I found some answers to the backfire (actual term "after fire" when occurring on the exhaust side) problem. I will continue to use the term "backfire" from this point on, even though it's incorrect, though most commonly used and understood by most of us, including me.
What follows is my "check list" of what I did to troubleshoot the back fire from the Honda based engine after I sorted the carb to a point of starting and idling the engine.
I ran the engine for 45 minutes and read the plug which looked to be on the lean side. Too lean can lead to a backfire problem. Two factors that I took into account on the intake side of the motor were improper jetting/mixing and air leaking into the carb and intake system. I've found no sign of air leaks on the intake side and decided to not chase carb gobblins off the jump, leaving those to last if required.
Going to the exhaust side I also looked at two factors, since it's the most common cause of backfire in my personal experience; I examined the copper gasket ring and it showed definite signs of a leak. The steel "washer" that I made to compress the copper gasket ring & seal to the manifold was slightly greater than the required diameter and was restricting the "washer" from seating correctly against the gasket. It was actually contacting the casting of the aluminum head just as it began compressing the copper gasket ring at the exhaust port. Bottom line was I had an exhaust leak at that point. A couple of minutes with the file and that was that.
Tested the affair and all was much improved, but with still an occasional pop. Which brought me to the next suspected cause for the engine leaning out. The relatively short, unrestricted free breathing stub exhaust and yet another reason for not buggering with the carb too soon or at all.
Manufacturers of non racing specific carbs, jet for average non modified street engines and moderate altitude operation. Carbs are set up for a mythical average to hopefully work right out of the box. After inspecting the induction system for leaks and finding none I expected to find that the lack of back pressure at the exhaust was leaning the air/fuel mixture (more air than fuel). Remember I'm chasing a quality fuel mixture at this point as the backfiring is just a symptom of the real problem which is to contain the detonation of the fuel/air mix inside the combustion chamber rather than partially igniting in the exhaust manifold.
I'd previously made an exhaust baffle ring (simple 1" long with a 1" hole in it) to install later for lowering the exhaust note a bit. To this I added an 8" section of 1" pipe with quite a few 5/16" holes in it, wrapped some stainless wool around the whole affair and inserted this into the exhaust pipe stub and secured with a C clamp.
No more backfiring! At which point I decided to turn my attention to another area, rather than run the little beast long enough to re read the plug to "see" if it was running richer, but I didn't and that's when the throttle cable decided to pull loose from it's lead keeper in the throttle housing so I'm buggered till a new one gets here next week. At any rate some real progress in the direction of a harmonious outcome...it appears. Alteration of carb setting and or jetting may yet be required. I'll save that for another time.
Rick C.
What follows is my "check list" of what I did to troubleshoot the back fire from the Honda based engine after I sorted the carb to a point of starting and idling the engine.
I ran the engine for 45 minutes and read the plug which looked to be on the lean side. Too lean can lead to a backfire problem. Two factors that I took into account on the intake side of the motor were improper jetting/mixing and air leaking into the carb and intake system. I've found no sign of air leaks on the intake side and decided to not chase carb gobblins off the jump, leaving those to last if required.
Going to the exhaust side I also looked at two factors, since it's the most common cause of backfire in my personal experience; I examined the copper gasket ring and it showed definite signs of a leak. The steel "washer" that I made to compress the copper gasket ring & seal to the manifold was slightly greater than the required diameter and was restricting the "washer" from seating correctly against the gasket. It was actually contacting the casting of the aluminum head just as it began compressing the copper gasket ring at the exhaust port. Bottom line was I had an exhaust leak at that point. A couple of minutes with the file and that was that.
Tested the affair and all was much improved, but with still an occasional pop. Which brought me to the next suspected cause for the engine leaning out. The relatively short, unrestricted free breathing stub exhaust and yet another reason for not buggering with the carb too soon or at all.
Manufacturers of non racing specific carbs, jet for average non modified street engines and moderate altitude operation. Carbs are set up for a mythical average to hopefully work right out of the box. After inspecting the induction system for leaks and finding none I expected to find that the lack of back pressure at the exhaust was leaning the air/fuel mixture (more air than fuel). Remember I'm chasing a quality fuel mixture at this point as the backfiring is just a symptom of the real problem which is to contain the detonation of the fuel/air mix inside the combustion chamber rather than partially igniting in the exhaust manifold.
I'd previously made an exhaust baffle ring (simple 1" long with a 1" hole in it) to install later for lowering the exhaust note a bit. To this I added an 8" section of 1" pipe with quite a few 5/16" holes in it, wrapped some stainless wool around the whole affair and inserted this into the exhaust pipe stub and secured with a C clamp.
No more backfiring! At which point I decided to turn my attention to another area, rather than run the little beast long enough to re read the plug to "see" if it was running richer, but I didn't and that's when the throttle cable decided to pull loose from it's lead keeper in the throttle housing so I'm buggered till a new one gets here next week. At any rate some real progress in the direction of a harmonious outcome...it appears. Alteration of carb setting and or jetting may yet be required. I'll save that for another time.
Rick C.
