Briggs Engine Will Not Start

[mtnlovrs]

Briggs & Stratton Model Number: 123K02-0258-E1 03012456
Craftsman 6.5 HP Self Propelled Mower Model Number: 917.377660
I have tried absolutely everything to get this mower started, and it will not start. This mower belongs to my mom and hasn't ran in two to three years. I knew the carb would be varnished and gummed up. I performed the following before attempting to start the engine:
1. I cleaned and rebuilt the carburetor, including cleaning all the ports and blowing them out with air; replaced the welch plug; the float needle and seat; the float bowl gasket and the air filter housing gasket; fuel hose; and tested the float seat by both blowing and sucking on the fuel inlet nipple to make sure it was seating. Please note, this carburetor does not have any adjustment possible... no fuel mixture or idle screws... no choke... the only moving part is a throttle plate.
2. I cleaned the mower and engine thoroughly from top to bottom, inside and out.
3. Changed the engine oil.
4. Removed and cleaned the gas tank, inside and out. I blew it out with compressed air and made certain it was clean.
5. Found the flywheel key sheared; removed, cleaned and replaced with new aluminum key.
6. Set the coil air gap to .006" (Spec is 6 - 10 thousandths).
7. Replaced the spark plug (three times). Checked the coil lead for cracks or damage. Checked and cleaned the kill switch wiring and switch.
8. Checked the cylinder compression and found it to be at 55 psi and holding.
9. Replaced the air filter and primer bulb.
10. I checked the spark and had a nice blue spark.
11. Filled the tank with fresh premium gasoline.

I tried starting it with starting fluid, carburetor cleaner, and WD40 with no luck. Then, I finally managed to get it running once by squirting brake cleaner in the spark plug hole and it ran perfect. After shutting it off, it wouldn't start again even with the brake cleaner. I tried squirting the fluids in both the carb and the spark plug hole. I tried using a known good spark plug out of another mower and three other brand new plugs with no luck. Finally, one more time it started, but only for a few seconds and then it quit again, not to be re-started. I pull and pull on the rope to start the engine, and it doesn't even seem like it's trying. I am so frustrated with this thing I can hardly stand it. I am a mechanic by trade and can't believe this this is kicking my butt! I am desperate for an answer... please help.

 

[ILENGINE]

The question is, and I may have missed it, did you actually check for spark. On a push mower it is hard to do by yourself. So remove the spark plug, put it against a good ground on the engine with the wire attached, and have somebody crank the mower and see if you have spark.

 

[Rokon]

I thought I heard somewhere that 60 psi is the minimum psi for a Briggs to be able to run. I could be wrong.

 

[Boobala]

An internal combustion engine requires 3 things to run :

1. Fuel .... ( you obviously have that covered ) ( vented gas cap ?? fuel shut-off open ?? )

2 Air .... Thats a given ... provided the air cleaner / filter is NOT restricted

3 Fire .... Spark is where I'd look ( sometimes when a coil is about to " go on extended vacation " it'll work itermittently )

PLEASE keep us informed ........ its kickin my "set- down" along with yours !!! BEST of Luck, I hope SOMEONE can find the solution !!! Boobala :confused2: :confused2:

 

[Mikel1]

Air- I can imagine people blowing in the spark plug hole right now:laughing:
Let's trade that for Compression & also throw in Timing as a 4th.

 

[mtnlovrs]

Thank you everyone for your quick replies. Yes, ILENGINE, my wife helped me and we did it just as you described. We had a thin blue spark - right through the plug to a bolt in the head. From what I have seen, this thin spark is pretty common on these newer engines. I was told that as long as the spark is "blue", then, it is a good spark. The compression may be the problem. I couldn't find any specs on what the compression is supposed to be, but I know it was holding the compression (not leaking off) until I released it.

 

[Mikel1]

So when you put starting fluid or choke cleaner in cylinder, it will sometimes start? Any backfiring when trying to start?

 

[ILENGINE]

Thank you everyone for your quick replies. Yes, ILENGINE, my wife helped me and we did it just as you described. We had a thin blue spark - right through the plug to a bolt in the head. From what I have seen, this thin spark is pretty common on these newer engines. I was told that as long as the spark is "blue", then, it is a good spark. The compression may be the problem. I couldn't find any specs on what the compression is supposed to be, but I know it was holding the compression (not leaking off) until I released it.

briggs doesn't publish compression specs for their engine. I like to see 90 or above on most engines, but have seen new briggs engines on push mowers run fine with 55-60 psi.

 

[bertsmobile1]

Problem is they all have automatic decompression.
The amount of pressure this will bleed off will vary with the speed the engine turning over and the amount of valve lash.
This makes compression figures not much use and why you keep hearing "Leak down testing" tlked about on the forum.
I use wet/dry compression testing for confirmation of rings but that is mainly becuse I broke the leakdown gear & have not had time to replace it as I don't like most of the modern stuff.

 

[mtnlovrs]

So when you put starting fluid or choke cleaner in cylinder, it will sometimes start? Any backfiring when trying to start?

I actually had no luck what-so-ever with starting fluid (may be too old) or anything except the brake cleaner, and then, only a few times did it do anything at all... usually just a single puff. A couple times it did start, and it ran good the first time, the second time it ran good for about 15 seconds and then quit. Today, I pulled the head off and found the bolts to be slightly snug. I think 140 inch pounds should have felt tighter than it did. I should have used a torque wrench to remove them, but it's too late now. I cleaned the carbon off the head, but didn't have time to get it back together before going to work. I want to clean the top surfaces of the piston and valves, as well, since they have a pretty thick coating of carbon on them too. No backfire.