Briggs and straton engine wont rev.

It idles fine but when the throttle is lifted it just idles , no revs at all.
Could bad/old fuel cause this? its a 4.50 motor.

 

Yes at first, then clean air filter I suspect this dry weather has bunged it up,

 

Is there a choke, and does it raise/lower revs with that? Maybe the throttle cable has come loose?

 

Cheers Lad, unfortunately I know nothing about this mower but I do know its been sat in someone's garage.
I got it home and started it and it would not rev. I checked the oil and it was way over full so I emptied some out to the correct level, took out the plug which was badly sooted up and cleaned it but still no revs.
I will try new petrol in there and see what happens.

 

No choke, just a primer.
It starts really well , just wont rev.

 

This is it , its a 9T502.

 

Built in May 2002 I restore and sell Lawn mowers.

Still think it's the air cleaner.

[/QUOTE]

 

I tried it with the air box/filter off and it was still the same.
Under the air box is what looks to be the throttle butterfly assembly, there are two springs. When the mower runs this lever flicks back and forth as the engine hunts a little, is this a normal set up?
When I move the lever by hand it revs normally and smoothly.

 

It sounds like something is disconnected to me?

 

Ive just had a thought , does this mower have a hand throttle and a cut off? I think the hand throttle is missing.

 

I would imagine so. do you know what the bracket at the left of the photo (right side on the mower) is for?

 

Ive just had a google , what i thought was the throttle was just a cut off , it has no throttle.
Now the question is why wont it reach full revs?

 

There should be a throttle lever somewhere, have you a photo of the mower showing it fully?

EDIT> There's a manual here for that series engine I believe. Maybe you could compare it to your mower, so you can see if there's parts missing?

http://bsintek.basco.com/BriggsDocumentDisplay/default.aspx?filename=18kvuIXKnfBhU7y

 

This is the kind of mower it is.

Yard Machines Push Mower — 148cc Briggs & Stratton Engine, 20in.W Deck, Model# 11a-020b000 | Walk-Behind Mowers | Northern Tool + Equipment

Apparently they run at full throttle.

 

Ah, you'll have to give it a whirl then. On mine there is a choke and throttle, which varies the rev speed.