Scooterotica

Hello,

I have a 65' Li150 that was bored out to 175cc by previous owner. It also has a SIL electronic ignition/stator installed. When I got the bike it had an indian Jetex carb. It ran very well for about 4-5 months but then started having hard starting problems that appeared related to carb flooding: mainly hard starting, fouling plugs, etc. Eventually it got so bad that the bike wouldn't run at all, and even had gas pouring out the air filter side of the carb--- that's how I attributed its hard starting and poor running to flooding.

I replaced the carb with this PHBL kit from casa lambretta - https://www.casalambretta.us/index.php? ... ct_id=2206 , which was highly recommended by many people, they all said my problems were probably caused by the Jetex.

The kit came with jetting that was said to be good enough to get me started. I was very careful when re-installing the intake and exhaust to get a good seal. I do not have the ability to do a leak down test but I think the intake and exhaust are sealed well.

I have very strong spark, compression that feels good enough to at least start, and of course fuel, but I wasn't able to kick start the engine at all. I did get it started with a bump start down a hill but it would not idle at all and I had to feed the throttle to get it to run. Ran like crap.

I have not checked the timing yet, but the timing was set and it's electronic so perhaps it's gone out of time? I hear that is very unlikely. The bike did not have any air leaks-- that I could deduce-- when it ran before, and I'm not sure how I might have caused one now. At this point the only advice I am getting is to check the timing, and tear down the entire engine. I can do the timing, but I need some tools, I am not prepared to do a tear-down, and at this point, I really do not suspect that.

I'm hoping to any advice that might point me in the right direction, I'm a bit stumped by this scooter.

Sounds like jetting to me. Set the scooter up as you intend to use it. i.e. running through the airbox or running open-mouthed, whichever you choose.
Change the pilot jet size until it starts easily (don't worry about revving cleanly through the range at this moment)
If it starts but needs to stay on choke, the pilot isn't rich enough. If it tries but splutters out and the plug is soaked, it's probably too rich. The mixture screw is involved at this point but is only a fine adjustment.
Patience is required:
Carbs can be considered to have three stages. Starting, middle range and high rev. running.
Starting is influenced by Pilot jet/mix screw and choke action.
Mid-range by the atomiser/needle combination.
High-revs, by the Main jet.
The air-scoop under the seat should have had the central bridge removed when the engine was raised to 175cc. If it wasn't ? do it, assuming you choose to use the airbox. Oh! and buy a decent quality air filter.

As a PS to all this. I've run about fifteen Lambretta restorations on Jetex carbs and don't subscribe to the "Jetex are crap" narrative. That's not to say one doesn't fail from time to time. But I find them easy to set-up, reliable when set properly, easy to clean and maintain and spares readily available.

I don't think it will be jetting at all. Most scooters will at least start with a bad jetting set up. Is the choke working correctly? Other than the carb', which after changing it looks unlikely, it could be that the rings are, stuck, badly worn or even broken!

Hopefully 'Kurtminus' will report back when he's had time to look into it.

Hey All,

Thanks for your input so far. I do have some progress to report.

My initial non-running issue with the new carb was traced to bad gas, I knew it had to be something simple and sure enough the gas that had been sitting for months came out all white and cloudy as if it had moisture in it. I pulled the tank and flushed it, and with fresh gas I was able to get it running!

The good: It runs great!
The bad: only runs great when you can start it, and that part is the problem and it's a problem I've just about always had with this bike.

When it's cold, I kick it over a few times and nothing, at all and when I pull the plug it's not dry. My plug is nearly brand new and is very white, not fouled. The only thing that reliably gets it started is to either bump start it down a hill, or if you don't have a hill, remove the plug, connect the plug to the plug wire and ground it, and kick the engine over 4-5 times, then re-insert the plug. When the engine is warmed up, it starts 1st kick, no problem at all.

Once running it needs a little while with the choke on, and then you can turn the choke off and it's good to go. With current jetting it has good response in the low rpm range, feels rich enough in the mid-range. I haven't had it out long enough to get the main jet set; I like to find the richest point for the main jet and go down from there to know I'm safe, but 100 is the richest jet I currently have. But once it starts, it's good to go. Oh btw once it's warmed up, if you turn the choke on, it kills the engine, so that seems right.

Here's my jetting:
pilot - 60
idle- 53
needle - D29 at richest setting
main - 100
choke is definitely actuating
spark is strong, timing is ~ 19-20 btdc

So the only issue I'm having now is cold-starting. This is a problem I have always had with this bike, even with the old Jetex carb. The Jetex carb, however, also seemed to be flooding very badly-- my reason for replacing it is eventually the scoot just stopped running at all, and there was gas pouring out the back of the carb. I hoped the hard starting was also related to that, but now with a new carb it persists, so.... ??

Any help would be greatly appreciated!