Mend > Lawn Mowers

Mend Poulan Pro PR1842ST Engine Riding Mower

18 h.p Briggs & Stratton engine backfiring through the carburator ?

I bought this riding mower at a garage sale. The intake valve had broken and knocked a hole in the piston. I've replaced all of the related components that were damaged and re-assembled the engine. There were no visible signs of damage to the head or the cylinder bore. The problem that I'm having now is that when I crank the engine grey smoke and some gas is back firing out of the carb. I did a compression test and the reading was "90". I have spark from the magneto and it is evident that I am getting gas.
The Lawnmower is a:
Poulan Pro 18h.p. #PR1842ST
The numbers on the valve cover are:
Model: 31H777
Type: 0202 E1
Code: 020211 ZA
Is there anyone out there that might know what I need to do to fix and/or troubleshoot this problem? Any help at all would be greatly appreciated. In dire need in Atlanta help !!!!!!

M. Adams
May 2008

Poulan Pro Poulan Pro PR1842ST Garden Tools, Lawn Mowers Engine Riding Mower

I would guess that the fly key is damaged it doesn't take much to damage the key

tom
September 2014

How do i know which is the intake rod and the exhaust push rod for a briggs model 31h777

dwight perkins
April 2011

check for blown head gasket, mine was smoking alot too.
5 dollar part and back in bussiness

bob
September 2009

sell the peice of sh*t I h*te B&S nothing but trouble buy a Kohler

steve
September 2008

I had a similar problem and found valves were out of adjustment; too much clearance, which caused compression release not to work, which in turn caused head gasket to blow from too much compression (it was only slightly damaged between cylinder and push rod area). Hope this gives you some clues to look at. This applies to overhead valve engines only, as far as I know.

W. Bush
September 2008

Replace or remove the debri from muffler, maybe muffler is clogged up causing engine to back fire or get hot.

Danny Ford
August 2008

timing is off

bg
May 2008

Beleive it or not it's SUPPOSED to do that! It's part of Briggs & Stratton's compression release mechanism - it pops the INLET (as opposed to the exhaust, as on smaller engines) valve open halfway up the compression stroke. This has a negligable effect at running speed, but at cranking speed it causes 'spit-back'.

Whatever problems you're having with trying to start it, this isn't one of them. If you're getting spark and gas, the only thing left is the ignition timing. Check the flywheel key - if the engine stopped dead due to the dropped valve, it may have sheared the key.

phil_saunders@bigfoot.com

Phil Saunders
May 2008