675EX Quantum surging

[XGamer223]

Hello folks,
back with a good old surging issue. It's a Briggs 675EX Quantum engine with surging issues.

At first it was horrible when it arrived. Replaced the air filter, removed and cleaned the carb, replaced bowl seal and assembled it all. Ran much much better afterwards but not perfect at all.
It has two throttle plates, one for choking that works on airflow from the fan, other one is the governor that has linkages to the back of the engine.

What I tried else is that i put some WD40 on the linkages at it smoothed out. Later I put on some grease instead of WD40 and it was back to some small surging, and that's where I am right now. Re-applying WD40 didn't help.

I'm pretty positive the owner before me did something messy with the springs, I left them as-is but I think there are changes needed. Also my float in the bowl seems suspicious to me, but I can't notice any flooding so far.

Engine starts smoothly and doesn't cut out. Only that it surges.

Any help would be great! Thanks in advance.
Here's a video preview of how it is:

https://imgur.com/iQvyNjB

 

[Scrubcadet10]

remove the metal engine cover and spray WD40 along the plastic intake manifold, if it has a hairline crack in it, it can cause surging. Also the O-RING between the carburetor and manifold can leak as well, or be missing.
If the WD40 makes it into the combustion chamber, the engine will either smooth out or blow white smoke or stumble.

 

[XGamer223]

remove the metal engine cover and spray WD40 along the plastic intake manifold, if it has a hairline crack in it, it can cause surging. Also the O-RING between the carburetor and manifold can leak as well, or be missing.
If the WD40 makes it into the combustion chamber, the engine will either smooth out or blow white smoke or stumble.

Thanks for your quick reply.

Tried spraying WD40 between the carb and intake manifold and nothing changed.
Will try spraying it on the intake manifold next time.
Figured the springs were setup wrong, but changing it did absolutely nothing but lower the RPMs.
Also, didn't note before: I put a new sparkplug on it.

And, I noticed that the ignition coild wire to the sparkplug has multiple cracks in it, revealing the white string-like additional insulation. Should that make any issues?

 

[Scrubcadet10]

That could cause issues, but usually it will be cutting out and running worse than your video.. typically surging is a LEAN burn, meaning too much air, or not enough fuel.

 

[XGamer223]

Hello again.
It definetly has too much air (or not enough fuel to be exact).
When I manually use the choke lever on the carb, and manually close it about 20% the engine smooths out how it should run. When I let off of the lever, it returns back to surging. Same for when I manually block the intake.

Replaced the o-ring at the carb where it meets the manifold as it was stretched, was sagging and super-thin, but that didn't fix it at all. Next to check is the intake manifold for possible cracks.

What I also fear is that I used dual o rings for the float bowl as when I used just one, it would leak all over the place. Now, what if it was that I can't fully tighten the main jet (due to the thicker orings) and starve the carb for fuel that way? Is there any possibility?

 

[Scrubcadet10]

i wouldn't think so.... but i;ve been wrong before.

 

[XGamer223]

Hello again.

Removed the intake manifold to check for any cracks (as I can't remove the cover while the engine runs as the dipstick is stuck to the cover).

Gasket seems fine so I filled the manifold with water and it shown multiple leaks at the engine side. Putting the water under pressure, even more leaks show. But I'm unsure if these are leaks or it's just normal, since wherever they "joined" the plastic parts together, a leak shows.
Video:

https://imgur.com/a/dqTtGvc

 

[Scrubcadet10]

shouldn't cause an issue since its inside the gasketed area.

 

[XGamer223]

shouldn't cause an issue since its inside the gasketed area.

sorry for late reply, was really busy.

You were right, the leak doesn't mean much. Replaced the gasket at the intake manifold (both), still nothing (BTW. both gaskets are "DIY", hard to get legit ones). Surges but less.
The springs are worrying, but I imagine it doesn't mean much until the engines gets under load?

I'm out of ideas

 

[Scrubcadet10]

One thing I should have picked up on first, have you tried bending the tab that the springs are hooked to, outward to increase rpms. These carburetors don't have an idle circuit so they're meant to run at a constant full 3200 rpm (depends on mower specs).