Briggs Commercial V-twin surging

[loneryder]

I've got a 3 yr old Ferris iz700 with the Briggs Commercial 27 hp engine. The engine model # etched on the valve cover is 497877. I has 95 hrs of operation. About 91 hrs I changed the oil/filter and airfilter. I used HDEO syn 5-40. Since then it's started surging and smell like it's running rich. With the blades engaged, it seems to run ok. Shut the blades down and it surges and smells rich. I ran some fuel system cleaner thru it and the gas I use is Costco's tier 1 with that Starbright enzyme treatment in the cans. It's fresh gas. Up to now it's been a great engine/mower.
Any ideas or thoughts before I take it to the shop?
Thanks.

 

[loneryder]

I'm sorry. The engine # is 49T877-0019-G1. Blame my old eyes on this one.

 

[Douglasdzaster]

Drain the bowl under the carburetor. If it has sat up for anytime there could be a little water in it or trash. Water will make it surge. It’s also possible to get a tank of bad gas anywhere. I always buy gas at the busiest place where they sell a lot of gas then I know it’s fresh.It’s worth draining the carburetor since it’s easy to do. Could be a blockage somewhere also. If it has a fuel filter check it. Check the vent on the gas cap by loosing it and see if the surging stops. Could also be the spark plugs not firing correctly. When’s the last time they were replaced? Make sure the gap is in spec with the manual.

 

[MParr]

So, you have around 100 hours on the machine.
Has the fuel filter been changed?
Have the spark plugs been changed?
It’s also time to change the hydrostatic filters and fluid.
As mentioned above, drain the carburetor bowl.

 

[bertsmobile1]

Unless you are at the top of the Rockeys or use it for pushing snow that oil is a touch on the thin side
You know when it is too thin cause you get a bit of oil smoke on start up that goes away after a couple of minutes.
Surging happens because the air:fuel ratio gets too lean
If it only happens at start up but get better when the blades are on then it is the pilot / idle circuit in the carb
So either something is preventing enough fuel getting into the engine or air is getting in after the fuel is added

 

[loneryder]

Unless you are at the top of the Rockeys or use it for pushing snow that oil is a touch on the thin side
You know when it is too thin cause you get a bit of oil smoke on start up that goes away after a couple of minutes.
Surging happens because the air:fuel ratio gets too lean
If it only happens at start up but get better when the blades are on then it is the pilot / idle circuit in the carb
So either something is preventing enough fuel getting into the engine or air is getting in after the fuel is added

Thanks. I was worried the oil might be too heavy. Book calls for nothing more than a 30wt.

 

[loneryder]

So, you have around 100 hours on the machine.
Has the fuel filter been changed?
Have the spark plugs been changed?
It’s also time to change the hydrostatic filters and fluid.
As mentioned above, drain the carburetor bowl.

Only the Hydrogear fluid and filters. Should I go ahead and change the fuel filter and plugs? Plugs look ok and I re set the gap.

 

[MParr]

Only the Hydrogear fluid and filters. Should I go ahead and change the fuel filter and plugs? Plugs look ok and I re set the gap.

Absolutely! I’ve had the best luck with Kohler brand fuel filters. This is my go to for mowers with fuel pumps.

Amazon.com: KOHLER 24 050 13-S1 Engine Fuel Filter 15 Micron With 1/4-Inch Inside Diameter : Automotive

Buy KOHLER 24 050 13-S1 Engine Fuel Filter 15 Micron With 1/4-Inch Inside Diameter: Fuel Filters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[loneryder]

Here's an update. My local repair guy sold me a small bottle of Motor Medic (I think). He said to run it thru the engine and let it sit overnight. He said if that didn't do it, nothing would. Said be careful because it would burn my hands. Changing the plugs and fuel filter didn't help the surging. I put the whole bottle in the tank and ran it for a while and let it sit overnight. No real change. Did it for another day/night and low and middle idle came back but high speed still surged. Did it for another day/night and shazaam, all idles are smooth.
Here's what I don't get: I fill my gas cans at Costco and use the blue enzyme stuff in each can. I use the gas within a month. You can't get fresher gas than Costco as they go through 3-15 tankers a day. I gave up on Stabil. And still I have these carb problems.
Thanks for all your suggestions.

 

[Douglasdzaster]

Here's an update. My local repair guy sold me a small bottle of Motor Medic (I think). He said to run it thru the engine and let it sit overnight. He said if that didn't do it, nothing would. Said be careful because it would burn my hands. Changing the plugs and fuel filter didn't help the surging. I put the whole bottle in the tank and ran it for a while and let it sit overnight. No real change. Did it for another day/night and low and middle idle came back but high speed still surged. Did it for another day/night and shazaam, all idles are smooth.
Here's what I don't get: I fill my gas cans at Costco and use the blue enzyme stuff in each can. I use the gas within a month. You can't get fresher gas than Costco as they go through 3-15 tankers a day. I gave up on Stabil. And still I have these carb problems.
Thanks for all your suggestions.

It’s possible Costco got a bad load it happens. Or the fuel you got came from the bottom of their tank. Did your guy check the fuel? Just wondering. Glad your up and running again. I just recently switched from Stabil to Star Tron myself. Time will tell.