Topic: 750 Carbs on a 550

[caferacer]

I have a 1978 CB550 race bike and i am trying to dial in a set of 750 carbs .
I have been told to rais the needles and put 117.5 main jets in is this the right combination or am i fighting a loosing battle .
I am new to this site so i would also like to say hello all .
I also have a 1974 750 cafe project that i will post pics of through its progretion .

[Tintop]

750 carbs on a 550 for racing was a cheap solution in the day, still being used.  Jetting will depend on what other mod's you have made to the engine.  Given your in Ontario figure you plan on racing with the VRRA.  Maybe you should post an inquiry there as well, in the 'technically speaking' thread. http://www.vrra.ca/board/

[caferacer]

The motor is stock and i have asked a few of the guys and they all say
rais the needles and 117.5 jets but she still bogs in the mid range coming of the slower tight corners ok on fast corners when you can keep the revs up .

[bwaller]

Hey Cafe, are you racing mid prod? We'll see you in a few weeks.

I'd suggest a plug chop with new plugs at that mid range point. Probably the mains are close but you might try lowering those needles again.

[Bill/BentON Racing]

One position on the needles leaner,bike would wheelie with the throttle in first,but bogged worse off slow turns,one position richer,didn't wheelie but pulled stronger down low....well mine was Yosh 592 and ported head and Yosh B cam!Good luck,pt being one position a lot,can shim it for in between postions,Bill

[turboguzzi]

not exactly your situation but in my 500/4 racer i run for two seasons VM26s, effectively 27mm carbs of a GS750, had to  go up to 135 mains if memory serves me right

youll cut your job short if you run a few WOT pulls on a dyno just changing mains until you get best peak hp, then you need only to play with the needle height

my 500/4 run later on CR29s so a 550 should not have a problem running on your 28's

[caferacer]

Thanks for all the help guys i will try all your suggestions , hopefully i can get it good for Shannonville then BWALLER might only lap me once .
I am on bike 734 with the rookie vest , you will see me at tech .

Dave

[Tintop]

I'm P2 sidecar #239 Dave, stop by and say hello.

Brian

[caferacer]

Will do

[caferacer]

One other quick ? . What size pilot jets should i run with , the stock jets or a bit bigger .


Dave

[caferacer]

I tried that Bret set the needles to the centre position , put stock pilots in and chopped the plugs to dpr7e , revs great over 6 grand but but stutters and bogs anything below , left the plugs black and sooty .
Might have to go back to the stock 550 carbs for now .

Dave #734

[bwaller]

Dave you might try hrcscott, until this season was using750 carbs. He'll have settings.


EDIT: had Scotty's handle wrong, corrected above.

[caferacer]

Thanks Bret i will ask him at Shannonvill , i have put the 550 carbs back on for now .
See you at tech .