Briggs and Stratton 'Hybrid' Won't Start

[LawnDawg43]

I am trying to repair the engine on a mower of my father's. He purchased an old Snapper Comet second hand with an engine that is a bit of a 'hybrid' in that the builder used parts from various engines to complete this one. Not a problem since so much is common from engine to engine on these but I have no idea of the correct engine number, type, code, etc.

From one usage to the next the engine simply would not start. I have done the normal service, replaced the fuel hose, cleaned out the tank, and checked the ground on the ignition. When I held the exposed ground wire close to the engine cowling and pulled the cord I got a spark but when I reattached the wire to ground it, the engine does not seem to fire.

It turns over fine, the compression seems good and I have determined it is getting fuel as there is gasoline in the carburetor. It does have an older carb. design in that there is an adjustment screw under the bowl and a short adjustment lever/handle to the right of the carb. if you are facing that side of the engine.

I love figuring this stuff out but I am at a bit of a dead end. Any suggestions?

 

[reynoldston]

Start with the basics, new spark plug, filters, fresh gas not much money spent, then if it still dosen't run go from there.

 

[LawnDawg43]

Thanks for your response but I've done all of that to no avail. Could the screw adjustment beneath the carb. possibly be causing it to flood? I have not adjusted the setting but I know it is tightened fully.

Thats another puzzle for me. I can tell that the carburetor is an older design but the cowling is for a newer 8HP Briggs and Stratton so I find myself contemplating different kinds of options. I also don't have a ton of carburetor experience so I am a little unsure of what to do at this point.

I may be over-thinking this (wouldn't be the first time) but I find myself wondering if the problem is lack of fire or something in the fuel delivery system making it seem as if the engine is not properly firing.

As always, I appreciate the help.

 

[Grass ala Mowed]

Is the timing correct? Does the plug fire when the cylinder is near TDC on the compression stroke? Should be able to check with an ohm meter or small continuity light across the points. With parts are parts build, it could have the wrong flywheel/points cam.

 

[SeniorCitizen]

I am trying to repair the engine on a mower of my father's. He purchased an old Snapper Comet second hand with an engine that is a bit of a 'hybrid' in that the builder used parts from various engines to complete this one. Not a problem since so much is common from engine to engine on these but I have no idea of the correct engine number, type, code, etc.

From one usage to the next the engine simply would not start. I have done the normal service, replaced the fuel hose, cleaned out the tank, and checked the ground on the ignition. When I held the exposed ground wire close to the engine cowling and pulled the cord I got a spark but when I reattached the wire to ground it, the engine does not seem to fire.

It turns over fine, the compression seems good and I have determined it is getting fuel as there is gasoline in the carburetor. It does have an older carb. design in that there is an adjustment screw under the bowl and a short adjustment lever/handle to the right of the carb. if you are facing that side of the engine.

I love figuring this stuff out but I am at a bit of a dead end. Any suggestions?

There is a procedure I often do under circumstances like this because I'm by nature a little lazy and the older I get the worse it seems to become.

To kill 3 birds with one stone, I remove the spark plug and make certain I have a good dry plug to plug the plug wire back on to. Next, ground the plug on the engine head with one hand while holding your thumb or finger of your other hand tightly on the spark plug hole.

Crank the engine ( a helper may be necessary ) and a good blue spark (purely subjective) should be seen at the same exact time your thumb or finger is blown from the spark plug hole. Be persistent with your thumb . Keep the pressure on as long as the engine is rotating. Watch and listen. If there is even a fraction of difference in the time the two take place we can possibly suspect a timing problem.

Ok, so we've taken care of two of the birds with one stone, so what's the third. It was a compression test you just performed. Remember we were going to hold our thumb or finger on the spark plug hole with some force. If it won't blow your thumb from the plug hole we have a compression problem.

See, I said I'm lazy. :laughing: In only a couple of minutes I've tested spark, timing and compression.

Oh, gas in the carburetor isn't doing much good there. It has to get to the cylinder for combustion via little openings in the carburetor. There must also be a vacuum to pull it through the system on the intake stroke ( 4 cycle ). 3rd bird, compression test, remember.:biggrin:

 

[Grass ala Mowed]

See, I said I'm lazy. :laughing: In only a couple of minutes I've tested spark, timing and compression.

Where I'm from we call that smart. I'll often spend more time figuring out the easiest way to do a job that it would take to just do the job. But we agree, a spark is useless unless it occurs at the right time.

 

[reynoldston]

Back to the basics, spark, fuel, compression, and timing and it will run. Start small and work up to bigger things. Basic tools would be a spark tester and a can of starting fluid. The only and proper way to check for spark is a tester. Less the 5 dollars from any parts store and will last a life time if you don't loose it.

 

[LawnDawg43]

The engine had been retro-fitted with a solid state ignition armature. This may be a dumb question but how do I adjust the timing?

 

[reynoldston]

You don't adjust the timing its set. Things to check for timing is flywheel key, coil air gap, valve timing

 

[LawnDawg43]

Crank the engine ( a helper may be necessary ) and a good blue spark (purely subjective) should be seen at the same exact time your thumb or finger is blown from the spark plug hole. Be persistent with your thumb . Keep the pressure on as long as the engine is rotating. Watch and listen. If there is even a fraction of difference in the time the two take place we can possibly suspect a timing problem.

I don't have a compression gauge yet (one is on the way) but I did the compression test this way tonight and, while I was unable to keep my thumb pressed against the plug opening, I got no spark. Last weekend I disconnected the ground wire attached to the ignition armature from a clip type fitting (this fitting was beneath the carb.) that appeared loose and held the ground wire close to the cowling while pulling the cord. I got a spark then and reattached it to a location with a screw to get a better ground. Tonight I also checked with a spark tester and got nothing.

What would I check next to verify that this is a spark issue and/or would improper timing give me these results?