I have a 4 year old MTD 22 inch mower with a Briggs and Stratton 90000 Series 3.75 hp engine. I've had a little difficulty with starting over the years but no other problems. This week the mower came down with a flooding problem. It starts and runs OK for around 5 seconds then bogs down with too much gas. It doesn't stall, just doesn't have much power. If I restrict the flow of gas by tipping the mower up to a 35 - 45 degree angle it has full power again as long as the gas tank is only partially full. There are no carburetor adjustments on this engine.
Any thought or suggestions would be appreciated. TIA.
Mike

 

Polydorus,

Remove the breather from the carb and verfy that the choke plate is opening completely while running and once warm. If it is you will need to remove the carb and give it a good cleaning with carb cleaner.

God Bless,
Dave237

 

Have you cleaned or replaced the air filter?

 

The choke is turning and I checked inside with a paper clip to make sure the plate was also. BTW this is the type with no manual control over choke or throttle.
Thanks for the suggestion,
Mike

 

Cleaned it about a week ago. Tried running it with the air filter completely off also. No improvement.
Thanks,
Mike

 

Sounds to me like you probably need to replace the diaphragm between the tank and carb.

 

Looks like I can give the carburetor a good cleaning at the same time. What's the diaphragm made of and can I make one given the right materials?
TIA Mike

 

Polydorus,

These diaphragms are made from a synthetic type of plastic that's rubber like but is not harmed by gas and many thousands of pulsing cylces. I suggest buying an OEM replacement from Briggs. After market parts just do not have the same fit/tol.

God Bless,
Dave237

 

Got the carb off. The diaphragm appears to be thin piece of black neoprene attached to a thicker piece of gasket material. There are no cracks or breaks in the neoprene but a half inch of one side was not sealed down to the gasket material. This was right next to the spring that I believe creates the pulse, so that was most likely the problem.
You are right Dave, I would be much easier to buy a replacement. I checked Briggs & Stratton's website and they show the gasket as two pieces, not one as I expected. Couldn't figure out their part numbering system, however. Not especially user friendly site IMHO.
Mike

 

Does the carburetor have a primer on it?

 

Yes it has a primer bulb.

 

I agree that the diaphragm should be replaced. I'd bet the area that wasn't sealing is the area just under the intake tube where the carb meets the engine intake. The carbs warp a bit, and the diaphragm eventually pulls out from under the thin area of contact in that spot.

 

This is on the engine side by the intake manifold. But since the gasket is only about a inch and a half square it's still close to the intake. I checked both the carb and its' mounting plate on the gas tank with a straight edge and they seem to be level. Of course it's hard to say what happens when you get them up to operating temperature.
Thanks for the input,
Mike

 

Polydorus,

It maybe too late but check the gas tank flatness with a straight edge and feeler gauge. If you can insert a .002 feeler between the tank and straight edge then it's questionable..????

Dave237,
God Bless

 

Thanks Dave,
I did check the top of the gas tank where the carb sits. With no projections its much easier to do that the carburetor. There were no gaps between the mounting plate and the straight edge.
Mike