Briggs engine

[dogdayz]

I have an OLD Roper yard tractor with a snowblower attachment that I use in the winter. It's probably 30+ years old but still works. The problem is it only runs with the choke almost fully closed (summer or winter). Even when it warms up the engine dies if I open the choke. I have tried tweaking the carb and it doesn't help. This summer I bought a whole new carb but it still needs to be choked to run.

Any ideas?

(There is good fuel flow, the air filter and fuel filter are clean)
The engine is a 16hp Briggs twin cyl.

[Terryl]

Does it have a foam type air filter??

[dogdayz]

It has a pleated filter that is covered with a foam pre-filter. They are both clean but even with the filters removed it still has to be choked to keep running.

[Terryl]

Sounds like it's getting too much air, the air/fuel mix is not right, it might be getting too much air and the engine is starving for fuel. (your not doing this with the air filter off are you?)

To test this go get some carb cleaner and spray it directly into the carb (small squirts only) when you open the choke, (after you get it started) if it runs then you may need to adjust the needle valve(s) on the new carb.

Carefully screw the needle valve in all the way till it stops (gently) then back it out 1-1/2 turns to start. With the air filters on.

And one last question...Did you torque the carb mounting bolts? if not then you may have an air leak around the carb gasket, usually 12 to 20 foot pounds, you can look this up on the OEM site for that engine.

[Terryl]

One other possible problem is a bad fuel pump or leaky fuel pump to valve cover gasket, the fuel pump runs off a vacuum supplied through one of the valve covers, if this gasket has a bad seal it wont supply fuel to the carb as needed.

I had this problem with my yard tractor, has a 22 HP brigs on it, a little bit of non-hardening form-a-gasket fixed it right up.

[dogdayz]

I guess I'll try playing around with the needle valve again.

[Terryl]

Do this with the air filters on, (engine off) and again start with it all the way in then back it out 1-1/2 turns, then try and start it, adjustments are done in small increments, try adjusting it out slowly, if that does not work then go the other way..

Another question...Did you get an OEM carb or a clone?

[The Noof]

My guess is the original carb had dirt in the main metering system, and your replacement carb is not jetted correctly for your application.Does it have adjustable low & high speed mixture adjustments, or only low speed?If it has only 1 mixture screw, that's for low speed only.

[runamok]

If the engine will run but not off choke then main fuel jet is blocked.Just needs a good cleaning.

[Terryl]

It's a new carb as he mentioned.

And if he didn't get an OEM carb then the new carb has a jetting problem, I would pull the jets out of the old carb and clean them, but be carfull as to what you clean then with, a correct diameter carb jet cleaning tool should be used, a paper clip or that may fit is not a good idea.

I find that some cases like this are due to spiders getting into the small spaces in the carb and trying to build a nest.

Also I always try to buy OEM carbs for my small engines, (if I can find them) the clone stuff does not always work right, and it that case swapping out the OEM jets may fix a problem with a clone carb.

[dogdayz]

It's a new carb so shouldn't need cleaning.

It's a B&S clone carb.

Can't see any mixture adjustments, but there is a big hex screw on the side, maybe a mixture adjustment under that. I'll have to take a look.

(I junked the old carb)

[runamok]

I was referring to old carburetor

[dogdayz]

hxxps://www.amazon.ca/Carburetor-693480-Replaces-Briggs-Stratton/dp/B07TQ5W9YG/ref=cm_cr_arp_d_pl_foot_top?ie=UTF8

[The Noof]

hxxps://www.amazon.ca/Carburetor-693480-Replaces-Briggs-Stratton/dp/B07TQ5W9YG/ref=cm_cr_arp_d_pl_foot_top?ie=UTF8

There's probably a mixture adjustment under the hex nut.Turn it counter clockwise to richen the mixture

[dogdayz]

There's probably a mixture adjustment under the hex nut.Turn it counter clockwise to richen the mixture

I'll try to check it tomorrow. Thanks.

[Terryl]

I can see why you went with the clone carb, the OEM carb is $233, too bad you junked the old one, as the jets can be interchanged.

[dogdayz]

There's probably a mixture adjustment under the hex nut.Turn it counter clockwise to richen the mixture

Well Noof, I took off that hex nut and all it did was drain the fuel out of the carb.......

I don't see any adjustments on the carb except for the idle screw.

[The Noof]

Well Noof, I took off that hex nut and all it did was drain the fuel out of the carb.......

I don't see any adjustments on the carb except for the idle screw.

Then it's fixed jet.Normally the jetting is close enough to work out of the box.Make sure that the engine doesn't have "false air" from an a vacuum like at the intake manifold to cylinder head junction or something like that.It is also entirely possible that your Chinese carb solution is defective, as usual.

[dogdayz]

I just noticed a jet under that nut that is removable with an allen key but there is no adjustments.

It's just weird that I put this carb on to replace the original but they both cause the same problem ie choke has to be closed.

I have new gaskets on and firmly tightened.

[Terryl]

Well the fact that the choke needs to be closed to even run could mean that the idle jet needs to be adjusted or the main jet is too small, the old carb's main jet was possible gummed up.

Closing the choke restricts the air flow, giving the engine a richer mix of fuel to air so it has a better chance of starting.

What is the model number of your engine, I want to look at a diagram of the carb, or can you post some photos of the carb?

[dogdayz]

I posted above in #13 the carb that I bought from amazon.

[Terryl]

I was looking for the parts breakdown, I found this on Eparts.


https://www.ereplacementparts.com/briggs-and-stratton-422447405901-engine-parts-c-16758_17347_22087_202378.html (view carb #4)

I would order a new main jet (#117) and a pilot jet if you want(#147) and replace the ones in the clone carb, (I would do the main jet first) the diagram shows where they are located.

All this because I think the main jet in that clone carb is too small for that motor, it's not supplying enough fuel to run the engine right when the choke is off.

[dogdayz]

I don't mind changing the jets but considering I had the same problem with the original carb I can't help but think there is another problem I'm missing.
I checked the crankcase breather and it looks ok. I'm just wondering if there may be an air leak where the intake manifold attaches to the cylinders like Noof was saying. I have never had the manifold off but the bolts are tight. I don't know if the gaskets may have deteriorated over the years. Unfortunately it's a big job to get at the manifold. I should have done this work when the weather was warmer. LOL

[Terryl]

One test to see if you have a possible air leak is to get the engine running (with the choke on) and using some carb cleaner spray around the manifold in question, if the engine changes speed then you know you have an air leak somewhere on that manifold.

Be careful around the exhaust manifold and muffler as the carb cleaner is flammable..

I sometime use WD-40.

[Terryl]

Well after looking at the carb diagram it looks like the pilot jet (#147 on the diagram) is inside the main body of the carb, this means you would have to disassemble the carb to get to it.

But the main jet (#117) is accessible by removing the hex bolt capping it off, I would try that one first, hopefully the new jet is the correct size.

[dogdayz]

If I get time I'll try the spray around the manifold tomorrow and see what happens. :thumbsup: