Recovery from a leakage
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Super Puller 1978
Joined: 19 Jun 2016
Posts: 24
Location: Far East
Thu Jul 30, 2020 1:30 am quote
Hello members,

Previously I had a serious fuel leakage from the carburettor (Spaco 20/20). I've replaced the float needle and it's finally gone.

I adjusted the screws (idle and mixture) to the original setting I've been using without any problems. After that I made a test ride. First, everything was OK then things changed. Engine got weak and misfiring at high rev. The plug turned black. I tried to adjust the mixture screw to give it a bit lean but after that it can't start until now whatever setting I try. I suspect that fuel level is still too high despite it's not flooding. I even removed the air filter to expose the air intake but it still doesn't start.

What are your suggestions?
Style Maven
74 50s x3 78 P200 84 Cosa PK50XL2 58 AllState 68 Sprint 80 50special '66(?) Super125
Joined: 22 Nov 2010
Posts: 7799
Location: seattle/athens
Thu Jul 30, 2020 5:04 am quote
Lets see a pic of your plug, sounds like it could be fouled if its black as you say. Have you tried a new one?


You can also burnish the brass seat that the float needle sits in. It's shown w/pics somewhere in the middle of this mess Random tricks, share your best little tips & shortcuts


It involves a kabob skewer and a small drill to spin it in the seat, some use toothpaste or fine grinding compound or polishing paste. I usually just push it in firmly and let it rip for a minute or two.

When I'm not sure, I like to test the whole system assembled, but out of the bike.

Here I'm just draining the tank after testing a freshly installed new fuel tap. Zero leaks now!

Hanging the carb level under the tank is a little challenging the first time, but well worth it if you have odd gas seepage and want to get it fixed. Just use baling wire if you have to. It's good to know your whole system works right and you can see it easily if there's a problem. Be sure to check your flow while you're at it. Good luck!

IMG_20200727_174133_419.jpg
I hang up the tank then suspend the carb beneath it using the fuel line that will be used in the bike.
Then I place a clean paper towel directly under the carb and look for any spots in the morning.

Style Maven
74 50s x3 78 P200 84 Cosa PK50XL2 58 AllState 68 Sprint 80 50special '66(?) Super125
Joined: 22 Nov 2010
Posts: 7799
Location: seattle/athens
Thu Jul 30, 2020 7:34 am quote

here's the test on a smallframe system. I placed a clean paper towel over the can and went to bed.

and here's the burnishing stick post with more info and another picture, etc http://modernvespa.com/forum/post1823915#1823915

I ALWAYS do this, on every carb rebuild. On the bike I leave my fuel tap open except when storing. This gives me a head's up if my float needle is seeping, which can lead to more problems, like fouled plugs. Are you using good synthetic 2T oil, mixed 50:1? And have you tested for strong spark?

Molto Verboso
1963 VBB2T
Joined: 07 Nov 2012
Posts: 1919

Thu Jul 30, 2020 6:25 pm quote
Nice setup Terry, nothing like an overnite test, I did that when I changed the fuel outlet in the tank.
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