I have some advice for anyone having issues trying to tune a Picco engine... This does not apply to every Picco engine tuning issue, but it definitely is a problem that will pop up on many of the engines........
first thing is Picco uses coated aluminum for the carb slide, unlike most engines that use steel... The issue with aluminum is it has a greater expansion when heated, what this means is when the carb slide gets heat soaked it tends to expand a fair amount, which results in the LSN being pushed slightly deeper into the needle housing/venturi ... So the hotter the slide gets the leaner the LSN setting will get.... The key to a Picco is to let the motor fully wamr up before you even attempt to tune it, as a rule on a cold start the Picco will run very rich on the LSN, but as the slide warms up and expands the LSN tune will lean itself out...many people attempt to tune the LSN when its cold and will find after a couple of laps the LSN setting gets very lean, causing you to chase a tune.... The key is to be patient and let everything heat soak before you even worry about the tune on the LSN..
Another problem is these carbs are very prone to airleaks.... You will very often find the needles will leak once everything gets up to temp, even the idle needle can leak at times.... to counteract this I use and recommend permatex high temp thread sealant http://www.permatex.com/products/Aut...ad_Sealant.htm
All you do is apply the paste to the threads on the HSN,LSN as well as the idle screw......You would not beleive the difference this can make on some of the engines, it is like night and day
Another area of concern is the actual carb body at the seam between the composite core and the metal end bell, similar to the older GO carbs.... What happens is once the carb gets heat soaked that seam will start to separate and cause a air leak.. This can be the most frustrating thing to deal with as its not a visible leak, and will only appear once the carb gets heat soaked, and the hotter the carb gets the worse the leak becomes... I use Lucky 7 sealant and coat the outside of the seam, once again on some carbs this can make a world of difference.
here is a picture of the seam I am talking about, i have applied a strip of masking tape to simulate where I put a bead of Lucky7
Now not every carb will have these issues, but as a rule these fixxes take all of 5 minutes and can in some cases make a world of differences in how a Picco will tune and hold a tune....First sogn of a tuning issue with a Picco is almost always a airleak in the carb, so I just go ahead and seal all of my Picco carbs right off the bat..