Scooterotica

many thanks !
good advices to start now..
@adam w. :interesting postings in the lcgb-forum, good anorak-infos.
thanks. a pleasure to read.

Ok,so here we are some 6 months and just over a 1000 miles later and i've blown a hole in my piston on the way home from Mersea!!!!!

faf wrote:Ok,so here we are some 6 months and just over a 1000 miles later and i've blown a hole in my piston on the way home from Mersea!!!!!

Jeting timing and compression ?
muppet,

Plug,piston,cylinder were all very grey,looked like it was running weak/hot! Checked plug last week and it looked fine! I presume you can check compression with a gauge but what should it be and how do you adjust?

FAF

Reading through the previous posts...........if you haven't developed an air leak and your timing is ok and you have a fast flow tap/good fuel flow, i would say its that lean looking jetting! It looks especially lean in the mid range where your going to spend most of your time cruising. When its fixed it maybe worth going to a different scooter dyno for a second opinion. I'm not saying its wrong but its your pride and joy so get a second opinion, i would.

Checking compression and which compression ratio to use is a different matter.If your unsure how to do it and dont want to start playing with calculations, burettes/syringes etc take your engine to a tuner and they will tell you. If you want to do it yourself get hold of a book or download the calcultations for geometric compression and corrected compression from somewhere. (two stroke performance tuning by A graham bell is excellent).

Cheers Nelson,gonna rebuild,check fuel flow,timing etc then re-jet carb nice and rich and go from there!

From your comments i presume checking compression is not as easy as it is on a 4 stroke engine then! If compression was found to be too high though,how would you lower it? Or should i just leave that to the experts???

Cheers.......FAF

Compression on Mugellos is pretty high but they come from the same tuning house that tends to work with auto advance/retard ignitions too, meaning that high compression is not so much of an issue... subject to correct timing and jetting. To get away with the standard Mugello head and compression ratio with static timing means that you should be setting up with pretty low ignition advance. Too much advance and holing a piston is the common outcome. NB: If you had been running an iron barrel then you woould probably have nipped up well before holing the piston... this is the benefit AND drawback of plated alloy kits (glass half full or half empty?).

Read up on checking compression and then decide if you want to give it a go. However, reducing compression is best done by removing metal from the combustion chamber area of the head, ideally without reducing squish band area. Fitting a fatter/extra head or base gasket is not a good idea if the squish was set correctly to start with, as increasing squish clearance can actually lead to overheating getting worse!

Adam

As Adam said,
if compression is found to be too high the best way to lower compression is to remove more material away from the combustion chamber which i would personally put in the hands of an expert.

Thanks for the replys chaps,interesting stuff!!! So would you say fitting an augusto or similar would be beneficial? Timing was set at 17 btdc does that sound about right?

Cheers......FAF

17 degrees if it was accurately set should be ok in my opinion but i set statics to 16 degrees on kitted lammys to be safe unles the compression is very low.
Advance/retard units are very useful in the fight against overheating.
A lot of people set there agustos to say 22/23/24 degrees so they retard back to say 16/17 at full revs however a very, very wise man once told me to set your maximum advance at 19/20 if running an agusto or similar on a kit and you will have a much cooler scooter at higher revs as the timing will be a lot more retarded and you will not have a noticeable lack of performance at higher revs. If you run an EGT gauge though, this will cause the gauge to read a lot higher as the heat is being thrown out of the exhaust more, rather than being retained in the head............which is a good thing for reliability.