Briggs 16HP Vanguard carb / fuel problem

[Forest#2]

Right about the ABF (anti back fire) solenoid plunger.

I've heard rumors that they can be tested on the work bench with a good 9v xistor radio battery but I always just use 12v. Make sure the plunger is fully retracting. I have cleaned up sticking plungers by using a oil and just keep on operating the plunger by hand, but if it's sticking just give her the clip/snip.

 

[Wurzel]

With workshop facilities still under construction for a couple of weeks I'm a little limited, but nonetheless I did get a bit more done this evening.

Carb: Had the carb off again and got into the transition ports and idle port with fine wire, plus compressed air. I can see clearly through the idle port, but it's impossible to say if one or another of the transition ports may remain partially blocked. I was however able to get plenty of air from the top of 72 (with screw 955 removed), in the diagram below through to the idle port and also out an air side port.

Carb back on and problem remains, however while blowing compressed air, I did see the welch plug above the transition jets (which looks to have been got at before), has a small air leak - which won't be helping. Rudimentarily I've put my finger over it while the engine is running and there's no difference, but even so it will need replacing. Also still need to properly check for any more substantial vaccuum leaks at the manifold.

Fuel: I'm getting a steady 12v at the fuel solenoid and good flow at the carb inlet. I haven't been able to bench test the solenoid yet. Float level checked and good. However having had a better look at the tank there's quite a lot of fuel in it, which means more of it will be old. Once I've found the drain plug, I will drain and refresh - so definitely some hope there.

Mechanical: I haven't seen the fly wheel yet or checked valve clearances, I'll get to those once I've changed the fuel / am not working off a concrete floor!

 

[slomo]

Typically the pilot circuit works at idle and off idle. Not mid and full throttle. It still draws fuel and air through that circuit when at full revs. Adjusting the pilot screw should either stumble the engine or smooth it out. That is if it's working as it should at low revs.

Old fuel and possible water contamination are definitely something to address first. Stop all testing until you have fresh (non E-10 if possible) gas. Get some Stabil fuel stabilizer and add it to your fuel can. Shake it well. Never worry about bad fuel again.

I would snip the anti-backfire solenoid plunger off. Just idle down the revs and turn the key off. You still might get a pop but it doesn't harm anything. Never worry about starting issues again.

So carb upside down, the float was hanging level with the bowl mating surface? If so that is good.

You might have to strip the carb down and boil it. Is that the OEM original carb, to that engine, you are working with?

 

[Wurzel]

Having that much old fuel in the tank (turned out to be about 4l) was a massive oversight given I only put a little fresh in - so I was convinced that would be the issue. But alas after dropping the tank, draining the fuel line and hooking it up to a fresh fuel source, it's made no difference. I do recall at least smelling the tank before I started and it was fine, plus the old fuel had a very red (not brown), tinge - so I think it must have had stabiliser in it.

So I'm back where I started, full revs with choke is no issue, but I can't past a quarter without. It feels like it's getting plenty of fuel without choke though, 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, then it stops having an effect too far the other way, but won't rev at all if too rich. It still doesn't start too well without choke though.

The float valve closes about parallel with the mating service, but upside down IIRC it rests beyond parallel, there's a little slack in float hinge. I will snip the plunger, but that would likely be affecting it with choke as well.

I don't have an ultrasonic cleaner but I think my last option is too boil the carb, maybe it will move something if that's the issue. As far as I can ascertain, it is the OEM carb for that engine, it's exactly as @Forest#2 's diagram on the link above.

I did accidentally leave screw and washer 955 off the carb a couple days ago and started it up. Needless to say there was a massive vaccuum leak and it ran very badly - but it seemed like the same problem but worse. So am wondering if there somehow could be a vaccuum leak somewhere - more testing there. I should add, I'm doing this without the air filter fitted, but it would be a long shot to say that's leaning it out too much?

 

[Forest#2]

You say:
It feels like it's getting plenty of fuel without choke though, as it sprays unburnt fuel forward back out the carb as it starts to splutter and die?

Tell us more about what you are saying here??????????
Is this as it's running fast with choke or what are you trying to indicate????

Reason I ask is I'm suspicious of something else as a issue, like maybe you have more than one problem with that engine???????????????

 

[Wurzel]

No that's only if it's running fast with choke and i take the choke off, or when I try to rev it more than it wants to go, without choke. It's like a carb backfire. I'll get a video tomorrow to demonstrate!

 

[Forest#2]

your Briggs twin Intek engine parts list.
You can also get a service manual for that engine if desired for around $25 TO30. (you might find a freebie download somewhere)
Look for a Briggs Twin OHV, part number might be 273521.

You have a problem with that engine that is not JUST the carb.
I've seen other things very similar to yours make me think it was the carb when it was ignition, timing, bad valves, etc.
You need to check elsewhere.

What I would start checking.
I would install new spark plugs NGK 6130 or champion RC12YC gapped properly.
First I would make sure that the valves on both heads are adjusted properly per specs and I would also look at the valve lift (compare the valve lift to each other) to make sure you do not have a flat or worn cam lobe.
I would make sure the flywheel key is good.

I've seen the single cylinder Briggs engines act like that due to the intake valve lobe worn down and the valve lash even though adjusted properly would not allow the engine to take gas properly. The valve lift should be same on both the exhaust and the intake valves.
Also I would confirm by using a Ohmmeter that both of the diodes in the kill wire harness going to the magnetos are Ok. (one not shorted) You can check on line how to ohm the diodes.
Those are isolation diodes and if one is shorted the ignition will be erratic at different rpms. While checking the diodes check the air gap on both magnetos as at .010-.012.
also make sure the engine is not running on just one cylinder. You can do this by grounding one spark plug wire at a time on each cylinder.
after doing the valve lash I would compare the compression on cylinder 1 to cylinder 2 and see if they are balanced.

 

[slomo]

The float valve closes about parallel with the mating service, but upside down IIRC it rests beyond parallel

Nope. Needs to be exactly parallel, to the bowl mating flange. Not about parallel nor close to parallel. These little tricks can cause grief. Too low a fuel level will starve the engine. Too high, well you get the email.

I will snip the plunger, but that would likely be affecting it with choke as well.

Go to the hardware store. Get a small bolt, SAME threads as the carb solenoid. Just something to attach the carb bowl on for testing. We are temporarily eliminating the carb solenoid. See if this changes anything. If not, reinstall the solenoid if you want to.

I don't have an ultrasonic cleaner but I think my last option is too boil the carb,

I myself, am not impressed with ultra sonic cleaners for carbs. Maybe some guys have better luck. Now the wife's dishwasher, greatest parts washer on the planet, yes. Good ol' pot scrubber cycle works great. Boiling carbs I feel is the best way to really get inside and do some good. As you can see, the carb is dunked in cleaning solution and the heat loosens gunk up. Strip all plastic parts out first. Lay the jets and emulsion tube in the pan. Bertsmobile1 has shared this tip with us. Summation don't sweat not having an ultra sonic cleaner for this.

If the engine is puking gas out of the carb, we are talking cam timing issues right? Been a while on that trick for my memory. Like a 2 stroke? Or it is a valve adjustment needed? Having a senior moment here...... LOL Flat cam lobe?? Going with a bad cam lobe for 20 bucks Alex.

 

[slomo]

Pull the valve cover/s and sparky plug/s. Rotate the engine by hand. Watch the rocker arms. Rockers should move roughly the same depth INTO the block. Might have a second small bump on the EX valve for compression release.

 

[Wurzel]

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?