OP
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Member
ET4
Joined: UTC
Posts: 26
Location: MA
 
Member
ET4
Joined: UTC
Posts: 26
Location: MA
UTC quote
I have ET4, 150cc, 2001 model.

I am quite familiar with general maintenance.

I am following this video for carb cleaning. The following pics are from this video.

Few simple questions

1)Please refer to Figure 1. I cleaned all jets (pilot, main, A/F mixture screw, ...). I also sprayed carb cleaner into the hole where pilot (idle) jet screw into. But if something is clogged in this passage, how does one physically clean it? I can not see the air opening (beginning) nor end of this passage where high velocity air travels to form Venturi effect for the pilot Jet (idle jet).



2) Please refer to Figure 2. My float bowl gasket is totally flat. If there is air leak through this bowl gasket, will the engine run like it has vacuum leak (idle poorly)? Please refer to Figure 2.

On the web for motorcycles, people say carb float bowl interior pressure must be "open" to atmosphere, so that fuel can be suctioned into carburetor by Venturi effect. Then for my scooter, where is the location of this opening (hole)?


3) Please refer to Figure 3. During normal operation, how high does gasoline rise in the float bowl?
Forum member supplied image with no explanatory text
Forum member supplied image with no explanatory text
Forum member supplied image with no explanatory text
@buggsy avatar
UTC

Addicted
GTV / GTS, 1961 Lambretta LI Series 3
Joined: UTC
Posts: 516
Location: Somewhere on the Island of Great Britain, East Coast, Last time I looked.
 
Addicted
@buggsy avatar
GTV / GTS, 1961 Lambretta LI Series 3
Joined: UTC
Posts: 516
Location: Somewhere on the Island of Great Britain, East Coast, Last time I looked.
UTC quote
I would strip the carb down and really give it a good clean thoroughly, if the mix screw is not making any difference when idling then it could be the idle jet channel is clogged, remove the idle screw and clean that passage as well as removing the jets and cleaning them thoroughly

You need to remove and inspected the diaphragm, does the needle move freely and its not gummed up. when reassembling check the diaphragm sealed properly and sound and also fit a new gasket/seal, but if the carbs out as I said I would fully clean everything with brake cleaner or your equivalent😉👍.
UTC

Veni, Vidi, Posti
Joined: UTC
Posts: 6901
Location: Tega Cay, SC
 
Veni, Vidi, Posti
Joined: UTC
Posts: 6901
Location: Tega Cay, SC
UTC quote
Strip it and put it in a sonic cleaner. This will work better than just spraying carb cleaner every where and might save you from getting some in your eyes in the process. Get a new float gasket. There are openings at the mouth of the carb for the idle circuit.
@greasy125 avatar
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Sergeant at Arms
Weird 80's Vespas & Cool Vintage Lambrettas
Joined: UTC
Posts: 14923
Location: The state of insanity, SoCal
 
Sergeant at Arms
@greasy125 avatar
Weird 80's Vespas & Cool Vintage Lambrettas
Joined: UTC
Posts: 14923
Location: The state of insanity, SoCal
UTC quote
bcdfh_jk wrote:
1)Please refer to Figure 1. I cleaned all jets (pilot, main, A/F mixture screw, ...). I also sprayed carb cleaner into the hole where pilot (idle) jet screw into. But if something is clogged in this passage, how does one physically clean it? I can not see the air opening (beginning) nor end of this passage where high velocity air travels to form Venturi effect for the pilot Jet (idle jet).
did you fully strip and dip the carb?

when you say cleaned the jets, did you remove them and blow cleaner and air thru them? sometimes you need to run a fine wire thru the idle jet-- you should be able to see light through it when clear. you'll need to remove the air/fuel mix screw to fully clean the idle circuit-- careful not to lose the tiny washer and rubber o-ring! and blow cleaner & air thru there.

you can spray cleaner (with the little straw) or blow air thru the idle circuit from the venturi, a/f mix screw port or thru the jet seat checking each leg of the circuit.
Quote:
2) Please refer to Figure 2. My float bowl gasket is totally flat. If there is air leak through this bowl gasket, will the engine run like it has vacuum leak (idle poorly)?
as long as the gasket seals without leaking fuel you have nothing to worry about.
Quote:
On the web for motorcycles, people say carb float bowl interior pressure must be "open" to atmosphere, so that fuel can be suctioned into carburetor by Venturi effect. Then for my scooter, where is the location of this opening (hole)?
the bowl is vented up thru the top of the chamber into the diaphragm area. there is an external port just under the diaphragm lid that the evap line connects to-- disconnect that, it's not needed.
Quote:
3) Please refer to Figure 3. During normal operation, how high does gasoline rise in the float bowl?
above the float bowl seal to about 1/2 way on the floats

how does your intake manifold look? how about the evap hose and vacuum hose for the fuel tap coming off the port on it? how does your air filter, filter box and intake tube look? everything clean and tidy and tight with no leaks?
OP
UTC

Member
ET4
Joined: UTC
Posts: 26
Location: MA
 
Member
ET4
Joined: UTC
Posts: 26
Location: MA
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RESOLVED!

I removed the carburetor, turned it on its side, and removed the A/F mixture screw. And the small washer & O-ring were missing!! Around ~10 years ago, I lost the metal washer, and I thought I was being careful enough.

The lesson is to never removed that A/F mixture screw unless you can visually verify that nothing fell out.

I went to local hardware and got smallest washer and O-ring. The symptoms are 90% gone. So missing O-ring caused symptoms of too much air and not enough fuel. This was what motorcycle owners (with manual choke) would describe as bike only idling with choke ON even after engine is fully warmed up (choke ON as an alternate path for fuel than the idle pathway).
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Forum member supplied image with no explanatory text
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