Scooterotica

Hello everyone

I recently built a new motor thinking of a quick and fun bike, but without seeking the last kilometers per hour, say it did not bother me going over 130 K / h.

The components are as follows: JL RH, Malossi 210, 60 mm crank mushroom type , head 11:1, reeds MRP (mrpracing) + RD 350 (BGM), Keihin PWK 28, RAMAIR, cases matched, piston machined.

18 º BTDC. Exhaust 186 º - Intake 126 º, 1 mm under the cylinder - 0.5 top of the cylinder, 1.2 squish.

In early tests it was determined that a 48 low jet was the most appropriate and standard needle JJH did well in the stand. Once on the road began testing with a 135 high, but never put the engine at top speed.

The engine feels perfect, sweet, until 4000 RPM, where he finds a wall, starts to vibrate and continuous flat until 5500, after which becames a rocket until I dont know how much (more than 120 km / h in third)

Because I did not have any Keihin needles I changed to a Dellorto 30 PHBH (Polini: low 55, 40 slide, X2 top clip, AV 264, main 125, Malossi: low 55, 40 slide, X2 top clip, AV 262, main 132) from my Polini engine: the problem persisted. We changed the coil, the same thing. We changed the stator: the same. The flywheel: the same.

Faced with such amounts of changes without results we proved a Malossi exhaust and the engine improved somewhat, but not much. We changed the atomicer AV 264 to a AV 262 and it is running better but not perfectly. I tried 16-17-18-19-20 degrees and does not clear the problem: at 4000 RPM begins to vibrate :flaming: :flaming: and does not react until after 5500 rpm were it starts to run like a plane.


Any ideas?

Possibly the crank is causing the problem. Theres a lot of meat from those mushroom type cranks.
They will also lower the primary compresion loads. This is fine if you have an exhaust to help the transfers scavenge but its very difficult to fit one on a Vespa.
The weathers probably a fair bit warmer over there than here but still your jetting seems weak to me.
You can use anything up to a 145 main. I would say 130 is minimum. Don't forget untill you really thrash the motor your not fuly onto the main but with a 125 mj you won't be for long.
X2 needle is right but I would say AV264 is minimum and more likely AV266 or even AV268.
With 186 degrees exhaust timing its always going to be fruity and I'm not surprised its a bit on and off.
You could but the whole 1.5mm at the top of the barrel as a head gasket. This will give you more mid range at the expence of top end but will also make it more rideable.
Stiff racing reeds won't help either. My choice is usually the boyson 2 stage reeds which I think suit scooters much better and last longer than race reeds.

Hope this helps

Of course it helps. Thanks.

It's a shame that after so much work and money I have noticed that this engine, to work properly, will need an exhaust that will necessarily be too noisy for a city like Seville.

I'll put 1.5 mm. up and return to SITO + for now until I rebuild the Polini. If I do not get it to do well, I will change the reeds for carbon ones.

What thickness do you recommend for the reeds?


(The 125 was in the Polini)

So..the mushroom type crankshafts will not work with all the exhausts, they need a special exhaust that will help them to scavange the mixture?
I've been fooled again by myself .....

I think you need an expansion chamber pipe like a jl , or sip etc

I changed the BGMreeds (resin) for carbon fiber ones and the problem is solved: THE CRANK WORKS.

thin reeds react quickly and favour low revving motors but suffer from "reed flutter " at higher revs ,
stiff reeds on the other hand cope with higher revs...but are somewhat lacking in responce lower down the rev range ,the best combo is as diablo says ,the duel stage reeds..
and that way you get the best from both worlds for your motor..

My problem was only arround 4000-5000 RPM: the engine ran well in low and high RPM. I think there was some kind of resonance. The carbon reeds are much harder now because I have not done the center cut, but the engine is perfect now: shame I can not use a good pipe due to noise (I am thinking about the SIP Roud).

Did you use two sets of carbon fibre one cut with a second smaller carbon reed over the top ??

Did you keep it with the standard reed stays in use ??