Carb/Fuel Problem - Will Only Run With Choke On?
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Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Fri Jun 28, 2019 11:51 am quote
I recently completed some work on the scooter including a clutch rebuild and fixing an oil tank leak. I also replaced both the oil and fuel lines. After getting everything back together I took the scooter on a 10 mile ride and it ran better than ever.

The next day I started her up and got about 100 yards down the alley and it died. I could start it with the choke on and it would continue running as long as I had the choke on. I fiddled with the carb and eventually removed, dismantled and cleaned it. I continue to have the problem. I can run it through the gears for a few blocks then it wants to die unless I pull the choke - then it will keep running.

Any ideas?
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Fri Jun 28, 2019 12:07 pm quote
Does it die when idling, or under throttle? Sounds like a clogged jet but you said you cleaned the carb.

Some other things to check... Replace the spark plug, and also check your ht coil resistance to see if that is still good.
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1437
Location: california
Fri Jun 28, 2019 12:16 pm quote
It could also be an air leak at carb or carb box.

If u have some starter fluid, get it running and using the red spray tube it came with, spray around the base of carb with air box off. Also outside of air box at base.

Do you hear the idle pick up? If yes it's being sucked in through the leak.

Check carb bolt tightness but don't over torque.
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Fri Jun 28, 2019 2:36 pm quote
I removed the carb and carb box. I made certain I had good gaskets/seals between both. I replaced the spark plug. Still will die at idle and at acceleration/speed after a while.

I have both a Haynes manual and Vespa Workshop Manual. Neither describe the ohm/\\resistance testing procedure for the HT. I have the blue Ducati ignition with the WRGG wires.

After messing with the gaskets it seemed to run a bit longer before dying - I think? It will keep on running nearly normal when I pull the choke out. How could this be related to tye HT?
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Fri Jun 28, 2019 3:16 pm quote
Maybe I should have mentioned that my mixture screw is kind of funky. The threads might be messed up so I'm not sure it is all the way in before turning it out 1.5 turns. Could this be related to my symptoms?

I'm tempted to spend $120 on a new 24/24 but not confident yet that it is a carb problem.

It seems like it runs on the fuel stored in the carb float bowl but after it uses that fuel up it dies unless choked. Does this make sense?

I'm tempted to look in the fuel/oil tanks cavity to make sure there isn't a kink in the fuel line but that job is a pain in the %#@.
Molto Verboso
62 VBB1T Round Tail W/ leaner sidecar
Joined: 26 Jan 2019
Posts: 1437
Location: california
Fri Jun 28, 2019 3:27 pm quote
Bhammer- if it's leaking air for some weird reason - it could have these symptoms.

Do the spray test I described if you want to rule this out.

If it's getting air through your mixture screw - it would suck in the starter fluid and race a little. U will know right away if u have an intake leak anywhere.

May not be that - but u won't have to guess after u do it - a $5.00 can will do the trick.
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Fri Jun 28, 2019 3:59 pm quote
I did spray around the carb - base of carb, under air box and around mixture screw. It did not affect the way the engine ran.

If I had too much fuel line (remember I replaced it) might that be an issue if it was too long?
Ossessionato
73 Rally, 74 Rally, 76 ET3, 80 P200, 06 PX150, 65 Li225 Silver Special, 86,95,96 Elite 80s, 2015 HD Road Glide Special, 2011 Ural Tourist
Joined: 18 Jan 2012
Posts: 3616
Location: Oceanside/ SF
Fri Jun 28, 2019 4:15 pm quote
Bhammer wrote:
Maybe I should have mentioned that my mixture screw is kind of funky. The threads might be messed up so I'm not sure it is all the way in before turning it out 1.5 turns. Could this be related to my symptoms?

I'm tempted to spend $120 on a new 24/24 but not confident yet that it is a carb problem.

It seems like it runs on the fuel stored in the carb float bowl but after it uses that fuel up it dies unless choked. Does this make sense?

I'm tempted to look in the fuel/oil tanks cavity to make sure there isn't a kink in the fuel line but that job is a pain in the %#@.
Mixture screw definitely could be a problem. That affects the first quarter throttle you give it.

I donít think your fuel hose/kink idea is the problem. That would show itself at wide open throttle/stop you in your tracks. Since youíre continuously refiring and using the choke it means your carb is getting gas.

Going back to the carb, is your mixture screw the super long 7mm, brass colored mixture screw?
Hooked
1952 Allstate 1955 Allstate 1958 lambretta 1965 Allstate 1968 sprint
Joined: 20 Jul 2017
Posts: 476
Location: Central california
Fri Jun 28, 2019 4:30 pm quote
Carb problem
Well when you say it will run until it quits that leads me to think that the float is getting stuck in the closed position therefore shutting off the fuel flow.
Also I know this has been said, but dbl check the main jet. Sounds as if it is plugged.
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Fri Jun 28, 2019 5:33 pm quote
So I disconnected my fuel and oil lines, got in under the fuel/oil tanks and took out about 6 inches of fuel line. I read it should be about 24 inches which is about where it is at now. Just drove it around the block a few times and didn't have a problem. Now I'll put the helmut on and go for a longer more adventurous drive.

I ordered a new mixture screw about a month ago and with my Dremel cut off about 1/2 an inch and put a flat slot in the end. I can easily adjust it with a long narrow screw driver. But like I said, the threads are messed up so I doubt I have it adjusted correctly. The engine runs when I turn it all the way in so I only back it out about one turn.It does seem to run quite well following the standard carb tuning procedure. After my drive I'll do a plug check.
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Fri Jun 28, 2019 5:51 pm quote
Just back from a few mile ride - no problems. Maybe a slight hesitation at first acceleration. I pulled the plug and it is black and sooty. I wish I could have faith in that mixture screw. Seems like if the mixture screw threads get messed up in the carb a guy is looking at a new carb since you couldn't tap it for a new screw that would fit.
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Fri Jun 28, 2019 5:52 pm quote
Oh ya, regarding the float - when I had the carb apart the float and needle were working just fine.
Ossessionato
1980 P200E , 2005 Stella 177
Joined: 20 Jul 2018
Posts: 2179
Location: Staten Island, NY
Fri Jun 28, 2019 5:54 pm quote
maybe the idle is too rich or air mix too rich? 1 turn out isn't much for a stella, not sure about your PX.
Enthusiast
05' PX150
Joined: 13 Mar 2019
Posts: 89
Location: Bellingham, WA
Fri Jun 28, 2019 8:34 pm quote
Agreed but with my messed up mixture screw I'm not sure what my starting point is. I'm thinking it may not be going all the way in so when I unscrew it 1.5 turns I may be much further out = too rich.

What puzzles me about the engine not dying since I shortened the fuel line is why did it run so well for a day with the long fuel line in there. I wish someone would confirm that a too long fuel line can cause that sort of problem.
Ossessionato
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Sat Jun 29, 2019 6:20 pm quote
Bhammer wrote:
What puzzles me about the engine not dying since I shortened the fuel line is why did it run so well for a day with the long fuel line in there. I wish someone would confirm that a too long fuel line can cause that sort of problem.
Air bubble where line dips , then goes uphill again.
Had full tank & therefore more head pressure.
Now its settled & fuel is lower bubble is created
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