CB550 Project Scruffy Racer

[irk miller]

They would have to be pretty far tight to cause that much of an issue. I would lean to igntion, like timing, or vacuum leaking. Have you blipped the throttle to see if the idle hangs. Are the plugs getting fouled to maybe point to ignition timing?

 

[Sderbyshire]

The ignition hangs sometimes Irk, i’ll recheck ignition but i think i have a leak !

thanks for the suggestions

steve

 

[Sderbyshire]

Took a long look for air leaks this morning, all the rubber parts are flexible and seal fine.
spraying wd40 about found no leaks

so i wanted to check the carb mechanism/throttle cables
both cables were new last year but the pull cable was always a bad fit, too long and not enough adjustment, and it seems a bit stiff to return.

inside the twistgrip there is a little kink in the cable Which might be dragging.

so i‘ve ordered a new pull cable from David Silver in the hope it might fit and work better.

what‘s the procedure for lubricating the carb theottle closing mechanism so it closes reliably?

steve

 

[Maritime]

I use a silicone lube spray after cleaning it up good. The kink could be you main issue for sure as well. Also on the mechanism if it was disassembled you need to make sure the spring was attached and re-tensioned exactly right or it can hang or not return fully when released. You'll need to close it with the push cable everytime.

 

[Sderbyshire]

I did rebuild the mechanism and refit the spring i think correctly, but am unsure how to ‘re-tension the mechanism’ ?

 

[Maritime]

It depends on the type and I am not 100% sure on the 550 but My GL had to be done just right or it would not return all the way, also same as my CM450T, both needed to be hooked up, turned to the right spot and then tightened down. It took me 3 tries on the GL to get the spring in the right tension to allow full open and full return. there is little locating nubs on the back side of the wheel that can go in more than one orientation and getting then in the correct indents with the spring right was the trick.

 

[Maritime]

google found this, has some spring details.
http://www.vintagebikebuilder.com/cb550k-carb-rebuild-demonstration.html

 

[Maritime]

And after looking at that, these don't have a clock spring like my bikes so the mechanism is not the same as I was picturing.

 

[Sderbyshire]

Also took a fresh look at the ignition today.

timing seemed a little off on 2&3 but i coildnt get it to line up, the cheap pounts i fitted are crap!

reinstalled the originals again and they time up perfectly !

decided to order the Dyna kit to remove this hassle in the future

 

[Sderbyshire]

And after looking at that, these don't have a clock spring like my bikes so the mechanism is not the same as I was picturing.

Thanks anyway !

i looked at it very carefully when building it up, i dont think there is any adjustement as the arms are woodruff keyed to the shaft and the actuator sits in a flat on the same shaft.

 

[Maritime]

I saw that after I looked into it a bit. All my setups have been clock springs, the choke on yours has a clock spring that may need adjusting though.

 

[Sderbyshire]

Those are the 77+ carbs, mine is a 76 amd has simpler carbs without a choke cable ( just a lever)

i’m going to look over the mechanism again tomorrow to see if there is a way to add more return tension

then i’ll fit the jew throttle cable if it comes and try again !

it’s all fun

 

[Maritime]

Ha, gotcha. good luck, I am sure you'll nail it down in time.

 

[Sderbyshire]

So i ordered the Dyna unit from 4into1 on monday and it arrived this morning, amazing transatlantic service !

fitted the unit and Scruffy fired right up.

awaiting a new, and hopefully better fitting, pull throttle cable from David Silver and hoping dor a test ride on Friday ....

steve

 

[Maritime]

Sweet.

 

[Sderbyshire]

New throttle pull cable arrived, fitted and tested

its a much better fit and the throttles all snap shut nicely now

a question on carb setup :

on the early , non cv pre 77, cb550 keihin carbs - should the bike idle on only the idle air circuit ?

ie with the slides shut and the thumb idle adjuster backed right off should the idle air circuit be sufficient for idling, or will a small amount of slide opening be required?

i think Scruffy’s carb and ignition setup is close to perfect now ......

TIA

steve

 

[Sderbyshire]

Rain stopped for long enough for a test fire, success!

scruffy fired right up and immediately idled well.

i’ll still need to set the bypasses and then vacuum sync the carbs but Stage 3 - Go Big is complete

Phase 4 , after some extensive testing, will be to tidy up the wheels, forks, probably renew wheel and head bearings to finish off.

it’s been a lot of fun resurrecting Scruffy

 

[Maritime]

Nice, so looks like your cable was the culprit after all

 

[Sderbyshire]

Nice, so looks like your cable was the culprit after all

We’ll see!

the crappy points and sticky throttle cant have helped.

its due to be dry tomorrow so am hoping for a small test ride, will report back!

steve

 

[Sderbyshire]

Managed to get Scruffy out for a short test ride this morning

something still not right!

bike fired up instantly but straight away it wasnt pulling smoothly

i filled up with fresh fuel but this didnt really help

i suspect that the carbs must have got some dirt in them, so will have them off/apart at the weekend
also ordered a pair of 5ohm magna coils and new ht wire to complete the new ignition setup

Any other suggestions ?

steve