Briggs 16HP Vanguard carb / fuel problem

[Wurzel]

Sounds like a head gasket issue.
Probably got full of thum grass clippings and oil, and ran too hot.
Once the covers been removed of course, things can be observed, flywheel magnet, coil, and any foreign matter trapped in the cooling fins. Some compressed air, or (pressure washing) works, (remove the coil first) to get the gunk off.

Yep next job, hopefully not

 

[Wurzel]

I hope you changed out the Fuel Filter.

Not yet, will do but have good flow at carb inlet

 

[Wurzel]

Are those composite floats or just really crusty brass floats? The composite floats are sometimes like the Bing composite floats and they absorb gas after the surface sealing fails making the float too heavy and the needle never closes. Thus, too rich as you say it appears to be.

Could be a thing, they're composite

 

[TobyU]

Whatever happened with this? I'm a little confused if I conflicting statements in the first post. Says they think it's obviously too rich but then when they give it choke it smooths out and runs better but only has 30% power.
Sounds to me like it's actually lean and even with the choke it's not getting enough.
It always irritates me when people , well actually customers, say they cleaned out the carburetor.. blah blah blah, as most people don't really know how to clean out a carburetor properly or don't no what the actual crucial part is to clean.

I got a feeling this carburetor is still gummed up and that's the problem. So where does it stand now?

 

[Forest#2]

From your post #24
You say
as it sprays unburnt fuel forward back out the carb as it starts to splutter and die? Fuel screw works at idle, too lean and it stumbles,.

Did you ever check to see if the engine will idle/run using only one cylinder doing the cylinder comparison test suggested previously?
Listening to your video in post #30 you could easily do such with the engine idling.
Also
Did you ever check the valve lash?

If you remove the shroud keep a heads up and do not run the engine long enough to overheat

How many times have we heard the story, it was running good when I parked it, therefore the engine will run great when a battery is installed, trust me.

 

[slomo]

So a couple of videos, the first showing it running flat out with about 80% choke, then the effect of removing choke, shown at the carb, where it starts stumbling and dies. The second is it starting at idle with no choke, then trying to gradually introduce revs.

Full revs to no choke: https://youtube.com/shorts/qQAejaOIz8E?feature=share

No choke idle to revs: https://youtube.com/shorts/mOj3QcGQN7k?feature=share

Poorly video'd on my phone so apologies for sound...

Had ocnfirmed by another this evening that it was running OK only a year ago, so I'm struggling to make the jump to a mechanical issue. I'm just bolting and unbolting the carb, will take the shroud off tomorrow and have a clean, is there potential for a vaccuum leak further in than the manifold / carb mating surface?

Your videos indicated it ran fine at idle and low revs. Pilot circuit seemed okay there. Just when you increased throttle is ran short on fuel. So the main jet is to be looked at. You need choke for higher revs. That also confirms you are shy on fuel from the main jet.

Remove the main jet. Look for a jet number on it and see if your parts schematic lists any jet sizes. You might have to SLIGHTLY open up that main jet. Just a little bit at a time.

I would verify no vacuum leaks prior to enlarging the main jet size.

 

[slomo]

Are those composite floats or just really crusty brass floats? The composite floats are sometimes like the Bing composite floats and they absorb gas after the surface sealing fails making the float too heavy and the needle never closes. Thus, too rich as you say it appears to be.

His engine is starving for fuel. He has to choke it to smooth it out in high revs.

 

[slomo]

Hard to tell for sure but I seem to detect that it's only running on one cylinder sometimes maybe. (or one cylinder is weaker) You can judge such by rpm drop as each cylinder is disabled, comparing one to the other.

You can easily confirm such by sliding back the rubber boots on both spark plugs so as to see the metal ends while on the spark plug and while the engine is running at idle ground each spark plug wire one at a time using a long blade screwdriver. If grounding one spark plug wire immediately starts killing the engine that is the ONE CYLINDER that it's using to run.
The cylinder that makes no difference when it's spark plug wire is grounded is the dead or weak cylinder.

Lightly lubing the spark plug wire itself just above the boot helps when sliding the boot back. (another way is to allow a small solid wire to stick out of the boot and ground the wire while it's running.
Just because you see a spark at both plugs IS NOT sure indicator that both cylinders are actually producing power. The other way is to use a fuse puller and momentarily pull the spark plug wire off the plug. I do not like to pull a plug wire for testing while running, I prefer grounding but sometimes I have no other choice.

Feel or measure the temps from both exhaust pipes directly off the heads. Both should be hot.

 

[Forest#2]

From your post #24
You say
as it sprays unburnt fuel forward back out the carb as it starts to splutter and die? Fuel screw works at idle, too lean and it stumbles,.

Did you ever check to see if the engine will still idle using only one cylinder doing the cylinder comparison test suggested.
Listening to your video in post #30 you could easily do such with the engine idling.
Did you ever check the valve lash?

 

[Forest#2]

Feel or measure the temps from both exhaust pipes directly off the heads. Both should be hot.

I've got a IR thermometer that is really good for fast checking for a cold dead cylinde or comparing cylinder temps..