Author Topic: 78' CB550.  (Read 3875 times)

Offline Hudson.

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78' CB550.
« on: July 26, 2015, 12:01:04 AM »
Hi,

Last weekend I bought this 1978 CB550 from a guy in Essex, listed as spares or repairs with a few relatively small issues to fix up.

Im not really sure if its original with all the right parts etc, but im planning to take this bike apart over winter and changing a fair amount. It'll end up pretty lean and simple cafe/brat style and mostly black i think.

- The kick start mechanism doesnt work as the splines has been stripped off, i guess the pedal was loose at some point and the splines got mashed up. Electric start works good though and the bike starts strong.

- Leak from the clutch cover

- Starts well but doesnt run great, the idle is a bit lumpy. Takes quite a lot of throttle to be able to pull away with out bogging and stalling. Its better at WOT but still not completely smooth. A lot of backfiring on over run.

Plans first off are the take the carbs off and inspect. Thoroughly clean them out and set floats, synchronise and go from there. The previous owner never actually rode it and potentially made a few changes. It has a pretty free-flowing exhaust fitted with a bolt on tip, so maybe the carbs havnt been re-jetted to suit the exhaust.

I plan to run pod filters eventually but want to get it running spot on as-is first and learn the bike before making too many alterations. I'll make all the engine changes before i strip the bike down this winter so i know I can put it all back together and not have any issues, hopefully! ;)













Hudson.
« Last Edit: July 26, 2015, 12:07:46 AM by Hudson. »

Offline Green1

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Re: 78' CB550.
« Reply #1 on: July 26, 2015, 05:08:53 PM »
Looks like a nice little bike not keen on the pipe though  ;)

Mick
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Offline hairygit

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Re: 78' CB550.
« Reply #2 on: July 26, 2015, 05:25:00 PM »
Is it actually a K as on the sidepanel? If it is, and the carbs are original, you're in for a fun time getting them sorted! And they are the most likely cause of the problematic running you described.
If it's got tits or wheels, it's hassle, if it's got both, RUN!!!

Offline SteveD CB500K0

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Re: 78' CB550.
« Reply #3 on: July 26, 2015, 07:11:11 PM »
Those are indeed 550K3 carbs...
2022 Tiger Sport 660
1971 CB500K0

Offline Hudson.

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Re: 78' CB550.
« Reply #4 on: July 30, 2015, 11:00:12 AM »
Looks like a nice little bike not keen on the pipe though  ;)

Mick

Im 90% sure its a stock exhaust with the silencer chopped off, the tip on the exhaust is held on with 3 self tappers! Not really my cuppa either but does sound quite good in my opinion!

Is it actually a K as on the sidepanel? If it is, and the carbs are original, you're in for a fun time getting them sorted! And they are the most likely cause of the problematic running you described.
Those are indeed 550K3 carbs...

The carbs are PD46A according to the stampings on the body. Are these the right ones for the model year? I've been doing some reading and heard these are the more troublesome carbs due to the emissions targets of the late 70's. Still the same principles though eh, so should be a bit of fun getting it all running proper!

Had some time to play with the bike, started by checking the mixture screws, which were ALL set differently, ranging from 1/4 of a turn out to 3-1/2 turns out! I set them all at 2 turns out and the bike was instantly running smoother, i was able to lower the idle a bit after this, much better!

Got a video of it starting well and running a bit smoother.

https://youtu.be/5ZcM3FnMFEA

A bit more satisfied with that, i decided to take the carbs off and inspect everything, for cleaning and a bit of learning. Not to mention piece of mind after finding all the mixture screws set different.













As you can see, all in need of a good clean up. One of the float covers was held on with sealant, all the floats were different heights and out of spec carb *1 was totally wrong which might explain the fuel flowing out of the airbox drain before.

The needle sliders looked pretty uniform heights bar carb *3 which was quite high in comparison.

So with a deep clean and proper calibration hopefully the bike will be nice and smooth under load!



Invested in a synchroniser, im sure it'll come in handy in the future!



110 and 115 mains, not sure what ones to try first, i think i'll start with the 115's first and work down from that if too rich.

Some individual pod filters are on there way at the moment, that will be fitted when the carbs go back on, so thought id make some jet adjustments while the carbs apart, to give me a starting point! From what i've read so far:

- Start with a high main jet size that pulls strong at WOT, lower the size until WOT becomes too lean, then go up a main jet size
- Adjust needle clip/height setting to imrpove part-throttle performance
- Raise pilot jet size if required
- Plug chops

Does that sound about right? Im learning, and enjoying it so far! I know the pod filters vs. airbox is a trivial topic, i understand that the R&D that went into the box means that its engineered perfectly and pod filters are therefore pointless. Im solely fitting pod filters for aesthetic reasons! If i wanted a fast/high performance bike i wouldnt have bought a 70's Honda! I've read some heated conversations on this subject and just think its pointless to argue, all personal preference really. It'll be quite satisfying to find the right settings and get the bike running as well as it can do.

Cheers



« Last Edit: July 30, 2015, 11:06:32 AM by Hudson. »

Offline mickwinf

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Re: 78' CB550.
« Reply #5 on: July 30, 2015, 04:00:54 PM »
good luck with setting the carbs, make sure the emulsion tubes are clear and the pilot jets as they are prone to getting blocked, not available in the UK but sirrius in America do them.
Love the 500 and 550 have a 500 called Lazarus under restoration

Offline Bryanj

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Re: 78' CB550.
« Reply #6 on: July 30, 2015, 04:17:10 PM »
You can tell the pilots have been out at least once by the grip marks!

 

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