Engine surge at idle and mid range RPM

[Neil P]

Good evening. I'm new to the forum & I am hoping I can get some guidance from the members here. I have a nearly new Ferris IS700 with the 27 HP Briggs engine. The machine has 55 hours on the meter. I purchased it in July 2016. I've had zero problems with it throughout the 2016 season, and no problems for the first 4 cuttings of my 5 acre yard for 2017.

Several times today, I would stop mowing and let the engine idle while I was pulling a weed or to grab a quick drink of water. The engine idled just fine. When I finished my last pass, I turned the blades off, and moved the throttle to about mid range while I traveled back to the garage. The engine started to surge like it was running out of fuel. When I stopped to open the gate and idled it down, the engine nearly died. I thought maybe the gauge was reading wrong and the tank was empty even though it needle was pointing to 1/4 tank. I pushed the throttle all the way open, and the engine seemed to run OK. I idled it back down & gave it a little choke, and the surging stopped.

Just to be sure I had plenty of fuel, I filled the tank. The problem continued. Next I removed the fuel filter. I blew through it with no problem. (No matter how well you wipe it off, you still get a taste of gas in your mouth ) Just to be sure, I ran into town & picked up a new filter...the problem is still there.

I did notice when the engine is running at 1/2 throttle, the fuel line between the filter and the pump moves with the engine surge, like it is having a hard time drawing fuel from the tank. That makes me wonder if I have a restriction up stream of the filter, maybe in the 90 degree elbow that is attached to the tank? Maybe something inside?

I am going to pull the fuel line off of that elbow tomorrow & stuff it into another fuel source to see if the surge stops.

IF that elbow is partially plugged or if the pick-up tube inside the tank is plugged, do any of you know how to remove them from the tank?

Any assistance or advice would be greatly appreciated.

Thanks in advance.

 

[Neil P]

This morning I removed the fuel line from the elbow on the fuel tank and stuck it into a jug of fuel. The engine surge is still there, so in theory, that eliminates the possibility of the elbow or fuel pick-up tube being restricted.

I guess I will have to load it up & haul it off to the dealer and let them figure out what's ailing it. Hopefully warranty will cover the repairs.

 

[bertsmobile1]

This morning I removed the fuel line from the elbow on the fuel tank and stuck it into a jug of fuel. The engine surge is still there, so in theory, that eliminates the possibility of the elbow or fuel pick-up tube being restricted.

I guess I will have to load it up & haul it off to the dealer and let them figure out what's ailing it. Hopefully warranty will cover the repairs.

Hunting is ALWAYS A BLOCKAGE in the FUEL system.
So it is off with the carb and clean it out properly.
Also check the shut off solenoid they can get sticky and partially block off the fuel flow from the carb to the engine.
Loose carb bolts / buggered gaskets can also do the same thing but generally associalted with hard starting and over reving

 

[Neil P]

Hunting is ALWAYS A BLOCKAGE in the FUEL system.
So it is off with the carb and clean it out properly.
Also check the shut off solenoid they can get sticky and partially block off the fuel flow from the carb to the engine.
Loose carb bolts / buggered gaskets can also do the same thing but generally associalted with hard starting and over reving

Thanks for the reply.

I suspect there is some gunk in the carb. The paper filter inside the plastic fuel filter housing was loose. I am guessing something may have come loose from that and is plugging the carb. Sad that the OEM filter may have caused the problem, and of course the dealer says it's not a warranty issue (even with 54 hours and the machine is only 9 months old)

Tell me a bit about the solenoid. If a person removes it, is there a plunger that moves when you turn the key on & off?

I am hoping I can find a break-down of the carb so I can take it apart if necessary.

 

[Neil P]

I decided to try one more thing before hauling it off to the dealer. I pulled the line off of the tank & ran the engine until it started to sputter. Thin I stuffed the hose into a can of Sea Foam and ran it until died. I let the Sea Foam sit in the bowl for 24 hours. I pulled the fuel solenoid and drained it into a clean pan. Perfectly clean & clear. So...whatever is causing the trouble is definitely in the carburetor.

I spoke with the shop manager this morning and told him what all I had done and that I suspect that the filter failed causing my problem. He told me to bring the mower & filter in & he would see if he could get Ferris/Briggs & Stratton to pay for the necessary repairs. He was skeptical that they would step up to the plate. Thats NOT what I wanted to hear!

 

[mvance]

I decided to try one more thing before hauling it off to the dealer. I pulled the line off of the tank & ran the engine until it started to sputter. Thin I stuffed the hose into a can of Sea Foam and ran it until died. I let the Sea Foam sit in the bowl for 24 hours. I pulled the fuel solenoid and drained it into a clean pan. Perfectly clean & clear. So...whatever is causing the trouble is definitely in the carburetor.

I spoke with the shop manager this morning and told him what all I had done and that I suspect that the filter failed causing
my problem. He told me to bring the mower & filter in & he would see if he could get Ferris/Briggs & Stratton to pay for the necessary repairs. He was skeptical that they would step up to the plate. Thats NOT what I wanted to hear!

Ive had the same doggone problem for three years, sometimes it'll idle sometimes it wont. Changed filters, etc. I sure wish id have gotten the Kawasaki.

 

[bertsmobile1]

Unfortunately Neil never came back.
Surging at any speed is cause by a fuel mixture that is too lean.
Two ways for that to happen.
Not enough fuel or too much air

Too much air is the easiest to rule out by starting the engine, setting it in to throttle position where it surges then liberally spraying the engine from the inlet manifold to the carb with WD 40 or some thing similar from a trigger pack because the propellants in spray can are flammiable and eyebrows are a necessary part of your anatomy.

If the engiene starts to blow clouds of white smoke you have an air leak.
Generally the spot where the throttle shaft goes through the carb will leak a little so a tiny bit of smoke when you get to there is no big deal.
If it is enough to drastically change the engine speed then it is new carb time.
The choke lever does not matter because it is before the fuel is added, other than a big hole will let dust in.

If it only surges at low speed then 99% chance it is a blockage in the idle circuit and on lots of carbs this requires removal of welch plugs so buying a rebuild kit.
http://outdoorpowerinfo.com/ have very detailed instructions on cleaning carbs.