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I have 2 John Deere JS60 push mowers, and bought them as is. One started up, but wanted to stall. The other didn't start.

I replaced the following:

Spark plug
air filter
oil
gas
carburetor

After all of that they started first pull, but than I go out, and try the next time I need to mow, and they don't want to start. If I spray a little starting fluid in the air filter they fire right up. Just wondering what I should do, cause its a pain to use starting fluid to start them.

I did rip the carburetors apart even knowing they are brand new, and cleaned all the small holes out even the bolt that goes in the bottom. So I am just confused as to why they both have the same issue, and what the next steps to troubleshoot are? I looked up this model online, and saw lots of people had the same issues, but found somebody who was able to fix it. They never said what the issue was though, but they did the same things I have done before finding that person.

That briggs engine is famous for the primer system not working. One fix is to use 2 gaskets between the carb and air cleaner housing. The other is to use a very small amount of sealant on the gasket. The problem is the primer bulb pushes air through the air cleaner housing through the gasket to a small hole in the carb. Those things can be a pain to make work. If you use a sealant like rtv you need to seal the channel between the gasket and the filter housing. That is where it doesn't seal. Be careful to not plug things up. Gasket number Briggs 795629

I have found that the float level may not be set right, even with new carbs, especially non OEM. Any time I install a new carb I set the float slightly rich, which reduces surging and hard starting problems.

The with the Briggs primer cleaner bases is two fold. One is that when re installed the techs are over tightening the mounting screws, this warps the cover. Second is that heat and age also warps these bases. As said two gaskets works at times but I have found taking the second and using a backbone razor blade or hobby knife bevel the second gasket ad to apply extra pressure only where needed. Using a light coated of wood glue between the two gasket to temp hold them together. After they have been mounted for a while they will fuse together. I see mentioning using RTV please don't as it only causes problems.

To see where the extra pressure is needed install a new gasket and lightly mount the primer base to the carburetor then remove it. This will a impression where and where not contact has been made. Once the new pair is made up install and torque to spec'd of 45 in-lbs. As you approach the spec'd test the primer for proper operation. Overtightening will warp the primer base and cut the gasket.

Thank you everybody for the replies. I forgot to mention I replaced the gaskets, and have tried 2 gaskets, but that didn't work. Maybe i'll try the wood glue to fuse them together. Thanks again everybody.

As I said look at the impression left behind and it will tell you where contact isn't being made.

I have used a paper thin coat of Permatex the right stuff on the bottom part of the gasket on many engines. Not a glob, just a paper thin coating on the cleaner housing side of the lower part of the gasket.