More Power from Jialing 250

Decided that the little 250 cruiser needed a bit more to cruise with the bigger boys, so -

Stage One - take off the head and open up the very restrictive exhaust ports, clean up the inlets, and remove the steps from the inlet manifold. This allows far better breathing, so my old complaint about carburation falls away.

Then, stage two - bore it out to 56mm and fit Honda CG125 pistons. You have to mill a small squish band on the head of the piston to accommodate the bigger bore. This pushes capacity to 265 from 233cc.

I had all this carried out by the local agents, TT Motorcycles. I previously changed the standard 32-tooth rear sprocket for a 29-tooth, giving a calculated true speed of 140kmh at 8500rpm and 120kmh at 6500. The bike now pulls this gearing with ease and has much more torque.

I intend to take the beast on a 1200km trip in the next two weeks, travelling with a bunch of kindred spirits on nothing less than 750s, so will report back on reliability, fuel consumption, etc on my return.

Whoa! :clap: That's really going the extra mile to get some more juice from the engine! I guess it's nice that these engines are so easy to work on.

Have you had any problems starting or accelerating? Noises like popping?

Lastly, what was the the total cost of the mod?

CC

I assume I could do this with the 250 zongshen engine? It's also 233cc from STOCK form.

Mine only does 85K max from stock form and I see all the other 250s in the 120 + stock form. But then again, mine isn't made for the ROAD, it's strictly dirt.

Either way, more power is more power and it might not hurt to try assuming you've got the time n' such. :icon10:

CC

Hi Carl

Cost of re-bore was US$60, but my dealer had old stock pistons and the head work was done in-house. I've been dealing with the guys at TT for over 30 years and my bike is the unofficial tester for all mods, so they charged me a nominal $20 for all the labour. I suppose a normal charge would have been somewhere around $300, depending on piston cost. Certainly worth it so far - I'll tell you more after next weekend's 1200kms.

ArcticMonster - the Jialing is a copy of a Honda CB250 motor so a parallel twin. If yours is a twin then the same thing should work. The same principle applies to a single, of course, but you'd have to find a compatible piston.

If your bike seems to be revving its guts out at 85kmh, you need to try replacing the front drive-chain sprocket with one a tooth larger, if possible. If a larger sprocket won't fit (as on the Jialing), fit a smaller sprocket to the rear wheel.

Have Fun

Thanks zimanimal. No, it's not the same engine, but thanks for the tips anyways. Might be a great winter project.

Going to try to find some different sprockets.

Quote:

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Originally Posted by zimanimal

Hi Carl

Cost of re-bore was US$60, but my dealer had old stock pistons and the head work was done in-house. I've been dealing with the guys at TT for over 30 years and my bike is the unofficial tester for all mods, so they charged me a nominal $20 for all the labour. I suppose a normal charge would have been somewhere around $300, depending on piston cost. Certainly worth it so far - I'll tell you more after next weekend's 1200kms.


Have Fun

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What size wrist pins in this engine?