So today me and my bro were blasting the beach, and on the way back I was blasting over 50! Then, Bam! no compression.
Got it home, took it apart. Huge hole in the piston!
av7
70cc parma kit
g3 pipe
21mm phbg
42 pilot
needle on leanest setting
88main jet
Seems rich and plugs are black, so why the hole and not seizure? Picks to come in a bit.
Timing?
sounds like it.
detonation
another epic FAIL for the poor moby:.(...
Other french homies have suffered the same demise.
I think I will be going av101 this would need a complete rebuild anyways.
now you've got me worried, i've got almost the same setup 'cept 78 main and CDI
but, i gotta get a better timing tool. right now i'm using a homemade one and i'm afraid the error margin is too great.
I also wonder if it is because I never shaved the top of the piston so that the exhaust port could open all of the way.
hmmm.
It looks like the aluminum is flaked...
See how it failed from the outside on the pick of the underside of the piston crown?
hmmm...
yea the metal is flaked all over
Ultimate lameness...was this on the rigid?
How thick is a new parma crown?
The black 50v
Not sure paul.
Damn that sucks...
been there, exact same scenario. bummer dude
So why did this happen, did my timing slip What did I do wrong?
We'll be strictly theorizing at this point, but....
Did you ever notice pinging before?
How far advanced were you?
What plug?
stock timing, and a b7hs plug i think....
b7hs, never noticed any pinging. I never touched the timing it was like that when I got it.
Ouch.
That sucks mang.
What octance fuel do you run?
I was running 93 octane with 50:1 saber synthetic.
it USUALLY is caused by over advanced timing. mine blew on a timing test run
so, jesse, you gonna go with the parma again or something different?
5% mix... Run the jetting super lean.. follow me kids I might teach ya something :)
Wow, sucks hard. Are you going to get the replacement piston from Treats?
I tuned/broke in my Parma 70 at Bomb Prom. My setup is odd... very rich:
AV7 Parmakit 70
Case Match
Two base gaskets (1.6mm thickness total)
Stock AV7 Head
Beer Can Gasket (leaky, leaving today)
Doppler Endurance Crank
LeoVince pipe
PHBG17
50 Idle
102 Main (!)
Leanest Needle
Malossi Red Filter
2mm BTDC
11/48 Gearing
50+ MPH
It is still not tuned right but I got color on the plug on a very careful plug chop (all WOT) and then proceeded to blast, big time, for 50 miles. I'll tear it down today and look it over but it felt very strong. I can't actually get WOT unless I roll it on slowly as it picks up speed. Plug chop was done this way too.
So you kitted a moped without checking the timing? Lesson learned I guess, but what a total bummer man!
Clean up the sides of the cylinder with some HCl and get a new piston and rings and keep riding!
yes I did! And I should no better, I just wasn't thinking.
do you use a piston stop under high torque for variator or magneto tightening? some of those stops leave dents in soft aluminum
Never used a piston stop on this bike.
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