Modern Vespa

Just finished cleaning my 2004 ET2 webben carb and going to reinstall it now...but noticed The larger Grey knob on The right side of my photo which i presume is The idle adjustment screw looks very far out (undone). Does this look strange or incorrect?

The smaller screw to The left of this idle adjustment knob i guess is The air/fuel mix screw?

Both correct. Mixture screw is usually 1.5-2.5 turns out from seated. Idle adjusted as necessary.

Thanks MJ...Will leave The idle alone until she is up and running and only then play around with it to get The perfekt idle.

Despite many attempts to start the scooter by kick start im still unable to get enough vacuum in order to get fuel to The carb. Thinking of ditching The vaccum controlled petcock and replacing with a fuel tap on The fuel tank instead. Must be a better and simpler solution than petcocks that require a lot of suction!

I seem to recall that when I ooened The float bowl to ckean jets i noticed there is NO Rubber gasket. Could this result in nit enough vacuum in order to get fuel into The carb??

-Do you have spark?

-There's usually a gasket on the float bowl - was it stuck to either surface?

-The vacuum tubing needs to be air tight on both the carb and petcock. The lower fitting on your petcock is for the vacuum line.

You can test your petcock by attaching a tube to the vacuum part of your petcock, and sucking on it - fuel should flow out of the petcock if it's working properly. If fuel comes out of the vacuum bit, your petcock needs replacing. 🤞

Yep got spark when kicking over....compression there but looks like The fuel doesnt quite get from The petcock to inside The carb. NO gasket on The float bowl when I opened it up to clean The jets. I can get fuel to Come out The petcock when I suck with my mouth to create suction so i know The petcock works fine. Vacuum tubing seems ok hence me thinking The lack of a gasket might be The cause of fuel not reaching The carb? Am I on The right track here?

For the life of me, I can't remember whether my Weber 12mm carb had a gasket or not… but it makes sense to have a gasket. 🤷‍♂️

You could attach everything, and suck on the vacuum line to see if that fills the bowl. You'll know if you have a leak pretty quickly. Make sure the bowl drain screw is closed.

You can also poke something through the vacuum fitting on the carb to make sure it isn't blocked.

This is what it looked like when I opened up The bowl...when I look carefully I notice that it appears The previous owner has applied some kind of liquid sealer for where The Rubber gasket should be...

Just removed The carb again to check whether The float bowl contained any fuel or not and it was empty....so obviously despite trying to kick start my scooter several times there is NO fuel is making it into The carburetor.

Do you have any pics of the bowl out of interest?

Here's a good thread about the ET2 Weber carb. I don't see any reference to a gasket, which seems odd to me. 2003 ET2 weber carb cleaning

You think fuel is not getting to the bowl. Have you checked if fuel is getting to the end of the hose? Remove the end of the hose from the carb and crank the motor over. Fuel should come dribbling out the hose.

That Weber carb you provided The link for appears slightly different from mine (mine has two jet screws and The choke is a long brass tube that is approx 1cm tall).

I tried sucking on The vacuum tube after removing it from The carb and that creates a good fuel flow from The petcock but replacing The vacuum tube on The carb and then cranking over using The kick starter only creates a very weak flow from The petcock...i just dont understand why...could it be that there is some air trapped in The system or something else??

Now i hooked up an external fuel source using a plastic bottle and plastic tubing but still doesnt start. But when I spray carb cleaner in The throttle cable or The air intake it starts up immediately but runs at very high revs for a few seconds before eventually dying....what does this tell me???

So, looking at your bowl - it appears there is a gasket in there. 👍

You could check your float, and float valve to make sure they're tickerty boo. Same with your jets. 🤞

There should be a gasket where the throttle slide attaches to the top of the carb - make sure that's in place too.

Hi Oscar and thanks for your input....realized at the weekend when cleaning the jets (for the third time) that it is not actually a Weber carb but rather a Dellorto 17,5 carb that a previous owner must have installed. I was sure it was a standard Weber 12 but just goes to show you can never take anything for granted.

Am now at the point of binning this carb and buying a new one on Amazon with a new manifold and reed valve set and hope this will get my scooter up and running for the first time! I also intend to replace the vacuum operated petcock with a manual fuel tap as my vacuum lines seem to be insuficient in pulling fuel from the fuel tank to the carb.

Never ending story with this scooter....would never have purchased it if i had known then what i know now regarding carb/vacuum/fuel line problems!

If you haven't already, remove the float and needle and run a small wire up the needle seat. Electric E guitar string is perfect for cleaning carbs and jets.

Thanks for that tip...not tried using a piece of wire or fishing line but rather just blew brake cleaner and carb cleaner in all The holes and jets i could see....which didnt solve The problem!

Ok that's good you at least shot carb cleaner through it!

On a different note, what is your engine compression? I had a ET2 that wouldn't start no matter what I did. It would only run when I sprayed starting fluid. It turned out the motor was seized and compression was too low.

Before you bin the carb, figure out what the problem is between the petcock, which you've proven to be functioning, and the carb bowl, which is a straight shot from the petcock. You should pretty easily be able to tell if the fuel hose is unobstructed and the needle valve is intact and moving correctly. Those are the only reasons why NO fuel would be getting into the bowl.

Tried checking comp by renoving The spark plug and placing thumb over The hole and manually turning over The engine using The kick start and did feel some air pressure on my thumb so guess i have some compression

And IF I can start it with carb spray for a short period doesnt that alone indicate that i have comp?

This just happened to me a year ago so it's still fresh in my mind. You have some compression, but probably not enough.

I spent an hour cleaning the carb and inspecting the manifold/ reeds before I finally got a tester. You need at least 100 psi for a two stroke, mine was in the 90s. Enough to feel it with my finger, but not enough to sustain combustion.

Can you borrow/ rent a compression gauge? Auto parts stores in the States have them for rent if you don't have your own.

Will do...and IF my comp is not up to scratch?? What is The next step?

Full cylinder replacement or new piston/bore the old cylinder.

Long story short, with my old ET2 (now sold to a friend), the cylinder had seized, lowering compression, so I swapped it to a 70cc kit.

If compression is good, I'd inspect the rubber manifold for cracks/tears or the reed petals for wear. Process of elimination

Sounds expensive....a DIY job or one for The local dealership??

Let's start with the rubber manifold inspection first and then a compression test.

If compression is too low, I'd say it's a dealership job/not for you. The money spent having them repair it will be cheaper than the time it will take you to learn the job, execute the job, buy the speciality tools and the cost of whatever parts you require.

If the ether is working for a few strokes and the bowl is dry you KNOW you have a fuel problem. There is no point in chasing potential low compression issues when fuel isn't getting into the carb bowl.

There is a good chance the needle valve, which is controlled by the carb float, is simply stuck closed and sealing off the bowl. That would explain all the symptoms you've described. Free it, crank for a while to create some vacuum to let the bowl fill, start 'er up, and ride off into the sunset.

Thanks for that Juan. Lets hope that works....Will get back on it this weekend

AJC- you said you've sprayed carb cleaner and brake cleaner through all the holes of the carb. Have you not sprayed it where the fuel line attaches?

If not, disregard the compression chatter.

Juan...from what i can recall i did spray carb cleaner into The nozzle on The carb where The fuel line attaches...Will redo it at The weekend

Just tried The spoonful of fuel down The sparkplug hole metod and it started up and ran for a few seconds...but at high revs...before dying again. I guess that points to The compression being ok right?

Now checked The compression And it was over 110 so looks like comp is not The problem here!

Beautiful! Thanks for taking the time to check. No compression is not your issue and you can focus back to the carb.

Have you removed the float and needle yet? There's a small pin that the float hinges on that gets pressed out and the float and needle are free. Drop those and squirt carb cleaner up into the needle seat. It should squirt out where you hook the fuel hose on.

Will take care of The float later today and hopefully a blockage in this part of The carb has been The reason why no fuel has been able to reach and enter the carb itself. Thanks for your help and advice!