OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Carby rebuilt now backfiring- Briggs 3.5hp

Had to rebuild my carby on a 091202 engine as it was running rich AF. Found the diaphragm was almost hard rubber (see hopefully attached), which was the reason it smelled like a petrol station when i used it and fouled plugs in 3 hours.
I reinstalled, turned the screw out 1 and half turns (it was originally turned full in), but realised the screw was vibrating when I was turning it in and out. It then started backfiring.
Is my screw supposed to have a spring on it? If it does, then it will not allow it to 'seat' and the one and a half turns would be pointless.
Hopefully makes sense and thanks in advance for any feedback

Most likely you're working with a pilot jet instead the older idle mixture. They are meant to screwed all the way in, lightly seated. These do clogged and must be carefully cleaned as they are a jet.

Now to the back fire and I know many used the term incorrectly. Is it out of the exhaust or the intake? Either one can a sheared flywheel. Out of the exhaust can happen excess unburned fuel is present as these engines uses the wasted spark system. IE: spark plug fires during the exhaust stroke.

Yeah that's my jet. Cleaned up when cleaning the carby but also did it again. Regardless of how the jet is seated it seems to run OK for 10 seconds then begins to surge and backfire (from the muffler).

Then it is technically an afterfire or preignition (timing advanced too much due a bad coil or partially sheared flywheel key).

Depends on how rusted the fuel tank is. I have seen a few that had internal clogging the carburetor tower that had to be manually cleaned. This internal trash could plugging the idle circuit once engine vacuum sucks up fuel. This not easy to do either as it requires removing the steel ball plugs. But first verify that the valve clearances are within specs. Also if you have a spare carburetor laying around give it a try to see you actually have a carburetor problem or not.

I have also seen a handful of coil electronic to go bonkers after slight heating as cause some strange things.

So went back to basics and changed the spark plug and put more fuel in. Amazingly the 'popping' has now completely stopped.
Problem is now that changing the idle seems to do little, if anything, to the speed of the engine. It's not spluttering or anything. Having said that, due to how rich it was running previously, the oil seems to have a fuel smell and quite watery. Might change that as well to rule further things out.
The engine was running OK prior to the carby clean, and is now back to running OK, so maybe need to fiddle with the settings. Thanks for your reviews so far.