OP
UTC

Hooked
PX 150 and GTS 300 HPE Super Tech
Joined: UTC
Posts: 419
Location: Dublin, Ohio
 
Hooked
PX 150 and GTS 300 HPE Super Tech
Joined: UTC
Posts: 419
Location: Dublin, Ohio
UTC quote
I have a 2005 PX150 which I acquired with no miles on it several months ago. It now 2300 miles on it. I looked at the piston top with an endoscope and I saw what looked like piston damage, so I pulled the head. It turns out the piston has no damage but what I was seeing was deposits on the piston and also on the head, particularly in the high squish area. The deposits are very hard and pretty difficult to chip off, though I am making progress with a nylon tool, WD-40, Kroil and 0000 steel wool. It also turns out that one head nut was not snug because the threads at the top of the stud were stripped. I can see where there was blowby between the head and cylinder in this area. My question is whether this is normal after just 2300 miles and if not, what might be causing this. Thanks.
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UTC

Veni, Vidi, Posti
Joined: UTC
Posts: 7058
Location: Tega Cay, SC
 
Veni, Vidi, Posti
Joined: UTC
Posts: 7058
Location: Tega Cay, SC
UTC quote
You will get some deposits, but as you mentioned, the head had a leak. Clean it up, get a new stud, do not over torque it and use a good 2 stroke oil. You may also want to lap the head slightly to get a better seal. Good luck and welcome!
@grahamlml avatar
UTC

Addicted
Vespa GTS 250 , Baotian 70cc rat scooter, Yamaha V50M 1979
Joined: UTC
Posts: 569
Location: Wales
 
Addicted
@grahamlml avatar
Vespa GTS 250 , Baotian 70cc rat scooter, Yamaha V50M 1979
Joined: UTC
Posts: 569
Location: Wales
UTC quote
Quite normal it's carbon deposits. Joys of a 2 stroke.
@waspmike avatar
UTC

Ossessionato
LXV 150 3v ie. Midnight Blue (Sold) Now Honda Zoomer X
Joined: UTC
Posts: 4129
Location: Kingdom of Lanna
 
Ossessionato
@waspmike avatar
LXV 150 3v ie. Midnight Blue (Sold) Now Honda Zoomer X
Joined: UTC
Posts: 4129
Location: Kingdom of Lanna
UTC quote
MOPAR has some combustion chamber cleaner, for their old K car turbos.

Just squirt some in routinely until engine stops, leave over night and smoke the place out when restating in the morning.

Use good "smokeless" or synthetic oil.
UTC

parallelogramerist
Joined: UTC
Posts: 5244
 
parallelogramerist
Joined: UTC
Posts: 5244
UTC quote
Burn the deposits off by riding it harder
@rb_prior avatar
UTC

Hooked
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: UTC
Posts: 320
Location: Central Ohio
 
Hooked
@rb_prior avatar
1963 Allstate, 2005 Vespa PX150, 2001 Harley 95 ci Dyna
Joined: UTC
Posts: 320
Location: Central Ohio
UTC quote
I believe much of this carbon buildup came as a result of the lose head bolt. Normally, carbon does not build up this quick (2300 miles). But, with a leak in the combustion chamber, who knows what goes on. I know the owner does ride the bike at WOT and uses a good grade of synthetic 2T oil that has the newest JASO FD standard to ensure a clean engine and low smoke.

Yes, 2 cycle engines need to be decarbonized routinely and here is a reference on the procedure:

http://www.vespamaintenance.com/engine/decoke/index.html

But as I said, I feel this carbon buildup was premature.
OP
UTC

Hooked
PX 150 and GTS 300 HPE Super Tech
Joined: UTC
Posts: 419
Location: Dublin, Ohio
 
Hooked
PX 150 and GTS 300 HPE Super Tech
Joined: UTC
Posts: 419
Location: Dublin, Ohio
UTC quote
I checked this morning what the specifications are on the two cycle oil I am using. When I bought the scooter several months ago the original owner gave me over 15 bottles of Motorex oil that he got on clearance when he bought the scooter new in 2008. The latest JASO FD specification looks like it was adopted by Motorex in 2009. The dozen or so bottles I have left are JASO FC. One of the primary differences from what I have read is the amount of detergent, with more being in the newer specification. Thus, as much as I hate to stop using a dozen bottles of oil that had a retail price 10 years ago of $20 per bottle, I am going to switch to the newer specification.
@safis avatar
UTC

Ossessionato
1979 P150X, 1983 P200E, 1987 PK125XL Elestart, 1988 T5, 1995 PX200E, 2011 Yamaha Fazer 600 S2
Joined: UTC
Posts: 4317
Location: Veria, Greece
 
Ossessionato
@safis avatar
1979 P150X, 1983 P200E, 1987 PK125XL Elestart, 1988 T5, 1995 PX200E, 2011 Yamaha Fazer 600 S2
Joined: UTC
Posts: 4317
Location: Veria, Greece
UTC quote
Your oil is fine. Engine design is the same since the 70s. Do you think they had these oil specs back then?? The air leak is likely the culprit on this one...
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