Mon Feb 22, 2021 5:57 am

Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
 
Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
Mon Feb 22, 2021 5:57 am linkquote
Hey Guys,

Long time lurker, first time poster! I'm having a little trouble with my 2006 LX150 project and have hit a wall on where to go next. I've restored quite a few neglected LX50's over the years but this is my first 150. I'm having an issue with getting my LX150 to start when cold or after sitting for a short period of time. It seems as if the bike does not want to start when the auto choke is engaged but once it disengages, the bike runs flawlessly. Here are the things I have done up to this point to help with the starting issue:

-New NGK spark plug
-New fuel and vacuum lines
-New Piaggio fuel valve
-Valve adjustment
-Evap delete
-Cleaned carburetor
-New #38 pilot jet and New OEM Piaggio Main jet
-Adjusted mixture screw to a variety of different settings
-New Malossi Red air filter

I've also done other things unrelated to the engine such as belt, rollers etc. When the bike is warmed up, it runs and rides perfectly with no hesitations. It will restart and idle flawlessly if the bike has been running. To get the bike started for the first time of the day it seems like priming the accelerator pump several times will help get it started initially but the bike does not fast idle like other LX's I've had. I will need to hold the throttle slightly open to keep it idling fast enough to stay running.

One thing to note is that the previous owner of this bike took it to a motorcycle shop for repairs. It appears the carburetor had been opened at one point before my ownership as the float bowl screws were replaced with allen head bolts. I'm not entirely sure what they were doing in there. The bike was 100% stock when I purchased it and it has 2600 miles currently. Any tips would be greatly appreciated!
Mon Feb 22, 2021 6:26 am

Member
ex 1986 Vespa PX125, 2007 Vespa LX150
Joined: 11 Feb 2021
Posts: 46
Location: Italy
 
Member
ex 1986 Vespa PX125, 2007 Vespa LX150
Joined: 11 Feb 2021
Posts: 46
Location: Italy
Mon Feb 22, 2021 6:26 am linkquote
Simply looks like it's having difficulty on the carburator, in Italian I'd tell you to check the carburator's "getto"............................................. which English translation I don't know, I'm sorry
Mon Feb 22, 2021 6:40 am

Addicted
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 581
Location: Bermuda
 
Addicted
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 581
Location: Bermuda
Mon Feb 22, 2021 6:40 am linkquote
Don’t worry particularly about the replacement bolts. The original bolts were JIS heads and are infuriatingly easy to strip with US Phillips head drivers. I replace them on all my carbed engines with Allen heads as well. (Same on the brake fluid reservoir BTW.)

Could you be more specific about what you tweaked? You mentioned the mixture screw, but not the idle speed screw. The idle speed adjustment is indeed a screw and it controls the minimum position of the throttle. You didn’t mention this. The idle mixture adjustment is a special screw with a D-shaped head that requires a tool to tweak, because mis-setting it can leave the engine overlean and susceptible to overheating.

To properly adjust the carb you actually tweak both of them at the same time. The ideal setting can be affected by ambient temperature.

“getto” = jet = maybe, but if it’s a new 38 jet and you’re positive the carb is clean, the jet is probably not the issue.
Mon Feb 22, 2021 7:25 am

Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
 
Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
Mon Feb 22, 2021 7:25 am linkquote
Juan_ORhea wrote:
Don’t worry particularly about the replacement bolts. The original bolts were JIS heads and are infuriatingly easy to strip with US Phillips head drivers. I replace them on all my carbed engines with Allen heads as well. (Same on the brake fluid reservoir BTW.)

Could you be more specific about what you tweaked? You mentioned the mixture screw, but not the idle speed screw. The idle speed adjustment is indeed a screw and it controls the minimum position of the throttle. You didn’t mention this. The idle mixture adjustment is a special screw with a D-shaped head that requires a tool to tweak, because mis-setting it can leave the engine overlean and susceptible to overheating.

To properly adjust the carb you actually tweak both of them at the same time. The ideal setting can be affected by ambient temperature.

“getto” = jet = maybe, but if it’s a new 38 jet and you’re positive the carb is clean, the jet is probably not the issue.
I have adjusted both the D shaped mixture screw as well as the idle speed screw. It appears the bike is running lean when the autochoke is engaged (doesn't make a whole lot of sense to me). By manually actuating the accelerator pump, the bike will run and idle just fine. I have made adjustments to both the fuel mixture screw (D shaped) and idle speed screw to balance out any changes. Idle speed is set to the service manual RPM using a tiny tach. I set the idle speed when the bike is warm and able to idle on its own. If I attempt to adjust the idle speed when cold starting, the idle speed of the bike when warm is very high.

I know the jets are clean as they are brand new, I'm wondering if there is another adjustment I am missing related to the fast idle/auto choke.

Thanks for the tips!
Mon Feb 22, 2021 8:21 am

Addicted
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 581
Location: Bermuda
 
Addicted
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 581
Location: Bermuda
Mon Feb 22, 2021 8:21 am linkquote
Like you I'm having a hard time understanding how the autochoke could be leaning out the mixture. It simply doesn't work that way.

I think what you're seeing is an overrich mixture at idle, and blipping the throttle is letting both more air and fuel in making the result slightly leaner.

My next step would be to disassemble the carb again, clean it in an ultrasonic tank, and blow out every single passage I could find with carb cleaner and compressed air.

I would also make very very sure the needle valve and carb float are set correctly. It is possible that the float is sitting too high in the bowl, a result of allowing too much fuel in the bowl, and the carb and jets are drowning in fuel. A tiny L-shaped bracket hinged on a pin interacts between the float and the needle valve. If the bracket is bent at more or less than 90 degrees, the needle valve will let either too much or not enough fuel into the bowl. I haven't had to tweak this on my Vespa so unfortunately I don't have any measurements or photos to offer on a proper adjustment, but as a rule of thumb the float is supposed to be horizontal when that bracket is just grazing the needle valve.
Mon Feb 22, 2021 8:40 am

Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
 
Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
Mon Feb 22, 2021 8:40 am linkquote
Juan_ORhea wrote:
Like you I'm having a hard time understanding how the autochoke could be leaning out the mixture. It simply doesn't work that way.

I think what you're seeing is an overrich mixture at idle, and blipping the throttle is letting both more air and fuel in making the result slightly leaner.

My next step would be to disassemble the carb again, clean it in an ultrasonic tank, and blow out every single passage I could find with carb cleaner and compressed air.

I would also make very very sure the needle valve and carb float are set correctly. It is possible that the float is sitting too high in the bowl, a result of allowing too much fuel in the bowl, and the carb and jets are drowning in fuel. A tiny L-shaped bracket hinged on a pin interacts between the float and the needle valve. If the bracket is bent at more or less than 90 degrees, the needle valve will let either too much or not enough fuel into the bowl. I haven't had to tweak this on my Vespa so unfortunately I don't have any measurements or photos to offer on a proper adjustment, but as a rule of thumb the float is supposed to be horizontal when that bracket is just grazing the needle valve.
I appreciate the input!

My initial thought was that it was too rich as well due to the bike responding to more air as a result of opening the throttle at idle. However, the reason I believe it is actually lean is when it is under cold start conditions, if I reach down and push down on the accelerator pump with my finger, the bike responds instantly and the idle smooths out as long as I continue to pump the accelerator pump. I imagine that if the bike was rich at idle, the engine would stall when actuating the accelerator pump from injecting additional fuel.

I have cleaned the carb several times now using my ultrasonic cleaner for various parts with no real change in condition. I am perplexed by the fact that the bike runs flawlessly once up to temp which leads me to believe the autochoke is causing the lean condition. I'm also trying to determine why the engine does not fast idle like most bikes do. It almost seems like there is some kind of blockage on the autochoke circuit which is not allowing additional fuel when it is engaged. I am having a hard time locating details on how the autochoke functions other than testing the actuator (which works perfectly).
Mon Feb 22, 2021 9:16 am

Molto Verboso
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 1353
Location: Toronto
 
Molto Verboso
2006 LX150 (carbed) | 2007 GT200
Joined: 29 Jun 2016
Posts: 1353
Location: Toronto
Mon Feb 22, 2021 9:16 am linkquote
So this bike is new to you, and has never run well since you've owned it, right? (In other words, it's not that these symptoms just developed?)

Have you checked for air leaks, especially given your comments on thinking it's running lean? Maybe an uncapped emissions vacuum port, or a cracked intake manifold? Any change to engine speed if you spray carb cleaner near the carb and intake areas?

I also have an old LX and at one point the brass fitting in the intake manifold came loose and there were cracks in the rubber (which were hard to see, except when I removed it and inspected under a bright light).
Mon Feb 22, 2021 10:42 am

Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
 
Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
Mon Feb 22, 2021 10:42 am linkquote
berto wrote:
So this bike is new to you, and has never run well since you've owned it, right? (In other words, it's not that these symptoms just developed?)

Have you checked for air leaks, especially given your comments on thinking it's running lean? Maybe an uncapped emissions vacuum port, or a cracked intake manifold? Any change to engine speed if you spray carb cleaner near the carb and intake areas?

I also have an old LX and at one point the brass fitting in the intake manifold came loose and there were cracks in the rubber (which were hard to see, except when I removed it and inspected under a bright light).
That is correct, this bike was not running when I purchased it and I'm not entirely sure when this issue developed. I checked for leaks and also confirmed that the vacuum port that was previously used for the evap system was sealed as well. Thank you for the suggestions! This issue really has me stumped. I may try to pull the autochoke actuator off again and try to clean the area where the plunger goes. I may also take a look to see if the float height is set properly.
Mon Feb 22, 2021 11:43 am

Addicted
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 581
Location: Bermuda
 
Addicted
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 581
Location: Bermuda
Mon Feb 22, 2021 11:43 am linkquote
This is a very thorough and interesting treatment of the autochoke, officially called an "enricher," "bystarter," or "auto bystarter." (I mention these terms for indexing purposes!)I don't think the author haunts MV but he chimes in regularly on Modern Buddy. Maybe the "failure modes" he notes at the bottom of the article will be useful for you to troubleshoot.

http://www.slonaker.net/helixforum/viewtopic.php?f=4&t=3084
Mon Feb 22, 2021 11:53 am

Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
 
Member
LX150
Joined: 22 Feb 2021
Posts: 5
Location: Orlando, FL
Mon Feb 22, 2021 11:53 am linkquote
Juan_ORhea wrote:
This is a very thorough and interesting treatment of the autochoke, officially called an "enricher," "bystarter," or "auto bystarter." (I mention these terms for indexing purposes!)I don't think the author haunts MV but he chimes in regularly on Modern Buddy. Maybe the "failure modes" he notes at the bottom of the article will be useful for you to troubleshoot.

http://www.slonaker.net/helixforum/viewtopic.php?f=4&t=3084
This is FANTASTIC! This is what I was looking for, thank you for sharing! I'm wondering if there is a way to clean the jet for the autochoke. If I had to guess, I'm thinking there is air being allowed to pass through but no fuel passing through the jet.
Tue Feb 23, 2021 7:31 am

Hooked
2016 Piaggio BV 350
Joined: 25 Sep 2006
Posts: 414
Location: Albuquerque, NM
 
Hooked
2016 Piaggio BV 350
Joined: 25 Sep 2006
Posts: 414
Location: Albuquerque, NM
Tue Feb 23, 2021 7:31 am linkquote
My BV350 had the same issue. I took it to the dealer and now it starts flawlessly.
Tue Feb 23, 2021 2:13 pm

Addicted
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 581
Location: Bermuda
 
Addicted
S150, Beo 500ie
Joined: 14 Aug 2019
Posts: 581
Location: Bermuda
Tue Feb 23, 2021 2:13 pm linkquote
alloo wrote:
My BV350 had the same issue. I took it to the dealer and now it starts flawlessly.
You left out the parts involving removing money from your account, not knowing or learning anything about how the scooter works, and not having the satisfaction of figuring out the travails of your internal combustion engine by yourself. Some of those steps are very important to some people!
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