Briggs & Stratton mower engine races and drops like clockwork
 

Hello,

I have a base-level 3.5 HP Briggs & Stratton engine that's about 6
years old. It's a throttle-free design with a primer bulb. Lately,
after I get it started, it goes in to a rhythm of racing and dropping
off about every second. This started rather suddenly. The plug is
OK. I started to take it apart, because I didn't even know if mowers
had "points". I assume it's some kind of induction ignition system
based on the setup of the cutoff switch and the magnetic flywheel.
The carb looks like nothing more than a plastic throttle body, and I
don't see a float/bowl of any kind. I generally don't repair mowers,
obviously. Does anybody recognize that surging/dropping behavior?
Thank you!

Thanks,

JM

Briggs & Stratton mower engine races and drops like clockwork
 

SOunds like the diaphragm, which is between the plastic carb body and tank

Briggs & Stratton mower engine races and drops like clockwork
 

On Sat, 23 Feb 2008 17:19:41 -0800 (PST), JM_newsgroups
wrote:

Hello,

I have a base-level 3.5 HP Briggs & Stratton engine that's about 6
years old. It's a throttle-free design with a primer bulb. Lately,
after I get it started, it goes in to a rhythm of racing and dropping
off about every second. This started rather suddenly. The plug is
OK. I started to take it apart, because I didn't even know if mowers
had "points". I assume it's some kind of induction ignition system
based on the setup of the cutoff switch and the magnetic flywheel.
The carb looks like nothing more than a plastic throttle body, and I
don't see a float/bowl of any kind. I generally don't repair mowers,
obviously. Does anybody recognize that surging/dropping behavior?

The governor would be a candidate. I had that with a broken governor
spring.

G

Briggs & Stratton mower engine races and drops like clockwork
 

"JM_newsgroups" wrote in message
...
Hello,

I have a base-level 3.5 HP Briggs & Stratton engine that's about 6
years old. It's a throttle-free design with a primer bulb. Lately,
after I get it started, it goes in to a rhythm of racing and dropping
off about every second. This started rather suddenly. The plug is
OK. I started to take it apart, because I didn't even know if mowers
had "points". I assume it's some kind of induction ignition system
based on the setup of the cutoff switch and the magnetic flywheel.
The carb looks like nothing more than a plastic throttle body, and I
don't see a float/bowl of any kind. I generally don't repair mowers,
obviously. Does anybody recognize that surging/dropping behavior?
Thank you!

Or, just a mixture adjustment.

Briggs & Stratton mower engine races and drops like clockwork
 

On Feb 23, 7:19 pm, JM_newsgroups wrote:
Hello,

I have a base-level 3.5 HP Briggs & Stratton engine that's about 6
years old. It's a throttle-free design with a primer bulb. Lately,
after I get it started, it goes in to a rhythm of racing and dropping
off about every second. This started rather suddenly. The plug is
OK. I started to take it apart, because I didn't even know if mowers
had "points". I assume it's some kind of induction ignition system
based on the setup of the cutoff switch and the magnetic flywheel.
The carb looks like nothing more than a plastic throttle body, and I
don't see a float/bowl of any kind. I generally don't repair mowers,
obviously. Does anybody recognize that surging/dropping behavior?
Thank you!

Thanks,

JM

Try taking off the top rewind (pull-starter). You may have the classic
"critter nest" under it preventing the air vane from moving. (If I
remember that motor correctly)

pz

Briggs & Stratton mower engine races and drops like clockwork
 

On Feb 23, 7:19*pm, JM_newsgroups wrote:
Hello,

I have a base-level 3.5 HP Briggs & Stratton engine that's about 6
years old. *It's a throttle-free design with a primer bulb. *Lately,
after I get it started, it goes in to a rhythm of racing and dropping
off about every second. *This started rather suddenly. *The plug is
OK. *I started to take it apart, because I didn't even know if mowers
had "points". *I assume it's some kind of induction ignition system
based on the setup of the cutoff switch and the magnetic flywheel.
The carb looks like nothing more than a plastic throttle body, and I
don't see a float/bowl of any kind. *I generally don't repair mowers,
obviously. *Does anybody recognize that surging/dropping behavior?
Thank you!

Thanks,

JM

It has a govenor controlled by air I believe from the flywheel it
could be dirty.

Briggs & Stratton mower engine races and drops like clockwork
 

On Feb 23, 7:19*pm, JM_newsgroups wrote:
Hello,

I have a base-level 3.5 HP Briggs & Stratton engine that's about 6
years old. *It's a throttle-free design with a primer bulb. *Lately,
after I get it started, it goes in to a rhythm of racing and dropping
off about every second. *This started rather suddenly. *The plug is
OK. *I started to take it apart, because I didn't even know if mowers
had "points". *I assume it's some kind of induction ignition system
based on the setup of the cutoff switch and the magnetic flywheel.
The carb looks like nothing more than a plastic throttle body, and I
don't see a float/bowl of any kind. *I generally don't repair mowers,
obviously. *Does anybody recognize that surging/dropping behavior?
Thank you!

Thanks,

JM

A very dirty air filter can cause it also.

Briggs & Stratton mower engine races and drops like clockwork
 

On Feb 23, 7:19 pm, JM_newsgroups wrote:
Hello,

I have a base-level 3.5 HP Briggs & Stratton engine that's about 6

Thanks, gentlemen. I had pulled the cover off and cleaned it. The
air filter, governor, and the air-controlled assembly looks OK. I
reassembled and had the same problem. I'll give Shopdog's suggestion
a try, because I had seen that mentioned for another B&S motor. The
condenser was kind of funny to reinstall, because there is enough play
to have it stick right to the flywheel.