walbro wt series carb help

[1 FMF]

have a poulan PL-25 weed trimmer. ways back after i got it the original carb (don't remember which make/model) [censored] out and rebuilding it didn't help. so i bought a whole new carb, a walbro wt-631 is what showed correct for that trimmer from whatever website. bolted it on and weed trimmer ran like a champ for past few years.
this year it's been slowly loosing power until it would only idle, if i gave it any throttle it would go blaahh and stall out. if i could get it to spin up managing the throttle there was no power and whenever cutting thick stuff the engine would stall right out.
so i bought a rebuild kit and cleaned the thing out, put all new gaskets, same problem.
undid everything including welch plug this time and soaked the body in a gallon of berrymans carb cleaner for 30 minutes. used 100 psi compressed air to really blow it out, then reassembled. engine will now run and have power but no where near it did when the carb was brand new. at full throttle you can still feel and hear it's lean, but at least it has enough power to cut. but it doesn't have that snap throttle response like it did when carb was new. I really don't feel like buying another new carb.
anybody know what i can do? the fuel lines are good, and the tank is clean and the stone thing in the tank with the fuel filter is bright white and completely clean. so i'm pretty sure it's not dirt clogging the carb, i'm guessing it's the @#$%'ing ethanol fuel varnishing up and clogging the carb over time.
if i do go a new carb again, anybody know how/where i can look up all the various models of walbro carbs? because this wt-631 does not have any adjustable jets so if i buy a new one i want adjustable high and low jets that i can remove when i eventually have to clean it.

 

[jhellwig]

I would change the fuel filter in the tank. They used to make a lot of them where the part that connects to the fuel line was a junky pot metal or maybe lead that would corrode and plug up eventually. With the fixed jet carb you don't have much choice on how it runs. Especially if it has been run lean and has a scored jug. You might be able to fund an adjustable jet carb but the thing might not be worth fixing for the price.

 

[Sawdusted]

Some carbs are tough as heck to clean and can never get it cleaned fully. You mentioned performance improved after cleaning but still not optimum means there is something Wong with the carb and not the fuel lines.

I would get a new carb. They usually cost about $20 from amazon. Not worth the time and hassle to clean.

 

[bvance554]

You're concentrating on the intake, but have you checked the exhaust? They can get pretty gummed up and cleaning the spark arrestor and muffler can work wonders on an older machine.

 

[Dean85]

Originally Posted By: bvance554
You're concentrating on the intake, but have you checked the exhaust? They can get pretty gummed up and cleaning the spark arrestor and muffler can work wonders on an older machine.

+1.
I have ran across this a few times. I take the muffler off, remove the spark arrestor and use a propane torch to burn all of the crud off.

 

[boraticus]

Agree with the recommendations to check the exhaust. Also, look at the impulse line if it has one.

 

[Woody71]

I've been looking for info on the WT series carb over the last few days. I found a WT series service manual on their site but no docs specific to model number. I'm running a WT-875-A

Mine dies during idle. Yesterday I discovered that there was too much oil in the air filter (not 2-cycle oil but rather the oil I used to lube the filter after cleaning). I cleaned the filter and am going to re-install it with only a few drops of MMO squeezed throughout the filter. If the problem remains, next step is to check exhaust port and if clean, move on to cleaning the carb.

My carb requires a special tool to adjust the hi/low mixture screws. That's on order as well. Unfortunately they're not cheap, I shelled out $35 for the tool but it would be double that to have the dealer do the work.

 

[1 FMF]

the exhaust is clean and free.
the fuel lines and in-tank stone filter is good.

i found out from the walbro site thanks to the epa that walbro no longer sells or manufactures carbs with adjustable mixture screws. and they also don't sell the tool to access the tamper resistant screw (i have one that's recessed on the wt-631), the tool is only available through distributors or to authorized service centers or some [censored] like that. so thanks a lot to everyone who has voted the way they have to give us our current state of parental govt. you owe me $30 for a new carb

 

[Woody71]

I read that same page on the Walbro site. You can buy the tools from Amazon.

 

[wag123]

Check to make sure that you don't have an air leak. In particular, where the carb mounts to the insulator and where the insulator mounts to the engine, and check to make sure that the insulator itself isn't cracked. They can also leak where the cylinder bolts to the cranckcase. These are common problems on this engine. Spraying carb cleaner around the insulator and base of the cylinder while the engine is running will tell you if you have an air leak.

 

[bvance554]

So the carb is clean, exhaust is clean, fuel lines are good and you say you've changed the gaskets so perhaps we can rule out air leaks. You're running out of possible sources for your problem. Compression maybe? Magneto or whatever it uses? I highly doubt that adjusting your carb with the special tools will help because it worked fine before and it didn't un-adjust itself, and unless you moved to a different elevation your air/fuel ratio hasn't changed. Poulan's are cheap. I went through the same issue with mine and finally had to give in a buy a new one. Definitely not worth buying a new carburetor for.

 

[1 FMF]

the engine is otherwise fine, engine has very good compression and the trimmer as a whole is very good. not spending $100+ for a new trimmer.
probably will take a dremel to the body that's around the mixture screw so i can access it and then remove it to clean out the carb more. freaking screwdriver tool cost more than a whole new carb.

 

[wvrailroader]

Take the Dremel slotting wheel and just cut a slot clear across the shield around the screws and across both mixture screws themselves. You can then use a flathead screwdriver to remove or adjust them and there is no need for the special tool.

 

[1 FMF]

yeah just did that, saved myself $30. this carb only has one mixture screw on the left side where L is marked. On the right side there's the H mark but only a dimple no mixture screw. I removed the low mix screw and blew the carb out again with brake clean and compressed air. fired up and was able to adjust the L screw to get full throttle power, turned it ccw and got the dieseling sound, turned it cw till speed fell off, then set it in the middle at high speed. i idle it down now and it's fine, and throttle response is good. and what i've had to do because the stop switch is stuck is to turn the idle stop screw out to lower the idle till it stalls. now i can basically undo the idle screw to lowest possible idle and it almost doesn't die. that whole tamper resistant thing is so stupid.