Briggs OHV Surges

[R4665]

Toro 20487 SR-210SBB Self Propelled with BBC
Engine: GTS 200 Briggs 123602 0132 E1 001106 EB

This is an 6.5 HP OHV engine.

Engine had not been maintained for years. Air filter was clogged with grass and dirt. Spark Plug fouled. Oil was black. However, Carb was in pretty good shape.

Current problem: Engine starts easily. However, the engine surges at all speeds and there is a “pufft, pufft, pufft” sound coming out of the muffler.

Summary: Here is what I’ve done so far:
• New spark plug and changed oil.
• Cleaned Carb
• Removed Head
• Removed carbon buildup from head, valves and top of piston.
• Lapped the valves
• Adjusted valves
• Replaced carb intake gasket and valve cover gasket.

I also put a different carb on the engine. The engine had the same problems – surging and the “pufft” sound.

Details
• Carb looked good. No vanish or debris. However, I went ahead and cleaned cab in my ultrasonic cleaner using DTI cleaning solution. Used compressed air.
• After cleaning carb and changing oil, engine started but surged.
• Removed carb and soaked in can of Carb Cleaner. Sprayed carb cleaner in all holes and welch plugs. Did not help. Engine continued to surge.
• Adjusted valves. Specs are Intake .003 - .005. Exhaust .005 - .007. I adjusted them to Intake .003 and exhaust to .005. Engine still surged and same noise.
• Removed the cylinder head. There was a good amount of carbon buildup on the inside of the cylinder head and valves. There was some, but not much carbon on the top of the piston. Removed all of the carbon.
• Lapped both valves.
• Put cylinder head back on and torqued to specs.
• Adjusted the valves again. Put on valve cover with new gasket and torqued to specs.
• Thinking there might be an air leak between the carb and the engine block, I replaced the intake gasket.

I have not adjusted the governor (yet) since they rarely need adjusting and I am dealing with both surging and the “pufft” sounds.

So, any ideas or suggestions? Your help would be appreciated.

Robert

[RoyM]

Hold your finger on the throttle shaft. If it smoothes out the governor is too sensitive. May be a linkage or spring problem. If it stumbles it is a fuel system problem.

[KE4AVB]

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.

Valve clearances for these engines are to be set when piston is between TOP DEAD CENTER (TDC) and .1” or 3/32” or
.250” or 1/4” after TDC on the power stroke, depending on Model Series. Turn flywheel until piston is at TDC at end of compression stroke and beginning of power stroke. Mark rim of flywheel at edge of armature. Rotate flywheel 1” past TDC when using the reference mark in relationship the armature edge and stop. Adjust the valves to the above specs.

Due to age I would try replacing the governor spring for the surging problem.

For noise from the muffler try running a leak down test to see if there leak valve train, head gasket or a ring problem.

Others here may have other thoughts too.

[okie]

adjust governor.
https://www.youtube.com/watch?v=9rO8AvDrdeM

Travis

[KE4AVB]

When adjusting the governor, note that this engine top no-load speed is 3000 rpm +/- 100 rpm and your idle speed should be 1750 rpm.

[R4665]

Thanks for all of the suggestions.

1. Since the last post, I did a leak down test. With the piston at TDC on the compression stoke, I can hear air coming out of the muffler, which is odd since I lapped the valves and they "appeared" to be seating well. I guess I need to pull the cylinder head again and see if the exhaust valve is closing properly.

2. Thanks for the specs on the valve clearances. I was using the specs in the Briggs Single Cylinder OHV Service Manual Part No. 276781-8/09 Page Section 12 Page 166. I'll adjust the valves with the corrected specs.

3.

adjust governor. https://www.youtube.com/watch?v=9rO8AvDrdeM

I viewed the video on adjusting the governor. I may give that a try later. I've found adjusting too many things at once can create other problems.

4. Replacing the spring is another good suggestion.

5.

Hold your finger on the throttle shaft. If it smoothes out the governor is too sensitive. May be a linkage or spring problem. If it stumbles it is a fuel system problem.

Throttle shaft - is this top of the throttle on the carb where the linkage attaches? or are you saying to hold your finger on the linkage. Do not quite understand. Is the idea to keep the throttle from moving to see if gas/air mixture is constant into the engine? I added an adjustment screw to the carb. By turning the screw to where it meets the throttle, I can increase the speed of the engine to a constant speed and there is no surging. But when the screw is backed off, it surges again.

Thanks for all of the suggestions. I'll keep you posted.

[bgsengine]

Throttle shaft - is this top of the throttle on the carb where the linkage attaches? or are you saying to hold your finger on the linkage. Do not quite understand. Is the idea to keep the throttle from moving to see if gas/air mixture is constant into the engine? I added an adjustment screw to the carb. By turning the screw to where it meets the throttle, I can increase the speed of the engine to a constant speed and there is no surging. But when the screw is backed off, it surges again.

Thanks for all of the suggestions. I'll keep you posted.

Education time:

Carburetors have different circuits for idle, transition, and loaded operation.

Holding the throttle shaft (or the linkage if you cant easily access the shaft) to prevent the throttle from moving is a valid test to determine if a surge problem is caused by mechanical (governor) or carburetor (Or in very rare cases, misfiring ignition or simply the wrong spark plug.)

If the problem is in the carburetor IDLE circuit , if you hold the throttle lever (or linkage) steady against the stop screw at the specified idle RPM , then the engine will sputter and stall out - If not, allow the engine to come off idle stop a little bit or even to top no load, and if the problem is in carburetor's IDLE TRANSITION circuits, likewise the engine will want to stall out if you hold the throttle shaft or linkage from moving.

If the engine is running LOADED and you hold the throttle or linkage steady and it wants to die out, the problem is in the main nozzle circuit of the carburetor.

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.

An engine running at top no load will be feeding fuel off the idle and transition passages because there's not sufficient air velocity through the carb venturi (due to mostly closed throttle plate) to pull fuel through the main high speed nozzle, so it feeds through the idle passages that are in the side of carburetor body right next to where throttle plate closes against the throttle bore. any of those passages blocked will cause it to surge because as the engine is running and starts to starve for fuel, the governor loosens up and allows the throttle plate to open further to where it starts feeding fuel through main nozzle - when that fuel and air mix reaches stoichometric ratio (14.7:1) , the engine is developing full power and speed, which pushes on the governor to slow the engine back to governed speed, but as it does that it starts closing off the throttle bore via throttle plate, and fuel no longer feeds through main jet - it is trying to pull fuel through the blocked idle circuits again, causing the engine to slow down again, rinse and repeat - which is manifested by the surging engine RPM's

[bobodu]

Anyone who tries to reach my stoichometric ratio is looking to get shot...

[okie]

Anyone who tries to reach my stoichometric ratio is looking to get shot...

I knew a man who was half shot....a lot.

Travis

[R4665]

Thanks for the explanation on how the Idle and Transition circuits work. Understanding the principles behind how the various circuits work and how it relates to surging is very, very helpful.

I'll do the various tests you recommended to see if I can pinpoint the source of the problem.

Thanks. Robert