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Couple of thoughts...... We need more information to really help you out. What year and model # is your Murray? Need to know that to take a look at a wiring diagram.

You more than likely have a Briggs engine, but it's the same thing, what is the Model and type #'s on the engine??

Is the "surge" at idle, or full throttle? Governor surge is almost always a fuel jet problem. Two different circuits --- Low speed & high speed

Is the starter relay you changed a 3-post, or 4-post relay?
 

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Yes it's the Briggs engine. View attachment 79473

Thanks for the reply. If I drive at full speed and/or blade on, the surge eases up.

Also. I have cleaned the fuel system. I have dismantled fuel system twice, each time I do, it runs smooth for about a minute. Then comes the surge.

The relay only has 2 posts. I'll send post pics as soon as I can
Briggs 21R707-0105 G1...... It's a Nikki carburetor. The weird part about that Nikki is that you can buy a complete replacement carb with air filter, plug, and fuel filter for less $$$ than you can buy the rebuild kit.

Nikki Rebuild Kit $30

Nikki Replacement Carb $27

Unless you've dealt with rebuilding a Nikki carb before, I would suggest just buying the replacement, they can be a PITA to get right sometimes.
 

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One screw is the idle speed screw. The other on left side is probably the low speed fuel mixture. Turn it IN until it bottoms out. Count the turns as you screw it in.

Back it out to the original setting and work from there a 1/2 turn at a time. Out is RICHER, in is LEANER. Governor surge at idle is usually to LEAN. Try out first. Keep turning it out until either the surge goes away, or the engine starts to sputter.

If out don't work, go in a 1/2 turn at a time (LEANER) from the original setting. If you can turn it in all the way and the engine doesn't sputter, the float level is set to low to keep up with the fuel supply needed. If it's a brass float, bend the float needle tab to allow more fuel into the bowl. If it's a plastic float, you can still bend the tab, but you have to GENTLY heat it with a heat gun, or dropping it in a cup of really hot water out of the microwave If fuel starts to come out the overflow tube, you went to far......

Post a picture of the carb so we know exactly what you're dealing with
 

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