Bought a used mower - hoping to get it running right.


Old 05-07-13, 09:38 AM
Thread Starter
Join Date: May 2013
Posts: 1
Bought a used mower - hoping to get it running right.

Bought a Murray with a 4.5Q Briggs and Stratton motor on it. Non propelled. I am at work at the moment and can supply all model / SN when I get home.

The Problem:
Previous owner mentioned the lawn mower had been turned over, upside-down. Mower will start, however bogs down, chugs, rough idle, smokes little to none... occasionally shutting off completely. Spark plug quickly becomes dry fouled with good bit of dark black carbon build up.

What I've Done:
Drained oil
Drained gas
Cleaned air filter
Carb cleaner on carb, gas tank, spark plug port
New oil
New gas
New spark plug

Unfortunately for me at about midnight last night.. cranked it up and got very similar results. At first the primer didn't even want to prime, then it started eventually. Spark plug quickly got the dark black build up... and mower just still idled very rough. I have pictures, and video and like I said will have SN's when I get home. Next I was thinking of replacing diaphragm... but after that it is kind of beyond my scope of what's next. Hoping to learn some new tricks here. Thanks in advance for anyone who takes the time to help me..... I am sure I am breaking some rules, and especially by not having the exact numbers, but hoping to have something to do tonight to get it running maybe, and if I need to buy some parts.... before it gets too late.
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Old 05-07-13, 09:59 AM
Join Date: Jan 2012
Location: Canada
Posts: 2,541
Welcome to the forum
Sounds like the carb may need a bit more attention. It may be as simple as a tuning, but I'd probably pull it appart, fully clean it and assemble it again.
I'm trying to remember where I started the air/fuel mixture adjustment at. I want to say 1 and 1/4 turns from closed, but I can't remember.
Old 05-07-13, 10:15 AM
Join Date: Jan 2013
Location: U.S.A.
Posts: 1,474
My thoughts exactly; it sounds like you are there except for some minor carburetor maintenance and adjustment. I usually start by gently, always gently so as to not damage the needle or seat, running the air/fuel screw in, counting turns as I go, so that I can get it back to where it was if necessary, then back it out about 1-1/2 turns, but yes, 1-1/4 works. Once you are there, adjust each way to where you get rough idle, then adjust to the halfway point.
Old 05-07-13, 11:15 AM
Join Date: Oct 2011
Location: USA
Posts: 433
If it has a diaphragm, replace it and be done with it, clean carburetor really good. Good luck
Old 05-07-13, 11:18 AM
Join Date: Oct 2011
Location: USA
Posts: 433
aka pedro,,sounds like he has the diaphragm style carb, as he did say he took the diaphragm off, and there are NO adjustments on that carburetor.
Old 05-07-13, 12:23 PM
Join Date: Jun 2006
Location: St. Louis
Posts: 2,365
If you have the diaphragm type carb here is the instructions.

You need to install a new diaphram kit, it is Briggs part # 795083 or old # 495770 also Lowe's has a kit #5083 which has the same parts.
Here we go:

Remove air cleaner, there are 2 bolts that hold things together, one on the front of the tank 3/8" and one into the block 1/2", remove these bolts, now "slowly" slide the carb/tank off the intake tube and breather tube, now tilt the tank in to release the throttle linkage and waalaa the carb/tank is removed. Check the intake tube to see if the O ring seal and plastic retainer are still on the intake tube, if so remove them and re-install them into the carb. Remove the 5 screws from the carb/tank remove carb(don't loose the spring) now spray all holes, cracks and crevases in both the carb and tank surface with brake parts cleaner, remove the main screen(looks like a thimble), now with a small screwdriver pry out the main jet(carefully) and clean it, check the O ring on the main jet for damage, if it is damaged it must be replaced, reinstall the jet, it can be difficult some times to get it to snap back in place(I use the rounded end of a screwdriver handle). Remove and clean the fuel pickup stem(not necessary if the fuel tank was clean). Clean any junk/rust from the tank. Install the diaphram on the tank then the gasket(no goo or sealer) now carefully replace the carb(the spring will try to misalign the diaphram), tighten all screws a little at a time so as not to crimp the diaphram until they are all tight. Install the carb/tank in reverse order and you are done. If I missed something one of the real mechanics will correct me. Have a good one. Geo
Old 05-07-13, 03:39 PM
Join Date: Jan 2013
Location: U.S.A.
Posts: 1,474
A carburetor with no adjustments? Whodathunk? Next thing you know, they'll have a man on the moon!

Naw, just kidding Mowerdude. Learn something new every day. In addition to my own mower, rototiller, snowblower, chainsaws and such, I end up doing a fair amount of maintenance and repairs on some of the neighbors equipment, and don't recall seeing one of those. Interesting. Thank you.
Old 05-07-13, 05:18 PM
Join Date: Oct 2011
Location: USA
Posts: 433
Your welcome,,A man on the moon?? When?? Just cutten up with ya. Most of the 3.5 and 4 hp Briggs engines have that style of carburetor on it and that diaphragm under the carb does not hold up to the wounderful 10% stuff. Have a Great day.

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