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Line trimmer starts briefly diaphram replaced

iarnstein's Avatar

Join Date: Apr 2009
Posts: 2

04-20-09, 01:33 PM   #1  
Line trimmer starts briefly diaphram replaced

Something I am doing wrong on two straight shaft line trimmers I am trying to fix. One is a Ryobi, and the other is a Snapper GN31SCN ::somethingorother:: I have replaced the diaphram on both of them and really cleaned the carb pretty well but I don't think I understand the basics here or I stoopid.

The problem is that they will start but almost immediately cut off. I can run them on starting goo so I believe the problem to be fuel delivery. Fuel lines have all been replaced.

Both trimmers use walbro WT carbs and after I have reassembled them they will start but not keep running. The thing that gets me is that I can push the primer bulb a few times but it pressurizes the system and can't be pumped after that. Perhaps that is what it is supposed to do, but I thought if it was over pressure fuel would return to the tank via the return line. I can pressure it up till the hose pops off so it makes me think that something is not did right. The diaphram takes the engine pulses and makes the crude built in fuel pump work, right?

Any advise or theory of operation you all can provide would help me, O River of Knowledge.


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hopkinsr2's Avatar

Join Date: Feb 2005
Posts: 1,561

04-20-09, 07:30 PM   #2  
If you go to the Walbro website, You can download & print an excellent shop manual from them with all specs & adjustments. The tool for adjusting the meetering lever (or the whole tool kit) can be ordered thru you're local Napa store... Verify the primer hoses are on the right fittings as most of these small carbs use the primer to draw air out of & fuel into the carbs, not pressureize or "prime " the engine with a shot of fuel. Hope this helps...Roger

Jbrokeit's Avatar

Join Date: Apr 2009
Posts: 24

04-20-09, 08:22 PM   #3  
I agree your fuel lines are not connected correctly. The primer should draw or suck from the carb and push or blow to the return to the tank.
If it is pressurizing you either still have a restriction or the fuel lines are crossed.

iarnstein's Avatar

Join Date: Apr 2009
Posts: 2

04-22-09, 07:22 PM   #4  
Thanks - that was one of the problems. The snapper start/stops but at least I know the issue is no longer the primer bulb. The ryobi runs marginally now - on partial choke.

cheese's Avatar
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Join Date: Jul 2001
Posts: 16,570

04-22-09, 10:18 PM   #5  
Open the high speed screw (the one of the two that is closest to the air filter) a little and see if that helps on the Ryobi.

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