Scooterotica

Small frames have rotary induction so you can get away with much longer inlet durations, so that is not really relevant. Piston port motors suffer badly at low revs when the inlet duration is long.
Get yourself a good book.......you might learn something

Isn't it a combination of long inlet and long exhaust timings causing a lot of overlap that is usually the problem rather than just the inlet??

Just so everyone knows. My comment about "getting a good book, you might learn something" is not me being a pompous tw&t!
It was in reply to a suggestion by someone earlier in the thread that i read an avatar which has comments about tuning books on it.

180 degrees does seem a lot. What are the exhaust and transfers etc?

Anyway getting back on point.....i dont think 160 degrees is too long! I was just saying that you have to expect a bit of spitback, thats all!

nelson pk wrote:Small frames have rotary induction so you can get away with much longer inlet durations, so that is not really relevant. Piston port motors suffer badly at low revs when the inlet duration is long.
Get yourself a good book.......you might learn something

pml! I did yrs ago when I was building a Sprint motor in my smallie.

Has anyone got an avanti piston to hand and can tell where abouts on the piston ring pegs are .

I know there on the piston












Kev.

Hello,

Just thought I would post my findings.

After receiving the Ron Moss Avanti kit I was very happy to find that Ron has made a full and complete kit, the spigot cylinder head fitting is great, the instructions are good Ron has even taken the trouble to supply different thicknesses of gaskets. For me I feel as though this kit has been designed, built and put together with a great sense of pride. Which is something unfortunately you can't expect when you buy any aftermarket parts for a Lambretta.
So I carefully built my engine over a period of a couple of months, with the following specification :-

Avanti Kit
Mec 58mm Crank
Sx200 Gearbox 17 tooth front sprocket, 47 rear, 4.31 final ratio
Standard Sil Ignition 17 Degrees
Delorto 30mm PHBH Carb (50 pilot, AV268, X7 second clip, 40 slide, 125 main)
Chiselspeed ADS3 exhaust
5 Plate clutch uprated springs

I soon had my new engine in my bike and it's fair to say it takes a strong kick to start. But it's not an issue. I was soon out on the road to put some miles on it and get it run in. Having put a few miles on it I went out for a ride with my son who has a well sorted RB20 (Thanks to Geoff Stevens). All things considered the Avanti faired pretty well. It's no screamer the power delivery is nothing like the RB but lower revs and greater torque means you just punch through the gears. After not very long and I really mean not very long this sort of behaviour led to this :-



One bad case of f**ed clutch syndrome.

At this point I was very disappointed, I needed to spend yet more money on this engine which had already cost enough. So out the engine came and in went my other engine (Rapido 250) while I saved some money. Now the good thing is the engine had to be making pretty good power to muller the clutch so fast and in such an awesome fashion. The bad news was I had to spend some serious cash on a serious clutch, heavier springs were another option but I don't like a heavy leaver for me it isn't fun .

At this point I had the engine out and decided that the engine spits out a bit too much petrol for what I need. My wife has to be able to come on the back and clothes smelling of petrol isn't good here. So I set about fitting a reed block to it. The MBD unit was the block of choice and I had one in the garage so I did the necessary to make that fit, only to find it wouldn't fit back in the bike! A mixture of the shape of the reed block and the angle of the inlet port on the barrel meant it failed on the frame tube as soon as I tried to fit the rear damper.

Eventually I Bought a LTH reed block and an AF 6 Plate surflex clutch. These both arrived this week, so today I was back in the garage.



We also had a spare Varitronic ignition kit lying around the garage, (something to do with my son) I dunno it was new and doing not much. I put the Avanti engine back in the bike with all of the above. I also have a franspeed tour pipe which I'm interested to do some comparisons with on the road, but for now let's see how the ADS3 goes.



I'm excited to see how this now performs, just hoping for some nice weather tomorrow and maybe I can head off out and tan the arse off a certain RB20.

Would i be right in thinking the higher the gear ratio the more strain on the clutch ?....4.31 being quite high.

How many miles did you do before the clutch failed ?

mick1 wrote:Would i be right in thinking the higher the gear ratio the more strain on the clutch ?....4.31 being quite high.

How many miles did you do before the clutch failed ?

Possibly Mick, but remember its not just about the final gear ratio BUT how you get there that can make all the difference. Think LI 150 using 15 x 46 and the gp200 using 18 x 47 .. both give 5.2 final ratio but one is designed to help the clutch cope with the extra power.