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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?

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

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.

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.

LawnDawg43 said:

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?

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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:

SandburRanch said:

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

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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.

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.

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?

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

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.

Click to expand...

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?

LawnDawg43 said:

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.

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If the wire you mention is a small wire and goes up under the cowling, that's the kill wire that grounds the mag to kill the engine when you turn the key to stop. Other switches, safety switches in particular, like the pto - blade engagement, can kill the spark to the plug as well via that small wire going under the cowling.

I would suggest removing that ground wire from its terminal again and see if that allows spark at the spark plug when grounding the side of the plug on the head. If that allows spark to the plug it will probably run. To kill it touch that little ground wire back to metal.

After reading your last post I would say that SandburRanch have a very good post and that could well be your problim.

I thought it was just the ignition ground wire. The engine is not a key-start design but a pull start with the throttle lever located below the steering wheel.

Even with no key ... that is the kill wire.
There is usually a place on the throttle linkage where it attaches around the carb... with the throttle pulled back to minimum, it grounds out the magneto & kills the engine... :smile:KennyV

That little wire is absolutely your no spark problem. As Kenny said, follow it from its connection at the armature, it should go to the throttle linkage where it will ground when you pull the throttle all the way back to idle. As for that little screw you mentioned hanging straight down from the bottom of the carb, does it have a spring around it? If so it should not be screwed all the way in. In this position it should be cutting the flow of fuel from the carb into the engine. After you get your spark issue corrected, back that screw out one full turn and see what happens, it should crank. Once it cranks, you will probably need to adjust it one way or the other to get it to run smoothly.

If there is still no spark have someone help you. Follow the kill cable down to the engine, have someone else hold the bale handle. Grab the control arm the cable is hooked to and manualy open it up. Have a inline spark tester between the plug and the boot. While holding the control arm open have your friend pull the recoil and see if it gets spark. If so you have a streched kill cable.

Okay folks, many thanks because I am much closer. The engine cranks and runs and I have adjusted the carburetor to get a good, smooth idle. Now, however, I am battling a runaway problem. The engine idles faster and faster and the only way to shut it off is by pulling the spark plug wire. When I place the throttle control in the 'Off' position I get no response. Governor?

You must have something off or binding At the carb linkage...
Look closely as you open and close the throttle on the carb... something is not right, the governor needs to be connected... there should be a spring that holds the throttle Open... and the governor linkage should be trying to Close the throttle... :smile:KennyV

Thanks again Kenny. I looked at it again tonight. If I follow the throttle cable it goes to a "panel" (a friend of mine referred to it as a throttle panel). The throttle cable is attached with a screw fitting and operates a slide up and down on the front of this panel. The fitting was loose and, instead of moving the slide up and down, the cable itself was moving up and down in the fitting.

I tightened that and now the slide works along with throttle commands but nothing between the panel and the carburetor moves. I can move the linkage between the panel and the carburetor and open and close the throttle that way but not with the throttle control so it sounds like your assessment is correct.

I will check that tomorrow after work and see what I can determine is going on behind that panel.

BTW, what is the correct term for that panel? Also, if anyone else has any suggestions please feel free to let me know. Thanks again to all of you.

After more trouble shooting I believe I have found the source of my problem and the maddening inconsistency with this thing. The control bracket on this engine consists of the slide design that moves up and down with "gears" on the interior of the bracket. The plastic slide is broken and was still sitting in place but not moving up and down consistently and as one unit. Therefore, it was not consistently choking the carburetor and/or fully opening the throttle.

I discovered this when the slide would no longer move upward. It moved out of position and the gears were no longer aligned, preventing me from opening the throttle. I suspect this upward movement has been inconsistent for some time and the reason my father has been unable to get the engine to perform to his satisfaction.

My father now wants this engine installed on a newer body. The old body (a Comet I'm going to rebuild and install a new engine on) has the throttle control mounted on the post facing the driver below the steering wheel. The newer body has the throttle control mounted on the left side of the body, just behind the driver.

My question is this: Will the same control bracket work with the throttle control mounted to the left of the driver?

Two things you are missing. One, you said that the screw on the bottom of the carb is fully tight. Bad
This screw controls the fuel going through the carb. Open this screw one and one half turns from lightly seated. this will allow gas to enter the air horn and engine. Two, try taking off the ground wiring on the ignition magneto. This wire could be shorting, which will give you a NO SPARK condition. This wire is the kill switch wire and if you have it grounded the engine will never start.