Motorcycle Repair: Backfire 84 GL1200, honda gl, electrical diagnosis

Question
My '84 Honda GL 1200 (48K miles) backfires when engine braking over 2000 RPM.  Nothing under 2000.  The higher the RPM the louder the backfire.  It is almost immediate, meaning it does not take a few seconds to build up the unburned fuel in the exhaust. It is difficult to tell, but it seems to coming from the left side exhuast.  It starts right up even when cold ands runs very well otherwise. I have had it about a year and this problem came with it (I knew it when I bought it).  I do not engine brake.  I engage the clutch when slowing down.

Thank you.

Mark Winstead
vwinstead4886@charter.net

Answer
Hi Mark,

I suspect the problem may be caused by one or more of the fiollowing:

incorrect air-fuel mixtures
varnished carbs
carburetors out of synchronization
valve clearances out of service limits
faulty ignition component
a worn or loose timing belt

Read the spark plugs. Ideally, the insulators should appear as light shades of brown. Visit NGK's website to see spark plug images: "www.ngk.com"  Click the following.... "spark plug 4-1-1" "problem plugs" to see the images.

I would perform a cylinder compression check followed by a leak-down check if necessary.

Check valve lash and adjust as necessary.

Check and clean the air filter.

Perform electrical diagnosis on the suspect ignition components.

I'll send a few tech files to your email addy.

Respectfully,
Mark Shively