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Hooked
'08 Vespa LX80, '07 LX50
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I searched but did not find any discussions about this for LX50 with a Malossi 80cc kit on it. It is really hard to start the scooter when I have ridden for a while and the engine is hot. What should I be looking at to try for improvement?

For a hot start I can not use the throttle and it just wont get there and start or I can use some amount of varying throttle and get a weak idle at first, a sort of bumbling and then she goes and is ready to ride. It's kinda frustrating but if there are any tips or things I should look into I am all ears.

Thanks
@greasy125 avatar
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Sergeant at Arms
Weird 80's Vespas & Cool Vintage Lambrettas
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@greasy125 avatar
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when was the last time you checked your valves? that's where I'd start.
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2016 Vespa GTS300ie abs/asr/ess Settantesimo '70'
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If that doesn't do it, it's probably a fuelling issue. A common thing after a Malossi upgrade is that the motor runs too weak when hot.

What parts were fitted exactly? What attention was paid to fuelling if any? Just come back and tell us the history of the bike since upgrade and who did it. Thanks!
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Hooked
'08 Vespa LX80, '07 LX50
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UTC quote
Thanks for replies guys. Valves checked 1000 miles ago when "I" put in the Malossi kit with cam. When cold she starts super quick and revs really high at first and then settles down to a normal idle.

When hot 95% of the time it's a struggle to get her going. I adjusted the valves too at the swap so perhaps a re-check as per the first service? Scooter runs strong other wise with no other issues.

As to fueling I am running the stock carb with a 35 pilot and a 82 main.

Thanks for any help here.
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Weird 80's Vespas & Cool Vintage Lambrettas
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@greasy125 avatar
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Yes, double check the valves after run in.

Just a random question, what plug are you running?

Personally I'd take a flyer and bump the pilot up a few.

Also double check your auto choke. make sure it is fully articulating.
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greasy125 wrote:
Yes, double check the valves after run in.

Just a random question, what plug are you running?

Personally I'd take a flyer and bump the pilot up a few.

Also double check your auto choke. make sure it is fully articulating.
I'm running the NGK Laser Iridium CR8EIB-10 4948

I did play with moving to a 38 pilot a couple times but I wasn't getting the response I wanted.

I will check the valves. Last time was with the engine out so easy! I hope not too bad in situ....

Checking the choke ? I know it works it seems like it works too well when cold! Do you remove it and watch it articulate when starting the scooter? Sounds dangerous! or is it a bench op with a 12v power supply kind of thing?
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Are you checking the valves with the engine stone cold?
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Mopedlar wrote:
Are you checking the valves with the engine stone cold?
I did since it was on the bench in my AC controlled garage! Should it be more warm?
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Nope, gotta be next morning cold.
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If the choke is working "too well" when its stone cold the float could be set incorrectly so the baseline mixture is already running rich overall. Check both the set height of the float and its condition, damaged or leaking floats can cause overly rich mixtures.

If the engine has been tuned and the carb not rejetted to match, the engine could be running lean and hot, this can cause the carb to heat and in turn cause the gas to evaporate or boil off in the carb immediately after the engine is shut down, resulting in very hard starting on a hot engine as the carb is drowning in fuel vapour. Engines which live in enclosed spaces are particularly prone to this issue as the hot air and excess fuel fumes tend to hang about the engine. I once had an engine that would boil its carb if it sat a a traffic light to long, immediately croaking when you opened the throttle when the light finally turned green... that took a bit to figure out!

Also check for partially obstructed airflow in the fuel system, I've seen everything from mouse and wasp nests to pieces of delaminated air intake boots stuck in carburetor inlets over the years.
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Kevin T wrote:
I'm running the NGK Laser Iridium CR8EIB-10 4948

I did play with moving to a 38 pilot a couple times but I wasn't getting the response I wanted.

I will check the valves. Last time was with the engine out so easy! I hope not too bad in situ....

Checking the choke ? I know it works it seems like it works too well when cold! Do you remove it and watch it articulate when starting the scooter? Sounds dangerous! or is it a bench op with a 12v power supply kind of thing?
Yep the manual tells you how to check the choke operation/impedance etc. Greasy's idea of bumping up the pilot may hold value but I'd checkout the float for damage and height as is mentioned earlier by one of the posters. I'm pretty sure you motor is running weak and things are getting way too hot.
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Interesting thread. I am learning just how little I know. I am in awe of all you guys.👍
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Fritz Katzenjammer wrote:
I once had an engine that would boil its carb if it sat a a traffic light to long, immediately croaking when you opened the throttle when the light finally turned green... that took a bit to figure out!
Interesting! How did you solve this?

You can't really move the carb. So was it a matter of getting the engine to run cooler with richer mixture? Or something else?
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berto wrote:
Interesting! How did you solve this?

You can't really move the carb. So was it a matter of getting the engine to run cooler with richer mixture? Or something else?
There were a couple of problems with this one. The carb was worn and so needed a new slide, float and float valve. It would have been nice to just replace the carb but the bike was beyond obsolete and parts didn't exist. The base gasket/insulator plate for the carb had hardened with age and begun to transmit heat rather that keeping it at bay. And finally, some knucklehead, that would be me, had tuned the poor engine to a razors edge and it really needed some better carburation as a result.

The final fix was to scrap the 26mm Jikov the engine came with and fit a more modern 28mm Mikuni for which parts were available allowing me to jet the silly thing so the engine could get the nice rich mixture it wanted.

The result was a nice torquey motor which pulled like a freight train and went like proper stink.

The final bike, after an extensive weight reduction program, proceeded to scared the shit out of me for about two years before i shelved it so it wouldn't kill me... lovely while it lasted though, i sure do miss street legal two stroke cafe racers!
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I would make sure the idle air screw is set correctly. That can cause this. If it's not set right, you have to open the throttle too much to make it idle.
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berto wrote:
Interesting! How did you solve this?

You can't really move the carb. So was it a matter of getting the engine to run cooler with richer mixture? Or something else?
this was only partially finished... maybe I went too far...
Forum member supplied image with no explanatory text
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'08 Vespa LX80, '07 LX50
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I am having a tough time finding the float height specification for my LX 50. I have two shop manuals but do not see anything for what height to set the float? Does anyone know where that info is for the Keihin carb? Thanks
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UTC quote
I swag'd the float height. I do think it may have been a little high. I found that my idle screw was a little too far screwed in too!

Checked valves, both were good. .006 exhaust / .004 intake.

Checked plug, definitely not running lean. I didn't think it was but I checked since I was there.

I may still have the warm start problem, I wont know until I can do a nice ride. So busy this weekend I need to get back to work to rest! lol


Should I be shopping for an exhaust so the engine can breathe better when hot?
Not that I want to spend any more money on this scooter but I could be talked into it...
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