Briggs OHV Surges

[R4665]

Problem #1 Surging

If you hold the throttle steady from moving *AT THE POINT IN ENGINE OPERATION* where the surge is happening, and the surge stops and engine runs smoothly, the problem is more likely a mechanical issue (Governor, linkage worn, spring tension or governor droop, etc.) , while if it wants to stall out and wont run smoothly, the problem is *usually* in the carburetor.

The engine quits surging when the throttle is held steady at low, mid and high speeds. I tested it at low idle 2,150 RPMS, 2,800 RPMS AND Full Throttle 3,100 RPMS. I did the test by backing out the throttle adjustment screw to low idle where only a couple of threads were showing and then holding the throttle against the screw (2,350 RPMS). The surging quit. I then turned the screw clockwise several turns and held the throttle against the screw (2,800) and then turns the screw until it just touched the throttle - full throttle (3,150). No surging. I also engaged the blade on the BBC. The speed deceased about 50 RPMS and the Engine did not surge.

So, it appears to be a mechanical issue. Adjust the governor next? Then replace the governor spring? Suggestions?

Problem #2 engine "Sputters"
The engine does not run smooth and makes a sputtering sound at all speeds.. It makes the sound when it surges and when the throttle is held steady and there is no surging. Could a governor problem cause an engine to sputter? It's hard to determine if this is one problem or two. As stated in the first post, I removed the cylinder head, removed carbon from the head and top of the piston and lapped the valves. I have adjusted the intake and exhaust valves to .006.

I did a leak down test and can hear air coming out of the muffler when both valves are closed and when the piston is ~1/4" past TDC on the compression stroke. What would cause the exhaust valve to not close completely thereby allowing air to leak around the exhaust valve? Would an air leakage around the exhaust valve cause the sputtering sound?

Suggestions?

Thanks. Robert

[R4665]

More info on Problem #2 - Engine Sputtering. I removed the OHV valve cover. As I turned the crankshaft I was looking at the behavior of the valves. Here is what I noticed when I manually turned the crankshaft:

1. Starting at TDC EXHAUST stroke, the Intake valve opens (Intake Stroke) as the piston moves down the cylinder.
2. Just before the piston reaches BDC, the Intake Valve starts to close and is closed at BDC.
3. Also, as the piston reaches BDC, the Exhaust Valve opens slightly. As the piston is coming back to the top (Compression Stroke) and is about halfway up the cylinder, the Exhaust Valve starts to close and closes completely just before the piston reaches TDC.
4. On the Power Stoke the Exhaust Valve begins to open just before BDC.
5. On the Exhaust Stroke, the Exhaust Valve fully opens and closes just before the piston gets to TDC again.

Question: Is it normal for the Exhaust Valve to open slightly and close during the Compression Stroke?

Thanks. Robert

[bgsengine]

More info on Problem #2 - Engine Sputtering. I removed the OHV valve cover. As I turned the crankshaft I was looking at the behavior of the valves. Here is what I noticed when I manually turned the crankshaft:

1. Starting at TDC EXHAUST stroke, the Intake valve opens (Intake Stroke) as the piston moves down the cylinder.
2. Just before the piston reaches BDC, the Intake Valve starts to close and is closed at BDC.
3. Also, as the piston reaches BDC, the Exhaust Valve opens slightly. As the piston is coming back to the top (Compression Stroke) and is about halfway up the cylinder, the Exhaust Valve starts to close and closes completely just before the piston reaches TDC.
4. On the Power Stoke the Exhaust Valve begins to open just before BDC.
5. On the Exhaust Stroke, the Exhaust Valve fully opens and closes just before the piston gets to TDC again.

Question: Is it normal for the Exhaust Valve to open slightly and close during the Compression Stroke?

Thanks. Robert

intake opens when the exhaust is closing at TDC following exhaust stroke, that's known as valve overlap and is normal.

Exhaust *or* intake may open slightly during compression stroke, which is the compression release system activating - that goes away as the engine comes up to full power - IF a *mechanical* compression release sticks (extremely rare but possible, more often a comp release failure involves it not opening valve as it should) it can keep holding valve open during operation (that is as opposed to the compression release that is ground into the cam lobe, and that's usually on an intake cam lobe) but otherwise what you describe is normal operation - one would wonder what your valve clearance is, however, as if there's insufficient clearance, that can affect the compression release duration.

[R4665]

- one would wonder what your valve clearance is, however, as if there's insufficient clearance, that can affect the compression release duration.

Thanks for clarifying that the valve operation I described is normal. As far as the valve clearances, I reset the both valves to be .006 according to KE4VB's suggestion. The manual I used only had clearances for the 120000 series and was not as specific as the ones he stated.

Correction valve to valve specs:
.004−.008” (intake and exhaust), Model Series 111600, 111600, 120600, 121600, 122600, 123600
Torque jam nut to 75−95 in. lbs.

I've done everything that has been suggested for both the surging and sputtering (cleaned carb; replaced head gasket, valve cover gasket & carb intake gasket; adjusted the governor; reset the valve clearances) - none which has helped stop the surging or the sputtering. As stated in my previous post, when the throttle is held steady at idle or top no-load, there is no surging. The only thing left that I know to do for the surging is replace the governor spring.

Any other ideas or suggestions?

[bgsengine]

if you got the service manual (and 120000 series is correct covering 122000 model series , unless you are looking at an L-Head manual, you DO have the OHV manual right?) then there in the manual is a procedure called a "static governor adjustment" - do that.