QuestionMy father is trying to repair some old (really old) 3 wheeler. It has no name brand. It has a 7hp horizontal shaft Tecumseh engine on it. He said him and his brother have taken the carb apart and cleaned everything, but it will not stay idling. My father is a very competant person at fixing anything and he says this has him stumped. Any ideas?? Thanks
AnswerHello Landon:
>>From your Description it Sounds like the Carburetor was Not Soaked but Cleaned with Spray Cleaners or there is a Bad/Rusted Valve Seat.
>>1- If the Carburetor was Cleaned with Spray Cleaners and Wire, then
>>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 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.
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. The Only Parts you May Need to Replace is the Needle Valve.
>>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. Set the Idle Screw so the Engine will Idle and then Using the Governor Arm (on chainsaws and trimmers use the Trigger) Rev the Engine Up and Down Until and 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.
>>1- http://www.repairfaq.org/samnew/lmfaq/lmclctc.htm
>>2- http://www.cpdonline.com/692509.pdf .
>>2- When a Small Engine Sit for a Few Years, the Valve that is Open and Not Seated will Usually Have a Film of Rust on Each Mating Surface.
>>Sometimes this Rust gets Blown Completely Off when you First Fire the Engine. Sometimes it Doesn't.
When it Doesn't, the Valve doesn't Seat Correctly and you have Incorrect Compression at Idle and you get this Problem.
>>Have your Dad Lap the Valves and Set the Correct Valve Clearances between the Valve Stem and the Valve Tappet.
The Engine Model Numbers should be Stamped Into the Blower Housing (metal engine cover).
>>Since this is a Tecumseh Engine, I have a PDF Site Addy that May Assist you Also. http://www.tecumsehpower.com/CustomerService/BSI.pdf . This Site Addy; http://www.outdoordistributors.com/Tecumseh/tmain.html has a Link to a PDF Trouble-Shooting Guide. Simply Select the Free PDF Download for the Tecumseh Trouble-Shooting Guide.
>>You can View a Breakdown/IPL of this Engine at this Site Addy, http://www.outdoordistributors.com/ and Select the T. Then Select Tecumseh. Then Select Don't have Part Numbers. Then Enter the Model Numbers . Then Select your Model and Download the File for Online Viewing.
>>The Following is a Basic Instruction File for Setting the Valve Clearances on Non OHV Engines. If you Provided me with the Correct Make and Model of the Engine then the Specifications are Included. If Not I May be Able to Provide the Specifications if you Supply me the Make and Model Numbers.
>>The Most Common Clearances are Listed for this Engine in the Following File. Thanks. Any Input is Appreciated.
>>On this Model Engine I Usually Suggest Re-seating the Valves if the Valve Clearance Requires Adjusting.
>>**Remove the Carburetor and the Crankcase Breather/Vent and the Valve (Stem) Cover so you have Access to the Valve Stems, Springs and Keepers.
>>Set 1 Cylinder (on Twin Cylinder Engines) to TDC on the Compression Stroke. Using a Blade Style Feeler Gauge, Check the Clearances. The Intake should be .005in - .007in and Exhaust .008in - .010in. If the Feeler Gauge will Not Slide Between the Valve Tip and the Tappet, then you Must Reset the Clearances.
>>**You Will Require a Small Engine Valve Spring Compressor to Remove the Springs and Keepers from the Valve Stems.** Some Engines Use a Valve Keeper that is like Automotive Keepers (2 Cone Shaped Keepers that Set in the Valve Retainer/Rotocoil Assembly)and the Other Style is a Slotted Retainer that is Moved (once the Valve Spring is Compressed) to the Larger Opening in the Retainer and the Retainer Slips Over the Valve Stem Tip for the Valve to be Removed.
>>Remove the Heads.
>>Set 1 Cylinder so the Piston is at TDC on the Compression Stroke And Check the Clearances Between the Valve Stem Tip and the Tappet. The Clearances are as Follows: Intake Valve Clearance is .005in - .007in and the Exhaust is .008in - .010in.
>>You have to Lightly Grind the Valve Stem Tip and Place the Valve Back Into the Engine (you can Hold the Valve Seated by Hand) and Check the Clearance Until you Reach the Required Clearances.
>>**++** For this Engine Model I Suggest you Re-seat the Valves while you are Setting the Correct Valve Clearance. For this you will Need a Small Valve Seat Suction Tool. This can Usually be Purchased for $10.00us and has a Suction Cup that Hold the Valve Head so you can Turn the Valve Back and Forth and Dress up the Valve Seat. Valve Grinding Compound is Approximately $5.00us a Tube and a Tube Last the Shop About a Year. It Doesn't Take a Lot to Re-seat 1 Engine.**++**
>> Once the Valve Clearances are Reached and the Valve Seat is Nice and Dull; Re-Install the Valves on that Cylinder and Turn the Other Cylinder to TDC on the Compression Stroke and Set that Cylinders Valve Clearances.
>>Once that Cylinder is Set, then Assemble the Engine.**
>>This Web Page; http://www.affordablegokarts.com/va
lve-lapping.php has a Fairly Good Description and Instructions on Valve Lapping and a Good Explanation of what to Look for when Seating the Valves.
>>You can Locate the Valve Clearance Specs at this Site Addy; http://outdoorpowerinfo.com/engine_specs/ and Select Valve Clearances Under you Engines OEM (). Then Set the Valve Clearances to the Specifications Listed on the Chart for your Engine.
>>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 Happy. Thanks.
Good Luck
Respectfully
John
PS: I am Allowed to Answer 5 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.
Respectfully
John
