carb probs

biker bob · L Plate Warrior Joined: 20 Aug 2010 Karma :

hi folks. can anyone help me? I am rebuilding the carbs on a cb250 superdream and need to get new jets but cant find anyone who knows what the standard sizes are. Local bike shop says its too old and he doesnt have any idea of it. It currently has 150 main and pilot jets which i have an idea are wrong. Its running a motad 2-1 exhaust which as i understand doesnt require rejetting. Bike runs but wont tick over and is a bit of a pig to start .So any info at all will help. Thanks

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

150 sounds high. My CB250RS, which is the same age but a single cylinder with a single carb, runs a 122 main jet.

The correct size will be listed in the haynes or Honda workshop manual. You should find a link to the superdream workshop manual in the manuals thread.

Have you given them a really good clean, including the mixture circuits? Hard starting and poor idling can often be attributed to them being clogged up. To fix, remove the mixture screws and their tiny springs and spray a good amount of carb cleaner in there, getting the nozzle right into the hole. Reset the screws to the setting in the workshop manual afterwards, probably about 2 turns out.

You are correct that a motad doesn't need rejetting.

paddlesat16 · Crazy Courier Joined: 07 May 2008 Karma :

From the honda workshop manual for the cb250nA

: jet primary main #72
:jet secondary main #105

Don't know if they changed the jets for later models, i don't have that workshop manual

Regards
____________________
I once saw a bloke shagging a donkey.... in Saudi arabia. Theory Test Passed 26/10/09 Mod 1 Passed 26/4/10, Mod 2 Passed 7/6/10 Current Bikes Suzuki GSX1400 K5, Aprillia Pegaso 650, Suzuki DR350T.

biker bob · L Plate Warrior Joined: 20 Aug 2010 Karma :

Thanks for your help i am going to order new jets and try again will let you know the results. Thumbs Up

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

Not sure how expensive individual jets are - depends on finding a decent supplier. If anything else is a bit dody in the carbs then rebuild kits are less than £20/carb from NRP in Manchester.

Worth it if the needle is worn around the clip. Mine was knackered after 30 years and only 25k, about a mil up up and down play and loads of lateral play. New needle and clip in the rebuild kit made the bike much smoother.

If it runs an accelerator pump, make sure to check the O ring between the float bowl and carb body on the pump. I forgot to refit mine when I rebuilt it, leading to fuel spraying out the back of the carb and not into the engine.