3.5HP Startup Concern

I have a Briggs and Stratton 3.5HP Model 929902 Type 3176-01. I picked it up at a yard sale and have been cleaning it up. The engine manufacture date is 8/24/1982 so she has a few years.

I have it running fairly well but have noticed that it does not start as smoothly as I would like. On a cold start it will fire up, get up to RPM and then die (I suspect as the automatic choke opens up.) On the second pull it will fire up again, get up to full RPM and run very well and restart with no problems.

The carb sits on top of the tank with the jets drawing directly from the tank instead of a bowl making the carb draw the gas up a slightly longer path. I have also noticed that later versions of this carburetor style have a bulb primer.

Is this startup behavior normal or will the carb benefit from a full cleaning? Given its age and condition I will likely need a carb kit with new gaskets and diaphragm so don’t want to tear it down for cleaning if there will be no improvement in startup performance.

Advice will be greatly appreciated.

that engine number doesn't come up when I search however 092902-3176-01 does come up. Check the number again.

That said, I have an engine from that period where the carb sits on the tank, and there is a diaphragm that acts as as a fuel pump as part of the carb kit. Make sure that if your model has that diaphragm you replace it. The photo below is for the diaphragm on a 092902-3176-01. The instructions come with some of the kits. Maybe someone can post them if they have a set lying around. The little flaps act as inlet and outlet valves on the fuel pump.

depends. If the mower runs to your satisfaction leave it alone. If it gets to where it is hard to keep it running then rebuild it. Quality of fuel, age of fuel, adjustments can all affect how an engine runs.

Generally with the diaphragm carbs that I've had when they go bad it runs real rich, smokes black, real hard on the aluminum cylinder walls too. If it runs decent after it does start and run I'd leave it alone. And if you do tear into it don't tighten the carb-to-tank screws too tight, can warp the mating surfaces and won't run right for long if at all. Not sure (?) but that engine might have a points ignition? Can have some effect on starting if they are going bad.

You might can just clean the carb if you can save the diaphram without tearing it and the gasket....... Your tank has a well in it that is a reservoir that the main jet tube fits into... That might have a drop or 2 of water in it and some crud....

The long stem you mentioned that goes in the tank is a fuel pickup tube that supplies the gas that goes into the reservoir.....

Kit number is Briggs and Stratton 494623 and just the diaphram is 391681......... Hope this helps you...


Let us know how it goes Mon Ami ~!~!

BTW Tom 3 is correct on what he said on the richness causing issues in the future..........