B&S 11hp engine question

[Rivets]

If the popping is still there, it is caused by one of two things. One sticking or burned valves. Two too rich of a fuel mixture.

 

[handirifle]

Ok I will check those out if need be.

 

[chance123]

I have seen/heard this popping sound from excessive carbon in the head and/or muffler, but I suspect a valve. If the valves were ground, were they ground at the respective 30 & 45 degree angle? Were the seats ground to match the valves?
The way I have grown to check this is when I lap the valves, I "DON'T" rotate the valves 360 around (lapper between your 2 hands) in the beginning. With fine oil based lapping compound I rotate the valve only about an eighth of a turn back and forth. After doing that, I remove the valve and clean the compound off and visually see that the marks from the lapping are "ALL" around the valve.

I have discovered this trick a long time ago from Taylor Offenhauser, that by lapping the valve in a 360 degree rotation with a seat that "might" have a high spot on one side of it, or is uneven, "that ONE high spot" will mark the valve all around giving the impression that the valve matches the seat when in effect, the seat is uneven. It doesn't take much.
If an exhaust valve has even a slight intermittant leak, unburned fuel will pass through and detonate in post giving a "popping" sound.

 

[handirifle]

Good infobto remember, I had honestly never considered that a 360 rotation might cover up an issue.
on this engine, due to a number of limitations, I will not be going into the valves, so if it can't be solved with fuel or timing, thats as far as I can go with it.

 

[Buckshot 1]

.010 air gap is the manufacture recommendation. Setting the gap at .012 will retard the spark timing and will produce a hotter spark, but also slightly shorten the spark duration, increasing the amount of unburnt fuel, which will cause a popping in the muffler. Setting the gap at .008 will advance the spark timing, producing a weaker spark, and again increasing the amount of unburnt fuel. Hope this makes sense.

:smile: My B&S single cyl. L-head repair manual states, air gap .010-,014 for 13 thru 28 alum series and cast iron series 23 thru 32 . that is why I always set the air gap @ .012.

 

[handirifle]

:smile: My B&S single cyl. L-head repair manual states, air gap .010-,014 for 13 thru 28 alum series and cast iron series 23 thru 32 . that is why I always set the air gap @ .012.

OK looks like they left some room for engine variables in there. Thanks

 

[Buckshot 1]

:smile: You are Welcome.

 

[handirifle]

OK finally made some serious headway with this thing. Had to lay off it for a bit. Neighbor had a oak tree split and I got some free firewood for next year.:wink:

I do NOT pass on free oak.

I finally decided to pull the carb, and went through it. Then re-installed and adjusted according to the owners manual it came with. Adjusted the idle mixture and idle speed, then adjusted the high speed mixture. Revs freely all the way to governor cut-out. Very happy with performance. I also finally got the breaks working. Took a new master cylinder. There is still a little bit of air in the line, kinda frustrating, but the parts guy in Michigan said they can be a real bear to get all the air out.

He pumps it in from the bottom up, which I did, but still got bubbles in there, darn it.

I also got the electrical all figured out, including a break pressure switch to activate the brake light. Got the headligh working, but had to make a switch for the handlebar. Most all are made for 7/8 bars, and these are 1". Most were also too expensive or had all sorts of extra switches, like horn, kill button etc. I have the bed installed again. All I need to do now is remount the seat and seat back, that have re-upholstered.

I will post pics as soon as it's all back together. Very close now. Thanks for the support here.

 

[Rivets]

Sorry to tell you this, but you'll have to go back and readjust the carb. The high speed mixture must be adjusted first, as it feeds the idle circuit. After the high speed circuit is set, then adjust the idle circuit, then idle speed.

 

[handirifle]

I actually think I did it in that order. I went by the book. Earlier in my posts I was just listing what I had done, no necessarily in the order I did them. Thanks for the warning I will remember that if there is a next one.