Briggs 3.5hp won't start with any filter.

[DemoFly]

Any filter, clean no oil, oiled, it doesn't matter.

Once it starts and runs you can put the filter back on and it runs great. Starts back up right away.

I am not a briggs guy. No idea what is going on.

 

[ripcord]

Does it seem to run rich? Leak? Maybe the air filter interferes with the choke operation?

 

[Greasymechtech]

Not enough vacuum to pull air/fuel thru the carb with filter on. So, change oil/filter with something thicker than whatever you're using. Or, carb oring/seal is not snug enough or leaking.

Run a can of this fuel thru it, or rebuild the carb. If no gravity filter, install one
https://www.lowes.com/pd/Briggs-Stratton-4-Cycle-In-Line-Fuel-Filter/1205339
https://www.homedepot.com/p/Briggs-Stratton-Fuel-Filter-5098K/205448640
https://www.homedepot.com/p/VP-Fix-It-Fuel-with-Mechanic-In-A-Bottle-6635/206585492
https://www.tractorsupply.com/tsc/p...-vp-small-engine-fuels-fix-it-fuel-32-oz-6635
https://www.walmart.com/ip/VP-Racing-Fuels-Fix-It-Fuel-Quart-Motor-Treatment-6635/176614090

Try starting it with the gas cap loose and then tighten it. Both of my briggs developed issues and start better with the cap loosened 1st. Snug it after its running. I've got defective caps that starve the engine.

 

[Warstud]

Sounds like low compression .

 

[blufeb95]

Not enough vacuum to pull air/fuel thru the carb with filter on. So, change oil/filter with something thicker than whatever you're using. Or, carb oring/seal is not snug enough or leaking.

Run a can of this fuel thru it, or rebuild the carb. If no gravity filter, install one
https://www.lowes.com/pd/Briggs-Stratton-4-Cycle-In-Line-Fuel-Filter/1205339
https://www.homedepot.com/p/Briggs-Stratton-Fuel-Filter-5098K/205448640
https://www.homedepot.com/p/VP-Fix-It-Fuel-with-Mechanic-In-A-Bottle-6635/206585492
https://www.tractorsupply.com/tsc/p...-vp-small-engine-fuels-fix-it-fuel-32-oz-6635
https://www.walmart.com/ip/VP-Racing-Fuels-Fix-It-Fuel-Quart-Motor-Treatment-6635/176614090

Try starting it with the gas cap loose and then tighten it. Both of my briggs developed issues and start better with the cap loosened 1st. Snug it after its running. I've got defective caps that starve the engine.

3.5hp briggs use the carbs that mount on top of the fuel tank.

 

[DemoFly]

Not enough vacuum to pull air/fuel thru the carb with filter on. So, change oil/filter with something thicker than whatever you're using. Or, carb oring/seal is not snug enough or leaking.

Took the carb off and I'll be ****ed.

These tank mounted diaphragm carbs seal with an o-ring to the intake. O-ring cracked in two pieces.

 

[skyactiv]

Is it a vertical or horizontal shaft engine?

 

[fozzdesy2001]

Took the carb off and I'll be ****ed.

These tank mounted diaphragm carbs seal with an o-ring to the intake. O-ring cracked in two pieces.

Good now you can source an O-Ring and be ready to mow. E10 gas probably killed the o ring

 

[blufeb95]

Good now you can source an O-Ring and be ready to mow. E10 gas probably killed the o ring

Or the fact that it's a 3.5hp briggs and they're all ancient may have something to do with it.

 

[fozzdesy2001]

It will cut grass like they have done for decades. The old 3.5 flat heads are "The" original Briggs mower engine, been cursed at and cherished since the 1950s

 

[FowVay]

I was given a small 20" Murray mower that was equipped with a Briggs vertical shaft 10 cubic inch engine (Model 10A902-2291-B1). The tank was corroded through, had no air filter, wouldn't run, etc. I figured I'd play with it and then disassemble it and haul it to the metal recycler if I couldn't get it running.

I bought a cheapy Chinese fuel tank that came with a carburetor along with a new foam air filter from Amazon for $15 and I went to work. I installed the tank and carburetor and it started but ran horribly. I took that Chinese carburetor off and put the original Briggs carb back on and it just didn't want to start. I'd use starting fluid or just pour fuel down the throat and it would fire and run but it just wouldn't prime using the primer bulb.

I noticed that when it would run the top of the fuel tank would get wet with fuel. I replaced the carb-to-tank gasket along with making a new fuel cap gasket but it still misted fuel when it was running. It turns out that the tiny metal ball plug that seals a passage in the carburetor was leaking and this prevented the carb from priming when using the primer bulb. This also likely caused mixture ratio issues.

I cleaned the tiny ball, put a dab of my wife's finger nail polish on the hole, and now it primes in three pumps of the bulb and fires on the first pull.

My apologies for the long story but I was proud of my accomplishment. I now have a nice little trimmer mower... for the cost of some Chinese parts ($20).