# Briggs and Stratton 450 Problems



## DMRider_10 (Oct 4, 2015)

Hi there i have a problem with my BS 450 mower. 

It started to foul the plug worse and worse until the point where it would no longer start (despite me cleaning the plug in between runs)

Ive since stripped the fuel tank and carb off the mower, 
cleaned everything out, 
the diaphragm is intact,
the plug has been cleaned, 
fresh fuel put in, 
oil drained and refilled,
primed and pulled the chord circa 10 times with the plug out.

Initially after doing all this the mower started instantly and ran for approx 2 mins during which it didn't seem smokey etc. however it then spluttered and cut out and sure enough the plug was blackened. 

Im not sure if the springs fitted to the throttle etc are correctly routed and/or doing their jobs (the mower was bought 2nd hand refurbished btw).Take a look:








































Also heres a video after re-cleaning the plug and starting for a second time:


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## MPR (Aug 28, 2010)

Is the carb staying at full choke?


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## DMRider_10 (Oct 4, 2015)

How would i be able to tell that?


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## Basementgeek (Feb 7, 2005)

Looks like you are using the original spark plug as it is painted black. Start by buying a new plug.

BG


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## AVB (Nov 28, 2014)

MPR there is no choke on this carburetor setup; just primer. 

As BG suggest I would change out the spark plug as it is probably failing under the compression load. Also I would change out that carburetor diaphragm and gasket as it is heavily worn. It not the cause of the rich burn just needs changing. Don't over tighten the carburetor mounting either as it will cause warp-age leading to more problems.

If changing the plug doesn't solve the problem a leak-down test is in order as you may have either a blown head gasket or a valve problem.

I don't think it going to be a carburetor problem as these carburetors are very reliable. The only things happen to them normally is a fail primer or the diaphragm which is primarily the fuel pump system.


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## DMRider_10 (Oct 4, 2015)

Thank you for the reply. I've ordered a plug and will get a diaphragm ordered too. 

The primer is working as it should: fuel can be seen squirting into the carb. 

Hopefully the plug will solve it....

Is there any documentation on setting up the throttle springs and the correct tension etc? As I'm sure mine don't "feel" right 

Thanks


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## MPR (Aug 28, 2010)

Another thing I can think of that might cause the engine to run too rich is an over-oiled air cleaner foam filter. Does the plug foul up with no filter?

It looks like the governor springs are hooked up correctly. See this thread:

Briggs and Stratton 450 series mower not stopping | Questions On Briggs & Stratton Engines | OutdoorKing Repair Forum


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## DMRider_10 (Oct 4, 2015)

Yeah I ran it with the filter off after id cleaned it all so its not that


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