Small Engines (Lawn Mowers, etc.): JD S1400 won’t stay lit, zama carburetors, john deere s1400

Question
QUESTION: Hello, John:
My  John Deere S1400 (UT20835) trimmer with Zama C1U-H46 carb only fires off when a shot of fuel is injected directly into carb throat, but will not continue to run.
  The machine was running well until it ran “wild,” i.e., continued to run at full throttle with trigger released.  Inspected throttle linkage and related mechanisms and found no obvious flaw.  Machine would not restart.  Disassembled trigger assembly and reassembled, ensuring all parts in proper location and function.  Disassembled carb and inspected gaskets and diaphragms.  All appeared ok except for metering chamber diaphragm which was somewhat stiff.  Blew out ports and galleries with compressed air (I know better, now) and reassembled carb.  No change in symptoms.  
  I then cleaned muffler & arrestor screen, ensured pulse port clear & clean and rebuilt carb using an RB-82 kit (but did not replace the Welch plug).
  Result:  Problem remains as stated, even with muffler removed.  Any thoughts?


ANSWER: Hello Wes:

You can View a Breakdown/IPL of the Carburetor and Get Technical Information on Zama Carburetors at this Site Addy; http://www.zamacarb.com/tips.html and Select the Technical Guide. Have you Replaced the In Tank Filter? Have you Checked the Flywheel and Key? Usually the Running Wild and Quits is a Sign of Lean Gas Mixture Before No Gas Mixture in the Carburetor. Did you Soak the Carburetor Overnight in Carburetor Cleaner? If No, then the Internal Carburetor Passages May Still be Restricted. What is the Compression? 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. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 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. Thanks.

Respectfully

John

---------- FOLLOW-UP ----------

QUESTION: Thanks for your suggestions, John. The trick was overnight soaking.  Even then, though, it would only start and run at idle.  Advancing the throttle even the slightest would kill it.  Judicious use of Valvtek De-Carbon sprayed into the carb throat gradually enabled me to advance the throttle bit by bit.  The faster it would run, the more I sprayed de-carbon until it ran normally. Sadly, though, after about four minutes of WOT use (with chain saw attachment) she quit.  Inspection revealed the bakelite intake manifold/heat dam was cracked through.  I know the torque on the two mounting screws was even, but possibly too much and the heat did the rest (I guess).  BTW, I found the internal check valves in the Zama carb to be very sensitive.  Tell your readers NOT to use compressed air to “blow out” the orifices or they will do just that.  The long soak, as you suggested, with periodic agitation is the key.  Thanks again for your help.  Hope my experience adds a little to your kit bag.

Regards, --w


Answer
Hi Wes:

Thanks for the Update and Input. I am Sure it will Assist Others that Visit this Site and Read this Correspondence. I had Forgotten About the Check Valves in the Zama Carburetors and will List it in a Carburetor Cleaning File for Trimmers and Saws that I am Writing. Thanks for Using All Experts. Till Next Time. May All Your Mechanical Problems be SMALL ONES and May the All Mighty Bless You and Yours. Thanks Again.

Best Wishes and Good Luck

Respectfully

John