Why doesn't this work????

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Ketje
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Fri Apr 03, 2009 1:10 pm

Hello, I just build myself a new engine lately. Here's the set-up:

Rapido classic bored to 71mm
Vertex piston shortened 3mm at inlet side
60mm Full circle crank
Fresco exhaust
Dellorto PHBH28mm 120 main, 50 pilot, 40 slide, X-13 1st clip, AV266
Ignition at 18°
AF 71mm head
0.5mm base gasket and 1mm head gasket

This engine doesn't perform as I expected and there are a some kind of explotions that seems to come out of the carb from time to time. The carb is almost impossible to set altough idle is fine.

Could it be that my port-timings are completely out or maybe I have too much compression?

Thanks, Mike.

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byron
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Main scooter: Li Special; scarred,but sound
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Fri Apr 03, 2009 1:17 pm

what are the port timings ?
any air leaks ?
was the timing checked with a light ?
that main seems small ?

interested in how you get on as I am building up a similar setup myself

camel
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Fri Apr 03, 2009 7:22 pm

what length of con rod is on the crank?,shouldnt the barrel be jacked up at least 1mm with a std length rod(60mm crank)and further more with a jap rod

J1MS
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Fri Apr 03, 2009 7:57 pm

Assuming all is built well, and the Ignition is working.....I would try a richer needle, or/and needle jet, to see if it stops the missfire.....If its the Ignition at fault, It could be anything.... but you could try substituting electrical parts from a working donor scoot, this usually works......If its a std Rapido Classic..??... I would have thought that the Inlet timing would work with only 3mm cut off the piston and a 60mm crank....and as you havn't jacked the barrel up the timings (Exhaust & Transferes) shouldnt be excessive...I would have expected it to run....It might just be the Ignition or carb at fault so long as the engine has been correctly assembled.... rirgs bore timing clearances squish etc....Hope you fix it.. :)

Ketje
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Fri Apr 03, 2009 8:58 pm

Complete ignition has been replaced yet with no ressult. Tried richer jetting, pilot, atomiser and needles with no result. Gonna put a 58mm crank in tommorow. Is bored with 0.08mm clearance, my squish is 1,7mm. Didn't check port-timings, it's standard con-rod, timing was checked with a strobe, main jet is ok, drove it for several kms full-throttle. The only thing worrying me a bit is that the plate holding the drive-side oilseal was not completely centered with the bearing. I had to adjust is. It probably still isn't perfect centered but the oilseal should do the job. Going to put a sealed bearing in it tommorow too.

Mike.

Ketje
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Sun Apr 05, 2009 8:37 pm

I've put in a 58mm crank again and the missfire is gone. It was defenatly a port-timing issue. So, missfire gone, possible to setup the carb now...exept.....a std 200 goes better than mine. Could it be that the transfers are completely out of angle now that it is bored to 71mm?
Also, I never have read somewhere that I would have to machine the crankcase and piston to put a 60mm crank :?
I think I'll just put a Mugello on the bike.

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