Timing

I own a 1985 Johnson 90hp that backfires more so at idle but less at higher rpm. I had replaced coils and power packs and plugs for other reasons so I have spark at all 4 cyl. The manual says the timing may be off, but I cant seem to find a section on ingition timing for this engine. How do I time this engine so that it will idle without a back fire? Thanks for any help.<br />Rick

Re: Timing

Welcome Rick!<br /><br />Is it a backfire or a lean sneeze or cough? There is a difference. <br /><br />A poorly done sync and link will cause this type of problem as will a dirty carb. <br /><br />Can you tell us a little about the engine...does it run well at rpms above idle, have any idea when the carbs were over hauled last, is this a new engine to you? Are you still using the VRO pump? What are the idle rpms? <br /><br />What kind of service manual do you have, generic or OEM? Your much better off with a OEM manual because it will give you specific info on your specific engine. And it has a whole section on setting up the timing and syncrnization. The procedure is lengthy, a little to lengthy to post here.<br /><br />A couple things to look at, make sure the throttle plates open at the same time and both are closed when the cam is off the roller, check the fuel lines, replace any that have become hard over time as they can lose their grip on connection points. Have you taken compression readings on each cylinder? A bad cylinder will cause a problem. Notice any spitting back through the carb?<br /><br />Stay in touch with us...lot of good people here to help.

Re: Timing

With the engine at idle, and the throttel all the way back, loosen the link screw that connect's the upper, and lower carb's together. This will let the bottom carb snap fully closed. See if the spit back goes away.