EH72FI surging

[KMA]

Hoping someone might have advice regarding my engine issue. It happened the other day when I was in the middle of digging an underground electrical wire run to a detached garage. At first I thought it was bad gas, so I drained and replaced it with fresh stuff. That didn't work, so I took off the intake and cleaned it and the injectors. I found a small rubber plug under the air filter that appeared to have been chewed or worn away. It may have allowed dirty air to enter through a small orifice. I replaced it with something else and put things back, but it still had the issue. I made a video showing the governor moving and the engine surging. It actually got a bit worse after I stopped recording. I think it is running lean since the exhaust was getting hotter than usual (pipes were red).

http://m.youtube.com/watch?v=98yiu6NqHLw

What do you guys think?

Thanks!

 

[MossRoad]

Go to this manual and see if you see the rubber thing you found under your air cleaner. I suspect it is something to do with the governer or speed control. Something to do with friction, perhaps, that keeps the thing from surging. Anyhow, just a guess.

http://www.subarupower.com/media/manuals/129248184237409238.pdf

 

[MossRoad]

Also, a picture of the part you found might be helpful.

 

[KMA]

Thanks Moss.

I have that manual, but the part isn't labeled. I've attached a diagram with the rubber cover/plug circled.

 

[ponytug]

With a fuel injected engine, I tend to think of air/vacuum leaks when an engine is surging. If it were me, I would be looking for other vacuum lines or plugs that might be leaking air. If you didn't have an exact fit replacement for your plug, I would tend to suspect the plug as being the primary issue and the replacement as leaking air.

Free advice...

Good luck.

All the best,

Peter

 

[KentT]

One way I've successfully found leaks around intake gaskets and such is to use a spray bottle of water while the engine is running. Carefully spray it around the intake gaskets, on vacuum lines, etc. while the engine is running and stumbling -- if it momentarily smooths out, you've found a leak. The water will tend to seal the leak for a tiny fraction of second before it is sucked into the combustion chamber and the leak resumes....

Small amounts of water being injected won't hurt the engine.

 

[MossRoad]

Thanks Moss.

I have that manual, but the part isn't labeled. I've attached a diagram with the rubber cover/plug circled.

Is that the same thing as shown on page 9, second picture down?
And on page 10 looking down at the cleaner adapter?
Wonder what its for?

Also, what's the 'pulsation damper' do?

Just throwing out questions. Don't know any answers. :laughing:

 

[KMA]

The "plug" appears to close off a port into the throttle body. Maybe it could be used for testing, or in a different configuration... not sure. I'm assuming the pulsation damper is intended to smooth the flow coming from the fuel pump, but that's just a guess.

I went ahead an ordered a new universal fuel pump that should replace the one there. Unfortunately, Robin does not list a part number for it anywhere, but I found the expected output pressure referenced in one of the diagrams and used that to located a different one. Hopefully I'll be able to swap it out this weekend. Thanks.

 

[Gravy]

Looking at the rest of the manual, it is clear that the plug goes into the air cleaner adapter, which is before the throttle body. Small leaks there may let in some unfiltered air, but should not cause surging. My first suspicion would be fuel starvation. Have you replaced the fuel filter?

 

[MossRoad]

On an old lawnmower we had with a carb, it started surging like in that video one day. I found a small foam ring that was under the linkage to the pin on the butterfly that the governor attached to was just hanging there. It apparently was a damper of some sort that suppressed the surge of the governor. That's why I suggested looking at the governor when he said he found a rubber part. Anyhow, could be fuel related, too. Gotta start somewhere! :laughing: