Small Engines (Lawn Mowers, etc.): Briggs 18hp I/C Intex backfiring, blown head gasket, ohv engines

Question
QUESTION: John, I have an 18hp Briggs/Stratton I/C OHV engine model #407777, type 0128E1, code 010711YG, familyYBSXF.7242VF 274844 that is driving me crazy by backfiring throughn the muffler. I have drained and replaced the fuel. Installed all new fuel lines and in line filter. Had the valve clearance checked, replaced the coils on both sides. Replaced the fuel pump. Replaced the regulator, installed new plugs for OHV engines, checked the kill switches, cleaned the carburetor twice, checked the flywheel key and after all this the engine doesn't run any better, It seems to run a little better under load with the mower deck engaged, but when I turn it off it backfires through the muffler. I run the choke out about an 1/8 of an inch to make run better. I have ordered a new caruretor per a lawn mower mechanic as it was only slightly more than to buy a rebuid kit. I bought the mower new in 2002 and have had no trouble with it until this year. When I pull the plug wire on the right it kills the engine. When I pull the left plug it keeps running, yet when I switch the coils around the left coil will kill the engine from the right side. Is this normal? I have good spark on both sides and the engine never fails to start. What am I missing? I only run regular gasoline in the engine that does not have the alcohol and do the regular oil, and filter changes.
Thanks for any advise as to what to do next.
Rick


ANSWER: Hello Rick:

You have a Dead Cylinder. The Engine Should Run on One Cylinder. Either One, it Does Not Matter. The Problem is on the Left Cylinder and Not the Coils. Check the Head Gasket or a Burnt Valve on the Left Cylinder. Unburnt Gas from the Left Cylinder is the Muffler and Exhaust Port is Causing the Backfire. Usually Due to a Blown Head Gasket or Burnt Valve. You can View a Breakdown/IPL of this Engine at this Site Addy, http://www.smallenginepartswarehouse.com/parts.asp and Select the Shop Online Parts Look Up. Then Select the Model Tab. Then Select the OEM and Enter the Model and Type Numbers. Then Double Click on the Model in the Results Area. Now you can Select the Section of the Engine you Wish to View. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. 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 9pm EST (US). My New Day Starts then. Thanks.

Respectfully

John

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

QUESTION: John wanted to let you know that today we removed the head inspected the valves ground both the intake and exhaust lapped both, set the valve clearance installed new head gasket torqued the the bolts, by the way the compression checked at 150 on the right and about 130 on the left side hooked everything back up fired up engine and it again ran the same. It's still backfires through the carbuertor.  the engine surges up and down until I pull out the choke about 3/4 of an inch. As soon as I disengage the deck pto it starts to backfire. Where do I turn next. I'm still waiting for the new carb that I ordered last week. Again thanks for any help.
Rick

ANSWER: Hi Again Rick:

From Our Correspondence, I am Like you and am at a Loss for a Cause. It May be the Carburetor and Until you have the New Carburetor Installed and Operate the Engine to Know for Sure, I am at an Impass. I will Show this Correspondence to the Mechanics in the Shop on Monday and See if the have Any Other Suggestions I May have Forgotten. Thanks.

Respectfully

John

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

QUESTION: JOHN, hello again. I wanted to let you know that I made a wrong statement about my last post . I meant to say that the backfire is out of the muffler and not the carbuertor like I stated. Could it be possible that I could have a stuck ring? I did another compression check and I get 110 on the left side and about 155 on the right are these readings ok?
Thanks again Rick

Answer
Hi Rick:

Did you Check the Cylinder Head on the Left Side for Warpage? The Compression Should be Within 10 Pounds of Each Other. The Cause is Somewhere on the Left Cylinder. What Clearance Did you Set the Valves at (Intake .004in - .006in and Exhaust .008in - .010in)? Thanks.

Respectfully

John