Old Briggs carb question

Dave Sherman

Thread starter
Jan 3, 2006
Trying to make some sense of a carb from a 1970s (or so) Briggs engine, model 130232-0169. This is on an old Black and Decker generator I'm resurrecting. After fixing the ignition points and cleaning the carbon out of the cylinder head, I got it running, but having trouble with getting it running reliably. On the plus side, the generator head makes power.

Here's the part I'm trying to figure out. The carb has two pickup tubes. One long one that goes to the bottom of the gas tank and leads up to the needle valve. The other is a shorter one that fits into this smaller tank that's internal to the gas tank, and leads up to a diaphragm pump. I'm trying to figure out if that shorter tube is return or another pickup. I haven't opened the pump cover to see if it's pumping gas yet, but the trouble I'm having is the engine runs fine at idle, and I've got the needle valve dialed in. Once I open the throttle close to operating speed, it seems to be leaning out badly, I have to give it choke to keep it from stalling. Possibly related, but it refuses to start unless I pull the choke even when it's warmed up; almost like when the throttle is wide open it's getting no fuel.

Any ideas? Things seemed to going along smoothly until I started adjusting the governor, it just seems determined not to run smoothly over 3,300 RPM (55 Hz on the AC side).

Edit: Forgot to say, the carb has been cleaned up, has new gaskets, and a new diaphragm/flapper valve for the pump.
The small internal tank works as a carb bowl. The fuel pump picks up fuel from the bottom of the tank through the long tube, and dumps it into the bowl area. Once that is full, the excess continually overflows back into the main part of the tank. The engine uses fuel out of the bowl area through the short tube. Thus the jets see a constant level of fuel in the bowl regardless of the level in the tank.

The fuel pump is based on a diaphragm on the side of the carb. Pulsating pressure in the intake moves the diaphragm, which also incorporates two flapper valves. There is a spring under the vacuum side of the diaphragm to push it back out.

The main fuel jet is in the short tube. In later models there is a screen sock on the bottom of that tube which can be carefully removed to clean the jet.
Sounds like the main jet orifice tube is partly clogged. Wear safety goggles and use carb cleaner to blow thur all holes, tubes etc. It doesn't take much on those small carbs to mess up.
Ah, got it now, the long one goes to the pump and the sub tank is the equivalent of a float bowl. Guess I'll see if I can get to the main jet without having to take it off again. This one gets an F in serviceability, the tank and carb have to come off together, the lower bolt on the intake is hard to get to, and you've got the governor linkage, springs, and intake gaskets to contend with as you put it back together.
Yeah they take some twisting and turning to get everything apart. If you are lucky the lower bolt on the carb has a slot in it so you can use a screwdriver. Most likely it has an adjustable jet. Take the jet clear out and blow carb cleaner in the hole to try to unplug the passage. I don’t remember where the idle circuit is in them.
I believe like most engines in order to produce the rated HP and output, need to run at a certain RPM. You should have a tach that can measure what the max rpm's it's running at. Any adjustments that need to be made, should be done that way. Otherwise your just guessing.If it's been sitting for a long time, I would disassemble it and do a ultra sonic cleaning. The small passage ways might never get cleaned with just using a spray can. It's easy to tell if it is cleaned properly by the way it runs after the spray can cleaning. Sure it's easy, but doesn't always work.,,
I have an old Montgomery Ward generator that my Dad had. I had to run it for 2 weeks when we had an ice Storm in 2009. Used it at both of our houses and at a friends house to keep freezers and fridges cold. Near the end of that time it started exhibiting those same symptoms. It would run at idle well but then stumble especially when it warmed up. I ran a compression test on it when it was hot and it had maybe 30PSI. What I found to repair it was that it was unhappy with unleaded fuel and the exhaust valve was not closing when it got hot. So the repair was to adjust the exhaust valve clearance which meant removing it and shortening the stem to get it back to .006 clearance. It should have a Stellite valve installed to take the no-lead but since i know what the problem is I just shortened it. I am not sure you can buy a new style valve for that old 5HP motor. Short answer is to check the compression.
On this engine it is much easier to work on the carburetor with the tank and carb assembly removed from the engine, and it is easy to remove from the engine. Either you have a restriction in the main jet (likely hardened varnish) or you have the mixture screw (needle valve) set too lean. The engine is supposed to run at 3600 RPMs continuously, there is no idle use or setting, and no dedicated idle mixture screw, the mixture screw adjusts for all RPMs. Some of B&S's carburetors didn't have an idle circuit because the engine's use (generators) didn't call for it, I would have to see the carburetor to tell if it has one. On this type of carb design the needle valve's seat also acts as the main jet.
Thanks all. This generator is a little unusual, it has a fuel-saver that pulls the linkage to idle when there's no load. I don't know if the circuitry for it works yet, but there's a solenoid that pulls on the governor arm so it can idle. I have the switch for it turned off for now. I tried adjusting the mixture when it was at operating speed, but I couldn't get it to run smoothly.

Looks like I can take the needle valve and seat out to get to the main jets without having to remove it all again and at least take a look in there. Good call on the valves and compression, I have not checked the compression yet. It did seem to run reasonably well for a few minutes until it warmed up, then this rough running at speed got more pronounced.
Woohoo! I'm thinking maybe the high speed jet had some gunk in it, and maybe there was some stray carb cleaner in places. Gave a shot of carb cleaner into the jets and let it sit for a few days. Today, fired it up and while it was hunting and misfiring initially, started tweaking the needle valve and the governor adjustment and got it up to 3600 RPM. After a period of misfiring, it eventually settled down and it's running smoothly now. Loaded it up with some halogen lights, and it handled it with no trouble. Not too shabby for a secondhand generator that was sold as parts. New air filter, new spark plug, cleaned up the ignition points to get the spark working again, and lots of carb cleaner, but it runs and makes power!
Congrats on solving the carb problems. At this point the only help I can offer is one way to set the rpm on a 60 Hz generator is to plug in an old corded electric clock and time it against a digital watch. One minute second hand to 60 seconds digital.