Lauson carb issue

shiftlessguy

New member
Got my 55 runnin today but will only run on choke.I suspect the carb throttle cylinder is worn and sucking air.Thought about shimmin it up or adding a gasket somehow.Any thoughts on this.Runs great on choke.Heres some pics.I customized it a bit on paint scheme.
 

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Bill Sherlock

Subscriber
Stale ethanol gas comes to mind as have had that happen before I discontinued buying ethanol gas for all my air cooled engines. Course it could be some other problem but I would try some gas from a different source before looking further.

Bill
 

dkirk

New member
For this type of suction carburetor, I believe you need a check valve in the fuel line that prevents fuel from running back into the tank.
 

shiftlessguy

New member
I tried to shim it up a bit but i knew it wouldnt work but
tried anyhow.Ended up putting a fiber gasket and putting some grease inside top of carb and throttle cylinder,was gonna try an O ring also but i think this will work.It at least moved wesr spot up just a bit and seems to have less play,and its not interfering with air flow.Havent started it yet as I have to play with crank end play a bit,pretty loose, .047
 

Craig DeShong

Subscriber
These 55S engines have a Lauson built carburetor. They are the devil to set. Mine is critical to temperature, moisture, the phase of the moon, the planet alignment, etc. :)

Having leaks by a warn or sloppy fit isn't going to help. I suspect with all the "play" you indicate, it may only run on choke, so you get enough vacuum to draw fuel into the carburetor throat.
 

shiftlessguy

New member
Well goopin it up didnt work sorta.Did discover that the fuel inlet to carb was covering the hole that feeds fuel at the top of carb,Itll start on its own without puttin a little fuel in carb,cant get it to idle though but high speed is there for the most part.Gonna try and raise fuel tank up to where owm hight is as the tank i have is not oem and its a few inches lower than oem.Ill try this next then if i have to goop up the carb again and fix the speed,maybe see if an O ring in the throttle cylinder where fuel enters
 

batrider

New member
I've never had any luck using silicone seal with gasoline. The gas gets underneath it and then there is no bond.
 

shiftlessguy

New member
Re: Lauson carb issue/mystery solved

Finally solved the problem.YEAH!!!!!!!Apperently tank has to be a certain height,runs like a champ.I used an old Briggs tank from a wmb and had it mounted on a board with motor apparently too low to get any suction,so even though carb is worn runs great!!Finally done and i can get it off my bench!
 

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