Rapido Classic 250 Help!!!!

[Oldgit Dave]

Hello all,

I have recently come back to scootering after 30 years away. I have restored my old TV175 (sx200 look alike) just the way I had it back when I was 17. I abandoned scootering after frustrations with the first 250cc kit I purchased from AF in Watford. I used to build lots of scooters and engines. But I never had much sucess with the original 250cc kit so I abandoned it and I had other responsilities at the time ... Kids/mortgage etc...

Anyways ... full resto done by myself everything including sanblasting and paint work all at my garage at home ... and its back



OK so heres where i need the help. I got a new Rapido kit from AF the classic repido coz i dont wanna be screaming around like I used to instead im after a more rideable scooter with lots of torque. I have still not managed to get this kit to work properly I seem to have heat issues perhaps, it likes to Ping and seize. After pulling it apart to check it out after yet another seize I droped in Reedvalve and ported the piston to allow for the reed induction along with the boost port.

Now this hasnt made the problem go away. Im running 19 Degrees of timing. 60mm Mec Crank I have been all over the crank case thinking perhaps I have an air leak. There isnt one I have even RTV sealed all the gaskets. Squish is 1.5mm. I started with the recomended 55 130 Av266 x7 needle second clip from top carb settings on a brand new PHBH Delorto. It seemed to be lean so I now have a AV268 140 and I can still hear it ping in certain rev ranges. approx half throttle, yet its way too rich up top. The exhaust is a PM tuning PM28 Evolution

So I have some questions. The cylinder head is a 9.5:1 static compression. is this too high?
Also whilst im on about the cylinder head the squish measured at the outer edge is 1.5mm come in a lil bit from the outer edge and its much more. Is this correct? Should the entire head other than the combustion chamber not match the profile of the piston dome?

I've also been thinking. I opted for the classic rapido goin by the number on the barel im assuming AF hasnt shipped many of these perhaps the race rapido is more popular. I know the difference is in the exhaust port, perhaps they run better coz its a taller port and that would make the running compression ratio lower?

So I got a new piston 72.4mm and a rebore comming, I just want this to run right.

I would like to get ppl opinions on these questions :-
Is the cylinder head correct?
Is the exhaust right for this application... im thinking this could be a problem?
Is the problem the compression ratio, if so how should I resolve it? Hack the exhaust port? Machine the combustion chamber more?

Im also concerned about the balance factor in the crank becuase it has a 72mm piston which weighs more? Am I being too anal? will this cause issues? is there anyone out there that can balance the rotating assemble to match the specific application?

All Feedback welcome

Thanks

[drunkmunkey6969]

See if you can get squish down a tad to say 1.2 or 1.3, try 17 or 18 degrees ign, make sure fan cowl fits snug as you can to the flywheel. Ask AF for low comp head profiled to their piston, if they dont supply an exact item to your spec, ring MB....explain the problem and ask them to supply a correct item to exact specs. Your jetting sounds odd....piston port and reedvalve have two different ballparks to start from....so if yours is now 'full' reedvalve (ie - 360 degree inlet) then look at RB and TS1 jetting specs to get your starting point.....and try an X13 needle to cure the midrage issue....if that helps, you can then dial in your main more accurately. Also, you say you want a setup with lots of torque, but isnt the PM28 a fairly revvy pipe? And as i recall.....isnt the stinger a tad narrow (my memory is shite) which can cause heat build up issues???

If you are not happy with the pipe, try a JL3 or one of the new ADS pipes from Chiselspeed.