Briggs choke help needed

[o2jmpr]

Hey all. I’m in need of your knowledge.

I just rebuilt a new to me Briggs 5hp model 135202. Everything looked really good and is in specs. I lapped and adjusted valves, new gaskets everywhere etc.

The engine will only run strong at 1 very specific point at about 3/4 choke while sitting in the bench with no load. It dies at full and dies at “run”. I’ve torn the carb off 3 times now and poked every port, flushed with aerosol carb cleaner and blew with air compressor. I’ve also added a good amount of sea foam to the gas and let it run a while. It has new springs and diaphragm. This behavior continues at any idle setting and it will run with the idle adjustment anywhere from 1 turn out to all the way out. I set the governor and found that if I hold the slider on the bottom of the tank assembly where the governor arm spring and throttle linkage is with jus the smallest amount of pressure then the engine will run (albeit roughly) with the choke completely off. If I move the choke back to the 3/4 open position it likes it will run smooth and hard again.


This still seems like a fuel delivery issue. I’ve sprayed all around and can’t find an air leak anywhere but I can’t possibly get this carb any cleaner. It wasn’t dirty or varnished to begin with when I bought it.

Anyone have words of wisdom other than buy a new carb? THANK YOU!

 

[J.S.@SMS]

Have you done any performance mods like and air filter, an open header, or head porting? These can cause an engine to run lean which would cause it to only run with the choke on. Or it could be a bad spark plug not igniting all of the fuel. Or one of the mixture screws isnt adjusted properly.

 

[o2jmpr]

She’s a completely stock engine. Spark seems good and I’m gapped properly. There is only 1 mixture screw on it. Thank you for the reply.

 

[Texan]

How is the gas tank? The fuel pick up tube screen could be getting clogged. Also, the carb to tank gasket is usually a source of an air leak.

 

[itsid]

Tank is indeed often a cause for insufficient fuel delivery..
check mating surfaces to be flat, threads in good working conditione etc.

And while you have the carb off the tank, make sure the pick up tubes are in correctly,

the pulsa jets have a combined idle and main jet.. and if that's set up correctly,
all you can do to stabilize the idle is to adjust the butterfly low end screw to open up a hair further.

And yes, the governor is supposed to fix minimal issues for you like that,
it not only limits the rpm it also raises the rpm if it feels it has to
(that's what you will have to do with the low speed screw on the butterfly now)

'sid

PS please post pics so we can identify the carb model and maybe find the specific common issues

 

[o2jmpr]

The carb to tank has a new gasket. Tubes are open. It will idle down ok, but only at that 3/4 choke sweet spot. I’ll get you pics but it will be a day or two. I’m frustrated and need to step away from it for a bit. Thanks!

 

[itsid]

In the meantime.. let me quote you the carb adjustment procedure (as adviced by Briggs in their flathead manual)

• Initial Adjustment
  1. Turn needle valve clockwise until it makes light contact with the seat.
     DO NOT FORCE.
  2. The initial setting of needle valve is made by
     turning out (counterclockwise) 1-1/2 turn.
     Final adjustment is made with engine running.
  3. Install complete air cleaner assembly.
• Final Adjustment
  1. Start and run engine at half throttle for five minutes
     to bring engine up to operating temperature.
  2. Place governor speed control lever in “FAST” position.
  3. Turn needle valve in until engine misses (clockwise – lean mixture)
     then turn it out past smooth operation point
     until engine runs unevenly (counterclockwise – rich mixture).
  4. Turn needle valve to midpoint between rich and lean so engine runs smoothly.
• Final Adjustment, except Low Emissions Carburetors
  1. Place equipment control lever in “SLOW” position.
  2. Turn needle valve in until engine slows (clockwise – lean mixture).
  3. Turn needle valve out past smooth operating point
     until engine runs unevenly (rich mixture).
  4. Turn needle valve to midpoint between rich and lean
     so engine runs smoothly.
  5. Adjust idle RPM.
     Rotate throttle shaft counterclockwise and hold against idle stop while adjusting idle speed adjusting screw to obtain 1750 RPM.
  6. Hold throttle shaft in the idle position.
     Move speed control to fast position.
  7. Release throttle shaft.
     Engine should accelerate without hesitation or sputtering.
  8. If engine does not accelerate smoothly,
     carburetor should be readjusted, usually to a slightly richer mixture.
• Final Adjustment, Low Emissions Carburetors
  (with Type Numbers ending in A1 through A9 or E1 through E9)
  1. Start and run engine for five minutes
     to warm up engine before making final adjustments.
  2. Place speed control in slow position.
  3. Adjust idle RPM.
     Rotate throttle counterclockwise and hold against the idle stop
     while adjusting idle speed adjusting screw to obtain 1500 RPM.
     
     NOTE:Current production carburetors have a
     pilot jet. These can be identified by not
     having an idle mixture needle spring.
     
  4. Release throttle and bend governed idle bracket to obtain 1750 RPM

That should cover all the possible carbs for your engine.

But for sure it requires the carb to be clean and fully functional first
it's still possible that you have a single gummed up passageway
or a faulty pump (say the tiny spring is kinked and the valve therefor non functional)
hard to tell, but if we assume you did everything correctly and carefully,
it's down to setting it up correctly.. hence the procedure above

'sid

 

[o2jmpr]

Here’s the pics. They aren’t great but hopefully you can see what you need. Thank you itsid for the adjustment procedure. The choke is completely separate on this model and I have to be able to open it fully before proceeding with mixture and idle adjustments.

 

[itsid]

A std Pulsa Jet.. good!

Now, that's the whole point, ain't it.. you cannot open the choke completely if your idle rpms aren't set up..
and the mix needle isn't preset correctly..

But you can alternate back and forth..
set the mix a hair richer, release a bit of choke until the engine starts to lean out,
then richen the fuel back up with the needle..
and so on and so forth until the choke is completely disengaged
(and the white'ish amber cam rests neatly against the carb body [it's lower half]).

IN case you surely can't
-the needle is all the way out but you still have the choke engaged in order to have a smooth running engine-;
I'm afraid you will have to redo the carb cleaning once more
You still have the internal fuel line clogged somewhere...

'sid

 

[o2jmpr]

Got it ‘sid. You’ve saved me again. I already know it will not run unless choked with the mixture full rich. At least I know I’m not crazy. This is the biggest SOB carb I’ve ever seen in my life. It has been cleaned multiple times with over a full can of carb cleaner and wire picks. Maybe I’ll just dunk it full strength vinegar and leave it for a week next step. I tried to pinch out that Welch plug but she isn’t budging and I’ll break something if I try harder. We’ll see. Thanks for your brain power.

 

[itsid]

for the price of both new welch plugs and a jet you can have a new carb from amazon (~20 bucks)

Not sure about a week of vinegar, but two hours in boiling lemon juice could do what most commercial carb cleaners can't for some reason

But first let's try the least aggressive ..
disassemble the carb entirely, or at least as best as you can
jet needle, fuel pump and butterflies (throttle and choke) removed if you can w/o removing the welch plugs (can't recall if you need them to be removed in order to remove the butterflies if you do.. keep them installed)
And now.. Shop AIR!
A nice sharp jet of air, install a short length of rubber hose to the air nozzle to create
as good of a seal at all those pesky little passageways... then hit it.
multiple times

You shouldn't be able to ruin metal with such air stream, but rubber gaskets can rupture..
so again: remove as much as you can.
And blow in every little hole you can find, don't skip the larger holes..
pump air through that thing as hard as you can. (well as hard as you think is reasonable )

Don't forget the pickup tube, remove it and blast it seperately (inside out)

I'm not a fan of wire picks frankly.. mono filament fishing line is thinner, stronger and less likely to catch on internal edges.
So if you have access.. use such to poke each nasty little hole you find.

repeat with air on all holes you don't see the other end of the fishing line
sticking out at some other place.

And if that still doesn't end up being successfull..

I'm afraid the next step would be this IMHO
https://www.amazon.com/Briggs-Stratton-Carburetor-135207-135202/dp/B06XDQJ2YF

'sid

 

[o2jmpr]

It’s been hit with air in each crevice after every time I’ve pulled and sprayed it. It’s not the matter of buying a new carb. It’s become the principle of the thing. I will not let it beat me.

The lemon juice boil is neat. I haven’t heard of that one!

 

[mckutzy]

Could go the Bronda rout and not have to worry about being beat... Just it being "temporarly set aside"....

 

[itsid]

A nice blogentry about lemon juice cleaning:
http://draftcycleworks.blogspot.com/2010/05/lemon-juice-party-cleanin-green-and.html

I heard some people hang the part in the pot (wire and spoon and such)
so it doesn't touch the bottom of the pot
and the agitation from the boiling juice moves more crud in shorter time..

But no matter.. lemon juice rules

'sid

 

[landuse]

From the Helpful Links post in the FAQ:

How to clean a carburetor the right way (with lemon juice)
http://ezinearticles.com/?How-to-Clean-a-Motorcycle-Carburetor,-The-Right-Way&id=1460030
http://www.diygokarts.com/vb/showthread.php?t=11976

 

[Kentucky Boy]

Make sure the pickup tube is not cracked and that the plastic part is properly sealed to the metal pickup tube. I havnt seen anyone mention this possibility.