Stumped, slow start, jumps to full throttle

[slow030]

Checked the fuel line, getting good flow. Had previously cleaned the tank. Replaced the thermostat on the exhaust with another used one, no change. Think I will give up at this point. Maybe use as a parts mower. Thank you everyone for all the suggestions.

 

[slomo]

After sitting for about 10 minutes it would start but would only run slow, never went to full speed.

Again those are a fixed speed as in RPM engines. Pull the cord. She revs to say 3500rpm all day long.

If she is not reaching full rpm, throttle linkage is messed up or maybe the top engine cowl is on wrong. Something is holding the carb linkage in a static position. Like grass and rust for two examples.

You can bend the metal tab the throttle linkage and spring are on to adjust the max revs.

Millions of Briggs autochoke videos on youtube. Very simple design which works pretty good.

 

[slomo]

Checked the fuel line, getting good flow. Had previously cleaned the tank. Replaced the thermostat on the exhaust with another used one, no change. Think I will give up at this point. Maybe use as a parts mower. Thank you everyone for all the suggestions.

If you pull the fuel hose off AT the carb inlet, draining a good amount into a glass jar, proves two things. One is the fuel tank cap IS venting proper. Next is the tank, fuel lines and any filter are not clogged up. Tank to carb has proper solid fat fuel flow.

 

[slomo]

After the above, clean the carb or replace.

Might verify spark with an open gap tester. They are $1.39 delivered to your door. Could be a weak ignition coil. I just replaced two, one just like yours in my fleet.

https://www.ebay.com/itm/136815746178?_skw=open+gap+spark+tester&itmmeta=01KREN514F1AA7FWYYYC03BQWN&hash=item1fdada9c82:g:WMsAAOSwm4VnVr~n&itmprp=enc%3AAQALAAAA8GfYFPkwiKCW4ZNSs2u11xDC2emQtiGVwJWR0blzKpXukWUYyXVIkhXmkq%2FmSCp8%2BovlnLvRGD1qH9cJnMdMBzqzxkMKspIQkcU0jHncKlgCvTSeDVkpib6D3Co%2BX9Je2UyH9vP%2Bx1jMm08OPmRYRBHbBgc55%2FASlZKQocIyRojqb%2F7IPclp3KEHqwgUXvmTOI34OvTfr7CkzOmoak8GIGf1XBXrVwlEx12qt8M%2Bq7lWa2jD5LVQ%2BAWsO5nwtCtgsEykXw%2FDgpNViY374sd3rBWnT%2FsCbE94UoDpGT4hToi0DvZMJaPTXVjsZQbh3cBkAg%3D%3D%7Ctkp%3ABk9SR7aSlNXDZw

 

[slow030]

I don't think the linkage is not the problem. It runs fine when it is started when it is cold. The running slow only happens when the motor is warm.

 

[slomo]

I don't think the linkage is not the problem. It runs fine when it is started when it is cold. The running slow only happens when the motor is warm.

Again, that engine, should operate, at say 3600rpm, all day long.

Yes one could have a throttle cable IF your mower has one to adjust rpm. You don't and shouldn't need to adjust rpm.

Autochoke is made for a single speed engine, for the most part.

Wondering if you possibly got the throttle linkage messed up?

There is a metal tab one could bend to increase rpm.

These are super simple machines.

 

[slow030]

yes, has the metal tab, moving it doesn't change rpm when it is running slow after it is hot. It increases rpm when the motor is cold.

 

[slomo]

Crazy but sounds like your throttle plate is on backwards or throttle spring backwards? Makes no sense. Should warm up and the revs follow.

 

[slomo]

I do see a small tweak you need to make on the thermostat.

The blue oval area needs to be in the center of the red lines on both axis. Push the metal arm (yellow arrow) the same direction as it is pointed. There are two plastic lines (red lines) on each axis telling you where it needs to be.

Think the front edge of the thermostat arm in blue is to be like 1/16" to 1/8" shy of touching the air vane.

 

[slomo]

Read the service bulletin StarTech posted. It has everything about the autochoke and how to set it up.

You might need to buy a new throttle spring and the air vane autochoke spring??