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@reginabud avatar
UTC

Member
1959 T/4 VGLA1T
Joined: UTC
Posts: 8
Location: Regina, SK Canada
 
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@reginabud avatar
1959 T/4 VGLA1T
Joined: UTC
Posts: 8
Location: Regina, SK Canada
UTC quote
Hi Folks,

I replaced the exploded original engine on my VGLA1T with a modern LML. It ran well for a while then started to act like it had a rev limiter, bogging down and backfiring under any throttle much higher than idle. I have rebuilt the carb, same thing occurs. Bike idles great.

I am looking for advice on where to start trouble shooting. Timing? Jets (all factory currently)? I do have the original exhaust on as the LML one wouldn't fit on the bike. Could that be an issue?

Any sage advice is appreciated. I am going to borrow a friends timing light and check that tonight.

Mark
Regina, Saskatchewan, Canada
UTC

Veni, Vidi, Posti
Joined: UTC
Posts: 6732
Location: Tega Cay, SC
 
Veni, Vidi, Posti
Joined: UTC
Posts: 6732
Location: Tega Cay, SC
UTC quote
Sounds like an electrical problem. Maybe the pick up is gone wonky
@greasy125 avatar
UTC

Sergeant at Arms
Weird 80's Vespas & Cool Vintage Lambrettas
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Posts: 14898
Location: The state of insanity, SoCal
 
Sergeant at Arms
@greasy125 avatar
Weird 80's Vespas & Cool Vintage Lambrettas
Joined: UTC
Posts: 14898
Location: The state of insanity, SoCal
UTC quote
Tierney wrote:
Sounds like an electrical problem. Maybe the pick up is gone wonky
that was my first thought as well.

I'd be chasing ignition and/or wiring before jumping back into the fuel system again.
@sjoerdo avatar
UTC

Member
Faro basso 53, Motovespa 58, V50 71
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Posts: 48
Location: Netherlands
 
Member
@sjoerdo avatar
Faro basso 53, Motovespa 58, V50 71
Joined: UTC
Posts: 48
Location: Netherlands
UTC quote
No changes were made between the running great phase to the bogging phase?
When you cleaned out the carb did you find any dirt or grime?
@psma avatar
UTC

Hooked
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: UTC
Posts: 277
Location: Madeira Island
 
Hooked
@psma avatar
125 GTR 1977, 50S 1975, GTS 125 Supertech 2021
Joined: UTC
Posts: 277
Location: Madeira Island
UTC quote
I had mine a few year ago with the exact same symptom - it was an electrical problem.
Replaced contact breaker and condenser - problem solved
@moto64 avatar
UTC

Molto Verboso
'64 Motovespa 150S (177) , '65 VBB, '66 Allstate SF, '66 180SS
Joined: UTC
Posts: 1835
Location: S.Salem, NY
 
Molto Verboso
@moto64 avatar
'64 Motovespa 150S (177) , '65 VBB, '66 Allstate SF, '66 180SS
Joined: UTC
Posts: 1835
Location: S.Salem, NY
UTC quote
CDI
OP
@reginabud avatar
UTC

Member
1959 T/4 VGLA1T
Joined: UTC
Posts: 8
Location: Regina, SK Canada
 
Member
@reginabud avatar
1959 T/4 VGLA1T
Joined: UTC
Posts: 8
Location: Regina, SK Canada
UTC quote
Thanks All,

Carb rebuild didn't show any excessive grime. Carb was fully rebuilt and ultrasonic cleaned. It does appear to be more of an electrical issue at higher RPMs. The problem appeared after a cold winter but the bike was never below -10C. I am using new fuel.

I plan on unplugging all of the bike electricals from the Regulator plus remove the kill switch wire to the CDI to eliminate that as an issue, troubleshoot the CDI/Ignition (spark plug wire, measure resistances, check plug, etc.). Will also check the exhaust if none of that yields a culprit. Will update the post as it's always good to find a similar problem and solution!

I may be back with dumb questions if I can't find an answer somewhere...

Cheers

Mark

p.s. It is +6C today. The riders are showing up despite the snow and ice on the side streets. Soon!
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