Modern Vespa

New to the forum so first off thanks! I've searched for ideas, but nothing.

I'm wondering if the issue could be timing or ecu or valve adjustment or something else.

Scooter wants to start and will run for a couple seconds on ether.

What I've verified:
Fresh gas
Good vacuum and fuel flowing to the carb
Cleaned original walbro carb
Purchased a new carb from scooter west
Compression is 150psi
New plug, confirmed I have good spark
Have all the keys, get single red flash when key turned on, so I believe immobilizer is working
Good battery
All lights and brake lights work
Kill switch is good

I got the scooter from a friend of mine in a non-running condition. Looks good and only 1900 miles it.

After it sits a bit, if I try to start - it will run for a couple seconds but sounds really rough, wondering if it might need a valve adjustment.

I've worked on many small engines, but this one has me scratching my head.


Any other ideas?

You've got it from a friend not running.

Can he give you any information on what happened with the scooter?
He ran with it for 1900 miles, which is nothing. Valve adjustment you can exclude.
I see the scooter is from 2001. That is less than 100 miles per year on average.
Maybe it was not in use for years. Maybe he did modifications to the engine.
That kind of information is valuable in your search for the rootcause.

You say you have spark and it runs for a few seconds on ether. Based on that the logic is the engine has spark but no fuel. So most probably there is a problem with the fuel not getting to the carb or to the engine.

You have installed a new carb. So the problem is most probably not in the carb.
I would first check the fuel line. Does fuel flow or not. And is it fuel. You have filled the tank with new fuel, but how well did you drain the fuel that was in the tank?

What kind of mixture enrichment (choke) does the carb have for cold starting? And does it work? If you have doubt you could remove the air filter and put a manual choke in front of the air inlet on the carb, a piece of cardboard with a small hole in it should be OK.

I would check the valve clearances anyway. Also, have a very good look at the rubber intake manifold, flex it a little while checking it with a strong light. When you pulled the plug after trying to get it to start, is it wet with fuel?

More info.

I'll have to ask about the history. I do know it set for a few years without being used. That's why i did a compression test. There are no modifications to the scooter.

When I installed the new carb, I replaced the intake manifold and new gasket. The old one was still good. It has an electric choke. Scooter acts the same with the new carb as it did with the original. The original carb wasn't that dirty. Jets were not clogged. Some bowl varnish.

It will start for a few seconds after sitting for a while, which makes me think it was a fuel issue. That said, if I remove the fuel line and turn it over with the starter, fuel flows freely. So I'm pretty confident that the tank fuel tap is working properly. If I draw a vacuum on the line that goes to the intake, gas will flow just fine.

Yes, tank is clean and gas is fresh.

Thanks and let me know if you have other thoughts.

Also, plug is dry when I removed it. It isn't flooded.

If this was mine, first thing I would do is to check your valves as already suggested. If within spec, at least you ruled that out. #2 hook up a temperorary fuel supply. Below is what I use. Remove the vacuum line going to the petcock and plug the nipple, Remove the fuel line going to the carb, and install temporary fuel supply. See if this will allow the bike to run. #3 Hope Greasy comes along and tells you what to do.

Thanks, I'll check the valve clearance tomorrow. This afternoon I rigged up an auxiliary fuel test bottle as you suggested. No change. It's definitely getting gas.

If valve clearance is good, check to make sure the mix screw is set to factory standard. And if the plug is completely dry, it's getting no gas into the cylinder.

you rang?

all kidding aside, some really great suggestions. sounds like it's close.

can you post a picture of the engine bay. like, from the top with the carb, intake and all the hoses and such. this will help in the process of elimination.

I'll check the air fuel mixture, but I don't think that is a problem. Interestingly, the new carburetor made no difference. I don't believe that I needed it, I've rebuilt plenty before, but decided to try it.

Just so odd why this thing won't run. That's why I did a compression test. Seems fuel related, but I'm wondering if a weak coil could cause these symptoms?

weak coil= weak spark. so, sure that's a possibility. check the coil, HT lead, cap and plug. you want a fat, bright blue spark that snaps.

if the plug is dry, then fuel isn't entering the cylinder. I'd be checking the float and needle to make sure nothing is obstructing or any trash got picked up.

new parts doesn't mean good parts; always verify.

Picture of the engine attached

ok, finished valve adjustment. exhaust was at .004 - adjusted it to .006. Intake was .0000 adjusted it to .004.

Still wouldn't start, although sounded better when it ran for a few seconds.
Battery is currently dead, so charging it up.

little more background on the scooter: The woman that had the scooter before said that the thing ran fine until she just stopped using it. she said it set for a couple years and she then couldn't get it to start - so she took it to some shop in Cumming Georgia. She doesn't think they knew much about scooters - they apparently cleaned the carburetor but it still wouldn't run. She said that they couldn't figure out how to get the spark plug out... good grief.

Anyway, she got tired of dealing with them and brought it home in 2022 where it continued to set in her garage. When I got it (last month) the starter was shot, it wouldn't turn over at all, so I re cleaned the carburetor, gas tank and installed a new starter. Still couldn't get it to run so I purchased an aftermarket carb from scooter west.
KEIHIN CVEK-2600A CARBURETOR ET4 2001-2007 LX/S/LXV/FLY 150 (2003 LT150) (SINGLE THROTTLE CABLE) (CM129208 CM129209 CM129211 CM129213)

I still think it is a carb issue, it acts like the electric choke isn't working or it has a clogged jet. i don't know where this particular carb was made, but I've received Chinese carburetors that wouldn't work... so i know it would be a coincidence, but there really isn't anything else i can think of. I mean it isn't that complicated??

Ok. Your intake valve had zero clearance? Correct me if I'm wrong, if you have no air on your combustion stroke engine won't fire and that will look like a carb issue?

yellow circle, if that is attached to the carb, remove it. it's evap and you don't need it.

pink circle, left side goes to vacuum fuel tap, make sure it is secure and no leaks. right side, pull off and plug. CONFIRM NO LEAKS.

green circle: what's up here? where's the clamp? is this secure and sealed to the airbox? (secondary, where's the clamp for the air intake. again, must be tight and no leaks)

airbox: do you have a filter in it, and is lid properly sealed?

did you pull the bowl and inspect the new carb? did you remove and test the auto choke? if not, I'd be looking at both.

on the carb, is the bowl full of fuel?

There are no leaks and I'll clamp everything down once I'm done messing with it. Yes, there is a new filter and the cover is secure.

I did not pull the bowl off the new carb, I'm talking to scooter west now about exchanging it. It was poorly packed when it arrived. The FME plugs were dislodged and the plastic cover on the choke was off. It came to Ohio from California in a box with nothing to prevent it from bouncing around.

Anyway, while waiting - I'll pull it off and take a look inside the bowl.

Appreciate the input.

As far as I'm aware, the auto choke never fails in the 'running' condition. If it has failed, it'll be stuck in the full enrichment position, causing very poor idling and low speed running when warmed up.

a quick and dirty way to check is just to remove the choke and cover the hole up with your thumb while you crank it.

but I'd crack the bowl drain and verify that fuel is entering the carb as well.

if not, then it's time to reset and sort that.

Yes, fuel is definitely flowing to the carb. I've confirmed that several times. Including running a separate test tank directly to the carburetor. I'm going to remove the new carb tomorrow and open it up. I'll post an update tomorrow.

Figured out the problem - mud dauber wasp built a nest in the tailpipe. Cleaned out the dirt with a screw driver. Released the back pressure in a big poof of dust. Runs great now. Add this to the list when something has set for years! Good grief!

Thanks for the follow up and something that doesn't occur to me

Wow. That must be a first..............