learned.

[ZanVooden]

Incredible build! So how long before I see you on the streets downtown here in Milwaukee?

[Bamboozler]

Hey Zan, don't make it as far as downtown Milwaukee, but was able to get the bike to work two time a couple weeks ago (Brookfield)!  I'm always keeping an eye out for CBs, hope to see ya around!

[Bamboozler]

-Fuel System, sans carbs (I'll do that next)

The fuel on the bike is feed from a customized petcock with a 3/8" hose barb (78F I think has M19x1.0 or 1.5 threads, I'll have to verify).  The petcock was made with a nut that threaded onto the tank and welded washer which was then welded to the 90 degree 3/8" hose barb, simple and functional, could be more elegant if desired.  Slack was taken up with the correct combo of washer/lock washer placed inside the nut of the petcock; this helped to clock the hose end where it needed to be.  I think that the smaller orifice of the stock petcock may have worked but is probably not the best idea; its much smaller than the pump's feed (3/8").  

3/8" fuel line feeds the inline shut off valve followed by a 40 micron fuel filter.  After the filter the fuel feeds a MSD 2225 12V fuel pump.  The pump itself feeds into a Aeromotive 13301 3-65psi bypass regulator with a 1:1 rising rate ratio with 5/16" fuel line.  From the regulator two lines depart, one is a -6AN return line that is plumbed back into the fuel tank from on top, and the other 1/4" fuel line feeds the carburetors.

The base fuel pressure is set to 4 psi (with the vacuum line removed from the regulator).  For those that may not know, the regulator needs to be a rising rate regulator. The regulator has a vacuum line that is connected to the intake manifold.  For every 1 psi of boost pressure the regulator rises the set base pressure (4 psi in this case) 1 psi of fuel pressure to accommodate the extra oxygen entering the motor.  At a full 8 psi of boost the bike should be seeing 12 psi of fuel pressure.

The fuel return was originally plumbed with -4AN line.  This was a mistake that stresses the importance of reading install instructions .  Bigger return lines are better and the -4AN could not shed enough fuel to keep the fuel pressure at the low 4 psi.  With the first few shakedown runs it wasn't clear that the return wasn't large enough.  After playing with the voltage regulator that feeds the pump I noticed the fuel pressure would rise with the increase in voltage to the pump... its not suppose to do that .  After the -6AN line was installed the fuel pressure was rock solid.

With an attempt to save on the CB's fragile/smaller output charging system, it was decided to feed the power thirsty fuel pump with a voltage regulator.  This helped to ration the power it was allowed to consume (the pump is well overkill for the requirements of the CB). The MSD 2225 pump measures around 66 watts (12V @ 5.5A) when fed with 12VDC.  I found that at 7.5V was a good input voltage to feed the pump to maintain pressure at up to 15-16 psi of boost (20psi pump output pressure with the 1:1 rise).  I could have tested it further than 15-16 psi on the regulators vacuum line, but fuel started pouring out of the over flows at the 20psi they were seeing. For the smaller 8 psi I could have probably gotten away with 5V but gave a bit of overhead at 7.5V.  I used National Semiconductor's WEBENCH designer to kick out a circuit that fit the requirements for the voltage regulator http://www.national.com/analog. I ended up using the recommended regulator, the LM22678-ADJ.  After buying the components and National's LM22678 proto pcb from www.Digikey.com and www.coilcraft.com it was all soldered together and wired up. The pump went from drawing 66 watts to around 15 watts and still performs as well as before!  I have yet to do this with the oil pump.

Two things I found out regarding the electronics. One is that you can not wire two pumps in series in order to kill two birds with one stone (same current path through both of the motors).  They both need a reasonable input voltage which is trashed when running them in series, you'll just get two pumps that are slower. The second is that when throwing a circuit together on a bread board (the voltage regulator) you can impair the circuit by poor routing of wires, not having a suitable ground plane and by generally not following good circuit layout practices.  The first proto of the LM22678 gave me terrible voltage sags and over shoots with different input voltages; the circuit would not regulate at all (and I quadruple checked the simple circuit for proper wiring). After I bought a correctly designed/laid out protoboard for LM22678 made by National the circuit regulated dead on at 7.5V no matter what my input voltage was; lesson learned.

Petcock


Fuel return


Fuel plumbing guts

[750goes]

Awesome............

[Bamboozler]

- Carburetors

While a rack of constant velocity carbs (or throttle bodies for that matter) would be a better choice to use with forced induction, I wanted to give the stock PD42A slide carbs a chance to shine and stay with the bike. As a backup, I acquired a set of 85 Nighthawk CB650SC carbs suggested by Cafebob's CV carb thread and kept them as a fallback if the stockers didn't pan out.

A few things were needed to be done with the stock cable slide carbs to make them usable with the turbo.  The biggest concern was weather or not they could be sealed up properly while under boost.  To make this happen it was apparent that both the throttle and choke shafts that pierced the carb's bodies needed attention.  As is, sunlight could be seen through the original felt and rubber o-rings; they were all removed.  A carburetor came with down to hardware store to find suitable replacement o-rings to replace the wore felt and rubber rings.  The o-ring size that best matched the choke shafts were 9mm/5mm/2mm (ID/OD/Thick), the throttle shafts got 10mm/14mm/2mm.

A slight bit of filing on the choke shaft was needed to removed the sharp transition to the thinner portion where the choke plate is fastened (see pic).  This helped the shaft slide back into place through the now much tighter o-rings without shaving off a part with the sharp edge; pure silicone or similar might help this as well.  After the better sealing rings were in place the choke and throttle shafts sealed up much better.  However, it was noticed that they were fitting almost too good.  Both throttle and choke shafts had noticeable resistance, sealing great, but were 'sticky'.  The next size down the hardware store or McMaster Carr had would be too much of a jump and wouldn't seal nearly as well.. it was determined to work with the sticky carbs; sealing properties being the most important.

When assembled back into the bike with the new o-rings the throttle was slightly sticky but would return to home, albeit a bit slow.  The choke's shaft however was a bust, after it was pulled the wimpy "helper" spring for carbs 3/4 was not close to strong enough to overcome the added resistance.  To address this I added a slight bit of weld to the linkage in order to help open all 4 choke plates with one pull; pulling up on the choke cable that's connected to carbs #1/#2 forces the #3/#4 carb's choke shaft to turn as well.  Hooking up the return spring a bit tighter helped it return easier as well (hooked it onto something further upstream).  The pic can tell the story as to were the weld was added. I did try lubing the o-rings with silicone spray and had some what ok results, but still not what it should have been.  During one of the carb tear downs for tuning I added some pure silicone to the o-rings (father's suggestion) and saw an excellent improvement, afterwards both throttle and choke operated almost as slick as before the larger o-rings were installed.  

A few boost compensation related things were done as well.  One atmospheric port on each carburetor was plumbed into the pitot tubes; the pic a few posts up shows this.  The fuel over flow/drain tubes were plumbed into the intake manifold as well.  I think that the over flow tubes could be plug or piped into the pitot tubes as well, depending on weather you have enough boost compensation or not enough, respectively.  In the initial tuning runs, prior to noticing I needed to plumb the over flow tubes into the intake, I had also drilled out the atmospheric port's internal passage ways into the fuel bowl.  I was figuring the passage ways might have been too restrictive and this was causing the fuel cutout at boost transition.  Weather it was 100% necessary or not I'm not sure (couldn't hurt), however both the horizontal and vertical paths were drilled with a 1/8" bit (if my memory serves me correctly).

All in all the stock slide carbs seem to hold up well to 8psi.  The air/fuel ratio is rock steady at wide open throttle is seemingly transitioning well from little to full throttle.  At this point I'm happy enough to keep them and keep the CVs shelved for the time being.

And last but not least.  I'm now a believer that cleaning the carbs with compressed air and choke/carb cleaner doesn't always cut it.  I cleaned the carbs twice (pulled the idle jets and all) before the turbo project and fought a idle that hunted high and low, and was a bear to start.  After I soaked them in a bucket Gunk brand carb clean she idled and started like a dream.


Filing points on choke shaft


Carb o-rings


Welded choke forward assist

[Bamboozler]

Graphing in a few posts from the turbo thread to explain how the bike has been working and tuned now that its rideable...


11/06/09 -

After a few out of town delays and a bit of troubleshooting my turbo CB has finally got a taste of 8psi of boost! I was having a problem with a lean out condition at the faint beginnings of where vacuum was transitioning to boost (WB A/F pegs at 18:1, more if the gauge would read it). After a sprint up the RPM band to about 5.5k-6k the bike would fall on its face stone cold dead. You had to let off the throttle and it would idle while you waited for the A/F to drop back down from the moon before you could produce power again and accelerate once more (throttling it did nothing). I increased the main jet sizes, then added a pitot tube, then a second pitot. Still there was not enough dynamic pressure being built in the bowls to overcome the pressure running through the carbs/venturis to force fuel through the main jets and into the air stream.  I mentioning to a friend that after the lean out test runs I was noticing fuel weeping from the overflow tubes... he asked why I didn't have the tubes plumbed to the intake like his turbo RX1.. the light turned on..  I had not come across this point being stress before, or not paid attention to it... I had a window open (over flow tubes) to let the dynamic pressure escape..  I routed the tubes to the intake and took for a spin and the fuel lean out was history; and I saw boost. 

How does the cheap $220 small T3 turbo spool?  I'll have to admit defeat in this department and concede to what you others where noting about the T3 being too big.  From the two small blasts of 8 psi I gave it (no wideband at the moment, broke, being warrantied, get a new one tomorrow), I was seeing boost being picked up at around 6.5k and a full 8psi at around 7.5k (wastegate limit).  I don't know if this will improve at all with a proper A/F, as I don't know where its at during that boost, I'll pick back up when I have a WB, dial it in, and see what the end results are (barring no surprises/delays).  I can say that when I did hit 8psi that CB was starting to move like it had never moved before... It was a very smooth and rapid pick up, it was grand, and I can't wait to play some more. 

If this T3 is an ultimate flop and too laggy to be enjoyable I will replace it.  I took the time and ran the numbers on the compressor flow maps (shouldn't I've done that before starting fab...) for three possible replacements, GT1548 (w/o water hooked up), GT2052 (if a rectangle opening T25 turbine can be used), and a GT2056 (winner so far?). There is a T3 to T25 flange 3/4" thick adapter plate on ebay that I hope might work if it gives enough clearance between the turbine (hopefully smaller in size) and the CB's oil filter housing to make it a painless swap... Otherwise I may have to fab up another header with a T25 flange and save the T3 header for a big bore kit down the road... 

**Edited to add, I think I found another cheap $230ish Chinese turbo on Ebay.  This one is a T25 flanged turbo that is comparable to a GT2056 or so in size.  May buy a T25/T3 adapter plate a hope for the best that it fits.




11/13/09 -

I'd like to add a few notes for the archives in this thread about my Chinese turbo setup now that I've gotten a wideband O2 meter again and 150 or so miles on the bike.

The tune that has been in the bike since it first saw boost was surprisingly close to what I was aiming for.  Quick carb setup review:

    * Boost compensation: Two 3/8" pitot tubes facing into the incoming air charge (one Teeing to #1/#2 carbs, the other to #3/#4)
    * Atmospheric ports were drilled out to 1/8 (I think 1/8", again I'll confirm this in the project thread when I get to my notes).  I was half way through doing this when I realized the breech with the fuel over flow ports; *may not be necessary*.
    * Additional boost compensation: fuel over flow ports plumbed to the intake manifold
    * Idle jets: #40 (stock #35)
    * Clip position: 78Fs have fixed needles, I added two #10 washers(I think, they're tiny) under the needles to enrichen about one clip position
    * Main Jets: 120 (stock 105)
    * Float height: 14.5mm (stock tolerance)
    * Idle fuel screw: 1 1/4 turns out (stock 1 3/4)


With a warm motor the idling A/F is around 14:1-14.5:1, this is very close to stoich (14.7:1). May be able to get away with stock slow jets as it didn't really need the choke at all to stay running when started cold. Or a 1/4 in with the fuel screw?. With out boost compensation at idle (shouldn't impact idle) and with stock #35 slow jets I was seeing ~16:1.

When at cruising speed (1/8-1/4 throttle) at in town speeds 25-35mph and up to low country highway speeds 50-60mph the A/R is sitting again around 14:1, which is good (bit on the rich side maybe).

As you kick it up to around 75-90 and maintain this speed the A/F drops to 11:1.  I happened to have a 65mph four lane highway on my way to work and the A/F was pegged at 11:1 while doing aroun 75-85 (think speedo is off a bit, slightly faster than traffic).  The speed and or wind resistance creates enough load that I was constantly at around 0.0-0.5 psi of boost; depending on the load to the motor. Easy to build boost quickly at this point.  I think either the removal of some boost compensation and or removing the extra needle shim(s) would help to get my cruising (1/4 throttle) high speed A/R back up to 14.7:1.

Twisting the throttle to wide open gives a solid 11.8:1 A/R in any gear or speed.  I think this is in the middle range of where things should be, the bike responds very well; no hickups, pops, bucks.  Haven't done a plug chop to confirm what the plugs say.  From other applications I figure (11.0-11.5:1 is rich/conservative, 11.5-12.0:1 is intermediate, 12.0-12.5 max power tune/getting close to opps too far), I realize this is a very subjective subject, many factors and motors details to consider when figuring this.

"Laggy" isn't the best word to describe the bike but rather the onset of boost.  From a stop the bike is very quick on its feet, as if there isn't a turbo installed at all; and may even be quicker than it was stock (maybe less restriction than an air box?).  The bike seems to be naturally aspirated with an afterburner.  With a big bore kit, bullet proof motor, and 15-20psi I think this turbo could be a real terror. When you lay into the throttle and get in the upper RPMs the bike starts to pull harder and harder.. to the point where the clutch starts to slip (around 7-8psi area). To be expected I guess, Barnett clutch springs will be hit up next.  However I think the season is almost gone and may be a winter project, 33-35F on the way to work and back two days in a row is making me dress like I'm snowmobiling.

[Bamboozler]

Due the the dismal snow conditions here in south Wisconsin attention has slipped on the sledding front and turned back to the warm weather machines.  Giving an update to the bike project and the sticks that are currently in the fire.

I'll be first to admit that I should've done my homework better when choosing a turbo for this project.  I kinda blindly choose the smallest thrifty (Chinese) T3 I saw and should've research a bit more.  After running the numbers from the Garrett turbo's faq on selecting a proper compressor map the numbers pointed to around a GT12-GT20 size turbo.  So going with the ebay turbos again I found another $230 turbo that fit in between a GT2052-GT2056.  Hey, 300 or so miles of trouble free riding with the current Chinese turbo, that should silence the don't touch the import turbo nay sayers right?... I kid I kid. Well see what happens with this one, the dice have been rolled again.  The stats on the turbo are as follows.

    * Journal Bearing - Wet Float Type
    * Internal wastegate set at Approx 7 Psi
    * t25 Flange
    * Oil Lub, Oil/Water Cool
    * 250 HP Capable
    * Compressor Wheel
    * 0.60 A/R Cold Side
    * Ind: 38.74 mm
    * Exd: 52.20 mm
    * Trim: 55
    * Turbiner Wheel
      .49 A/R
    * 4 Bolt T25 Flange
    * Ind: 40.38 mm
    * Exd: 48.90 mm

One issue with this turbo is that there was no 5 bolt exhaust flanges available for its turbine, or none that I nor the sellers of these type of turbo/turbines could find.  A friend helped me out and drew one up in ProE by dimensioning off the gasket and I had a few water jetted up.  The other issue is that I have a T3 turbine flange on the header and this is a T25 style turbine flange.  An adapter on Ebay was purchased and did a good job of mating the new turbo to the header. Being that the T25 turbine is a bit smaller than the T3 there was more clearance than before, even with the adapter lowering the turbo a bit more.  The oil filter housing has no problem coming off with the turbo installed.






Another change that is under way is adding a full muffled exhaust.  The short route had just a bit of edge at around 4k, to the point that it was on your mind when passing through towns at night prompting you to shift into 5th gear in a 35mph zone to help quiet the peaky drone down a bit.  I was shopping for a slip on exhaust when I came a across a thread here that linked to www.coneeng.com which was a perfect solution for a stainless 2.5" core to match the 2.5" exhaust pipe with 10" long 4" stainless outside tube.  I talked with what I think was the owner when I ordered the parts, nice guy. He described how to construct/pack/weld the muffler.  The exhaust will still be 2.5" straight through from turbine to exhaust tip, but I'm hoping that it will dampen the peaky resonate frequency that's annoying when trying to be quiet.  Components are acquired and ready to have a friend TIG up.

]


Something that I wanted to see on the bike was a cafe azz end.  I really think it makes these bikes sexy in a lust for speed sort of way and I've drooled over the many bikes on this forum that crafted such works of art into their bikes.  A friend of my passed me a link last year of a Yami RD in which the owner crafted a cafe rear cowl out of a rear end of a gas tank from another 70s era bike.  The tank fit the RD's lines perfectly, cost little, and was able to be done with a welder (not fiberglass which I have no experience in playing with thus far).  I've had the project in the back of my mind wondering what tank would be a good match. Then this same friend passed me a link to a awesome CBX500 project where the owner did the same rear end of a gas tank cafe seat.  http://choppercharles.com/cs/forums/1/56497/ShowPost.aspx#56497 I instantly saw the tank that matched the rounded lines of the CB F's gas tank; or in my opinion it does.  The owner did a knock out job on his CBX and I'm going to pursue a similar route (a shame he sold it, someones a happy new owner tho). I picked up a dented front end CB360 tank off of Ebay for $20 shipped and will be starting on it after the other projects are done. Pic of tank with tenative cut line below.



Lastly, if there wasn't enuf going on, an intercooler will be gracing the front of the bike as well.  I like the idea of getting more performance by cooling the intake charge if at all possible and or detonation suppression that comes with methanol/water injection system.  I don't think that its a huge problem with the 8 or so psi that this bike has been seeing.  But there is something to be gained by dropping the intake temps 50-100+ degrees on a hot summer day, something that you can actually notice if you had it taken away.  I was trying to figure out if setting up a meth/H2O injection system would work, or going with the intercooler would be the better idea.  Ultimately I don't think the bike can afford another (3rd) pump added to the CB's electrical system. Didn't verify, but suspect in the worst case scenario that the 12v system voltage would drop with an additional 4-6amp load during the pumping of meth/H20 which is right during peak boost. Thinking dropping the 12V would tank the spark energy during this time too.  Kinda wanted to make the rear gas tank cafe seat into a dual purpose cafe seat/meth/h20 tank, ah well, would be trick tho!  The intercooler won out because there are no fluids to keep on top of and no additional load on the electrical system.  Though I will still miss not having the octane increase from the methanol... won't call the idea 100% dead..  

I've ordered up a intercooler from Bell Intercoolers www.bellintercoolers.com this last Thursday (1-2 week turn to complete the IC with endtanks welded).  If I can correct my order tomorrow morning the size will be 9" long, 4" tall, 3.5" thick, flows around 256cfm (the new turbo flow around 121cfm @ 8psi, plenty of head room).  Otherwise I originally speced out 8"x4"x3"; I think the larger heat sink will work though.  The brake pad box in the pic happens to be 9"x4"x3.6" and gives a rough location.  I'll post IC plumbing pics down the road when acquired.

[JLeather]

Looks great man.  This is a stock motor you're putting 8pounds to?  Can't wait to see what mine'll take

[Flying J]

i have the same style seat on my f bike.d Its a yamaha tank. i liked keeping the stock seat pan.

[754]

 Just a question, does the turbo need a guard?
 ..just thinking, when its at full heat, and you hit a large puddle or water running across the road...

[Bamboozler]

Thanks JL.  The motor is stock with ~16k miles on it, the wastegate actuator is fixed at 8psi so that what it'll get.  The bike should be a bit less stressed with the smaller turbo that's on there now.

With the stout motor that you have I think you get the luxury of picking what boost you want to play with.  You have as bullet proof as motor as you can pretty much make from what I remember.  I've thought about what the limits are with these CB motors, and it all seems to center around the primary chain from what I've read.  I'm thinking you read the threads here as well describing the primary chain stretching on the +/-100HP circuit racers after a few races, or the teams that have to pull the motor to replace the stretched primary after x amount of races.  

I'm wondering myself what the fine line of boost/HP you should shoot for on these bike if in fact these chains are the weak link. I'd love to double+ the HP but if it means splitting the case annually or bi-annually to replace the primary chain it would sour me to push it that far.  I recently checked my primary chain stretch, on a scale of 1 being a new chain and 10 being the service limit the chain's stretch is sitting at a 3. With the 8 psi that it'll see I'll monitor the stretch on it and see what happens.  I'll do some pulls on a local dyno this spring to get a base line HP to see where the bike sits and to help correlate HP vs primary stretch.  You already have one of RR/Nippon super chains, that will be my next step if mine goes south. I'll probably stick with the stock motor for the time being and see how well it plays with boost.


edited for name correction

[Bamboozler]

ffjmoore - I should've paid more attention to your build, that is an excellent shinning example of the gas tank seat cowl I'm looking to implement.  Lovin' the upholstery!  Question for you, how did you anchor the seat to the pan/tank?  I see the CBX guy used boat seat snaps which look fine and is functional, wondering how you went about locking the cushion down?  Also, how much did the leather work set you back if you don't mind?  Wondering what I'll be expecting to pay for a custom upholstered seat; ball park figure.

754 - At the mercy of the elements as is.  I'm not sure what would happen with a constant spray of water on the turbine. I don't know if it would eventually split the cast iron turbine or anything that extreme or just be a steam generator.  I'm a fair weather rider, so if there's hints of rain the bike stays home, but it would be foolish to say that I'll never be caught in the rain.  Best I can think of is tubular headers from say a V8 car/truck extend down into the elements and don't crack.. hope the same holds true for a cherry red turbine... A simple shield might not be a bad idea.

[NitroHunter]

Great job!
My .02. the weakest link on a stock motored turbo bike is the operator not using high enough octane fuel for the boost / timing being run.
 Don't rattle that motor and you probably won't ever find broken wrist pins, 'S' shaped rods, or reverse dished pistons.  
I've heard bad things about stock F-2 retainers failing, it never happened to me personally, but there are plenty of guys who've had dropped valves.
I forsee tranny undercutting in your future.  
Seem to remember that hard downshifts are much worse than hard up shifts on our primary chains, but I'm all in favor of those mega chains.

[Bamboozler]

Don't rattle that motor

I saw another thread you posted this in and thought to myself "spot on" when reading it.  You would definitely would be one with experience in the boosted realm to have seen a fair share of the good and the bad.  True is that its 'game over' before the limits of the motor have been reached if improperly tuned.  Thanks for pointing that out and reinforcing the idea!

I was really happy to see that primary chain tension in an acceptable tolerance range... I was thinking I could push on fabricating and not have to divert my plans to splitting the case... then you bring up the undercutting idea and crash my happy thoughts of fab...   From the short time I was able to play with the prior turbo I only remember once where the trans bounced while trying to get into gear.  Something that I will keep a closer eye on now that the bike will be spending more time in boost (early in the RPM band). 

As for the retainers, I guess I'll be sure to change them out next time I'm into the motor.  Thank for the heads up on that F model issue.  I hope the motor will let me take my time getting to it.

[NitroHunter]

Don't rattle that motor

Voice of experience...   

My tranny never had any problems... as long as I rode like a little girl!   
 
OF COURSE I was terrible on my trannys! With lots of horsepower on tap, I just couldn't keep my senses about me when the boost gauge would rocket up. OK so it was that way long before the turbo days, my other motors didn't fare much better.
Some of my pals could do it, but my foot shifting wasn't exactally world class. Later on I got better at it but whacked plenty of gears along the way.
 I finally installed an air shifter and quit beating the dogs up, but I doubt you'll have any issues if you don't ride it like a nutcase.

Your project is well thought out and I'm sure you are being careful along the way.

[Bamboozler]

Don't rattle that motor

Voice of experience...   

Uh oh, I wonder how many four letter words have been issued throughout the years of trips to the track...   I suppose it goes hand in hand with the game, no one's immune when pushing motors to the limits seen at the track.  Its bound to catch up with the best sooner or later.

This bike is being build for a fun ride around town, work, and maybe a long trip trip or two if I feel gods of reliability are on its side. It may see a trip down the track for amusement, but that's all.  I hope she keeps together a bit longer because of it. 

Seeing that you have had CBs with high boost, if given a proper safe tune, have you ever had to be worried about primary chain stretching or is the worry unfounded?  If not the chain, what was usually the culprit for downtime on the bike(s) in your experiences?

[NitroHunter]

Myself, I never had any chain issues. I have the RC hub, that may have helped.
When you crack the cases next time, check the chain stretch and replace. I can see a 20K mile bike needing one, but short of downshifting so hard that you lock up the motor, I just don't see a street tired bike able to kill the chain - especially on acceleration alone.
If you don't do abusive things to the motor, clutch, and gearbox, that thing should be as dependable as a stocker - with a bad boy attitude at your disposal. 
Short of something goofy breaking, my guess is that you'll be replacing the head gasket sometime down the road. An oil leak or whatever. That would be a good time to install big studs and check out valve wear.

[Bamboozler]

Thanks once more Nitro for your thoughts on the primary chain.  All in all that is encouraging to hear regarding these motors, that a bit of boost seems to be within the CB motor's means.  I'll do my best to give updates on what becomes of the motor.  This will be the third summer I've had the bike and have put probably no more than 500 miles on it.  Never got too interested into it until the whim to make a project out of it. I plan on taking advantage of it now, and will be looking forward to putting some miles on.  It'll be interesting to see how it holds up.

[JLeather]

Robbie, what's different about the RC hub?  Is there anything I should do to my clutch like having the basket welded or anything?  Sorry for the hijack.

[NitroHunter]

As I remember RC installed new dampening rubbers and HD rivets.

I've been looking for the recent thread where there was a good discussion about this, it's not showing up on my search...

http://www.m3racing.com/graphics/parts/hvydtyprimdrrbrs_lg.jpg

Heavy Duty Primary Drive rubbers.

Designed and tested at M3 Racing HQ, these are heavy duty primary drive
dampeners to fit Honda CB750. Complete with new rivets to make rebuild easy.
A must for any engine with over 90 HP.

[Bamboozler]

Sorry for the hijack.

Feel free, I mind not.  

Thinking I remember that thread that's being talked about, regarding Nippon and the Germany club that was making the cush rubbers.  



edited for name correction.