Air leaking tips from P. Morganti (Serpent- Mega USA)
Originally Posted by Bundy_Bear
I have a Mega ZX12 currently and both the LRP & Mega engines are Picco based so i have a few questions for you:
Have there been any leaking issues with the LRP from around the carby area etc?
Is there any tuning issues during longer races with the carby and people have swapped the carby as a result?
Look forward to hearing from you shortly...
The 2 cams that you use to fix the carb at the crankcase, in some cases are some tenths too long, and so even if you tight the screw all the way down, still the carb is not really tight and some air leaks from there.
To solve this, you need to take out the 2 cams, grind a little bit and then the problem is solved.
Another tip is the "o" ring inside the crankcase (there is an internal o ring inside the crank where the carb is located). In some cases the fit is so tight that when you install the carb you strip the o ring and the black parts goes in the crankshaft making a mess (not a big problem, is easy to solve).
Tuning for long mains (from several posts on this thread and on the Mega Thread)
Engine works better on the rich side (HSN) and normally needs more than a couple of laps to reach the operational temp. Start on the rich side (HSN) and after 4 or 5 laps tune the engine. Doing this process on the bench (or starter box) normally overheats the engine driving you to a wrong tuning and maybe causing a damage (this is not only in our engines, is for all). Start here:
HSN: 4 1/2 turns out
LSN: 5 3/4 turns out
This is very close to factory setting.
Run the LSN a little bit on the rich side and still the engine has a good idle (Very low rpm idle, is better for fuel consumption and handling of the car after off throttle).
After pre-heating a little bit the engine, open your throttle fully for 2 sec. than back off and let the engine idle for 30 second than just pinch the fuel line and the rpm should remain the same for 4 to 5 second and then the engine revs up and shuts off. That’s the best option for a large track with long straight away. If the track is really short, and full of hairpins, LSN need to be more lean, because the engine never revs up for a lot of time and so if you keep the same setup described before is always rich out of the corner.
Set the engine a little bit rich (if you progressively open the carb, the engine responds quick but at 3/4 rpm becomes rich (not really 4 stroking but rich) Then at the track after several laps (at least 5) if the engine is still rich lean it.
In general, if the engine does not keep it’s tune and starts to lean out after a few minutes of racing, the bottom end needle needs to be richened. That happens quite often and it is always the first thing to check when tuning the engine.
You tend to lean out the bottom end during static setup of the carburetor. In most cases, the engine has not warmed up completely (including chassis and all other aluminum parts) thus it is changing its tune during driving.
If the engine is still cold, or it was only warmed up in the pits, then set the bottom end a tiny bit too rich in order to compensate the above behavior.
If you use a Nova carburetor you'll be unable to restart the engine once it has warmed up entirely. That's because it has no thermal isolation between engine and carburetor like Picco based carburetor have.
This is also the reason why you have to start with richer setting when using the Picco based carburetor, it simply takes a while to warm up!
Experience running Picco based engines dictates that before your heats you need to warm up the engine first. Try to refuel not more than half tank and then tune the engine. To check your low end, try to idle the engine for 30 second and punch max. If you find that it screams to loud, richen a bit. It should bog a little but not shut off.
Check the temp, the best is 105º C
Plug No. 7 for heats. Plug No.8 for a 1 hour final. (on 20 -25% Nitro)
For final try to tighten a bit your 2 speed and tune your engine around 100º C.