15.5 will not start! I give!

Ok Before you post a response read every thing. Nothing bugs me more then the person that reads half way and then posts something Listed as tried.

1997 Briggs single 15.5 OHV
Tested has spark
Tested has compression
Valves checked and adjusted
Kill wire disconnected
Carb rebuilt still no go so pulled off and put on matching engine runs fine.
Starter fluid for the hell of it still no kick over

Ok so before I take it over to a fellow youtuber friend that does bullet testing and bugs me all the time for dead engines I need ideas.

Have you checked the timing (flywheel) key? All the spark in the world won't net you fire if it's happening at the wrong time.
Try another spark plug. Once in a blue moon, I come across one that will fire in the atmosphere but not under compression.
Check (and reset) coil air gap to 0.010". If it's too wide it may screw up timing and cause a weak spark.

No fire with a shot of ether down it's throat tells me it's not a carburetion or fuel delivery issue. You say it has compression. How much? With regards to "has spark", exactly what did you do to determine this? I ask, because different test methods can yield different (and not necessarily reliable) results. For example: An inline spark tester (plug installed in block) will reveal whether the juice is being delivered from the coil, but won't tell you if the plug is actually firing. In this case, do not assume the the plug is doing it's thing simply because the tester lights. Another test method involves holding the base of the plug against the engine block and cranking while observing. Two problems here: 1)It's subjective. Is that spark actually strong enough to ignite the mixture? Simply having a spark is not good enough. It must be a nice bright blue. 2)Twice in my life now, I have come upon a plug that tests well using this method, but will not perform under compression.

What this all comes down to, is always have a known good plug kicking around. Even if it's the wrong type for that particular engine, swapping plugs for a test is always advised, and eliminates the possibility of a bad plug. I have even seen a brand new, right-outta-the-box plug refuse to work.

Back to timing- The timing key, or flywheel key, is an engineered weak link. It's usually made of aluminum or other weak metal, and indexes the flywheel to the crankshaft. The purpose of using a soft material is to protect the engine from more expensive damage if the engine were to come to a sudden dead stop or back fire. The inertia of the flywheel could twist the crankshaft if a steel key were used.

The downside to that engineered weak link is that if the last person to install that flywheel did not torque the flywheel nut or clutch to spec (generally around 150Lb/Ft), one simple backfire can easily shear the key. When the key shears, the flywheel turns on the shaft, losing it's index and therefore the ignition timing. Only a few degrees out in either direction can cause the engine to run like total garbage or even not fire at all.

Removing the flywheel nut (or clutch) and the washer underneath will usually allow you to see the key and keyway. Generally, you don't have to actually pull the flywheel to check it. The Keyways in both the flywheel bore and the crankshaft must appear to be perfectly aligned. Do remember that when reinstalling the nut, to torque it back to spec, usually 150 Lb/Ft.

The Armature air gap (coil gap, magneto gap) will not become too wide by itself. If the mounting bolts were to come loose, it will actually be pulled in too tight by the magnet. But- Since I don't know the history of this engine, I will mention it anyways. Spec is more often than not 0.010". A standard business card (no fancy raised print or anything) is generally about this thickness and makes for a super easy check.

Apologies for the long read, but- you did want a thoughtful answer. Good luck, and do let me know if you get anywhere.

You said it wont start does it pull on the starter and sound like its going to start . There is a difference when you pull or start an engine that will fire as you will get some feed back. If you are getting this far . Check the fuel line has not melted on the exhaust manifold. There should be a guard around this . Changing this pipe can make a real difference if its been heat damaged. The best way to check is to pull it from the carb did you get fuel?

FOSWMT wrote:

Check the fuel line... Changing this pipe can make a real difference if its been heat damaged. The best way to check is to pull it from the carb did you get fuel?

Maine Mud Mower wrote:

Ok Before you post a response read every thing...Starter fluid for the hell of it still no kick over  

Doc Sprocket wrote:

No fire with a shot of ether down it's throat tells me it's not a carburetion or fuel delivery issue. .

Just spitballing here... But bad fuel or even no fuel delivery at all, and we'd still have fire with the starting fluid if everything else was okay.

Doc Sprocket wrote:

Have you checked the timing (flywheel) key? All the spark in the world won't net you fire if it's happening at the wrong time.
Try another spark plug. Once in a blue moon, I come across one that will fire in the atmosphere but not under compression.
Check (and reset) coil air gap to 0.010". If it's too wide it may screw up timing and cause a weak spark.

No fire with a shot of ether down it's throat tells me it's not a carburetion or fuel delivery issue. You say it has compression. How much? With regards to "has spark", exactly what did you do to determine this? I ask, because different test methods can yield different (and not necessarily reliable) results. For example: An inline spark tester (plug installed in block) will reveal whether the juice is being delivered from the coil, but won't tell you if the plug is actually firing. In this case, do not assume the the plug is doing it's thing simply because the tester lights. Another test method involves holding the base of the plug against the engine block and cranking while observing. Two problems here: 1)It's subjective. Is that spark actually strong enough to ignite the mixture? Simply having a spark is not good enough. It must be a nice bright blue. 2)Twice in my life now, I have come upon a plug that tests well using this method, but will not perform under compression.

What this all comes down to, is always have a known good plug kicking around. Even if it's the wrong type for that particular engine, swapping plugs for a test is always advised, and eliminates the possibility of a bad plug. I have even seen a brand new, right-outta-the-box plug refuse to work.

Back to timing- The timing key, or flywheel key, is an engineered weak link. It's usually made of aluminum or other weak metal, and indexes the flywheel to the crankshaft. The purpose of using a soft material is to protect the engine from more expensive damage if the engine were to come to a sudden dead stop or back fire. The inertia of the flywheel could twist the crankshaft if a steel key were used.

The downside to that engineered weak link is that if the last person to install that flywheel did not torque the flywheel nut or clutch to spec (generally around 150Lb/Ft), one simple backfire can easily shear the key. When the key shears, the flywheel turns on the shaft, losing it's index and therefore the ignition timing. Only a few degrees out in either direction can cause the engine to run like total garbage or even not fire at all.

Removing the flywheel nut (or clutch) and the washer underneath will usually allow you to see the key and keyway. Generally, you don't have to actually pull the flywheel to check it. The Keyways in both the flywheel bore and the crankshaft must appear to be perfectly aligned. Do remember that when reinstalling the nut, to torque it back to spec, usually 150 Lb/Ft.

The Armature air gap (coil gap, magneto gap) will not become too wide by itself. If the mounting bolts were to come loose, it will actually be pulled in too tight by the magnet. But- Since I don't know the history of this engine, I will mention it anyways. Spec is more often than not 0.010". A standard business card (no fancy raised print or anything) is generally about this thickness and makes for a super easy check.

Apologies for the long read, but- you did want a thoughtful answer. Good luck, and do let me know if you get anywhere.

It was the stupid key it snapped it and was rotated 1/8th around

Yeah it happened to lapavonimac with his 18hp, I was gonna say that also, but doc beat me to it. Lol, that's a common problem, that is a pain. I would rather clean a sparkplug or change gas line than remove a flywhhel and put in a key.

I know what the problem is it is the fuel shut off switch on the bottom of the fuel bowl

Maine Mud Mower wrote:

It was the stupid key it snapped it and was rotated 1/8th around

Fantastic! I'm glad you're sorted out!