1982 Honda CB900F Barn Find restoration - Episode 5 - Carb Rebuild part 2

Re-assembly & bench test of the CB900F Carbs

[@mindovermatter3988]

I like to use a brass brush on the outside to knock all that gas Gunk and varnish off and then I like to normally use a steel wire from the same type of brushes pull a single fiber off and take it through and kind of make sure it touches all the edges.

[@HorsepowerHouse]

FOR THOSE VIEWING: When reassembling, it's good to leave the "flaps" / Butterflies a tad loose until everything is fully assembled. Same for the long braces that hold all of the carbs together. Then make sure all movement of the choke and throttle mechanism move freely. THEN and ONLY THEN finalize tightening the rest. Tighten everything in opposing form (across, then across, then every other, etc.) Otherwise, binding can occur that can prevent free movement of the rods and flaps. I recommend replacing all of the rubber hoses as well. If one looks bad (and none seem to be replaced) you can bet they MIGHT AS WELL be replaced. And, no, the floats are not adjustable on these specific models. (why? I dunno.) These Keihin VB carbs are very finicky little kittens. Ask me how I know......

[@chrisraven-bb4jc]

Hi there: I use a Brass brush and that cleans the outside of the jets quite nicely. The other thing I do is use some Silvo or Brasso on a Q tip to clean the needle seat since they are not removeable. I did notice that you replaced the rubber plug but you did not remove the jet that was underneath the rubber plug. You have to trim a slot screwdriver to fit and make sure that the tip is thick enough at the end so it does not damage the slot. It will come out but just have to be careful. I believe it is part of the idle circuit and if not cleaned you will have a hell of a time to get it balanced properly, thanks

[@true-moto-resto]

Thanks for the tips! And for taking the time to write a comment ! In a later video I remove the rubber plug again and drill/tap the jet inside to remove it. These were pre 84 carbs, and to remove that jet in the pre 84 you have to drill/tap and use a small nut and bolt to extract the jet

[@mindovermatter3988]

Carburetor cleaner brake fluid and or starter fluid all leave a thin white film, I like to use a brass brush and knock all of the dusty tarnish off of the brass parts of the carburetor I also use a separate brass brush on any aluminum parts that may have some form of oxide

[@TonyCBX6]

You are doing a sterling job Dave. Strongly recommend removing the AFV (Automatic Fuel Valve) again and stripping it and clearing out any crud. Ack you may have already done this. If not, it is the first recipient of any crud that may come inbound from the tank before it gets to the carbs. You MUST install an inline fuel filter between tank outlet and the AFV, else all your good work may be undone as soon as you turn the fuel back on. (DAMHIK) Also, while the carbs are off and still full of fuel, be sure to check all four accelerator pump jets are working vigorously as the throttle is operated. These can easily be blocked and can be difficult to clear. Check by opening the throttle butterflies quickly and watch carefully on the airbox side of the carbs for a solid squirt of fuel from the small brass jet located at the 5 o'clock position on the floor of the carbs. With the carb slides removed, fuel should spurt out through the carb throat and out the other side.

[@true-moto-resto]

Cheers Tony, I’ll check that out !! I filmed this 3 weeks ago but easy enough to refill them and test it out

[@ThatOldHonda]

I never worry about the jets being shiny easy, to get the outside shiny, but the bit that matters is the inside and as whatever you use always requires rubbing trying to find something you can jam inside to get them shiny risks getting stuck inside. Thanks for the detailed videos some good tips in here. Most people just throw them in the ultrasonic and think they are clean, nope, clean them again, then if you think they are clean, clean them again - I use some Murex welding jet cleaners (like your carb cleaning needles, which I think are welding ones too) but the guitar string is a great idea for getting into the idle jet hole. A tip I picked up was to wrap tape over the straw that comes with carb clean to make a plug and use that to push carb cleaner down those small holes - better than just air - just make sure you wear eye protection in case it sprays back at you, ask me how I know that

[@true-moto-resto]

Cheers! Good tip in the tape to create a seal.

[@myaccount13579]

Instead of matchstick, I found that an old O ring with one side cut off to make a C shape will slip in and hold it perfectly. Place the open side of the C toward the metal notch that will be inserted and it will just push it out as it slides in. Use a fatter O ring for the one in the middle where the metal notch is thicker.

[@true-moto-resto]

Cheers, good tip !

[@mindovermatter3988]

Where can I get that carburetor rebuild kit, I'm about to pick up a $200 cb 900 but after checking it out it seems locked up and and will need a fresh carburetor clean and restore. My first time ever messing with four in a row I've done single cylinder stuff for the longest time and then got into parallel twin my first ever four cylinder. And I feel the exact same way you do about not having the confidence in the amount of information on those carburetors I've done all sorts of carburetors, I'm just not the biggest fan of diaphragm carbs especially when there's four of them. But yeah anyway if you can put me in the direction of maybe a rebuild kit for the carburetors and potentially thinking there could be something with the points

[@lornetontegode6986]

Nice work on the carbs. You mentioned the plastic floats and this is my guess. Lots of cost-cutting drives engineers and managers to do stupid stuff and they're likely a result of that mind set. New ones are probably accurate enough but over time, they probably sag and deform. If the level doesn't check out okay, they probably want you to replace them. If replacing them, hopefully you can find floats which have the integrated steel tab that you can bend. Just a theory.

[@true-moto-resto]

Thankfully the float levels were all good

[@karlvanboxel561]

I didn’t c u locktite the throttle or choke plate screws in with red loctite or stake them if they come out and go into the engine !! Disaster!!

[@true-moto-resto]

Your right Karl, I had to go back and to that later as I forgot . I didn’t take the throttle plates out

[@HorsepowerHouse]

The factory does not LocTite them. If they are going to just "vibrate" out after being tightened, there are greater issues that need to be resolved prior to then.