Rich_T wrote:Because they are two kitted scooters where, quite possibly, the overall engine configuration does not allow for the tolerance in fuel supply and ambient conditions to conspire. Fuel is produced to a standard and it will vary, as do the other factors.Steve S2 wrote:In my case, there was no leaks the timing was spot on and on the dyno it was below 12s all the way through the revs, and I had covered over 2000 miles in the last 12 months with not a single problem.
And no tuning work was carried out on the dyno all we did was push them on and pushed them off.
I am not saying that all holed pistons are down to petrol. But why would 2 scooters hole the piston within 5 mins of each other, after filling up from the same with the same fuel.
My point is that if the piston gets holed this is a "real world" occurance, dyno's are a simulation of real world events where some basic elements have a degree monitoring. If it does not happen on the dyno then this only goes to underline that it isn't an accurate model and exactly the reason why I am very cautious of what dyno information to use and what not (time in the saddle is worth a lot more).
If it were soley fuel from that specific station there would be an ring of dead RS125's and all other manor of two strokes littered about in a radius of 6 miles. This does not mean that fuel was not the perverbial straw, it could have been. If no tuning was done on the dyno this is not a conclusively vindication that everything in the garden is rosey, and to be honest 2000 miles is not a huge distance to sign off on.
The fact of the matter (for road going scooters) is that you can not control the ambient conditions (weather) and you can not control the exact specification of the fuel you put in the tank (you buy it and get going-you don't stand there with test tubes, and a lab coat). The things we can control are how we build the engine, what compressions, ignition timings and jets we use. The logical process, to me, is to configure the settings we can control to counter balance the ones we can not. This builds in a certain amount of system redundancy and this is what should make a Lambretta engine reliable.
If the AF ratio is flat-ish between mid to full rpm on WOT then it would be no surprise to me that you have a lean AF ratio if you rolled off the throttle when you were up to speed (or exactly the wagon example DT mentions).
hi Rich
in your own personal scenario as a manufacturer of a cylinder kit how do you provide meaningful data for kit users and arrive at port specs/compression ratios suitable for road scoots ,i reckon there could be 30+ combinations of kit/bore/stroke/rod length options along with the various machining tolerances on cylinder decks and port widths and heights as cast x up to 20 pipes x up to 10 different ignitions with multiple cdi,s x 30 different carbs and 2 different inlets x multiple different air filters then theres build variables to consider
i see your building a carb settings database but how meaningful can that data be with so many variables in place
every engine is different so the way i see it all variables considered the only control to put in place after a good build to preset specifications is to dyno test to find good values as anything else is surely nothing more than assumptions,what would you reccomend a customer fitting a kit of yours to find a good baseline setting
cheers
