- Location
- Granbury, TX
Was out brapping around on Sunday after I had "fixed" my electrical problem (http://www.x-h2o.com/threads/109489-Superjet-electrical-problem-bouncing-revs-at-low-RPM). Was keeping myself from holding the throttle too long since I wasn't quite sure where I was at jetting wise. Well, after about 4 seconds of a throttle grab the motor slowed down and stopped... sad to say I already knew something was wrong.
Got home, pulled the head off and found my front piston melted:
Rear piston is in perfect shape, if not a bit lean judging by the piston wash, but no signs of detonation:
Looks like I will need at least another 1/2mm bore, hopefully I don't need more. The area above the exhaust port looks worse than it is because of all of the aluminum deposited from the melting piston. The good thing is, the dome is in fine shape and the pic makes it look worse than it is. The marks the camera shows aren't really perceptible with a fingernail. It seems to have just flattened out the original tooling texture.:
First thing I did next was to pull the carbs apart to see if maybe the internal filters were clogged. Carbs were spotless, filters clean, jets clear, check valves had no creases or tears. The following pics are of the fuel filter pulled out of the front (mag) carb:
A looked at the carb base gaskets too, they looked good and nice imprint still remains. Carb nuts were all as tight as when I installed them.
Next I pulled the flywheel cover to check my stator timing and make sure it was still aligned with the notch. I am running a RAD flywheel but from what I have heard it was the Jetinetics flywheels that had the problem with improperly set advance (just thinking out loud). Stator was still in the right spot, screws were tight, woodruf key intact. Stator stayed nice and dry, and the cleanliness of it makes me debate if the crank seal was leaking. The drip in the second pic is grease left over from when the seals were installed. Motor was built with new Jetmaniac Japanese seals
So now the question is.. was I just plain lean? The jetting specs I am using are fatter on bottom than Factory Pipe's recommendations. The gas I was using wasn't the freshest but it wasn't old enough for me to be worried about it (~a month or two). The fact that the front piston smoked and the rear has NO signs of detonation kind of has me stumped. The carbs were clean. The motor was pressure tested when it was built and didn't loose any pressure (~9psi @ 10 mins). Heck, the plugs always looked black when I checked them. Cooling was unrestricted and my pissers never stopped flowing. The only other thing I could guess at is maybe my enhancer is going bad and timing got advanced but that's just me throwing random ideas out.
Following is my setup:
62T/61x (crank, pistons, seals new - built 1 year ago) Motor is NOT ported
81.5mm Weiscos
BR8ES plugs
ADA w/ 35cc domes (I ride at sea level and run 93 octane)
Boysen Pro series (normal tension) reeds
Factory B Ltd pipe - true dual cooling to the manifold
Stock SN waterbox
RAD Flywheel
MSD Enhancer
Hooker 9/15
Stock 38's with stock F/A
135 H
75 L
1.5 n&s with 90g spring
HS 1-1/4 out
LS 1 turn out
Your help would be greatly appreciated, I assume I will go with larger high jets, and keep digging, but does anybody have an opinion? Thanks in advance.
Got home, pulled the head off and found my front piston melted:
Rear piston is in perfect shape, if not a bit lean judging by the piston wash, but no signs of detonation:
Looks like I will need at least another 1/2mm bore, hopefully I don't need more. The area above the exhaust port looks worse than it is because of all of the aluminum deposited from the melting piston. The good thing is, the dome is in fine shape and the pic makes it look worse than it is. The marks the camera shows aren't really perceptible with a fingernail. It seems to have just flattened out the original tooling texture.:
First thing I did next was to pull the carbs apart to see if maybe the internal filters were clogged. Carbs were spotless, filters clean, jets clear, check valves had no creases or tears. The following pics are of the fuel filter pulled out of the front (mag) carb:
A looked at the carb base gaskets too, they looked good and nice imprint still remains. Carb nuts were all as tight as when I installed them.
Next I pulled the flywheel cover to check my stator timing and make sure it was still aligned with the notch. I am running a RAD flywheel but from what I have heard it was the Jetinetics flywheels that had the problem with improperly set advance (just thinking out loud). Stator was still in the right spot, screws were tight, woodruf key intact. Stator stayed nice and dry, and the cleanliness of it makes me debate if the crank seal was leaking. The drip in the second pic is grease left over from when the seals were installed. Motor was built with new Jetmaniac Japanese seals
So now the question is.. was I just plain lean? The jetting specs I am using are fatter on bottom than Factory Pipe's recommendations. The gas I was using wasn't the freshest but it wasn't old enough for me to be worried about it (~a month or two). The fact that the front piston smoked and the rear has NO signs of detonation kind of has me stumped. The carbs were clean. The motor was pressure tested when it was built and didn't loose any pressure (~9psi @ 10 mins). Heck, the plugs always looked black when I checked them. Cooling was unrestricted and my pissers never stopped flowing. The only other thing I could guess at is maybe my enhancer is going bad and timing got advanced but that's just me throwing random ideas out.
Following is my setup:
62T/61x (crank, pistons, seals new - built 1 year ago) Motor is NOT ported
81.5mm Weiscos
BR8ES plugs
ADA w/ 35cc domes (I ride at sea level and run 93 octane)
Boysen Pro series (normal tension) reeds
Factory B Ltd pipe - true dual cooling to the manifold
Stock SN waterbox
RAD Flywheel
MSD Enhancer
Hooker 9/15
Stock 38's with stock F/A
135 H
75 L
1.5 n&s with 90g spring
HS 1-1/4 out
LS 1 turn out
Your help would be greatly appreciated, I assume I will go with larger high jets, and keep digging, but does anybody have an opinion? Thanks in advance.
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