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#472142 - 07/21/08 11:50 AM poulan trimmer carb. adjustment
hornet41 Offline
newbie

Registered: 07/21/08
Posts: 24
Have a Poulan Pro gas trimmer that needs almost full choke to keep running. Tells me it needs more fuel. Which of the two adjustment screws on the carb are for increasing fuel flow??? Thanks 'Mo

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#472143 - 07/21/08 02:23 PM Re: poulan trimmer carb. adjustment [Re: hornet41]
JasonB Offline
Sharp -Shooter
Carpal Tunnel

Registered: 04/27/04
Posts: 14149
Loc: Cape Spencer, New Brunswick, C...
Your problem won't likely be fixed simply by twiddling the screws, assuming the machine ran previously, but you can try. If this is a very new trimmer (last 5 years or so), there may well not be any Hi and Lo mixture screws. The EPA has mandated them away, so now we must live with more or less fixed mixtures on small 2 stroke engines. Recently made engines have only an idle speed stop screw, and we can only fix mixture issues by cleaning and rebuilding the carb.

Assuming your engine is old enough to have the Hi and Lo needles, the Hi one will be further from the engine, and the Lo will be closest to the engine. Most any Walbro carb'ed engine will start and run (very richly, tho) with both screws between 1.5 and 2 turns out from gently closed. Once she fires, she should run with the choke open, tho the engine will be down on power and smoke alot. Time to start tuning.

First, hold the throttle wide open, and slowly close the Hi needle (further from the engine). The engine will smoothe out and speed up. Note where the engine begins to sound smooth, and continue closing the needle (called leaning) until the engine begins to stumble and get rough again. Note this position, and then set the Hi needle to a little to the rich side of the middle of the 2 points you noted..... Hope that's clear...

Now, go to idle. Let the engine idle a little bit (30 seconds or so). Open the throttle and see how it performs. Probably it'll stumble, sputter, smoke and maybe quit. If so, lean the Lo needle a bit (closest to the engine) and try again. If it simply quits immediately, it's idle is lean and you'd need to open the Lo needle slightly. Repeat this until the engine accelerates from an idle cleanly to full throttle.

Because the idle jet has some effect on the main jet, after you get the idle working right, just revisit the Hi needle as described above to fine tune it. You want it set a bit towards the rich side of the 2 stumble points for best performance and engine life.

More than likely, though, your carb has either got varnished gasoline in it (most likely if you're just trying to get it going after a season in the shed unused), or the diaphragms are tired, and you should install a rebuild kit.

If you need help rebuilding the carb, post back, we can help!

Good luck,

J
_________________________
er, somethin'....

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#472144 - 07/21/08 03:13 PM Re: poulan trimmer carb. adjustment [Re: JasonB]
hornet41 Offline
newbie

Registered: 07/21/08
Posts: 24
Thanks, I'll give it a shot. I always keep good fuel in it with Sta-bil. Hope tweaking will fix!!

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#472145 - 07/21/08 03:22 PM Re: poulan trimmer carb. adjustment [Re: JasonB]
CabinConnection Offline
Bigfoot
Carpal Tunnel

Registered: 01/20/04
Posts: 38809
Loc: The Indianhead's Left Nostril....
Nice mixture screw description.

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#472146 - 07/21/08 08:46 PM Re: poulan trimmer carb. adjustment [Re: CabinConnection]
JasonB Offline
Sharp -Shooter
Carpal Tunnel

Registered: 04/27/04
Posts: 14149
Loc: Cape Spencer, New Brunswick, C...
Thankee, and good luck!

Also worth a look (it occurs to me this evening...) is the clunk filter in the tank. Just be sure fuel can flow freely to the carb inlet.

If you feel the need to remove the carb, take a digi photo or 2 first, so you don't get confused with all the fuel tubes to/from the carb, tank and primer. Trips alot of folks up, that.

J
_________________________
er, somethin'....

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#472147 - 07/23/08 04:32 PM Re: poulan trimmer carb. adjustment [Re: hornet41]
mech12 Offline
journeyman

Registered: 08/10/06
Posts: 86
Loc: minnesota
ive noticed with trimmers coming into service, the carb mans are using special needle caps. some still have the plastic restrictors on them. i mainly deal with homelite. the offer the "special" tools need to adjust these carburators. homelite, poulan, husky troybilt doesnt matter the carbs themselves are either a zama or a walbro. there a 4 different configurations of needles, there is the standard torx, single d, double d and a pac-man as its called. i believe you can go to gardnerinc.com and purchase these. pretty handy. i used to remove the insert on a ball point pen and press the plastic onto the needles as an adjustment tool.

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#472148 - 07/24/08 08:27 AM Re: poulan trimmer carb. adjustment [Re: JasonB]
hornet41 Offline
newbie

Registered: 07/21/08
Posts: 24
The instructions worked like a charm!! I bought the tool to deal with those pesky little adj. screws. I found the Hi screw was only 1/2 turn from fully closed!!! After fiddling with the hi/Lo that thing hums!!!! Thanks

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#472149 - 07/24/08 08:44 AM Re: poulan trimmer carb. adjustment [Re: hornet41]
JasonB Offline
Sharp -Shooter
Carpal Tunnel

Registered: 04/27/04
Posts: 14149
Loc: Cape Spencer, New Brunswick, C...
Hey, great! Glad it worked out for you! thanks for the feedback, too.

A quick caution for you... When the engine is being tuned, don't tune it so it's always running completely flawlessly smooth. It's safer if you rich it just slightly, so once in a while it burbles slightly. That's a sign of a slightly rich mixture, and since our oil's in the gas, it helps ensure adequate oil. Just the slightest, most occasional burble when the engine's under low load (not cutting) is great. Once line meets grass, the load goes up and the engine will produce best power.

J
_________________________
er, somethin'....

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#472150 - 07/28/08 06:21 PM Re: poulan trimmer carb. adjustment [Re: JasonB]
pondman Offline
first timer

Registered: 07/28/08
Posts: 1
Thank you, JasonB! Your description of how to tune the H/L mixture screws helped me get my Poulan Pro blower running again. After pulling the screws and grinding slots with a Dremel, I made the adjustment and away it went. I really appreciate it.

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#472151 - 07/29/08 07:44 AM Re: poulan trimmer carb. adjustment [Re: pondman]
JasonB Offline
Sharp -Shooter
Carpal Tunnel

Registered: 04/27/04
Posts: 14149
Loc: Cape Spencer, New Brunswick, C...
Just glad to keep small engines singin' their songs!

J
_________________________
er, somethin'....

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