Vintage 3.5hp Briggs and Stratton 148cc Engine won't go past idle

[volvofan94]

Hi All,

I'm working on restoring an older 3.5hp Briggs and Stratton engine with the pulsa jet carburetor which hasn't ran in 10+ years. I'm able to get the engine running, but it will only idle and not rev unless you manually flap the choke plate. I'm thinking it's not getting enough fuel pressure to run the engine at higher speeds.

I replaced the diaphragm between the carb and gas tank (non OEM model), cleaned the carburetor and gas tank very well, cleaned the crankcase ventilation system, and replaced the ignition coil. However no such luck getting the engine to run at higher speeds for mowing. It's used on a Snapper Hi-Vac lawn mower.

What other areas should I check?


Thank you!

 

[Bertrrr]

If the carb was sitting up that long - not sure you can clean it well enough also the soft goods are probably shot.
If it idles the engine evidently is in good shape so it's most likely fuel issues - don't think that model has a fuel pump only the pulse off the crankcase working the diaphram via a small hose that's probably dry rotten

 

[volvofan94]

Checked the rubber elbow going from the crankcase ventilation port to the choke of the carburetor and it appears to be in good condition. No cracks were found doing a quick soapy water test with the engine idling.

Did some more research and found the problem may be with the crankcase breather system which operates the auto choke system and diaphragm fuel pump. If the valve rattles it's good; if not, replace it. I cleaned the one on the engine then the engine ran better, but not great.

Hope the new OEM one fixes it. Will post back the results.


Thank you.

 

[Rivets]

What are the model, type and code numbers for the engine? Did you preload the diaphragm when installing? Did you install diaphragm and gasket in to correct order?

 

[volvofan94]

Model: 92502 (could be 92503?)
Type: 3136 01
Code: 8412110

I’ve been using 92502 3136 01 to find parts on Briggs and Stratton’s website.

How do you preload the diaphragm when installing?

By installing the gasket and diaphragm in the correct order, are you referring to the spring which sits in a recessed area of the carb above the diaphragm to control the fuel flow into the float chamber?

 

[Rivets]

This manual will help you understand what I’m talking about. https://www.wheelhorseforum.com/fil...&t=1&csrfKey=d6af3634f2935fa124ed1ca13797786e

 

[slomo]

Fuel tank MUST be spotless.

Probably have to remove all soft parts and boil the carb body. Cheap hot plate and a pot. Little pH neutral car wash soap. Blow out with carb spray and compressed air. Might take a couple cleanings to make her run right.

 

[Rivets]

Slomo, do you realize that this is a 39 year old engine? Boiling a plastic carb will ruin it.

 

[slomo]

Slomo, do you realize that this is a 39 year old engine? Boiling a plastic carb will ruin it.

Check that. Didn't realize it was plastic. Thanks for the correction. My bad.

How about 120F with a candy thermometer? Little heat to loosen up some varnish. Then blow out with carb spray.

 

[Rivets]

NO!