Engine Running Rich

[KOninjalody]

I have an AE71 2 door sedan that i just bought and it seems to be running rich. It has no muffler just straight pipe back from the cat. I was told that this could cause the engine to run a little rich, but could also be the timing. Could having no muffler be the main cause?

 

[Scott O'Kashan]

Too little backpressure in the exhaust system could cause a lean running condition.

What symptoms is the car displaying that make you think it's running rich?

What is an AE71?

 

[KOninjalody]

I can tell from the smell of the exhaust. Other than that it runs strong. AE71 is the model of Corolla, for example the AE86 is the 2 door hatch back. I'm thinking putting a muffler on would help alot, but im also going to rebuild the carb this week and adjust the timing, then go from there.

 

[Scott O'Kashan]

Why rebuild the carburetor? What's wrong with it?

A rich running condition can be determined by the appearance of the spark plug tips, (dark in color and smells like gas), and also the tailpipe, which will look dark and sooty on the inside, from black exhaust.

 

[KOninjalody]

Hmm that makes sense, I'm getting the black film in the tail pipe, but I just changed the spark plugs and they weren't all black and didn't smell like gas. I'm going to rebuild the carb mainly to increase performance and gas mileage. Its a stock carb and i think it will help a lot.

 

[Scott O'Kashan]

Sometimes it's best to let a sleeping dog lay. If there's noting wrong with the carburetor then there's no benefit in rebuilding it. A modern carburetor can be very complex and not easy to rebuild properly and you could actually end up with reduced performance, fuel economy and power.
A rich running condition will have black exhaust coming out the tailpipe and in many cases can be caused by an oxygen sensor that is plugged up with carbon and needs to be replaced.