Briggs 12H802 Surge, don't think it is carb...

[pylek]

I will check the intake tube again. After cleaning and inspection, I installed it with a new gasket, and hand tightened the screws with a nut driver, tight, but not twist off the heads tight. I couldn't find a torque spec in the Single Cylinder L-Head service manual.

After performing the static governor adjustment, and after I got the engine running, I adjusted the spring tab for as close to 3200rpm as the surge would allow. I will check again.
Surge was the same at 3200rpm as it was at 2800rpm, and as at idle.

Thanks!

Seth K. Pyle

[bgsengine]

I will check the intake tube again. After cleaning and inspection, I installed it with a new gasket, and hand tightened the screws with a nut driver, tight, but not twist off the heads tight. I couldn't find a torque spec in the Single Cylinder L-Head service manual.

*EVERY* piece of hardware on these engines has a torque specification - Those that are not specifically listed fall under the "General torque Specification for standard hardware" category. (Should be in the first section of the manual)

[pylek]

Point taken.

[pylek]

Alright, after a hiatus, I am back on this pushmower. I have pulled the head and valves. I cleaned most of the carbon from the head, piston, and valve area. I lapped the valves and set the clearances. Put it all back together with new gaskets. Couldn't find a listing for the intake pipe screw torque, so I used the general hardware spec.

Started the engine, no change...

Last night, I checked the spark while it was surging. Spark looked good at .165" on my tester. However, with a larger gap, the engine started to stutter, spark was failing.

So, I put a known good used ignition armature on it. No change, engine still surged.

I liberally sprayed the exposed portion of the intake pipe, and sprayed brake cleaner into the blower housing around the intake pipe. Again, no change in the surging.

Now, with the engine good and warmed up, if I hold the throttle, the engine speed seems to settle out. I say seems because, by ear the engine sounds better, but I am unable to get a stable reading on my TA100 SmartTach. The reading cycles from 1500 to 4100rpm. The engine does not sound like it is surging when I hold the throttle.

So, I am running out of ideas...


Seth K. Pyle

[David]

Detective mystery.
Something wrong with the cam-not enough lift or something? Weak flywheel magnets?
Would be curious as to whether it smooths out when a little propane is presented to the air intake while it is running and surging-or run with a jetnut that has an oversized (just for test purposes) jet hole.

[bgsengine]

Alright, after a hiatus, I am back on this pushmower. I have pulled the head and valves. I cleaned most of the carbon from the head, piston, and valve area. I lapped the valves and set the clearances. Put it all back together with new gaskets. Couldn't find a listing for the intake pipe screw torque, so I used the general hardware spec.

Started the engine, no change...

Last night, I checked the spark while it was surging. Spark looked good at .165" on my tester. However, with a larger gap, the engine started to stutter, spark was failing.

So, I put a known good used ignition armature on it. No change, engine still surged.

I liberally sprayed the exposed portion of the intake pipe, and sprayed brake cleaner into the blower housing around the intake pipe. Again, no change in the surging.

Now, with the engine good and warmed up, if I hold the throttle, the engine speed seems to settle out. I say seems because, by ear the engine sounds better, but I am unable to get a stable reading on my TA100 SmartTach. The reading cycles from 1500 to 4100rpm. The engine does not sound like it is surging when I hold the throttle.

So, I am running out of ideas...


Seth K. Pyle

1. Check flywheel key
2. New plug (just for the heck of it)
3. If it seems to stop surging when holding throttle steady, it's more likely a governor issue - check carb throttle for any sticky points, check throttle shaft for wear (air leak) or any binding in the linkage , worn linkages, or try adjusting the governor to a different RPM setting - lean misfire can make tach jump around a bit, as well. also depending on governor type, check linkages and shafts for even the slightest binding ior stickiness, if mechanical governor, time to pop the crankcase cover and check gear and flyweights as a last resort.

[pylek]

Thanks for the ideas!
I checked the flywheel key recently by removing the nut and starter cup. Keyway in crank and keyway in flywheel still lined up, key did not look sheared. Torqued it back down.

I will put a new plug in.

I don't think it is sucking air, as hosing the carb and intake pipe with brake cleaner had no effect. Lightly spritzing brake cleaner into the carb just caused the engine to bog.

I have played with the governor spring tension, sped up, slowed down, no real change in surging. Though, surging seems a little less pronounced at lower rpms.

May very well have to remove the sump.

Thanks!

Seth K. Pyle

[pylek]

For giggles, I put the air filter housing and air filter back on, as that is what bit me in the a$$ on the Honda EB6500SXA generator I did a few months ago.

No love, still surged. It primed and started right up, but still surges.

I put a new plug in. No change, still surges.

Here is what the old(less than an hour run time since new) plug looked like immediately after 5 minutes of surging.




Here is a link to a 10 second video of the engine surging.

http://s1229.photobucket.com/albums/ee473/skpyle/?action=view&current=100_0904.mp4


Still trying...

Seth K. Pyle

[pylek]

Hmmm...I think I have found it, and I am not pleased...

Once again, with the engine surging on full throttle, I hosed everything down with brake cleaner. No change. Then, I aimed the straw nozzle directly at the foam seal of the throttle shaft where it enters the body of the carb. In the past, I had just sprayed the general area of the carb throttle.

Anyway, the engine started to bog. Again spray, again bog.

Rats, this means the throttle shaft and/or throttle bore in the carb is worn. I am assuming there is no fix for this, other than new/another carb...

Seth K. Pyle

[David]

But that engine still did that stuff when it had a known good carb on?
I hope Braklean isn't too strong for the foam seal-