VB22A carburettors

[buster]

[buster]

picked up a set of carbs on ebay, I'd guess that they are american spec cm400, I can confirm they are jetted as 118's so it looks like they are off an 80/81 model. I confess to making a slight cock up here, I was aiming to buy carbs with removable pilot jets and assumed that the non adjustable floats and removable pilot jets went hand in hand, turns out I was wrong (again) the pilot jets are the pressed in jobbies.

as they arrived







they look to me like they've been off a bike for some considerable time (rust in unlikely places) so time to split them and check a few things out







looking at the fuel tubes and the cut off diaphragm its a good job I took them apart

[buster]

onto a quick float test, mug of water and pin it gently down with an old screwdriver for a couple of minutes, lift out the screwdriver and the float should bounce straight up to the top.









fuel tubes sorted with new o rings, the key part of this bit isnt the new rubber, its getting all the aluminium corrosion out where ever the rubber rings contact, I carefully scrape the crud away with a small screwdriver then finish with a bit of red scotchbrite. they're seated nicely now





same thing applies to the cut off valves, clean all the crap and corrosion away and then I spend a couple of hours blasting carb cleaner through all the little passageways and following with the airline

[buster]

I'm now at a point where I can put the two carbs back together, fiddly and lots of swearing should be involved. the way I now do this is to fit the fuel tubes in the left carb (the one where the cables attach) then gently jiggle the spring loaded link for the throttle butterflies into position, the carbs arent parallel at this point, then I can carefully guide the fuel tubes into the righthand carb while also (with my third hand) jiggle the choke mechanism into place. yep its as fiddly as it sounds. providing nothing has popped out you should now be able to squeeze the carbs together and feel for the fuel tubes seating themselves in the righthand carb, a quick visual check to make sure everything is as it should be, then get those braces on sharpish before they fall apart again. last little job is to hook the spring in for the choke butterflies and check they are operating in synch, if not try an extra turn of tension on the fiddly little spring.





rare to have to do this next bit but I didnt like the look of the rusty screw heads in the throttle butterflies so I took them out one by one and gave them a clean up, then refitted them with a dab of thread lock, one of these coming out could cause untold top end engine damage

[buster]

as for how to clean the pilot circuit, well I bombard it with carb cleaner and engine degreaser and the airline and sadly the only way to know for sure if its right is to try them on the bike, it really was a dumb bit of design





so for now the carbs are loosely back together again, I need to rob a few parts from the 400 things carbs to finish these off (needles, guides and rubber bungs) but its too hot this afternoon for taking carbs off the bike.

[CTB]

Great thread Buster 👍

[bawbag]

Sept 9, 2023 14:26:57 GMT buster said:

as for how to clean the pilot circuit, well I bombard it with carb cleaner and engine degreaser and the airline and sadly the only way to know for sure if its right is to try them on the bike, it really was a dumb bit of design





so for now the carbs are loosely back together again, I need to rob a few parts from the 400 things carbs to finish these off (needles, guides and rubber bungs) but its too hot this afternoon for taking carbs off the bike.

What about getting some fine guitar wire down there?

[buster]

I'm generally against poking anything through jets, they really are delicate and precisely engineered things, also its not the main passage way through the jet thats difficult to clean, its the little perforation type holes in the sides that you struggle to get at when the jets pressed in. its similar in design to that hidden bugger (more on this tomorrow)

pic of the pressed in jet for reference 

[buster]

had another daft idea last night, I decided to boil the carbs in a pan of water with some of the supersonic fandangled cleaner fluid that I'v got left over. it did absolutely nowt as far as I can tell





then this morning I remembered the posh tooth pick thingies in the bathroom cabinet, so I gently went at the pilot jets with those

[buster]

so onto the rebuild, if I'm changing needles I always change the guide tubes with them, they can be fiddly to get out, I tap them with a screwdriver handle, it usually shifts them





worth noting that they they are held in place by the main jet emulsion tube



fitting the new guides can be fiddly, the thinner end goes in first and they can take a bit of a shove to get them home, its a case of using something that wont damage them, once seated the emulsion tube can be fitted and nipped up with a 7mm spanner.

now I can drop the needle into the slider and fix it in place with the aluminium cap, good fitting screwdrivers go without saying









then fit the plastic top ensuring that the o ring os good





then I fit the black plastic cap thats secured with a single screw (doubles as a guide for the slide) and then drop in the plastic ring, ridge side up





then carefully lower the slide into the carbs main body ensuring the needle goes into its guide tube, once thats home you can refit the slide return spring and the carb tops

[buster]

onto the float bowl and jets, firstly the hidden bugger sat on top of the hole it goes in. had to go out and buy a new screwdriver to get these out





on top of that one goes the secondary jet #72 in this case and on top of the needle and emulsion tube goes the main jet #118 in these carbs. the problematic (non removable ) pilot jet is covered over with a rubber plug





in the pic above its #72 on the left and #118 on the right

I suspect these have been owned by some throttle tuning halfwit as they were jetted #132 over #118

the fuel cut offs slide into the floats very loosely I lower them in together making sure I'v got the float pin in my other hand ready to set them as an assembly 









then its time for float bowls on, these have pattern (badly fitting) rubber gaskets. I deal with these usually by throwing them in the bin but I'v not got any genuine ones so I sit them as best I can into the groove on the float bowls then I hold the carbs up vertically and very carefully lift the float bowls (one at a time, obviously) up to the carbs, if they feel to seat ok I hold them tightly in place with my thumb until I get the screws home

[buster]

last couple of bits are the fuel cut off valves, pretty straight forward, the little o ring has a flat side and a round side, I always fit the flat side to the carb body (probably wrong and someone will tell me I'm sure) it seems to seat better that way





last thing to fit is the pilot/mixture screws

assembly order






I then build the parts onto the screw and again holding the carbs vertical ( no risk of o rings or washers falling off) I screw them home

[buster]

and hey presto one set of finished carbs ready to be fitted and tested on the bike





the only real issue with these carbs was a bit of corrosion on the throttle slides and correspondingly in the carb tops, basically I carefully smoothed them off with red scotchbrite just until they felt smooth to the touch. both slides have had my dodgy patented test of blowing into the two holes on the air inlet side and they feel to be operating very nicely

[buster]

so after all that I finally found some time to get them on the bike, always a joyous job but I'v done it so many times now that it becomes fairly straightforward. filled the float bowls with petrol, gently tapping the bowls with a screwdriver handle as I go, and pleased to report no leaks. put the key in and pressed the button and it cracked straight up on both cylinders. I'm well pleased with that, looks like all that time soaking and beggaring about with the pilots was worth it. I'll have a quick test ride this aft and check the plugs for colour

[buster]

ok new problem, bikes running lovely up to about 5000 rpm then starves for fuel, probably my own fault as one of these was quite corroded





I'm guessing its not letting the float operate as it should, new ones on order...