25 HP Vanguard with Nikki carb keeps surging yet I cleaned it

[driz]

This is on a 2016 Simplicity Regent 48”mower . 300 hours. Last year it started surging so I followed a pictorial and yanked the carb. The fuel rail under the chrome plate was full of solids gunk. I cleaned it out and checked the needle and sear cleaning everything up with spray carb cleaner. it ran fine a few hours then started hi speed surging agin. This time I did the same and pulled and cleaned the brass eustation tubes. I noticed that one of the hi speed jets under them seemed different than it’s mate and figured it was partly plugged. i blew it out did it’s twin the tubes and put it back together. I even changed the small gas line filter in the fuel line I’d put there a few years back. Off it went fine again.
Now a few hours use on its surging the same exact way again. So what else should I be looking at here? the plugs are original but they were clean so I doubt they are making it do this. the one thing I just noticed and it only happened when I first started it this last time was when I let up on the brake pedal the motor kept trying to cut out . I doubt that can make hi speed surge and it went away ?( but I know nothing goes away for long). Any ideas , this surging stumps me. Lastly the fuel pump seems to send out fuel well enough for its needs . What am I missing???

 

[bertsmobile1]

HAe a good look at the debris in the carburettor
It could be the fuel line falling apart.
Surging is always an air:fuel ratio too lean to maintain running at constant speed.
Apart from not enough fuel , air can be entering after the carb, particularly if you have the plastic manifold.
So get a trigger sprayer, remove the blower housing start the mower and saturate the manifold with WD 40 or similar.
If the engine suddenly changes speed or blows white smoke then it is sucking the WD 40 in through a hole some where, usually around he gaskets .

 

[driz]

Interesting. The debris from the 1 st adventure was looking more like cuttings crud all pulpy and a lot of it. The second time it was clean under that cover plate just a slight difference in the visible opening of one of the main jets that got blown out easily. I’ll give it a try. My tank has a debris filter built right I and with the second filter I’d put on its highly unlikely that it’s getting in via fuel. I use those same cans for my large boat so they don’t sit around unused as well.
I have noticed that the air filter seems to go into the housing quite easily, seemingly too easily by my standards. I also mow in a lot of wind sometimes and the dust gets pretty intense coming back at myself and the mower. I will give that sniff test a try after I take apart yet agin, thanks.

 

[bertsmobile1]

Did you take the the main jets out of their tube ?
If so did they go back in the right sides ?
One is bigger than the other ?

 

[driz]

I certainly do intend to swap out that entire fuel line. When I pulled the bowl that was spotless 2 weeks ago and found a few specks of blackish spuge in there. Definitely looks like the inside of fuel line probably from the far side of the new mini filter I’d stuck on there and changed a few hours back. There wasn’t any goo in the old one when i yanked the old one with 340 hrs.though? I’ve got to order up some new large gaskets before putting it back together .
When looking through those 2 tiny fuel passages they were blocked until I shot brake cleaner through and whatever was there must have blown out. More goo ?? The passages got all blown out with hi pressure air and cleaned up awaiting the gaskets.. time will tell.