Briggs 16HP Vanguard carb / fuel problem

[slomo]

Yep - I certainly should have, I got distracted chasing down a fuel issue, I even have that tester...

Not being familiar with these engines I'd totally missed it was only running on one as well, had it been a four pot it would have been obvious. In any case, coil ordered, fingers crossed it works. Noted re orientation, the one I've taken off was clearly marked as such, will check on install of new one.

Make sure your working coil can throw a good strong spark. Put that tester to work.

 

[georgPru2]

Hello All - am hoping the knowledge bank here may be able help. I'm resurrecting a John Deere LT166 lawn tractor with 16HP Briggs engine. It has sat for 2-3 years but was running fine, save for a snapped deck belt, previously. I've stripped and cleaned the carb and got it started, driving and mowing, but not very well. It basically won't run properly without choke. I've double checked the jets in the carb. I can just about get it to tick over without choke by adjusting the fuel screw, but it won't rev and it's obviously running far too rich. In any other position it won't even idle, or only for 10-15 secs before stuttering and dying. With choke it will rev, but is maybe at 30% power and clearly not running as it should. Oddly it can manage forwards, but reverse pretty much kills it.

Have I missed something on the Aisan carb? I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be? I've checked the tank cap breather as well. It has clean fuel, albeit mixed with whatever small amount of bad might have previously been in the tank, but I think it was bone dry. Is there a hidden jet anywhere on those carbs?

Thanks in advance...!

Make sure you have good flow of fuel from the tank. A collapsed[internally] fuel line behaves in this manner.

 

[Wurzel]

Quick update - coil has arrived and is fitted but while it revs much better without choke, the problem remains, it will only take maybe 70% throttle. I've been a little short of time of late, but will get into valve clearances etc next.

 

[slomo]

Quick update - coil has arrived and is fitted but while it revs much better without choke, the problem remains, it will only take maybe 70% throttle. I've been a little short of time of late, but will get into valve clearances etc next.

When you get time, change the plugs. A cheap long shot here. Rare but sometimes they get dropped or just fail.

Can you confirm now you have a strong spark on both cylinders?

 

[Forest#2]

but while it revs much better without choke, the problem remains, it will only take maybe 70% throttle.

????????????Give us a hint as to how it acts when it QUITS TAKING throttle.
Does it backfire, just hump up and start smothering like it wanting more gas through the carb or starving for gas.

Since that has a separate choke control what happens if you give it a part choke at 70% throttle????

 

[TobyU]

Quick update - coil has arrived and is fitted but while it revs much better without choke, the problem remains, it will only take maybe 70% throttle. I've been a little short of time of late, but will get into valve clearances etc next.

These things rarely have any valve adjustment issues that will prevent them from running or running just fine UNLESS someone has been in their monkeying around.
If you hear one popping out of the intake after it gets up to even slightly past a slow running speed then you can guess that the intake valve is adjusted to tight but that's because somebody messed with something.
These engines don't wear tight like car engine still.
When they wear and when they haven't been adjusted in their entire life etc you will find the clearances are three or four times what they should be but as long as you can get the engine to start and get past the correct compression release issue as it cranks, it will run just as perfectly as any other engine.
You would have to try to miss adjust the valves on one of these to cause a running issue or a specially a revving up engine issue.
The other valve train problems are not adjustment or wear issues at all but rather lack of proper assembly and safeguards when they're put together normally from a rocker arm stud loosening up and things getting out of whack with the angles or bending a push rod also.
The other common valve train issues are when a valve guide slips mainly from overheating because of grass and dirt and greasy grime build up on the cooling fans of the engine but in reality, more because it's a lousy design to begin with!
They pressed these guys into the heads so poorly and so loosely that a machinist and a machine shop who routinely sees car engine heads with just roll his eyes and shake his head at the poor setup.
They could have solved this problem over 20 years ago but they don't care because they don't mind when they fail and they don't mind selling replacement heads because that's the shops answer to everything is throw new parts at it.
I have NEVER replace the head due to a slipped valve guide but have fixed many.
They could have used several methods to fix this problem the easiest of which would probably have been to pin them.
But anyways, when this happens you'll get that pushrods and valve issues and usually a Pop-Pop here and there and then it won't start again.

I think you're going in the wrong direction worrying about the valves right now but I don't know if they've been adjusted properly before or not.

If it seems to only get up to 70% of proper operating speed and especially if it's leaning out like starving for fuel because it's either leaning out or it's bubbling and running extremely rich and coughing a little bit and maybe blowing a little bit of black.
Most commonly they starve for fuel though and this boils down to still a carburetor restriction in the jet.

I forget after all this time and comments if this is a walbro for a Nikki carb but after just saying this I remember it's a twin so it's not the same carb as the singles where on the Nikki people often put the jet in the wrong way I call it or at least the worst of the two ways you can install it and it often falls out and then the machine will run but excessively richly.
From but I remember you can also have the same problem with the jet falling out on one of the twin engine carbs.
One of the common one has two jets.

Regardless, to troubleshoot this now I would use my hand or a folded shop
cloth or microfiber towel to slightly restrict the airflow going into the carburetor as you try to rev It Up or even get a spray bottle with some gas in it or use some carb cleaner to slightly spray or even trickle a little bit of gas in there when you try to rev It up to see if by giving it more fuel it will rev up higher and smoother.
This is one way to confirm that you need more fuel and there is a restriction somewhere in the flow and the atomized mist getting through the carbon into the intake.

Also, have you cancelled out cylinders while this thing is running to make sure it will sit there and run on each cylinder independently?
This is very important because you could just have a very weak cylinder now not producing much power.

 

[smallenginerepairs]

check fuel hoses to make sure they are not swelled up inside them.

 

[Wurzel]

Finally had some time to get to it this afternoon, have confirmed spark on both cylinders and also that it will run on either. I also made the governor / carb connection more permanent as it had been hooked over temporarily, which made me take a closer look at how it was working. I'm fairly certain the carb connection is OK, but I've no idea if the lower springs on the throttle cable are right - certainly the way it's connected at the moment mean it needs about 20% throttle before it starts moving the carb. There's a lot of slack in the mechanism due to how the springs are currently attached.

I'm wondering if the governor is somehow killing the engine at higher revs, it looks as though is opening the throttle way too much? If I partially cover the carb when it starts to splutter it recovers, as it would if I used choke to the same thing. It starts sucking really hard which is when it dies. If I gently manage the air going into the carb I can get it revving pretty hard, but left to it's own devices, the governor goes wide open and kills it.

I'm not sure re cause / effect here, but see video below:

 

[STEVES]

Governor not killing it, starts to die - rpms get less - the governor opens throttle to bring rpms up. Issue not governor, it's .....

 

[TobyU]

Finally had some time to get to it this afternoon, have confirmed spark on both cylinders and also that it will run on either. I also made the governor / carb connection more permanent as it had been hooked over temporarily, which made me take a closer look at how it was working. I'm fairly certain the carb connection is OK, but I've no idea if the lower springs on the throttle cable are right - certainly the way it's connected at the moment mean it needs about 20% throttle before it starts moving the carb. There's a lot of slack in the mechanism due to how the springs are currently attached.

I'm wondering if the governor is somehow killing the engine at higher revs, it looks as though is opening the throttle way too much? If I partially cover the carb when it starts to splutter it recovers, as it would if I used choke to the same thing. It starts sucking really hard which is when it dies. If I gently manage the air going into the carb I can get it revving pretty hard, but left to it's own devices, the governor goes wide open and kills it.

I'm not sure re cause / effect here, but see video below:

It's not

Finally had some time to get to it this afternoon, have confirmed spark on both cylinders and also that it will run on either. I also made the governor / carb connection more permanent as it had been hooked over temporarily, which made me take a closer look at how it was working. I'm fairly certain the carb connection is OK, but I've no idea if the lower springs on the throttle cable are right - certainly the way it's connected at the moment mean it needs about 20% throttle before it starts moving the carb. There's a lot of slack in the mechanism due to how the springs are currently attached.

I'm wondering if the governor is somehow killing the engine at higher revs, it looks as though is opening the throttle way too much? If I partially cover the carb when it starts to splutter it recovers, as it would if I used choke to the same thing. It starts sucking really hard which is when it dies. If I gently manage the air going into the carb I can get it revving pretty hard, but left to it's own devices, the governor goes wide open and kills it.

I'm not sure re cause / effect here, but see video below:

It's not the governor. The governor is doing its job and when the engine starts to slow down RPMs it opens up to try to maintain the speed which eventually and pretty quickly in this case it opens to full throttle trying to get more speed.
It can't do that because there's not enough gas flowing through somewhere..
That's why when you use your hand your accomplishing two things. Firstly, you are blocking off the airflow and restricting how much air goes in so that Richard's whatever mixture is in there and secondly after that brief second it probably allows a little bit more suction through the jet because obviously some gas is going through so it does get a little bit more fuel flow but overall you're not getting enough fuel flow on its own.
If you stood there with a spray bottle of gas or carb cleaner and tried to rev it up and gave it a little trickle of extra fuel source you could also get it to speed up smoothly without bogging.
What's happening, it looks like to me, is the governor is opening and the throttle is going to wide open and it doesn't have nearly enough fuel so it just bogs and starts to die.
I forget all the previous discussion but that carburetor looks pretty simple like you remove the bowl and they will be a jet screwed into the side of the center section of the carb or maybe it's got one of the jets screwed up into the bottom of it into the middle.
Those have to be removed with a skinny screwdriver that just fits The notches in the brass jet.
It sounds to me like a simple main jet is partially restricted