CB750K5 for the strip

[UJM]

Long story short, aquired a CB750 chopper everyone loved to hate.

Sat and sat and sat - finally, decided to do something with it.

There is a fellow in town with a old RD350, 1975, chambers, fresh pistons, perfect for a grudge match against the same year CB750.

I dropped the forks, dumped the K&Q seat, highway bars are gone, got it running and now, as soon as weather permits, we'll be trackbound,

I'm hoping to do a test and tune night as soon as weather permits, need to get a better feel for the bike before the big race

Here the CB750 is -



Rather than a grudge match, maybe we should be calling it a grunge match

More here:

Classic fight night CB750 sohc vs RD350 - CycleWorld Forums

[GDJAM]

Dude that thing is SWEET!

MisterMike will be all over this.

I like the grudge match idea too

[secondchance]

what where the 750 running back in the day.....HP

[ratdog]

I'm lovin the fork drop

Give'em Hell H9R !!

[Simpson]

Alright, if I was going to race a RD350 with my CB750, here's what I would do...

1.) Replace the the front sprocket with a 16T, 1975 have the 17T I believe. This will be the easiest and best bang for the buck. Big difference. Come over you can have mine.
2.) Run a little on the lean side by adjusting air screws, or advance timing slightly
3.) Reduce the weight, but it looks pretty striped down by the picture. Maybe you can take the chain guard off and take a dump before.
4.) Run it hard!!!

Man, I'd love to race a RD350 and try to stomp those little over heating turds.
Good luck, please post results!!!!

[SV650s]

The carbs. with individual K & N's can hurt you if not jetted properly. Since this will be a WFO twist of the throttle concentrate on the main jets. A stock K5 had I believe 110 mains. Those Kehins needed 140 to 160 mains depending on the exhaust configuration. Might also help to bump the needles up one notch.

Will this be a shoestring project or do you want to spend a few $$. You can squeak a little more performance but it's going to cost.

Good luck... SOHC 750's rule...

[UJM]

Thanks guys, tomorrow is test and tune night, we'll see what it will do.

Stock countershaft sprocket was an 18 - I slipped in a 15......

Fake K&N's, they are Emgo's, and I'm not oiling them due to my fear that will kill air flow - thinking about installing the stock black velocity stacks from the airbox.....

Main jets, had 115's installed at last carb rebuild and to match the baffled 4-1 pipe.

No more baffle, and I went with 127.5 mains, seems to run good - will check plugs tomorrow.

Needs a lot of TLC, and it is a budget bike, got laid off in January and times are tight.

Like to slap on a 1/4 turn throttle, different clutch perch/lever and come up with something cool for the switches.

Smaller master cylinder (or cut the forks so the stock one fits) and correctly sizes brake hoses - or maybe even removal of the whole front brake, heck, back works fine -

Move the footpegs back - a lot.

I'd also like to check the cam timing - if I keep it, a big bore kit would be nice, ported heads, cam - all the normal hot rod stuff.

No title kind of sux, be a fun street toy - may have to try and borrow a d-tag.......

Thanks again!

[SV650s]

Just a few things to ponder in the way of engine mods.

* 29mm Mikuni smoothbore carburetors w/K&N individual filters.
* Dyna III electronic ignition.
* High energy Andrews coils.
* 750cc bored out 3mm to 812cc.
* 11:1 compression ratio.
* R.C. Engineering aluminum alloy golden rods.
* Andrews D grind cam.
* Ported and polished combustion chambers.
* Balanced pistons with custom designed crowns.
* Heavy-duty valve springs.
* Reinforced cam towers.
* Precision ground 4130 heat-treated alloy cylinder studs.
* Custom fabricated 0.5mm aluminum head gasket.
* Add countless hours of grinding and polishing with the trusty old Dremel.

[UJM]

If I was dreaming -



1080cc big bore.......

but, that's too much, and while we all know that is never enough, well -

Thank you MisterMike -

I'll try and post up the times tomorrow, wish me luck, been a few years since I've been to the track.

[scrat]

sweet cheezus, there's another monster being born! have fun, hi from norway!

[Simpson]

Hey UJM, I realize this is for giggles, but from reading the thread in the other forum the other guys has sizable advantage.

1.) Hopped up bike
2.) 40-60 lbs weight

Since large engine mods are not likely...
If it were me, I'd strip off what ever I could off the bike, IE fenders, whatever...
His bike is going to be fast!
Not to bug you, but I'd just like to see you beat the RD.

[UJM]

I'm just not convinced I can take enough off to make a difference.

Already put a tiny little battery in, that saved a fair amount -

I can probably loose more weight in a week that I could take off the bike, maybe I am wrong, I will put some more thought into this -

Rain kept me from the track last night

THANK YOU!!!!!!!!!

[zookmor]

have fun UJM

[secondchance]

Originally Posted by secondchance

what where the 750 running back in the day.....HP

secondchance thats a hard question ...cant really answer that being back in the 70s an all..besides who are you anyway...well im guessing high 13 if lucky but should be a ...like riding your grand mother

[UJM]

Originally Posted by secondchance

.......like riding your grand mother

Dude dude dude, you know what, I woke up one day and I was a Grandfather, that was hard enough for me -

But the day I realized I was doing a Grandma, well - uh, never mind.....

Seriously,

The bike should easily run in the 13's, but as secondchance said, running a 13 on one of these olds bikes is probably harder than running a 9 second on a modern machine.

The old POS I am working with is downright scary at speed - might be the skinny bias ply tires, might be the raked frame, might just be it is 30 year old technology, but I'm going to tell you, it's not a pleasure cruise at speed.

Here is my estimated speed in gears (Thanks in part to LDH)



And a couple more pic's of the machine....





I hope I find a job soon, and one that pays enough for a modern motorcycle, but until then, this one rocks, and while it has plenty of faults, it's got plenty going for it as well.

[tvetree]

I ran one of these for a while(street not track).
I had put on a -1 front sprocket made it real squirrelly off the line and in the lower gears.Bad news is at the end of point A-B(short run but don't know how short. it's not there anymore) it was going slower(by the speedo)than with the stock sprocket by as much as 10mph.Now this was seat of pants no timing so it may have gotten there faster time wise ,but with a lower trap speed.

[secondchance]

[QUOTE=UJM;325491]Dude dude dude, you know what, I woke up one day and I was a Grandfather, that was hard enough for me -

But the day I realized I was doing a Grandma, well - uh, never mind.....

Seriously,

The bike should easily run in the 13's, but as secondchance said, running a 13 on one of these olds bikes is probably harder than running a 9 second on a modern machine.

The old POS I am working with is downright scary at speed - might be the skinny bias ply tires, might be the raked frame, might just be it is 30 year old technology, but I'm going to tell you, it's not a pleasure cruise at speed.

putting it that way a grandmother aint so bad lol....my teeth hurt everytime i see the top of the forks......looks like no baffle in the exhaust..do you ride around with one...thanks for posting the mph sheet..one of my first bikes i ever rode was a 750 chop... after all the bikes ive owned nothing ever came close to that feeling

[UJM]

Thanks for the comments

Track is supposed to be open tonight, but it is also going to be a heat index of 110.....

I've been in 115 in Phoenix many times, and I'd rather be in that than 100 in Missouri.....

May try and make it out there anyway -

Regarding countershaft changes and speedometer error, the old CB's read off the front tire, changing gearing does nothing to the speedo.

My old 919 had the speedo pickup at the tranny, and yes, gearing changes made a difference.

We'll see how the day goes...

[Bigdaa]

Originally Posted by secondchance

what where the 750 running back in the day.....HP

63
Bikes ran in the 12.9 region.
My 75 750F ran 12.93 according to the mags.

[UJM]

Originally Posted by Bigdaa

63
Bikes ran in the 12.9 region.
My 75 750F ran 12.93 according to the mags.

Good info, thanks.

Our local track is only an 1/8 mile - and it's a blast!

Went out tonight, dodging a storm.

Unpacked the van, started changing clothes -

And they cancelled because of a little freakin' tornado warning

At least they gave us a refund, that was cool, maybe next weekend.

There are a few things I would like to get done, like, uh, bolting the seat down -

And maybe the gas tank too

[secondchance]

Originally Posted by UJM

Good info, thanks.

Our local track is only an 1/8 mile - and it's a blast!

Went out tonight, dodging a storm.

Unpacked the van, started changing clothes -

And they cancelled because of a little freakin' tornado warning

At least they gave us a refund, that was cool, maybe next weekend.

There are a few things I would like to get done, like, uh, bolting the seat down -

And maybe the gas tank too

Tornado can only help your time...63 hp now 600 get over 100...who would of thought that

[UJM]

Exactly, the new 600's will leave what "we" used to consider superbikes in the dust.

A CBR600RR will blow the doors off a CB900F/919 - and that one one points to tuning more than anything else.

I could mop the floor with the 600cc sportbikes on my old 919 - in a street drag.

Give them any shot at the horizon (or some corners) and the taillight was all I got to see.......

It's funny, what "we" used to consider quick and fast is not considered slow - we put "kids" on beginners bikes that are quicker than the widow makers of a few decades ago.

All good stuff......

[secondchance]

when buying the 919 i knew it wasnt on top of the food chain as far as power and performance....i wanted to get away from the race wars, did that for the last 30 years...but im having more fun then ever before..and its equil the the 1150 e i had and that was a great bike......im not to sure about a 600 kicking ass..imsure can in all out race mode.....for street performance i like to roll it on and take off...something about having to down shift to make power seems lame to me

[UJM]

The 919 was possibly my favorite motorcycle of all time, but at the strip, back to back, I could ride a new CBR600RR down the strip quicker -

Maybe not the first 60 feet, but at the finish line, those little bitches were hard to beat once they got would up.

I'd take a 919 over any of the 600's any day.

I'm really hoping for two things:

1, I find a job.

2, Honda releases the latest CB1100F!

[secondchance]

Originally Posted by UJM

The 919 was possibly my favorite motorcycle of all time, but at the strip, back to back, I could ride a new CBR600RR down the strip quicker -

Maybe not the first 60 feet, but at the finish line, those little ####hes were hard to beat once they got would up.

I'd take a 919 over any of the 600's any day.

I'm really hoping for two things:

1, I find a job.

2, Honda releases the latest CB1100F!

HELL I HOPE YOU FIND A JOB ALSO...im thinking the 1000f wont be cheep

[UJM]

Weather is supposed to be good tomorrow.

Did a little work on the bike today, rode it 20 miles or so - runs really well when fully warmed up.

Hit the ton on it, indicated, felt good (the bike and the speed).

Maybe there will be some figures, pictures and maybe a video or two to post this week....

[UJM]

Loaded the van this AM - lots to get done to make it all happen.

1st, have to get to the shop and ship the daily eBay items

2nd, well, have to install a new water heater....... 1st time for everything, should not be too bad, but the new one, looks different, but - well, those water valves do seem locked up, and - well, uh, should not be a problem......

3rd - GET TO THE STRIP!!!!



Ouch, bad pic, sorry! OK, I see the jacket is there, helmet, gloves and boots - check



motorcycle is there, road ready -



Small tool box, ramp, toss in some iced down bottle of water, maybe some snacks, don't forget the wife and son and camera -

Now, wait.......

Wait - ship eBay, gotta get goin'!

[UJM]

Hahahahahaha

The strip is closed for the holidays

[SV650s]

Steve : One big word of caution which you probably know. The chain is the weak link(no pun intended). A failure while you are WFO spells DISASTER. Be prepared for a hole in the engine case or worse!

[Super Sneaky Steve]

Yeah and you'll get those fork tubes in your face.

[UJM]

Originally Posted by MisterMike

Steve : One big word of caution which you probably know. The chain is the weak link(no pun intended). A failure while you are WFO spells DISASTER. Be prepared for a hole in the engine case or worse!

Thank you - it has a brand new chain, I'll be extra sure to keep an eye on it.

[secondchance]

nice thing about thin tires,,easy on the chain an tranny

[UJM]

Well, we are going to try again for this Wednesday, July 8th.....

Let's hope the sun and the moon and the stars and everything are in alignment.

[sbeau1960]

Hope you get to run, good luck!

[scrat]

no matter what you run, it's gonna be fun as long as you make it through the lights, and back down the return road in one piece! i never ran my first 750 down the track, but i did drive a ford aerostar, i had to drop the fairing, bags, rear fender, trunk, and luggage rack to fit it in when i bought it out of a basement for 75 bucks... it was fun! my current 750 is a barn find that i rode a few times and began to butcher. remember, if it's for the track, you don't need a rear fender, tail light, pass seat, pass. pegs, all those frame tabs...
a few places that might help for ideas, advice, or parts:
Team Hansen Honda
CB750 Honda M3 Racing - Classic motorcycle parts for Honda racers

i know those addies by heart as i have a handful of vintage Hondas myself
HAVE FUN! RIDE HARD!

[UJM]

Originally Posted by scrat

no matter what you run, it's gonna be fun as long as you make it through the lights, and back down the return road in one piece! i never ran my first 750 down the track, but i did drive a ford aerostar, i had to drop the fairing, bags, rear fender, trunk, and luggage rack to fit it in when i bought it out of a basement for 75 bucks... it was fun! my current 750 is a barn find that i rode a few times and began to butcher. remember, if it's for the track, you don't need a rear fender, tail light, pass seat, pass. pegs, all those frame tabs...
a few places that might help for ideas, advice, or parts:
Team Hansen Honda
CB750 Honda M3 Racing - Classic motorcycle parts for Honda racers

i know those addies by heart as i have a handful of vintage Hondas myself
HAVE FUN! RIDE HARD!

Thanks for the info, advise and link -

and there are times I like to slap a plate on and ride it around town -

Just to show the Harley riders what LOUD really is!

[UJM]

Weather check shows tomorrow as beautiful, so far so good.

Everything is still loaded in the van from last week, check.

Called the owner of the RD350, I'd like to get some benchmark passes made "under cover" but hey, whatever!

Had a volunteer for pictures, got that end covered, hopefully we'll have some numbers and more by Thursday evening.

[UJM]

I was able to make 19 passes - 3 timeslips scanned and attached

Best reaction time on a .500 clock was a .537
Best 60' time was 2.044
Best ET was 8.595
Highest MPH was 80.07 (Yeah!)

Shake down runs complete -

Clutch needs to be looked into, also started running a little rough towards the end on the night, although the last run of the night needed a .573 reaction time, a 2.119 60' time, 79.5 MPH and 8.719 ET.

Need to check clutch and check points, valves, all basics - look into a 1/4 turn throttle and cutting the fork tubes down - $$$???

Pictures and YouTube movies later, time to rest, thanks all.

[scrat]

cutting tubes is work. you can prolly find a few sets of stock cb750 forks on evilbay. you can get them pretty awfully cheap. i have a set, but they are holding the frame and exhaust of my current 750 off the garage floor. work on that clutch! my 450 runs 8.05 in the eigth...(insert evil smile here)

[ratdog]

Great Stuff !!

2nd the notion of getting some spare forks...gotta love the raked out setup you have for riding 'round town....don't trash'em.

honda cb750 forks, Motorcycle Parts - buy and sell on eBay Motors

gotta be something in there... a $35 pair?
1980 HONDA CB750 CB 750 C FRONT FORKS 900:eBay Motors (item 390059450529 end time Jul-15-09 11:12:58 PDT)

run'em short and strap'em.

Heck the WT Drag Racers fund has some $$ left in it, we could cover the paypal expense just for the grins of taking on the RD.