Briggs 16HP Vanguard carb / fuel problem

[Wurzel]

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...!

 

[slomo]

It basically won't run properly without choke.

Engine wants more fuel.

I've double checked the jets in the carb

Even the sometimes hidden or hard to reach pilot jet?

Have you checked and cleaned the emulsion tube?

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.

Is the choke stuck on?

Have I missed something on the Aisan carb?

I would say yes. Sitting for a couple years, the carb needs to be COMPLETELY opened up and probably boiled out. You've missed something inside. Or buy a new carb. Done deal.

I thought maybe a fuel pump issue but if it runs at full revs, albeit it badly, it can't be?

Have you pulled the hose AT the carb fuel bowl inlet? Verified good steady flow from tank? Drain into a glass jar so you can see what is going on.

I would pull and flush the fuel tank. Most likely full of dirt and grass which hinders flow.

I've checked the tank cap breather as well.

Please explain this procedure? Curious......

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.

Dump the tank completely. Get fresh today fuel in there, no E-10 if possible. Fuel stabilizer is your friend. Let's see, when did I get mower gas last??? I personally forgot what I had for dinner last night.

Is there a hidden jet anywhere on those carbs?

I covered this above. Yes there is.

 

[Wurzel]

Thanks for your pointers @slomo !

I'll double check fuel supply and also drain and refresh the tank so can be sure there - I've run with the tank cap on and off as well. Choke definitely not stuck on, I'm watching it at the carb. I'll take the carb apart a third time and make a note of each jet, tube and valve cleaned, my slight concern is that emulsion tube. I can't remember if I've done it as looking at the diagram (142), it looks like it's in the tube next to the main jet tube which is under a welch plug? If it is, I definitely haven't.

 

[Tiger Small Engine]

It is running lean if carburetor needs choke. Clean the carburetor again. Every passage poke with tiny wire, carburetor cleaner and compressed air. Get the emulsion tube out if it is removable. If that doesn’t work, order an aftermarket carburetor by model number.

 

[slomo]

142 is the emulsion tube. It has super tiny holes so be thorough. Use a magnifying glass and fishing line to verify holes are open. Start saving bread ties. They have small gauge wire under that plastic coating. I found a couple that work great for this. You might have to use a radiator hose angled pic tool to get the emulsion tube out.

Wear safety glasses when spraying carb cleaner. Face shield even better. That stuff burns the eyes let me tell you.

 

[Forest#2]

Your carb appears to be maybe a Walbro LMT and Briggs quit using it and went to the Nikki and ruxing carbs.
It's worth your effort to try to stay with the Walbro LMT because it's the most user friendly carb to repair and the smoothest running when all is correct.
I'll post below couple links, one is how to repair a Warlbo LMT link and the other is to view one for sale on flea bay. You have to keep a heads up because some call the Nikki carbs and kits Walbro just to trick you into buying the Nikki stuff.
Their are two type of them Walbro LMT's for attempting to remove the emulsion tube. One has a little main brass jet in the side of the that must be removed first. This type usually have the solenoid on bottom of bowl. The other type does not use this main jet on the side.
It's very important to use a correct fitting Hollow ground screwdriver (gunsmith's type screwdriver) when attempting to remove the emulsion tube and some of them have to be reduced in width on their sides so as to fit down inside the hole by grinding. If too wide the screwdriver will ruin the threads in the hole as it's turned A regular tapered screwdriver will usually ruin the screwdriver slot and the emulsion tube cannot be removed.
If a emulsion tube is stuck and cannot be removed I have as a last attempt effort to get the carb to run is use a Ultrasonic with heater water and white vinegar then high pressure air. The emulsion tube has several tiny holes and if any are clogged the carb no go. when re-installing a emulsion tube just get it snug, then back off and re-snug.
You can get a Nikki China clone as replacement for around $15, but getting one to run correctly is usually a roll the dice. If you have Amazon Prime you can use a free return if it don't run correctly.
Engine model, type, and code will be good for us to reference for more detail.
Carb repair link
https://outdoorpowerinfo.com/repairs/

Walbro LMT on fleece bay

Carburetor for Briggs & Stratton 696179 Original Walbro LMT Replaces Nikki Carb | eBay

Find many great new & used options and get the best deals for Carburetor for Briggs & Stratton 696179 Original Walbro LMT Replaces Nikki Carb at the best online prices at eBay! Free shipping for many products!

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[slomo]

Love the gunsmith screwdriver mention. Make sure the slot fits snug and doesn't hurt the threads.

Take a sanding roll and make your own if you don't have a good fitting flat blade. Use a larger driver than required. Sand away the tip in a parallel fashion. Then grind the sides off to fit the hole.

 

[Wurzel]

So have had the carb out again, also emulsion tube out this time as well, but it was already clean. I found three tiny holes just on the air side of the fuel screw hole which I thought might have been blocked, but they're clean as well. All back together and same problem - it will tick over without choke but won't rev at all. I haven't dumped the fuel yet, that's next but it is revving Ok with choke so will see if it has an effect.

@Forest#2 it says it's as Aisan carb, are they rebranded Walbro LMTs? It has the solenoid that also keeps the bowl on, and the little jet on the side perpendicular to the main jet, pics attached (jets removed).

 

[slomo]

Still no details on the pilot circuit. Even at mid and higher revs, it still pulls fuel combined with the main jet. Does yout carb have a pilot screw of either fuel or air for adjustments?

Your engine wants more fuel. Revs better with the choke on from what you are saying. Find out why you lack fuel delivery.

What does your float height look like? Put the float back in and take some pictures.

Verify you have a good flow of fuel AT the carb inlet pipe.

Lastly IF the carb says Aisan and OEM is a Walbro, something is off there.

There's more to it than a clean main jet and emulsion tube. I would enrichen the pilot circuit.

 

[Wurzel]

@slomo thanks and agreed I can find no pilot jet and there's no evidence of one on the diagram above, so I don't know how the pilot circuit works on this carb. It has a fuel mixture screw which I've checked and the tip and seat it sits in are good. It does seem to be ticking over a touch better without choke now than previously, but I can't find a mixture setting that allows it to rev without choke, I've started from half a turn right out to three turns or more.

When I do try to rev without choke the carb chucks fuel forward out of the air side and kills the engine straight away.

Can't take a pic of float height as bowl would be on? Or have I misunderstood? Float is on in the above pic but I can turn it over and support it at closed level if that's what you mean?

Will un-attach fuel inlet with engine running to check the pump is pulling fuel up from the tank, as you mentioned earlier.

I should add this is a UK, not US machine, in case that accounts for the Aisan carb - Googling indicates they were fitted to a few. The engine is model 303777.

Starting to think it might be easier to find an aftermarket carb and hope it works - grass is growing!