Recent Posts

Members
Stats
  • Total Posts: 1,038
  • Total Topics: 313
  • Online today: 11
  • Online ever: 275
  • (January 22, 2020, 07:39:54 PM)
Users Online
Users: 0
Guests: 6
Total: 6

Briggs autochoke on Stihl

Started by Gregs mowing, October 23, 2021, 09:19:26 PM

Previous topic - Next topic

Stihl mower autochoke problem!!

Autochoke sensor fail.
1 (100%)
Modern Briggs crap.
0 (0%)

Total Members Voted: 1

Gregs mowing

A friend bought a new Stihl roller mower. Rm545. Briggs autochoke engine. It fires up fine. Then after a minute of use the engine starts to rub very rough. As though carb is dirty but it runs smooth after firing up. The mower is new with correct amount of oil and fuel cap isn't too tight. Thoughts please.

Mick

I would first check to see if the thermal device is pushing the choke off completely when warm. This can be simply the plastic lever which pushes against the actual choke shaft has jumped over the choke shaft and therefore can't push it off.

Gregs mowing

Thanks Mick. I'm sure this is right. image.jpg

Mick

Yep the linkage does look right.  :tup:   So is the thermal device pushing the choke off when warm / hot?

Gregs mowing

Hi Mick. I ran the mower like this and it was fine but gradually the rod was pushing back down towards the air filter cover thus choking the carb. So new thermostat I recon?

Mick

Greg if it's moving towards the air filer husing then it's pushing the choke off as it should do. 

I'm presuming that it's when it pushes the choke completely off that's when it starts running rough?  If so then there's some sort of blockage or restriction that need cleaning.  Or just fit a new jet module and see if it cures it.

Gregs mowing

From using it the further the rod is towards the exhaust then choke isn't on . I recorded a video for memory purpose and when the rod pushed air filter direction it turned choke on thus making it cough and splutter, I could see through the carb that choke was on too.
If jet I would think it would sound rough as soon as it starts up?

Mick

#7
The spring pulls the choke on (closed), and when warm the rod pushes the choke off (open).

In your photo above for example the choke is in the on / closed position.  Ready for a cold start.

Mick

By the way, just wondering, if the machine is brand new, then why doesn't your friend contact the dealer he purchased it from and get it sorted out?  Messing with it yourselves could screw any chances of getting it fixed under the warranty.

Gregs mowing

Hi Mick he bought it online. The local Stihl dealer is an absolute twat.
After seeing your comments and seeing some videos online it seems a common issue is the jet on these plastic carbs are so small that it's a common issue. So took it apart which was quite easy and cleaned the jets.
Used to run fine for a few mins then rough. Now it ran for half hour no issue.
Interested carb design and fairly easy.
Not sure why Briggs are using both 7mm and 8mm bolt heads on everything. Means swapping bit all the time.

I did see a Canadian guy on YouTube use a .5mm drill bit on one of the jets to make it slightly bigger and it seems to be lot less problematic now. Have you tried this Mick?

Mick

I haven't modified one, to be honest we just change the plastic jet module for the latest one if required. Some had the wrong jet modules fitted, but as this is a new machine I'd imagine it already has it fitted. 

The carbs are very basic and simple to work on as you said, and yes the screw head sixes are annoying at first, but you get used to them.

Make sure there is good flow from the tank when the fuel cap is on, had some that don't breath properly and act like a fuel tap. Also make sure the little brass jet on the left side of the intake is clear.