paddyshepherd
Active Member
So I've stripped down the motor in my CB250RS.
I now have 3 options:
a) Freshen it up with new seals etc and bolt it back up, run it how it is (it's in good condition, we initially only stripped it due to it having sat for a long time. It did actually run)
b) Try and add a few ponies while I'm in there.
c) Swap it out for the 500 motor - this would be great, if I can find one......
I've rebuilt engines often enough in the past, especially ones as simple as this old thing. I've not however, really delved into the tuning aspect of it, so I'm after some advice!
It'll be getting a completely custom exhaust system and I'm considering upgrading to a bigger carb too.
First of all, I'm kind of struggling to think of a carb to use that will be suitable.
Secondly, I can't find anywhere doing aftermarket cams, so if I want to go that route I'll have to get a regrind done.
I'm unsure on what to with the displacement side of things, though. Unfortunately nowhere seems to still do big-bore kits for these things. The motor is pretty much the same as the XL250 and XR250 of the same era, but IIRC a better tuned version of it (did those bikes use the 4 valve head? I'm assuming they did). I'm able to find slightly bigger pistons from Mitaka (up to +1.5mm) but that's about it. No "high comp" pistons that I've seen either. Will an XR or XL big bore kit work? I'm of the impression they were lower compression motors so not sure how much benefit it would be.
I'm in the UK and these kinds of parts are difficult to find - I do however have friends in both US and Aus that could ship parts across if I find any there.
Cheers
I now have 3 options:
a) Freshen it up with new seals etc and bolt it back up, run it how it is (it's in good condition, we initially only stripped it due to it having sat for a long time. It did actually run)
b) Try and add a few ponies while I'm in there.
c) Swap it out for the 500 motor - this would be great, if I can find one......
I've rebuilt engines often enough in the past, especially ones as simple as this old thing. I've not however, really delved into the tuning aspect of it, so I'm after some advice!
It'll be getting a completely custom exhaust system and I'm considering upgrading to a bigger carb too.
First of all, I'm kind of struggling to think of a carb to use that will be suitable.
Secondly, I can't find anywhere doing aftermarket cams, so if I want to go that route I'll have to get a regrind done.
I'm unsure on what to with the displacement side of things, though. Unfortunately nowhere seems to still do big-bore kits for these things. The motor is pretty much the same as the XL250 and XR250 of the same era, but IIRC a better tuned version of it (did those bikes use the 4 valve head? I'm assuming they did). I'm able to find slightly bigger pistons from Mitaka (up to +1.5mm) but that's about it. No "high comp" pistons that I've seen either. Will an XR or XL big bore kit work? I'm of the impression they were lower compression motors so not sure how much benefit it would be.
I'm in the UK and these kinds of parts are difficult to find - I do however have friends in both US and Aus that could ship parts across if I find any there.
Cheers