Modern Vespa

ok, I'm getting pretty confused determining if I have a fuel flow problem, blocked jets, or simple my idle mix needs an adjustment. My mind changes everyday which tells you how good my process of deduction is..

ok over the weekend I thought it was fuel..

https://modernvespa.com/forum/topic53819

then I read a post about the fuel line getting pinched if it's too long (mine I can just about rest the tank on the frame when out) so I re-seated the tank, ensured fuel was flowing at the carb end and then took the scoot for a test ride.

The scoot started up fine, and after a few seconds I could close the choke and it idled fine without me feathering the throttle etc..
Took it around a few blocks accelerating hard through the gears to get as fast as possible. Then once the scoot was warm it started cutting out at intersections again.. It would however start up fine and keep on running with me feathering the throttle but if I let the throttle return to idle it would cut.

I replaced most of the carb gaskets over the weekend, sprayed the jets with carb cleaner, made sure needle looked/felt good, cleaned out carb bowl etc..

I haven't messed with the idle mix yet since the scoot seems fine idling when cold. Is it normal that the idle changes when the scoot gets warm..?

Any other suggestions...? I'm getting pretty confused although I think I'm learning quite a bit..

have you adjusted the idle at all? maybe increase it just a little bit?

You should do any Idle and AirFuel adjusts when the scoot is warm!

I've not fiddled with the idle adjustment at all yet.. I'm still slowly working my way through things fixing stuff as I go. Thanks for pointing me in the direction of adjusting a warm engine though! It's one of those things where you could dial it perfectly in, then go riding and find you have to do it all over again once it's warm..

Is it a fine balance between getting the air gas mix right or should I just start with the idle adjustment (which I think just adjusts the slider closed position) and leave the mix alone...? Is there a best practice way about this..?

It's these simple hints off people in the know that make life alot easier! (I learnt the 'easy way' to rotate the crank to close the hole from the air box into the engine when the carb was out from a friendly expert. I'd hate to have to learn that the hard way!).

I also note that there's a really frayed wire from the coil to the connector box which I have to fix. I'm not sure if it's causing a problem but best not to ignore a frayed wire when you see one.. Does anyone know what wire rating is used..? I suppose I need the amps rating. (sorry not sure exactly which wire it is right now without further investigation tonight).

thanks for all the hints.. they're really appreciated!

Idle is the easiest adjust on the stock dellorto carb. They put the idle adjust right on top so you can readily adjust it as needed. The fine tune of the air/fuel, is a little more tricky. I would start with the easiest first, especially if you say you are still fixing other things.

On a stock carb if you have already been adjusting the air/fuel. That is the screw on the back of the carb facing rear. It is adjusted through a hole in the carb box. I would turn it in all the way( not tight! ). Next turn the screw all the way around a full two rotations back out.

Then with the bike nice and warmed up adjust the idle so it runs at your desired speed.

This is not the full way to fine tune your carb. You can probably find more in depth instruction by searching the forum. But this should get your bike so it will idle ok!

Until you get the wire that is frayed, fixed, Put a small piece of electrical tape around it? That can make sure it keeps from getting worse.although I would prefer heat shrink tubing

Still confused but I think I'm getting closer. I'm back to the belief that it's still a fuel delivery problem. When I start the bike it seems to idle fine but if I start riding it starts cutting out once I idle with the clutch in. I started changing the idle settings but I got to the point of having the idle setting fully open and it still cut out. Then I did an experiment... I lent the bike towards the engine side and idle revs went up, lent the bike to the glove box side and the bike cut out. I then removed the fuel hose from the carb and did the same thing and as suspected the fuel runs when lent towards the engine, but no fuel when the bike lent towards the glove box. I filled the tank to make sure it wasn't related to the fuel level and still get the same thing.

So back to square one. I can't see how this can be a fuel hose kink because as the bike leans the hose doesn't move...

Anyway I'm going to go back to the start and make sure the tap works the same at an angle (can't imagine this is the problem but I have to start at the top).

Does anyone think the fuel hose might just be a little too long...? The length of the hose enables me to just about rest the tank on the frame and maybe I need to shorten it to avoid the line getting two twisted when the tank goes back in the frame.. I suppose it's just a question of elimination between the carb and the tap.

When the bike is lent towards the engine side the idle revs too high so once I get this dialed in it would seem my adjustments are too high...

The fact that idle speed changes when leaning the bike toward/away from the engine leads me to believe it's a fuel delivery problem upstream of the carb.

First, the physics of it: the fuel line is not changing relative to the gas tank and carb (the two ends of the line) but the angle of gravitational fuel pull is changing. When you lean toward the engine, it drops the carb end of the fuel line lower (relative to the fuel tap in the center of the bike) and the relative gravitational pressure at that end of the line is decreased, resulting in greater fuel flow. When you lean away from the engine, the opposite happens.

I would shorten your fuel line until you can barely rest the tank on the frame when you pull it with just the tiniest bit of slack. Then, once you put your tank back in the bike, pull the fuel line off the carb end and turn your tap on to see if fuel starts burbling out at the carb level. Be ready to turn your tap off right away. This second step is to confirm that your fuel line isn't pinched at all.

If fuel flow is not a problem, it's something more insidious and you might want to clean your carb thoroughly. Also, make sure your head is tightened down to the correct torque and that your case bolts are tight.

Ok,

so left bike in bldg garage for a couple of hours and someone knocked it over..! Found it with headset out of line and scratch on side and now lights don't work.

The good news is that I took the carb out again and blasted every orifice with carb cleaner and made sure cleaner came out of another hole when sprayed in one hole. Put it all back together and now it's idling fine. When I tip the bike the revs stay constant! So that problem solved. Lesson learnt is you cannot clean the carb too much.. Now, if the front bulb is blown should that affect the brake light... I need to start looking at the electrical diagram

thanks everyone!

Holy crap that sucks!!!