Re: Engine Backfires?

Posted by Mike C. on April 01, 2002 at 09:04:49 from (64.17.237.124):

In Reply to: Engine Backfires? posted by Mark on March 31, 2002 at 09:01:33:

Assuming that the backfire happens after you turn the key off, you must be talking about afterfiring through the exhaust. Keep in mind that an engine is nothing more than an air pump and by turning off the ignition, you are only eliminating spark. The engine continues to spin pumping air/fuel mixture into the exhaust until the engine stops. This air fuel mixture is then ignited by heat from the exhaust system.

Exhaust systems are heated up to high enough temperatures to ignite fuel by engine running either too rich or too lean. Too lean of a mixture will heat up the exhaust as well as burn valves. Too rich is less damaging on the engine but dumps raw fuel into the exhaust causing it to burn there creating the heat which causes the afterfire.

A simple method for proper carb adjustment is known as "Propane enrichment method". All you need is a small propane torch and a tachometer.
Remove the torch tip and attach a 1/4 in diameter hose about 2 ft long to the tube after you remove the torch head or tip. Start engine and allow to run to operating temp. At idle, allow propane to enter through air intake of carb and watch tachometer for an increase of 50 rpm. More than 50 rmp, engine is running too lean. Less than 50 rpm or if engine stumbles or stalls, engine is running too rich.

This adjustment will set the Idle air/fuel ratio but will not compensate for an improper size main jet. After you make this adjustment, run engine under hard load for a while and shut down quickly then check plugs. Chocolate colored cone indicates correct air/fuel ratio for main jets. Black is too rich, white is too lean.

If your not into changing jets, allow engine to idle for a short time allowing exhaust to cool first as pointed out by the other replies.

best of luck...

Follow Ups:

Post A Followup Name: E-Mail: Subject: Re: Re: Engine Backfires? Comments: Optional Link URL: Link Title: Optional Image URL: Email Notification: If you check this box, email will be sent to you whenever someone replies to this message. Your email address must be entered above to receive notification. This notification will be cancelled automatically after 2 weeks.

TRACTOR PARTS	TRACTOR MANUALS

We sell tractor parts!  We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]