OP
@pdxjim avatar
UTC

Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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Molto Verboso
@pdxjim avatar
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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UTC quote
I usually don't winterize my bike because I try hard to ride it all winter long, with the longest break being maybe 2 weeks.
But this winter we've been practically underwater with record breaking rain and on top of that I've moved, so I've only been able to take it out twice in the past 2 1/2 months, the last time being 5 weeks ago. It's always in a garage with the tank topped off with E0 92.

Today I had a chance to take it out so I did. It was a beast to get started and it idled like crap for a long time, but I figured it'd sort itself out once I got it thoroughly warmed up.

A few miles later, it starts revving like crazy and the kill switch doesn't stop it, nor the ignition switch, so I slip it back into gear and use the brakes to stall out the engine as I pull it over.

The plug looked normal and a flashlight down the hole revealed a normal looking piston crown.

I manage to nurse it back home to check carb and head bolts and all are right where I left them last several months ago. There is no sign of leakage in the carb/airbox area or the cylinder gaskets.

I check compression and it's really high around 185 so I figure that must be why it's pre igniting, though why it's that high I haven't a clue.

So, I'm going to pull the head and see what I find.

The last many times I had it out it was running perfectly. Why this out of the blue? F***ing PX. This is really tiresome.
@subetherbass avatar
UTC

Ossessionato
1997 Italjet Formula 125, 2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
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Location: Australa, Mate
 
Ossessionato
@subetherbass avatar
1997 Italjet Formula 125, 2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
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UTC quote
I think you are onto potential answers...

Self revving after long WOT run
OP
@pdxjim avatar
UTC

Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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Molto Verboso
@pdxjim avatar
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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UTC quote
I forgot to mention that I had a #7 plug in the head and the CHT never went over 200F.
@subetherbass avatar
UTC

Ossessionato
1997 Italjet Formula 125, 2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
Joined: UTC
Posts: 4861
Location: Australa, Mate
 
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@subetherbass avatar
1997 Italjet Formula 125, 2 matching N.Z. '69 VBC Super, 177cc Racer, VespaCross Bodge, Puch SRA150, Piaggio Zip 100! & others
Joined: UTC
Posts: 4861
Location: Australa, Mate
UTC quote
Gunk in the filter where the fuelline goes onto the carb...
Fuel evaporates, oil is left & flow is diminished, causing leaning
@socalguy avatar
UTC

bodgemaster
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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Posts: 7194
Location: So Cal
 
bodgemaster
@socalguy avatar
63 GL, 76 Super (x2), 74 Primavera (x2), 79 P200, 06 Fly 150
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Posts: 7194
Location: So Cal
UTC quote
Idle sometimes goes weird if scoot's not run for a few weeks. Readjust mixture and idle speed. Compression rise is strange... test again.
OP
@pdxjim avatar
UTC

Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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Molto Verboso
@pdxjim avatar
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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UTC quote
It's an autolube, so there won't be any oil in the fuel filter, but along those lines, would condensation in the fuel line cause this kind of running? I've cleaned the jets and air filter didn't think of the fuel filter.

I'm thinking the compression may have already been too high and a little bit of buildup pushes it even higher and over the edge. I'm expecting to find some moderate carbon in there and may have to get the compression lowered.
UTC

Molto Verboso
Lambretta GP200, Vespa P200e, Motovespa do Brasil PX200E
Joined: UTC
Posts: 1215
Location: United States
 
Molto Verboso
Lambretta GP200, Vespa P200e, Motovespa do Brasil PX200E
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Location: United States
UTC quote
What oil are you running? Synthetic should leave near zero carbon, also- does it have the catalysed exhaust? I wonder if that thing got plugged up somehow?
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@pdxjim avatar
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Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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Molto Verboso
@pdxjim avatar
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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UTC quote
I used Motul 710 and have a SIP Road.
I haven't pulled the head yet. This head was worked by HRA and I believe the compression is just too high to start with. I bet if I clean the top end it'll come down a bit, but not much.
What I don't get though, is what could've changed from just being parked several weeks? It must be a fuel issue.
I'll check these things out probably tonight when I get home.
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a lambretta or two
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Location: San Francisco
 
Ossessionato
@sfvsr avatar
a lambretta or two
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Location: San Francisco
UTC quote
It is cold. Your carburetor slide stuck open.

Hose it down with some carburetor spray and then run the engine.




I would not start pulling the engine apart. If it ran fine before you stopped riding it, then there won't be any point in looking around inside the cylinder.
UTC

Molto Verboso
Lambretta GP200, Vespa P200e, Motovespa do Brasil PX200E
Joined: UTC
Posts: 1215
Location: United States
 
Molto Verboso
Lambretta GP200, Vespa P200e, Motovespa do Brasil PX200E
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UTC quote
pdxjim wrote:
I used Motul 710 and have a SIP Road.
I haven't pulled the head yet. This head was worked by HRA and I believe the compression is just too high to start with. I bet if I clean the top end it'll come down a bit, but not much.
What I don't get though, is what could've changed from just being parked several weeks? It must be a fuel issue.
I'll check these things out probably tonight when I get home.
well if you are and have used Motul 710 the whole time there shouldnt be any carbon to clean. Maybe just wipe down head and piston. But thats not going to cause crazy issues and high compression.
OP
@pdxjim avatar
UTC

Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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Molto Verboso
@pdxjim avatar
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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UTC quote
After talking to HRA, I pulled the head off anyways since he wants to rework it.
You can see the buildup again, which is really starting to annoy me since I spend $$$ on Motul full-synth 710 and by all other accounts, i.e, plug appearances, chops, CHT temps, and generally excellent running, that it seems to be properly jetted.

Some comments about this head. It was provided by HRS when they repaired the rotary pad and enlarged the transfer ports. As soon as I installed it the compression was so high I suspected my gauge had suddenly gone bad. When compared to a stock 150 head from FA Italia, you can see with your eyes it's going to have higher compression. Using solder, the squish band on it measures about 1.5mm which doesn't seem that high, but the compression chamber itself is much smaller than stock. The squish on the stock head is about 3.5mm.

I'm tempted to put the stock head on and see how it runs. At least it won't diesel on me.
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@glscoot avatar
UTC

Molto Verboso
Vespa GS150, Messerschmitt GS150
Joined: UTC
Posts: 1062
Location: Glasgow
 
Molto Verboso
@glscoot avatar
Vespa GS150, Messerschmitt GS150
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Posts: 1062
Location: Glasgow
UTC quote
If you feel your squish is to neat, fit a head gasket you can buy them in several thicknesses.
UTC

Molto Verboso
px200
Joined: UTC
Posts: 1269
Location: london
 
Molto Verboso
px200
Joined: UTC
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Location: london
UTC quote
Suprising amount of carbon for a full synth oil.

Regards

Grumpy
OP
@pdxjim avatar
UTC

Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
Joined: UTC
Posts: 1873
 
Molto Verboso
@pdxjim avatar
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
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Posts: 1873
UTC quote
I couldn't agree more.

I'm stumped. It doesn't seem like it's running rich and doesn't excessively smoke. I know, "there must be a leak!", but a pressure test on the crankcase doesn't leak. No sign of seepage around head or cyl base.
SIP Road exhaust.

I do know the compression is too high and that's being remedied.
@drona avatar
UTC

Molto Verboso
59 Vespa, 65 Vespa, 66 Vespa, 57 Vespa
Joined: UTC
Posts: 1322
Location: Portland Oregon
 
Molto Verboso
@drona avatar
59 Vespa, 65 Vespa, 66 Vespa, 57 Vespa
Joined: UTC
Posts: 1322
Location: Portland Oregon
UTC quote
What's your timing?
OP
@pdxjim avatar
UTC

Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
Joined: UTC
Posts: 1873
 
Molto Verboso
@pdxjim avatar
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
Joined: UTC
Posts: 1873
UTC quote
Dead on 18deg - just checked it again.

I'm thinking of trying the stock head with "normal" compression and see what happens.
OP
@pdxjim avatar
UTC

Molto Verboso
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
Joined: UTC
Posts: 1873
 
Molto Verboso
@pdxjim avatar
2005 PX150 In a Part-time Relationship with a 2-Stroke Vespa Since 2007
Joined: UTC
Posts: 1873
UTC quote
UPDATE:
I tried the stock head from FA Italia with the ginormous combustion chamber and squish band and was only getting compression just over 100 psi, which seems really low.

I'm getting my other head back with lowered compression from HRA by the end of the week and will see how that goes.

As far as the buildup, I may have been running the main on the rich side out of paranoia of seizures, and will also try a #6 plug during these damp winter days instead of the #7 I was using all during the dry months.
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