Carb High Jet Lean After Rebuild - How to Fix?

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sean donato

sean donato

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You can see some of the other pump diaphragms in the bottom of this picture. The one I replaced was a tan color.
View attachment 927616
That blue one is trash. The tan was the better one and the black rubber would be a good choice if it's never gonna see ethanol in its fuel. Likely there wasn't anything wrong with the tan one.
 
SteveSr

SteveSr

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You can see some of the other pump diaphragms in the bottom of this picture. The one I replaced was a tan color.
View attachment 927616
I don't see the tan one in the photo. The one near the Philips screwdriver handle is one possibility as is the blue one as they both have the large pump area intact but are obviously different.

There are two circuits to the fuel pump. The impulse circuit bends the pump diaphragm in and out and must be sealed properly (correct part installed correctly) to work. The second circuit is the fuel circuit with the two one-way flapper valves. The output of the pump feeds the main needle via the screen. Your job is to figure out the flow of both circuits through the carb and then find the correct diaphragm and orientation to make this flow happen.

I would say to look at the diaphragms that came out of the carb but at this point it is not wise to assume that they were correct either.
 
rking453

rking453

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Well, I got my new Walbro carb in the mail yesterday and got it installed. Saw fired right up, and ran well at all speeds at factory 1-turn out on L and H screws. I did a little fine tuning, very happy with it now. Guess I will box up the old problem carb, and maybe work on it some rainy day I am very bored. For now I'm happy to get the saw running right again. Thanks everyone for your help.
 
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Just rebuilt a WT series Walbro on a Stihl 026. The saw starts and idles great at one turn out on the low jet. When I give it throttle it runs way too lean, two turns out on the high jet before it will stay running, and with the high screw a few more turns out its still really lean. I can't get it to richen up at all. I started thinking air leak, despite it idling well. I swapped an identical carb from my other 026 on the problem saw, and it runs as perfect as you could hope for.

What did I do to mess up this
 
DanAyo

DanAyo

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Well, I got my new Walbro carb in the mail yesterday and got it installed. Saw fired right up, and ran well at all speeds at factory 1-turn out on L and H screws. I did a little fine tuning, very happy with it now. Guess I will box up the old problem carb, and maybe work on it some rainy day I am very bored. For now I'm happy to get the saw running right again. Thanks everyone for your help.
I read the entire post. It was very informative and a great source for learning. Since you invested so much time and effort, wouldn’t a vacuum/pressure gauge have helped with the troubleshooting?
I have never used one, but hope to get mine early next week. It looks like an extremely handy tool to have around.
 
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