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Hot!New Carb Won't Idle

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Dave9
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2019/08/04 10:11:59 (permalink)
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New Carb Won't Idle

I have a Craftsman 358.794730 25cc leaf blower.  No longer made, but it looks identical to what's sold under several brands and is the older version of this:
 
(Edit:  I can't yet link to this  newer Craftsman 41AS99MS799 that it looks like)
 
It uses a Walbro WT-875 Carb.  Started running extremely rough, hard to even start.  As old as it was (around 10 yrs), I bought a generic carb kit including filter, fuel line, spark plug, carb & more, replaced all these items plus smaller fuel line that didn't come in the kit.  Here is the kit: 
 
(Edit:  the carb kit is called a  Carbhub WT-875 Carburetor for Craftsman Poulan Pro Blower BVM200C BVM200VS P200C GBV325 P325 with Fuel Line Filter Gasket Spark Plug Replace 545081855 WT-875 WT-875A ), pictured below.
 
Still ran rough.  Pulled muffler off and saw cylinder exhaust port was practically blocked.  Cleaned that out and it runs good at partial and full throttle but won't idle.
 
I turned the idle screw out 1 turn, no difference.  Can't really tell when the idle screw is fully seated, seems like the threads in the carb for it are pretty sketchy, poorly cut and it's loose.  Turned the carb screw out more, and more, and it still won't idle.
 
It wouldn't even bother me if it idles high, just want to get it to idle.  The carb is past the return period and I'd like to keep using it if possible.  Is there some easy way I can check or modify it to get it to idle even if i lose the idle adjustment and/or it idles  high?
 
Can I take the carb apart and put back together using the same gaskets or are they one time use?  Once apart what do I look for, or should I stick a piece of wire down the hole the idle screw sits in or spray carb cleaner down that hole?   If the screw is really loose would this create a vac leak and I could lather some silicone grease on the screw or just plug its hole entirely with epoxy?
 
I guess if I have to, I'll just put the old carb back on but I hate to put an all original 10 year old carb back on and would like to learn what is wrong with the new one already on it.
 
I do have a drill press and tiny carbide PCB bits, etc, if that would help?   I mean if I just enlarge or clear out the hole that idle screw is metering (I mean the internal tube or jet or whatever it's called, not drill down through the idle screw hole), is that a slam dunk to get it to idle or is it possible that a little enlarged hole would make the mix too rich to idle?  Should I instead run something soft down through that passage like plastic monofilament (like fishing line but thicker)? 
 
I'm wondering if the idle screw threads in the carb body are horribly machined, got chewed up and sheared off creating a blockage.  Externally nothing looks wrong with the carb besides the looseness of the idle screw.
post edited by Dave9 - 2019/08/04 12:23:12

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    MdStamen
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    Re: New Carb Won't Idle 2020/07/10 08:50:20 (permalink)
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    You need to remove the plastic intake manifold. Check the manifold for cracks or a bad gasket.
    Dave9
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    Re: New Carb Won't Idle 2020/07/10 10:28:49 (permalink)
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    ??  The only plastic on the intake is before the carb and holds the air filter.  Carb bolts straight to the engine unless I'm remembering a different engine?  Gasket between carb and engine was changed.
     
    Pretty sure it's the terrible quality of the Chinese carb, either the mix screw threads are stripped out or other metal casting defect.
     
    For the time being I just bought a cordless electric blower.  Terrible runtime and ridiculously expensive batteries but I can make due.  I've also found new uses for it that I'd never have used a 2 cycle blower for, like blowing water off vehicle glass after washing it, clearing dust out of computer cases (or any use really...) indoors.
    AVB
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    Re: New Carb Won't Idle 2020/07/10 12:34:41 (permalink)
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    The plastic being refer is item 9 and the gasket is item 20 on the following IPL, under Muffler/Crankcase page.
     
    https://www.searspartsdirect.com/model/mqlpqqq97s-000247/craftsman-358794731-gas-leaf-blower-parts
     
    As for the Chinese carburetor clone what you are describing is why I quit buying them. Too many pieces of crap.
    MdStamen
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    Re: New Carb Won't Idle 2020/07/10 13:11:06 (permalink)
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    The part number is Adapter - Carb. Part Number: 545084901. Most are made of plastic.Dave I see you have done a lot to try to resolve the problem. This is just my free suggestion. This area if it has a hairline crack will suck air and at idle that is a no no. Also remember the port for the carburetor pump is there also. Anyway good luck!
    MdStamen
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    Re: New Carb Won't Idle 2020/07/10 13:15:46 (permalink)
    Dave9
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    Re: New Carb Won't Idle 2020/07/10 18:40:29 (permalink)
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    Hmm, I didn't remember that piece. Thanks.
     
    I'll check it when it get a chance but I'm doubtful that's the problem as it is acting differently than it did with the old carb on, and it's plain observable that the mix screws are just flopping around and creating a vac leak.   I mean they won't even say set, vibrate and rotate around like crazy.
     
     
    I wonder if I could create a hot glue plug over them, if I could somehow get them dialed in right.  Then again I don't know what temperate that portion reaches, but hot glue would be temporary then I could epoxy it in.  Ultimately, I should have just bought a major brand carb or exchanged the generic but I got tired of fooling with it and with fall here when I made my post, a cordless electric skipped right over any of these kinds of issues.
    post edited by Dave9 - 2020/07/10 18:42:23
    TownsendsFJR1300
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    Re: New Carb Won't Idle 2020/07/17 21:54:33 (permalink)
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    .
    post edited by TownsendsFJR1300 - 2020/07/18 17:13:38
    Dave9
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    Re: New Carb Won't Idle 2020/07/18 00:24:15 (permalink)
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    It seems people aren't reading a lot of the details.
     
    The generic carb I bought, has serious defects and the adjustment screws wobble around and move themselves when it runs.  It's so bad that they barely stay threaded in and cause a vac leak too.
     
    There is no other issue I need to focus on when that happens.  That is a show stopper.  Nothing else I do, changes that this is an unworkable problem unless I dial in the mix and seal those screws.
     
    NOTE that there was no other problem observed, nothing cracked, no seepage, it was a very straightforward repair until I received chinese garbage in place of a working carb.  Time to cut my losses, since I have already bought a cordless replacement.
    post edited by Dave9 - 2020/07/18 00:28:08
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