B212 running hot

[RickoHB212]

Just joined forum today. Very nice site!! I just purchase an AC B212. While mowing near dark evening time I noticed the exhaust pipe and muffler were glowing orange (hot). I did rebuild the carb and someone has added a coil to replace the magneto. Thought I might have a rats  nest in the engine. Tore engine out and no nest. It had some 50 year crude in the outside engine fins but not enough to make it hot. Do these briggs engines run this hot. My AC retired mechanic said you won't notice it in daylight and they do run hot. anybody else experience this.

[GregB]

Probably running a little lean, check the main jet in the carb for shellac buildup and maybe an adjustment.

 

Some one else may come along with some other suggestions.

 

Welcome, lots of good info here, and guys to share their knowledge.

[RickoHB212]

Thanks greg, my AC mechanic said the same thing.

[wwbragg]

I concur with @GregB but it could also be a timing issue.  My old Dodge Omni ran like a banshee with timing way advanced but the exhaust manifold turned RED hot.  But timing on a Briggs one-lunger is pretty much static.  Maybe something to do with that battery-charged coil ignition system.

[Chris727]

Welcome to the group! Yes the suggestions made are s possibility. I had a cast Briggs in a Wards with that problem but luckily it was just a nest in the engine. 

[kwt]

11 hours ago, wwbragg said:

My old Dodge Omni ran like a banshee

This is the first time I've ever seen banshee and Dodge Omni in the same sentence. Looks kind of strange.

[LMichaels]

Too lean or too rich can cause this. Another like said is ignition timing. If timing is retarded too much combustion is still taking place during exhaust stroke and will cause exhaust to become cherry red along with exhaust valve(s) which is not a good thing

[wwbragg]

1 hour ago, LMichaels said:

If timing is retarded

But is it even possible to retard (or advance) the timing on a Briggs single???

[wwbragg]

1 hour ago, kwt said:

banshee and Dodge Omni in the same sentence

"With me, words are but a plaything."  (Tommy Smothers)

[kwt]

8 hours ago, wwbragg said:

But is it even possible to retard (or advance) the timing on a Briggs single???

It most certainly is if you are using points. The bigger the gap, the more advance you will have.

[kwt]

And just because nobody has said it, in all my years of running K-series Kohlers and cast iron Briggs, I've never seen an exhaust pipe glowing red, and I second the part about the exhaust valve. Not good.

[wwbragg]

2 hours ago, kwt said:

The bigger the gap, the more advance

The spark plug sparks when the points OPEN, not when they close.  But if the points are open too long, the charge buildup  (in this case) from the battery to the primary winding, will automatically jump to the secondary winding (because the points are open) and light up the spark plug resulting in a secondary firing.  The points are opened by a lobe on the cam (or is it the crank shaft?) and is fixed.  You can't adjust the timing by turning the distributor like I did on my Dodge Omni.  So the only way for it to be firing late (or early) is if the crank and cam are not in sync.  As @LMichaels pointed out, combustion is still taking place when the exhaust valve is open.  I'll bet a dollar to a dinner that if @RickoHB212 breaks the case apart he will find the dimples on the crank and cam gear are not lined up. 

 

 

Edited May 12, 2019 by wwbragg
clarification

[kwt]

It's like this Bragg, in order for the points to have a larger gap, they have to start opening a little sooner. I'm aware it cuts into the dwell and it may be negligibly sooner, but if you've ever set the dwell on an early seventies GM product while looking at the strobe of a timing light on the crank, you will have seen the timing change. Note: setting the "dwell" on these was in actuality setting the point gap with the engine running. GMs preferred method. Set the dwell, then the timing. 

 

OP should check that his point gap is @ .020", and IMHO if it is turning the exhaust red I would try opening the gap up more. Of course I wouldn't even think about going this route with out checking that the carb mixture was good. With engine warm and @ low idle, you should be able to snap the throttle wide open and have NO stumble or hesitation. A little black smoke while doing this is OK.

[wwbragg]

11 minutes ago, kwt said:

they have to start opening a little sooner

OK, but help me out here ---- The points CAN'T open before the lobe comes around.  And they close when the lobe passes.  That is length of the dwell and is not variable.  I concur that improper gap setting will contribute to the manifold over heating but not enough to turn it red hot.  I still think it is not firing at the right moment.  

Furthermore, because it is a battery-charged system, there will be an initial large (50,000 volts) spark at the plug when the points first open, but there will be diminished but continuous spark at the plug until the points close.  Not sure how this plays in, other than burning up points.

[wwbragg]

It's going to be easy to tell.  Just pull the head and put the piston at top dead center on the combustion stroke.  If both valves are not fully closed, there it is.  For that matter, It could be a chipped exhaust valve - - firing through the exhaust system.

[LMichaels]

I am not sure of the finer points of changing timing on a small air cooled motor. So my answer was more theoretical than practical. Though there is most certainly some variation in timing to be had by changing the points gap. How much I am not sure. I do know VERY well the relationship between dwell and timing. As a GM employed Cadillac tech back in the late 60's early 70's I knew it very well

[wwbragg]

1 hour ago, LMichaels said:

some variation in timing to be had by changing the points gap

But you are spot-on, Larry.  And the question lingers; how much does point gap contribute to an overheated exhaust? 

Most small engines have a single ignition-timing setting.  If this setting varies, the engine will lose efficiency and power.  Some engines (such as those manufactured by Tecumseh and Kohler) have a spark advance mechanism that allows timing adjustment with the engine running. But the B212 had a Briggs 300421 single.

A partially sheared flywheel key will also cause a mistimed spark.

But these conditions will result in diminished power and/or poor operation.  I'd look for a burnt or cracked exhaust valve or a misaligned cam gear.

[kwt]

So do we all agree that OP shouldn't have a glowing exhaust system?

[Tom45]

Don't forget that on a stock briggs engine there is a timing adjustment at engine assembly where the coil mounting bracket is shifted so that the coil is in the proper place over the magnet.  When a magnatron is installed this same setting is kept.  With an external coil, the point gap is the only timing adjustment, like on a Kohler.  

[wwbragg]

3 hours ago, kwt said:

we all agree that OP shouldn't have a glowing exhaust system

Copy that, Red Ryder.  And I don't mean to minimize your comments @kwt.  In fact, my solution approach would be to first conduct a dry and then a wet compression test.   If the wet test yields about the same result as the dry test,  there might be a valve problem.  Then I would check the fuel mixture jet.  Then check the point gap and while the flywheel is removed, check flywheel sheer key.  So do the easy steps first.  If that doesn't yield results, then pull the head and inspect the valves.  If the exhaust valve checks out ok, then as a last resort, split the case and check crank/cam gear alignment.

I hope @RickoHB212 will keep us posted as to what he finds

Edited May 12, 2019 by wwbragg
add an event

[RickoHB212]

I think I'm going to start with the carb mixture and check my point gaps since these two are the easiest to do. We will let you know later. Thanks for all the input.

[MrSteele]

Checking first things first. Folks, we all overthink things. Check the carb settings. That is likely as far as he needs to go. If not there, check to see if the exhaust valve is closing completely. If not, take the head off, the valve cover, and grind the valve stem. Lap the valve if necessary. The problem ain't under the flywheel or the point cover. If lapping the valve, CLEAN all the compound off before assembly. A compression test will let you know about the valves

[MikeES]

What do you have for a muffler?  One time I swapped a nice stainless muffler from a junk 12hp B&S engine and put it on my HB212.  This was a see-through and did not run as quiet as the original Nelson, so it did not have any restrictions. but after about 10 mins of running the muffler was glowing red!

So maybe it is as simple as your muffler...wrong design, partial plugged.

[RickoHB212]

Thanks for all the replies guys. The muffler is not a Nelson but the round aftermarket. I checked and cleaned the points, they were dead on .020. I tuned in the carb and this solved the problem. Mowed over an hour and muffler was fine. Just needed the rebuilt carb dialed in.

[MrSteele]

On 5/12/2019 at 3:06 PM, wwbragg said:

Then check the point gap and while the flywheel is removed, check flywheel sheer key. 

A Briggs shear key can be barely marked, sometimes barely visible to the naked eye, and the engine will simply not run. It will not run hot or cold or redden the exhaust system. It will not run, Period. They have driven me to drinking many times looking like nothing was wrong. Change the key, and cranks on first or second pull. Keys are cheap. I usually change them every time I pull the flywheel, then I do not have to wonder