3.5 hp Briggs and Stratton hard to start when cold

[Popinski]

I have an old Briggs and Stratton 3.5 classic engine. When the engine is dead cold, the primer has trouble sucking in fuel. The primer itself is in good condition. After about 10 pumps on the primer, I can finally feel fuel coming in and my mower is ready to start. When the engine starts, it hesitates on idle and I have to push the primer to force fuel into the engine or else it'll stall. After doing this for about 3 minutes, the last 2 minutes where it is forcing fuel itself, the engine is weak. After about 5 minutes, or when the engine is warmed up, it goes to full power and back to normal; starting is good and strong with one pull.

Note: All maintenance has been done and I put carb cleaner mixed with gas every year.

 

[demarpaint]

Are you sure the primer is good, and the little hose that goes to it? I had one that was pumping well but the hose had a small tear in it, and was leaking. It could appear to look good and not be delivering enough fuel when you pump it. The carb float could be out of adjustment as well. Those are two areas I'd be looking at. Is the choke working properly?

 

[Panzerman]

I think its the hose going to the primer, just one pin hole lets it suck air. I had a hard starting lawnmower once, I just gave it a snort of ether and it fired right up first pull. Not very healthy, but those Briggs are indestructable and the motor still outlived the deck.

 

[Popinski]

If it's the primer hose then why does it act normal when the engine heats up? I checked for gas leaks, there are none.

 

[yeehaw1960]

Ain't no hose. Pull the tank, remove the carb and blow it out. Empty every drop from the tank. Replace diaphram if necessary. Will be a whole new engine. OLD POST FOLLOWS.

Take the air filter off the carb. Take a digital picture from top view to remember what's what. Take the two bolts out that hold the carb/tank assembly on the engine. One in center close to engine ½ or 3/8 inch, one on spark plug (right) end, 7/16 or 3/8 inch, as you look at assembly. As you pull the assembly off, you’ll have to finagle the linkage off the top of carb. Remember how the rod and spring(s) look (take digital picture) for reinstallation.

Take the 5 screws out that hold the carb to tank. Pull apart. Push primer bulb to get all gas out of carb. Blow it out with air if you have it, but remember to keep track of the spring on bottom of carb. If you blow compressed air into the little hole at the base of the long pick up tube, you may pop your primer bulb. Dump as much gas out of tank as possible. Blow air into reservoir on top tank or wipe out with rag as good as you can. Go to repair shop (with diaphragm/gasket) and get a new one. Reassemble and mow away! The thin diaphragm goes on the tank, then the gasket, then the carb. Have fun!