High-low Adjustment screws aren't screws.

Joined
Oct 15, 2022
Messages
5
I'm having a problem where my backpack leaf blower only idles, but does not run when I pulled the trigger. Spark arrestor is clean, air filter is clean, fuel filter is clean, carb is clean.
I was thinking about adjusting the high and low screws but I can't because they're not screws. Does anyone know what tool I can use to adjust these? It doesn't look like a PacMan screw
Any other suggestions are welcome.
 

Attachments

  • HighLowAdj.jpg
    HighLowAdj.jpg
    94.6 KB · Views: 78
You need to go to Amazon and buy a carburetor adjustment tool set. Many brands use different screws to keep people from tampering with things so you just need to get the proper tool. Here's a selection of choices that come in just one of many kits:

1665860339319.jpg
 
Wow I figured the adjustment tools had to be purchased from the manufacturer and they wouldn't sell to a mere customer.

I've always used the brute force and ignorance method of taking the carb off and grinding or cutting the shroud down enough to get a pair of needle nose pliers on the screws.
 
I found out this shape is called "ecentric." Pretty fitting if you ask me.
11 Pcs Carburetor Adjustment Tool Screwdriver Kit for Common 2 Cycle Carburator Adjusting Small Engine Carb Tune up Adjusting Tool,11 Carburetor Adjustment Tools+Bag by Lucky Seven https://a.co/d/0lfQxu5

Any other thoughts as to what the issue might be?
 
I'd check for all of the usual OPE problems: plugged fuel filter, cracked fuel line, dirty carburetor, hard fuel pump diaphragm,. You don't mention the age of the machine or if it the issues have only recently occurred but it might be time for a fuel system refresh.

Buy all new fuel lines, fuel filter, carb diaphragm kit, and start with fresh fuel and give it a good tune up. A new plug probably wouldn't hurt either. These items usually last only a 3-5 years before they start causing issues so it might just be time to replace the lines and rubber items that come in contact with the fuel.
 
Thanks FowVay. This backpack blower is just under a year old and has maybe 10 hours of runtime. It's never ran great but it at least ran about 2 months ago.
I appreciate and will go through your suggestions one by one then give it a shot. Thanks again!
 
Adjust on the ''fat'' side to allow for the cooler days. Lean is mean, IE lean mixtures burn pistons. Too rich is safer piston wise.
Factory sets them on the lean side, hence meeting the compliance hours for EPA. Richer non complaint settings make for happy equipment owners.
 
Well, since it's so new then you might be lucky and get by with a simple needle adjustment. Start it and let it warm up to full operating temperature and then adjust the high speed needle (furthest from the engine) to the slightly rich setting (turn needle counterclockwise). Then adjust the low speed needle (closest to the engine) until the engine is responsive with a blip of the throttle. If it lags when you give it fuel then it's too lean. If it slowly loses speed while at idle then it's likely too lean. As repairman54 stated, always err on the side of too rich when dealing with two cycle engines.
 
Thanks for the detailed instructions. I was hunting for how to do it. 😁
I just got the carb tools today so hopefully I can tackle it this weekend.
 
Just a cautionary note, on many of the small carbs like weedeaters the low speed screw is actually an air bleed rather than fuel metering and opening the screw is going leaner, not richer. Opening the low speed needle admits more air making the engine speed up to a point, but often the "optimum" sounding idle mixture is too lean to get the engine to start and as FowVay mentioned, cause a stumble on throttle blips..
 
A carb adjustment was all that was needed! A little tweak to the high and low screws, using the specialty tool, and it's working perfectly!

Thanks all.
 
Back
Top