Briggs 33R877-0034-G1 Surging Heavily

[StarTech]

Okay guys here is one for you to diagnosis.

Briggs 33R877-0034-G1

Originally shattering starter gears. Other techs including JD replaced the starter and the gear a least several times. Never found that the camshaft ACR was broken.

Replaced starter Bendix assy and camshaft. Mower was return with it running fine. Before the customer could even unload it, it surging heavily. I found the stator destroyed because they didn't keep track of the wire clip. Replaced regulator due the shorted stator.

Engine continued to surge so I went back in to check the governor which was like new.

Now here what else would surging and it is not the static governor adjustment. Note: a new carb and ignition coil was also tried.

Just to note I do have a final solution to this just seeing if anyone can figure it out.

 

[ILENGINE]

Being a JD I am going to guess clogged or collasped fuel line between the carb, and the underseat fuel tank. Seems like every JD I have worked on this year needed new fuel lines.

 

[StarTech]

Nope...Was not a fuel supply issue. And yes it a JD E110 that engine is mounted on.

 

[Scrubcadet10]

Air leak in this area?

 

[StarTech]

Not an air leak.. Not a compression problem per say but related in a way if my thinking is correct.. And here is a strange thing the engine could be started at idle and no surging until you advance the throttle. Now if you were to very slowly advance the throttle from idle it would make to high idle speed. But as soon as apply the deck load it was back to surging heavily until you shut down the engine.

Root cause is outside the normal box of known causes. Actually I have never seen this problem in all my years of working on engines until this one. But I got a feeling it will show up again in the future.

 

[hlw49]

Air leak in the intake manifold.

 

[StarTech]

Air leak in the intake manifold.

As said not an air leak.

 

[Scrubcadet10]

Not an air leak.. Not a compression problem per say but related in a way if my thinking is correct..

I'd be looking at a Valve or firing/timing issue...
Like the surging isn't necessarily from a lean mixture but another problem causing the rpm to vary.

 

[StarTech]

I'd be looking at a Valve or firing/timing issue...
Like the surging isn't necessarily from a lean mixture but another problem causing the rpm to vary.

Well Scrub you are the closest to the problem.

Wasn't a lean mixture or mechanical timing and actually not ignition/flywheel timing. It was a dang bad spark plug only failing under heavy compression loads. First one I seen in my 45+ year of working on engines. Don't me wrong here as I seen plugs fail under compression but usually it is very obvious that they are failing.

That why I finally said to myself it had to be a spark plug issue after going in three times, changing the carb and the ignition coil. The new carb and coil are on the shelf for the next repair that actually need them.

 

[Scrubcadet10]

Wow. that is very interesting. Like you said, it's usually obvious when a plug is failing.
sticking this one in the filing cabinet.