Briggs idling rough on start up

[medic2575]

Hey Guys
I have a problem with a mower I am working on. It is Briggs 6.5 HP self propelled with the following Briggs info:
Model: 126T02
Type: 0299-B1
Code: 11050558
The problem im having is when I got the mower the original owner had attempted to clean the carb after it had sat up for the winter. It wouldn't start at all but had spark. I removed the carb and cleaned it thoroughly and reinstalled. The mower started but on start up it idles horribly and spits and sputters. After doing this for approx 2 minutes it will suddenly clear up and runs like a new machine and on subsequent warm start ups it fires right up and runs fine only to return to the same rough idle upon start up after cooling off and then after 2 minutes its smooths out and runs fine. He had totally jacked up the governor spring and it was all stretched out. I replaced the governor spring with a new one and replaced the air filter. The fuel tank is clean.
So I figure the carb has an obstruction that I could not get cleaned out on initial clean up. I replaced the carb with a new one and it repeats the same symptoms. Im Stumped. Could anyone give me some ideas on where to go from here please?
I was also thinking maybe flywheel key stripped and mower is out of time but from what I have seen in the past this makes no sense because it would "jerk back" on startup and would not idle smoothly at all. Like I said, I am stumped.

 

[Lawnranger]

About six months ago I had one doing the same thing and it was puffing black smoke until it warmed up. It appears your engine has an auto-choke the same as the one I worked on. After I removed the blower housing I found out that someone else worked on the mower and installed the auto-choke to flywheel vane linkage incorrectly. I don't have a picture to post for you but the vane linkage is supposed to go in front of the auto-choke lever loop, not in the middle of the loop. Your linkage may be correct but it is just one simple thing to check. There is a measurement for setting the linkage and I cannot recall what it is at the moment. There is also a service bulletin out to help diagnose this symptom. A phone call to B&S may be helpful in getting the bulletin and linkage spec.

 

[medic2575]

Lawnranger
All I can say is YOU ARE THE MAN!!! That is exactly what was wrong with this mower. The blower vane was installed right through the middle hole of the auto choke lever, just like you said. They say the devils in the details. That's what got me on this one. You saved me brother. Thank you so much for your help. Im really not sure I ever would have figured this one out without your help. Thanks again.

 

[Lawnranger]

I'm really glad I could help. I got stumped on this very same issue and after taking the blower housing off after the third time I looked at other possibilities. And now you know the rest of the story.

 

[Lawnranger]

Turns out I did have a picture saved on my phone. Let me be perfectly clear . . . . . this picture shows the INCORRECT installation of the linkage. The black vane linkage is supposed to be in front of the silver auto-choke thermostat linkage, not through the middle.