Ideas please chaps (Lardy Help)

[daisyb]

Got a mate with an Autisa (v old school!) 200, mushroom crank, malossi reed valve, 30mm delly, Scorpion pipe. Barrel jacked to give decent timings, ports all opened & matched. Standard flywheel & ign.
Put it on Johns (Jahspeed) dyno & got up to 17.7 bhp at 7700 rpm where it dropped off a wall in a fit of hesitation and "holding back" John felt it looks like an ignition problem - air fuel trace showing just slightly rich at that point- I've changed the coil,lead,plug (& narrowed gap), stator and flywheel & disconnected the ignition to headset wire. No difference.
Obviously I've told him to throw it away and get a Smallie, but just on the off chance, anyone got any ideas?
Cheers
Dave

[tony]

Hi dave. Unless you have a step or load dyno the afr is mainly irrelevant. The reason is that by the time you have spun the drum up to your peak rpm it tends to run on its own inertia and so the motor is not loaded , not producing its correct heat and giving off incorrect afr. John knows his stuff however and I trust him to correct for that.
re your misfire... measure the pipe... the skorpian was designed for a bolt on road tune I believe. If you are working with increased timings and areas its possible you have a mismatch. A missfire is possible as the pipe will be squabling with the ports.

[daisyb]

Thanks Tony, I'll give that a try, plenty of other fat girl pipes around!

[tony]

what you can try dave for a quick check is to fully advance the timing and test... then fully retard it and test.