John Deere popping and sometimes backfires when idling

richfranklin · Aug 19, 2014

Hi Everyone,

I have a John Deere 155c with the Brigg and Straton engine that has a problem I can't seem to track down. When running under load mowing everything is perfect. Plenty of power cuts great no issues. However, when I am just idling it makes a popping noise and sometimes will back fire or makes a spitting sound. I was told by the JD Dealer that a clogged jet would cause this. I've installed new ignition coils, plugs, air cleaner etc. I've tried running some "Seafoam" fuel treatment with no change. There is one interesting thing. If it starts popping at idle if I add more choke it seems to calm down.

Any ideas ?

Thanks everyone !

Jerry/MT · Aug 19, 2014

The idle mixture may be too lean. Don't know how your idle mixture is controlled; some control idle air others control idle fuel. If there is no mixture adjustment at idle than the control orifice maybe clogged.

Texasmark · Aug 23, 2014

Looks like you got 2 for 2; JD dealer and Jerry. Open your low speed jet till it quits. Usual opening for low speed jets in my life were 1 1/2 to 1 3/4 turns for initial setting. Might see where yours is currently. When turning in to seat the needle before backing out, a thumb and index finger only on the screwdriver and stop when you feel resistance. Too much force and you will score the conical tip on the needle (make a circular indentation) and that makes proper adjustment nearly impossible.

Other thing that I had in mind that could cause it would/could be a sticking intake valve. With that when the mixture in the engine explodes on the power stroke, some of it blows out the open valve and comes out the carb.

Mark

DJ54 · Aug 23, 2014

If adjusting the carb. doesn't help, might be worth investing in the smallest bottle of Marvel Mystery Oil, and give it the prescribed dosage in the crankcase oil AND gas. I know it made a world of difference in my older engines with sticking exhaust valves.

richfranklin · Aug 29, 2014

You are awesome! It was the carb. I took the easy way and ordered a new carb. I may play with rebuilding the other later. It was easier to just install a new one.