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vespa PX 125 disc
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vespa PX 125 disc
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Hi, I was hoping to get peoples thoughts on my set up. From my 2003 stock px 125 I have fitted a SIP road 2 exhaust, drilled my filter, up jetted main to 100 and fitted a 48-140 idle jet. She runs great but with my CHT gauge with sensor fitted under spark plug my temp has increased its max from 320deg F to 365deg F at full throttle. Is this too high any thoughts?
Plug chop looked good also.
@bob_copeland avatar
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Ossessionato
2013 Vespa 300 Super, 2022 Kymco AK 550
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@bob_copeland avatar
2013 Vespa 300 Super, 2022 Kymco AK 550
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UTC quote
Head Temperature
You are obviously speaking to other Gear-Heads.

Bob C
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Mr. Clean
P,SUPER,V90, 50 Special
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Mr. Clean
@vader19 avatar
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UTC quote
Re: Cyl head temperature
haggis120 wrote:
Hi, I was hoping to get peoples thoughts on my set up. From my 2003 stock px 125 I have fitted a SIP road 2 exhaust, drilled my filter, up jetted main to 100 and fitted a 48-140 idle jet. She runs great but with my CHT gauge with sensor fitted under spark plug my temp has increased its max from 320deg F to 365deg F at full throttle. Is this too high any thoughts?
Plug chop looked good also.
365F isn't too hot.. start to think about it at 400F. If the changes you made were the SIP Road AND drilling the filter, I'd think your main jet would need to be a little bigger than a 100 but if it runs good and your plug looks good you may just want to leave it alone.. as I said.. 365F at a max at wide open isn't too hot.. it's not cool, but you've still got room to go before I'd be worried.

If you want to check your main jet.. try going up a couple/few sizes and ride it wide open, and if it bogs then go down one size until it stops bogging and it it runs well stop lowering the jet and leave it at that.. start rich on the main and work your way down.
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Hooked
1979 P200E
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Hooked
@skotieono avatar
1979 P200E
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Ya I start to get nervous around 400 degrees. I've gotten up to ~420 by mistake, still no problem but definitely don't want to stay in those ranges.
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'74 50s x3 '78 P200 E '84 Cosa '91 PK50XL2 - & - '58 AllState '68 Sprint '66(?) Super125 and '72 DanMotor Super150
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@v_oodoo avatar
'74 50s x3 '78 P200 E '84 Cosa '91 PK50XL2 - & - '58 AllState '68 Sprint '66(?) Super125 and '72 DanMotor Super150
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UTC quote
scary territory
External inline image provided by member with no explanatory text
After long, hard uphill pull, testing on hot day. Usually around town it's half of that even when flogged hard.

Aluminum doesn't melt until past 1100 F, but the physical properties for most alloys start declining quickly between 450 & 500 F. Some alloys are formulated specifically for strength at higher temperatures. NASA has been on the case though and actually developed some of these specialalloys fairly recently(published 2003):
Quote:
Originally developed by NASA as high performance piston alloys to meet U.S. automotive
legislation requiring low exhaust emission, the novel NASA alloys now offer dramatic increase
in tensile strength for many other applications at elevated temperatures from 450°F (232°C) to
about 750°F (400°C).
Much more here from NASA's own website http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030106070.pdf - Malossi, Polini and all Vespa piston vendors, please take note! Nerd emoticon
OP
UTC

Member
vespa PX 125 disc
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Posts: 7
Location: Aberdeenshire
 
Member
vespa PX 125 disc
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Location: Aberdeenshire
UTC quote
Thanks for the replys. Its a hard one on another forum no one would go above 290deg F but I have never had any bother being above 320deg F. Is it a case of each engine could have so much difference in perameters?
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UTC quote
haggis120 wrote:
Thanks for the replys. Its a hard one on another forum no one would go above 290deg F but I have never had any bother being above 320deg F. Is it a case of each engine could have so much difference in perameters?
Where did you read (which forum) not to go above 290F ? ... must be the cooler heads prevail forum.
OP
UTC

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vespa PX 125 disc
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vespa PX 125 disc
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UTC quote
Vader it was in vespa.org but to be honest so far the psots I have read no one likes to go above 350deg F. I know all engines are different but why get a CHT if all engines are different. no one can seem to say, right piaggio says ---deg F is the max!
@ginch avatar
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Location: Victoria, Australia
UTC quote
Re: scary territory
V oodoo wrote:
...but the physical properties for most alloys start declining quickly between 450 & 500 F.
So if you're in the low 400's measured under the plug, the temperature in the small area around the exhaust port is going to be much higher... hence the melted aluminium all stuck to the inside of the cylinder!
@ginch avatar
UTC

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
Joined: UTC
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Location: Victoria, Australia
 
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@ginch avatar
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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Posts: 8595
Location: Victoria, Australia
UTC quote
Re: Head Temperature
Bob Copeland wrote:
You are obviously speaking to other Gear-Heads.

Bob C
Tell us about your cup-holders Bob.
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Hooked
P200E
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Location: East Lansing, MI
 
Hooked
P200E
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UTC quote
CHT = "Cup-Holder Temperature"
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