My 12.5 briggs engine is approx 12-15 yr old. Runs fine when started but won't re-start after shut-off due to too much compression. I need to know where the compression release adjustment (internal I presume) is located and how to adjust it. I have had the solonoid checked & no problem there and the battery is new. Actually, it starts OK with just a little boost from a charger but I obviously don't want to have to rely on that method.

I have a similar problem with the compressors I have had too.

There should be a pressure release port by the area you use to plug in the air hoses,it looks like a simple pop-off relief valve with a pull ring(of ring is missing it'll be just a straight brass rod with hole in it),pull the release out and while pressure is releasing,try to restart,this has worked for me many times,cold start being the worst.

If not,the bleeder plug(where you NEED to drain upon each use) can also be a goo place to ri some additional pressure.

*Note: If the plug is blowing out brown sediment,you might need to run and bleed many times to get the system back to tip-top running condition.

Answer 1 is true, but is not the answer to the original question. Most small engines do have a compression relief valve, however, there is no adjustment on a four stroke engine. If your engine.makes a half round then gets stuck, the relief valve is often the pfoblem. Fuel treatments such as sea foam can remove the deposits that cause these valves to hang in the closed position. I have found this to be true in both horizontal and vertical shaft engines and Briggs are not the only ones with the problem. Remove the spark plug, make sure the wire is pulled back out of the way and not grounded(you do not want it to spark!) Pour sea foam into spark plug hole and crank the engine, this will usually free the valve. The sea foam can then move past the valve to the stem and spring and do its job. Replace the plug and the engine should crank much easier. If if does, replace plug wire and start otherwise repeat. Many starters are in bad shape from trying to start these engines and that may need to be checked as well especially if they have gotten hot(smells like burnt wire).