Question about Poulan Pro 42CC 2 Cycle Chainsaw, 18"

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Wich is the best position for the screws H and L (turns)? also the primer buble sems to dont get enouf gas only works good when i turn in the screw L completly. Tanks for your asistanse

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Turn the high needle valve in until you feel the slightest resistance and turn it out 1 and a half turns. For the low turn it in the same way until you feel the slightest resistance and turn that one out 1 turn. The carburetor probably has to be rebuilt since the primer is not working like it should.

Posted on Mar 17, 2011


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TB4SC Leaf Blower unused for months. Replaced Gas tank, Choke assembly and Primer bulb. Starts and runs at idle speed. When throttle is pressed it dies out.

The carburetor has 2 adjustment screws. One for idle and one for high rpm. They have weird heads on them to keep you from adjusting them without purchasing the proper adjustment tool. Look on ebay for carburetor adjustment tools for your particular blower. After you get the too, you can start the blower and make your adjustments. First one screw at idle, then the other while holding the trigger on full. The best way is to first turn the screws all the way to the right (closing the jet) then turn them back to the left 2 1/2 turns. This can be done prior to starting the blower. Then adjust accordingly until the blower runs at the best speed for the idle then at high rpm. You'll notice that the rpm's drop if you go too far either way. If you screw it up, go back to closing the jets all the way to the right, then open them back up to the left 2 1/2 turns. Good luck!

Sep 21, 2017 | Garden

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Gas leaking from carburetor bowl drain screw when pushing in primer. Push primer two times and couple drops of gas on floor. Any way to tighten spring screw on carburetor bowl?

Sounds like you need a gasket on that screw. Don't over tighten as you could mess up the threads. I think this is the screw that has the
fuel jet in it. If you take it out its good to clean out that jet as well to have a good running machine.

Jan 05, 2014 | Mtd Snowthrower 208cc 26"

1 Answer


If you rebuilt the carb did you turn any of the screws on the carb while cleaning or take out, you might have just the low idle screw closed a little to much open half turn and see what happens. If you look at the carb where needle screws are located on the side,if you have two screws it will be stamped with an " L " and?or an " H " next to each screw. If you only have one screw then turn that one, to left to get more fuel. Good Luck...

Aug 27, 2011 | Troy Bilt Tb70ss Gas Trimmer

1 Answer

Troybilt chainsaw 20'' bar. will only run until primer fuel is burnt. Replaced gas filter, and soaked carb,and installed a carb.kit.Can`t find any vaccum leads, flywheel and key ok .Help thanks

The idle screw may be turned all the way in on the carb adjuster which should be a very small screw in a 3/16 hole through the plastic cover on the side between the starter rope and the trigger on most saws. Bottom it out and then turn it back 1 and 1/2 turns. Have the saw on a low bench, so you can control it when she starts up - if the revs are too high the chain will spin up which can be dangerous. Now screw the idle down until the chain stops and the motor starts to stall, screw it out a little to get a running idle which will not stall but never starts the chain spinning up. Some have two screws, one for air during idle, the other for the gas during idle. They both should be out about one and a half turns which is industry standard and then you can fine tune from there, but usually only a half turn cw or ccw would be way too much difference from the standard positions.

Apr 10, 2011 | Troy-Bilt Mtd Troy Bilt TB4218CC 42cc 2...

1 Answer

Stihl 021. Starts but will not continue to run.I replaced the carburetor kit but it still won't run. The spark plug is recent and it's good.

Hi scooterbu850,
You indicate you replaced the carburetor kit, did you check for dirt and clean the carb and install the kit very carefully, and make sure all the gaskets on the carb and between the intake and carb have no air leaks? The first thing is to try to adjust the low speed screw to give you a faster idle, it is the screw with a spring, on top of the carb where the throttle cable hooks up. Turn it in (clockwise) to give more idle speed. Now locate the mixture screws on the carb, they are on the side of the carb and also have springs on them. They are marked with an L or H on the carb body beside the screws. Turn them both in (clockwise) until lightly seated then turn them out (counterclockwise) 1 turn or if you prefer turn them to the position they were before you took the carb apart. 1 turn out is the recommended position by the manufacturer so the engine starts and runs, sometimes this is the right position. If it does not idle properly, remember this position and turn the idle mixture screw out (counterclockwise) in 1/8 turn increments until it runs properly 5 or 6 times or more if it runs better. (When turned out you are adding more gas to the mixture). You could also try the high speed mixture screw and see if it helps with the idle, but do not turn in (clockwise) to less than 1 turn out from a lightly seated position, to prevent overheating. If this doesn't help, check the air and gas filters, the gas tank and fuel lines for blockages. Check the spark plug to see if it is wet and if it isn't no fuel is getting to the engine. These are a few suggestions for you to try. Hope this helps a bit. All the best and good luck.

Mar 04, 2011 | Stihl Garden

1 Answer

My ryobi ss30 trimmer will only run in the choke position when i put it in the run position it dies instantly or when i give it gas also the primer bulb takes forever to come back up when pressed so far i...

Did you take plastic of the needle screws. Pull them on with a pair of vise grips. Mine had slots in them. While counting the number of turns, gently turn them in till they bottom out. Then turn them all the way out. Label which hole they came from Spray out the passage ways with carb cleaner. Put screws back in, all the way in, then screw them back out the number of turns it took to bottom them out.

Take off the back motor shroud, be careful, it also holds on the gas tank. Also, when removing it, it will open up the crankcase, so do not get any dirt in there, Take the restrictor out of the muffler. It is under the cover on the exhaust port. Remove the two screws and it is underneath. Put cover back on with the two screws. Re-install the motor shroud.

Then thing should run.

You might want to replace the gas lines and fuel filter as well.

May 17, 2010 | Ryobi 30 Cubic Centimeter Curved Shaft Gas...

1 Answer

Lawn mower is bogging down and there is not enough gas going into it. It helps when you keep pushing the primer.


If this is an OHV Engine, then Set the Valve Clearances or the Carburetor Requires Soaking and Cleaning.
>>You can View a Breakdown of this Unit at this Site Addy; and Select OEM Parts at the Top of the Page. Now Use the "OEM Parts Diagrams Look Up by Model Fit" Section. Select the OEM (Toro Consumer). Select Snow Throwers. Select your Model. Now you can Select the Section of this Unit you Wish to View by Select it from the Drop Down Menu at the Upper Right of the Page that Loaded After you Select your Model.
>>The Following is a Basic File I Made for Cleaning Carburetors. Any Input is Appreciated. Even though the Carburetor Looks Clean, the Internal Passages May be Restricted with Varnish that Gas Causes to Build Up over Time.
>>Spray Cleaners Remove this Varnish in Layers, so Soaking is the Only Sure Way to Remove ALL this Varnish.
>>I Suggest you Make Sure the Gas is Free Flowing to the Carburetor Inlet Port (if the Model does Not have a Fuel Pump). If the Gas is Free Flowing to the Inlet Port, then
>>**Remove, Disassemble and Soak the Carburetor Overnight in Carburetor Cleaner (I Use Gunk).
>>The Primer Bulb is Held in Place with a Locking Collar at the Base of the Primer Bulb. Use a Small Flat Screw Driver and Carefully Pry the Lock Ring Up in Small Amounts All Around the Lock Ring until the Lock Ring and Primer Bulb can be Removed from the Carburetor Body. Usually a New Primer Bulb is Required when you have to Soak the Carburetor. The Rubber is Usually Rotted to Much for the Primer to be Reused.
>>Your Primer Bulb May Differ Slightly, but Removal is Usually Almost the Same Except for the Primer Bulbs that are Bolted to the Carburetor. These are Simply Unbolted and Changed with the new Primer Bulb.
>>I have Found that Most People can Use a Breakdown/IPL and Disassemble the Carburetor Enough for Proper Cleaning.
>>You Only have to Remove the Bowl (if Applicable), Float Pin (if Applicable), Float (if Applicable), Needle Valve and Needle Valve Seat if Applicable. This is a Flat O-Ring Located in the Inlet Port the Float Needle Rests in. Use a Strong Wire with a Slight Bend to Remove the Old Seat. Sometimes a Small Pocket Screw Driver can be Use Also.
>>The New Seat will have a Slightly Beveled Side and a Flat Side. The Flat Side goes Towards the Carburetor Body when Inserted into the Inlet Port. Spray the Seat with Spray Lubricant to make Installation Easier. The End of a Drill Bit that is Slightly Small than the Seat can be Use as an Insertion Tool.
>>Wear Gloves or Use a Rag when Handling the Sharpened End of the Drill Bit. Remove Any Adjustment Screws that Go Into the Carburetor Body. The Welch Plugs Do Not have to be Removed.
>>If you are Able to Remove and Disassemble the Carburetor and Keep the Gaskets Intact, then Usually these Gaskets can be Reused. Even the O-Ring Around the Bowl can be Reused if it is Not Broken. The Only Parts you May Need to Replace is the Float Needle Valve (and Seat if Applicable).
>>The Float Needle Usually is Not Replaced Unless it is Not Operating Properly (the gas flow not shutting off and the carburetor is Flooding). Do Not Remove the Main Nozzle. This is a Pressed Fit and Removal is Not Required for Cleaning. Soaking and Blowing the Carburetor Out After Soaking will Clean the Nozzle.
>>Once Disassembled, then Soak the Carburetor Body and Parts in a 1 Gallon Can of Gunk Carburetor Cleaner Overnight. The Can has a Parts Tray Inside it for the Small Parts.
>>Once the Carburetor and Parts are in the Cleaner, you can Replace the Lid for Safety and to Prevent Accidental Spillage. Then Blow Out the Passages with Compressed Air.
>>***(Do Not Use High Pressure Air for the Zama Carburetors, they have Check Valves for the Primer and these are Usually Blown Out of the Carburetor if Not Careful. Allow the Zama Carburetor to Set on a Drip Pan and Dry)***.
>>****All the Carburetor Adjustments are the Same for Lawn Mower and Trimmers. There are Several Location for the Air Mixture Screws. The Idle Air Mixture Screws are Usually Located at the Top of the Carburetor Bowl and the Top of the Carburetor Body.****
>>If the Main Air and Idle Air Mixture Screws are Side by Side on the Side of the Carburetor, then the Idle Air is Nearest the Engine. The Main Jet Air Mixture Screw is Located in the Bottom of the Carburetor Bowl or Beside the Idle Air Screw on the Side of the Carburetor Body.
>>Some of the Older Model Carburetors have the Main Jet Mixture Screw Straight in from the Top of the Carburetor Body (this is Rare anymore). If you have Cleaned the Carburetor (Disassembled and Soaked Overnight in Carburetor Cleaner (I Use Gunk). Then Blow Out the Passages with Compressed Air and Install a New Kit if Required. Now Setting the Air Mixture Screws:
>>****Turn the Idle Air and Main Air Mixture Screws In Until SNUG **Do Not Jam** Then Reverse Both Screws 1 1/2 Turns. Holding the Throttle Full Open, Start the Engine. Turn the Main Air Mixture Screw Clockwise Until Proper Revs are Obtained. Occasionally you May have to Turn this Counter Clockwise to Achieve the Proper Revs. Now Allow the Engine to Idle. Set the Engine Idle Screw (Not Idle Air) so the Engine will Stay Running if Required. Now Set the Idle Air Mixture Screw so there is No Hesitation when Throttling from Idle to Full Throttle. Reset the Engine Idle if Required.****
>>If This Carburetor has a Single Air Adjustment (Except Tank Mounted 9200 and 100900 Engine Model Carburetors), Use the Section Above that Pertains to Full Throttle RPM Air Mixture Screw and then Adjust the Screw if Required to Eliminate Any Hesitation when Throttling from Idle to Full Throttle.
>>For the 9200 Model Tank Mounted Carburetor Adjust the Air Mixture Screw Full In, then Reverse 1 1/2 Turns. Set the Throttle Lever to Full Throttle and Start the Engine.
>>Now Carefully Use 1 Finger and Open the Throttle Plate and Over Rev the Engine Slightly. If the Engine Over Revs and Does Not Struggle to Over Rev, then the Carburetor is Set. If the Engine Struggles to Over Rev, then Turn the Adjustment Screw In 1/4 Turn and Repeat the Over Rev Test.
>>If you Adjust to 1/2 Turns In and the Engine Still Struggles to Over Rev, then Return the Adjustment Screw to 1 1/2 Turns Out from Snug and Turn the Screw Out 1/4 Turn. Do the Over Rev Test. Continue this Process Until you have the Engine Over Revving without Struggle.
>>By Adjusting the Carburetor on this Style Carburetor Until the Engine Over Revs without Struggle, you have Adjusted the Air Mixture to the Best Possible Setting.
>>This file was Intended to Give you the Basic Carburetor Cleaning Instructions and May Not Reflect Your Carburetor Components.
>>If you have Questions, Please Ask. The links above Provide Good Directions on Cleaning the Carburetor. Make sure you use an Compressed Air to Blow through all the Carburetor Passages to make sure they are Clear.
>>2- .
Please, Do Not Hesitate, If you Hit a Snag or this Does Not Correct the Problem, I am Here if You Require More Assistance.
Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Be Happy. Thanks.
Good Luck



May 08, 2009 | Toro Lawn Mower With Toro Power Tools

1 Answer

How do I adjustment the carb on an almost brand new weed trimmer?

The H is for high rpm (Main mixture) and the L is for Low rpm (Idle Mixture). First turn in both screws all the way in and then turn them both out 1 and a half turns. Pump the primer bulb if the equipment has one. Start the engine, once it is idling, turn the L (Idle Mixture) screw out (counterclockwise) from the preliminary setting until the engine speed decreases (rich). Note the position of the needle. Now turn the adjusting needle in (clockwise). The engine speed may increase, then it will decrease as the needle is turned in (lean). Note the position of the needle. Set the adjusting needle midway between the rich and lean settings as in the picture below. Don't touch the throttle during this procedure. Once you have found the best idle speed for the engine then you need to adjust the high rpm. This process is the same as with the idle rpm process but you need the to hold the throttle wide open while you are adjusting the H (Main Mixture) needle on the carburetor.


May 03, 2009 | Poulan Garden

1 Answer

Snapper SS312 weed eater. Cranks when primed but won't run

I am sorry to say this, but the compression for that type of engine should be atleast 120 psi. Remove the muffler and look at the cylinder, it is scarred beyond repair.

Mar 30, 2009 | Garden

2 Answers

94 kawasaki bayou 400 not geting gas priming pump dont get hard

Lets start with the basics. Is the gas valve turned on? Do you have plenty of gas in the tank. If not, turn the gas valve to the "reserve" position if your valve has a reserve setting. There may be a water trap bowl at the base of the gas valve. Turn the valve off and remove the bowl if you have one and then clean and replace it.

Next, drain the carburetor. There should be a screw on the lower side of the carb float bowl. Remove the screw then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. Install a new stock NGK spark plug and try to start the engine.
If the bike doesn't start after a couple of minutes then shut off the gas and remove the carburetor.

Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray all the little airways and fittings in the carb. Remove the two screws on the outside of the carb and spray into the screw holes as well.

Be sure to put each screw back in the hole it came out of. IMPORTANT > do not tighten these two screws down. Only screw these in until they LIGHTLY seat. Now turn each screw one and one half turns outward. Put the rest of the carb back together, clean the air filter and install the carb. Let the float bowl fill then start the engine. This process should get you back on the road.

Pleas rate this as " FixYa " if my solution works. Thanks

Mar 26, 2009 | 2004 kawasaki KLX 400 SR

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