Topic: 1981 CB650A Carbs - damaged piston question

[CB650Tex]

I've finally started stripping down the VB44A carbs on my bike to give them a good clean and renew things.  Unfortunately, I've discovered score/wear marks on the piston and bore of the no.4 carb.  Not had a chance to pull the others yet and see if they're bad too - that's tonight's joyous task!

According to my Haynes manual, "damage of any sort will require the renewal of both components".  So the starter-for-10 question is,


How bad does the scoring/wear need to be before I really need to find a new set of carbs?


And the bonus question is:

Could score/wear damage to the piston/bore be responsible for the various problems I had with the bike's running?

Those problems being, needs at least a small amount of starting fluid into the airbox to get started, unless it's been running a while; in neutral, RPM fluctuates of its own accord (sometimes it's worse than others); backfires out of the exhaust periodically (more frequently, get dark smoke out of the exhaust)  Prior to pulling the carbs off, I had sprayed WD40 onto boots from carb-to-cylinders and carb-to-airbox with the engine running, both had no effect.


Last question: I've followed the instructions in the Haynes manual and taken out everything it says to remove.  Am I now safe to plunge the carb body into Berryman's B12 without risk of melting any hidden plastic/rubber pieces?

[kettlesd]

Any chance you can post pics of the scuff marks? How deep is the scoring - can you catch a fingernail on them? How much friction is there between the pistons and the bores - do they slide up and down easily? They should drop back down smoothly with their own weight.

Bad scoring can affect the operation of carbs - especially on CV's like your 650, but a slight amount of scuffing can be present from running them dirty or without a filter. Hard to say with out seeing them.

But it also sounds like they do indeed need a good cleaning, float adjsutment & sync.

[cb650]

Are thee carbs seperated?   There are 2 rubber T vent tubes (regarles of what some people think) between outer carbs that doesnt like harsh cleaner.   Also FYI no float adjustment on these.





                              Terry

[CB650Tex]

Here's the gruesome evidence!

Haven't looked at no.1 yet as one of the cover cap screws is being a pain and I didn't fancy starting on it so late.

No. 4 is the worst, 3 pretty similar and 2 much less - marks on no. 2 bore were small enough not to show up in a photo.  All three are showing pretty similar patterns of wear, just differing amounts.

You can feel the scoring when you run your finger/nail over it on all three of them but not very much - certainly not enough to catch my nail on it.

They all seem to move up and down freely enough and descend under their own weight without any hesitation.

One question from a friend of mine - should there be any form of lube on them?  Haynes says nothing and I've not found any evidence of any so am assuming there shouldn't be.  But my friend couldn't understand why you'd have metal on metal surface movement without some kind of lube.

And to answer the other q's:  3 and 4 are separated, 1 and 2 are still together (but have already ground off the ends of the screws on the choke plate shaft, ready to split them) so have got one of those t-pieces off already.  I was planning to split all down to individual carbs and then dip clean them one at a time.

re:float adjustment - thanks for the heads up.  Having now taken one apart completely, I see what you mean!

[CB650Tex]

Oops. Those photos came up a bit bigger than I expected - how do I get them smaller?

[cb650]

I used scotchbrite and a hone on mine but that one looks like it pretty bad.   






                                Terry

[bryanj]

Thats what happens when no aircleaner is fitted. they will run but see if you can get a better set

[tomkimberly]

I would agree with Terry, clean them up with some scotch brite. Make sure you replace the plug wires and caps, it will make the world of difference in starting that bike when cold.

Tom

[CB650Tex]

Thanks for the info/advice.

Dumb question though...what sort of Scotch-Brite product?

I've not seen heard of it before and have just googled it and got 3M's website, where I found umpteen different Scotch-Brite items, many of which don't seem appropriate.

I was going to use some really fine wet'n'dry paper and see how much I could sort out by hand with that.  Is that any better/worse than some kind of Scotch-Brite?

[cb650]

Its the green $hit on one side of some cleaning sponges.   You can get it in small "sheets" at auto or hardware stores.  It comes in diffrent grades also.



                                Terry