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CB250 Engine

Discussion in 'Technical and Troubleshooting Torque' started by nodz, Feb 1, 2005.

  1. Have a CB250, wanted to get a spare engine for it and make it a little more trick, so that when the current engine needs a rebiuld I can put it in the bike. Any suggestions on what could be done e.g overbore, reduce deck height, decrease head chamber size (increase compression ratio), mild cam to give it more top end etc, etc. Where to go for assitance?

  2. Nodz,

    Which CB is it. The current twin, or an earlier single?
  3. ibast,

    Its the current twin

  4. Not the best engine to play with really is it? :?

    Best you're going hope for is:

    Making sure compression is 100% (may need to plate the bores/get new rings/re-bore).

    Make sure the timing is right and you're getting a good set of bright sparks at the plugs.

    Skim the head or fit a thinner gasket.

    Ditch the air-box and go for some k&n filters with a couple of slightly larger diameter carbs from a 125 single and get rubbers to fit.

    Hack your pipes (cut them open and remove baffle pathway restrictions (loop-the-loopy go the gasses)).

    Jet and tune to suit (don't run too lean, you'll kill it).

    Should give you at least 2 extra bhp :) :p
  5. Sounds like a fun project.

    I don't know the engine that well and I can't think of another engine that it is in.

    So as stated, pipes, air filter then rejet.

    If you have then engine out try degreeing the cams.

    also make or buy an ignition advancer. Then put the fuel in that you are going to use and find out where it pings, then back it off a bit.

    Shave the head if you are willing to use premium fuel.

    After that it gets expensive.

    I think this is a single cam engine, so pull it out and get it reground. Talk to someone in the car world about this as bike places charge like wounded bulls.

    Then you will probably need bigger carbies. Because you are starting small you should find someing slighting larger at a wreckers. Jets and balance once again.

    Also check european web sites. Sometimes germans on the french get excited over certian bikes and all sorts of stuff pops up

    Take it in small steps. Have fun and let us know how it is going.
  6. Would a larger engine fit in the frame, such as one from a CB350 or CB400? To give a little something etra to play with.
  7. Doubt if either a CB250 or 400 would fit without major work. A tuned CB400 engine would probably prove too much for the little CB250 frame to handle anyway...

    Just get yourself an RGV and tune that to destruction instead :twisted:
  8. HUUUge effort and expenditure for very little gain. :( :(
  9. Don't listen to the woysers Nodz. 10% is 10% and it's usable 10% on a 250.

    I think the earlier 250 twin was a sownsized version of the 400 twin. The result is that the 400 won't fit in you frame. It was a heavy bike too (so I am told).