Engine starts okay, has a rough idle but will not rev up to full throttle

[BuffordT]

I have a "Brute" push lawnmower which has a Briggs and Stratton engine, 7.25 EXi on it. I am not well versed in small engines but am hoping this is not a major issue.

While push mowing the lawn (it was running normally at that point) the engine sounded like it revved up higher than the normal full throttle speed, then started to run at a
much lower speed, just above idle speed but seems to be running rough. It still starts fine and will chug and run rough but not nearly at the full throttle rpm's. It will not come
up to normal speed. Is this a carbonator issue? It seemed very odd that it would rev up for a very short time, and now only runs at a much lower rpm, and roughly runs.

Any ideas would be greatly appreciated.

 

[bertsmobile1]

Put your finger on the governor and move it by hand
If you can make it rev up & down to "normal" speeds with your little pinkie then you have a governor problem
If the carb does not respond normally then you have a carb problem

We will also need to know weather your mower has a mechanical governor or an air vane governor
Also if it is an auto choke model
If you think I am taking jibberish then post the full model & code numbers stamped into the blower housing ( US made ) or electro etched into the crankcase behind the carb ( Chinese Version )
Those with access to the B & S dealer site will be able to look it up .

 

[BuffordT]

Put your finger on the governor and move it by hand
If you can make it rev up & down to "normal" speeds with your little pinkie then you have a governor problem
If the carb does not respond normally then you have a carb problem

We will also need to know weather your mower has a mechanical governor or an air vane governor
Also if it is an auto choke model
If you think I am taking jibberish then post the full model & code numbers stamped into the blower housing ( US made ) or electro etched into the crankcase behind the carb ( Chinese Version )
Those with access to the B & S dealer site will be able to look it up .

I kind of understand what you're asking for. It's my father in laws mower so I didn't have it at my place, but I will grab it and physically take a look at
it. I did get some pictures and some of the info you were asking for thought I think.
The engine model number is : 104M02-0004-F1.
Serial number : 15 0506 58 45626
There is a second Model Number : 2A-B2A3778
Serial Number : 1D216KC2226

I believe it is an auto choke, he does not manually engage the choke on this mower.
I will need to take a look at the mower when I get it to my house and see if it is a mechanical governor or air vane governor.

Thanks!

 

[bertsmobile1]

Most newish engines are mechanical governors because they use the old air vane for the auto choke

 

[BuffordT]

Most newish engines are mechanical governors because they use the old air vane for the auto choke

I have taken the cowling off around the engine and think I've done what you've suggested. I had a video that could let you hear how it is running when started and when I pushed on the rods to increase the speed.
When I push on the lever my finger is on in IMG_7029 the engine does rev up.
When I push on the rod/lever in IMG_7030, this too increase the engines rpms.
When I push or rotate on the piece my finger is on in IMG_7031 it does not seem to have any affect?
When I push on the lever coming off of the assembly my finger is pointing too, it does increase the rpm's of the engine. Is this an automatic governor?
IMG_7035 - different angle on device.
Throttle cable from handlebars down to mower / engine. IMG_7040
Father-in-Law found a spring where the mower was being stored before I picked it up. It looks like a carb spring, but the mower did it's rev up / rev down to a slow constant idle out in the yard. Not sure this spring is even
associated with the mower.

I had my father-in-law listen to the engine when I was able to get it to rev up to a high rpm, and he thinks that it
was close to normal.

Does any of this info or these pictures help out?

I thank you very much for your assistance!

 

[Scrubcadet10]

GREEN: is the choke and choke link , when the engine is cold, this closes the choke, it is attached to a thermostat located on the muffler. the engine starts easier when cold if the choke is closed, which gives the engine MORE fuel (less air) which it likes when cold. as the engine warms up, the thermostat arm moves and it pulls the choke open and allows the engine to come up to speed,(which happens pretty quickly).
RED is the throttle link, which controls and changes the engine speed. it is hooked to either a air vane governor, which works off of air from the flywheel fan, if it slows down (thick grass, heavy load), the vane pulls the throttle open to give it more fuel to maintain a steady speed. If it does not use an air vane governor, it uses a mechanical flyweight governor, which works off centrifugal force and a set of weights that push a pin in and out moving the governor shaft and link. when the engine slows(again, heavy load), the pin located on the governor gear moves outwards, pushing on the governor shaft, which is connected to the carb by the governor link, which is pictured above. and when the load is removed and the engine speeds up the pin on the governor moves back in slowing the engine speed, to either the factor set steady RPM by the governor spring tension or to whatever the governor spring tension is set at by the operator using a throttle cable.
BLUE: is just a return spring to aid the choke in returning to full open while running.

 

[slomo]

Better clean those cylinder cooling fins and all that dirt off the top of the engine block. This is a yearly maintenance item in your engine manual. All that dirt insulates the block and restricts cooling. These are air cooled engines and reach full temp in 1-2 minutes. If you neglect this cleaning, look for spit out valve seats and blown head gaskets = engine damage.

Dad had one not nearly as dirty as yours spit a valve seat. Use compressed air, power washer, soapy water and a scrub brush or ANYTHING that will clean for you.

slomo

 

[Scrubcadet10]

Better clean those cylinder cooling fins and all that dirt off the top of the engine block. This is a yearly maintenance item in your engine manual. All that dirt insulates the block and restricts cooling. These are air cooled engines and reach full temp in 1-2 minutes. If you neglect this cleaning, look for spit out valve seats and blown head gaskets = engine damage.

Dad had one not nearly as dirty as yours spit a valve seat. Use compressed air, power washer, soapy water and a scrub brush or ANYTHING that will clean for you.

slomo

I use a Scrub brush..

 

[BuffordT]

Hey, thank you for the info! I will get that baby scrubbed up and clean! So help me understand (sorry, slow learner) should I be dig deeper to see if it's a governor issue? Admittedly I'm very much a newbie with this stuff. I don't mind digging into it, but want to make sure I know what I'm looking for. He said that it happened in the middle of a yard he was mowing, it just revved up then then dropped down to a rough idle. It will run at a rough idle for a bit then it eventually will stutter and die. That is what's confusing me I'm not sure if it's a throttle / carb issue or a governor issue I should be looking for. I'm sorry for all of the questions, and do appreciate your help and info!

 

[slomo]

Could be several things. Need to verify you have fuel, spark, air and compression.

1.Remove fuel line AT carb. Drain into a glass jar. Should have good flow here.
2.Take an old spark plug. Gap to 1/4". Ground the threaded area on the engine block. Should have a good blue spark.
3.Air is remove the air filter FOR TESTING ONLY.
4.Compression you will need a compression gauge.

Most likely you need a carb cleaning internally. Very well could be messed up throttle and governor linkages and springs. Need to verify all those springs are installed per your engine parts diagram.

slomo