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weak ignition? (small engine)
I have an old tiller with a Kohler single-cylinder 4-stroke engine. It
lost all power (over about 30 secs), and now won't start. Since then, - Replaced spark plug. (Which does spark, when grounded to the head.) - Points look OK. - Compression looks OK (75 psi). - Cylinder is getting fuel (plug gets wet, and exhaust smells.) - Carb float valve works, and float seems OK. - Coil resistances look OK. - I cranked it in the dark, and didn't see or hear anything bad around the coil. I wonder if I have a weak spark when the plug is installed. But, a new coil costs $75, which is a kind of expensive experiment. To test the coil, I made a 10:1 voltage divider (with a HV 10M resistor), and looked at the spark plug voltage with a scope. With the plug not grounded, I see a 4-6KV pulse. When the plug is grounded, this drops to about 1KV. I get the same 1KV when the plug is in the cylinder (no fuel). Questions: - Is above consistent with a 'weak' coil? - Is there another way to test that? And, any other thoughts would be appreciated. G |
#2
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weak ignition? (small engine)
George Wrote: > I have an old tiller with a Kohler single-cylinder 4-stroke engine. It > lost all power (over about 30 secs), and now won't start. Since then, > > - Replaced spark plug. (Which does spark, when grounded to the > head.) > > - Points look OK. > > - Compression looks OK (75 psi). > > - Cylinder is getting fuel (plug gets wet, and exhaust smells.) > > - Carb float valve works, and float seems OK. > > - Coil resistances look OK. > > - I cranked it in the dark, and didn't see or hear anything bad > around the coil. > > I wonder if I have a weak spark when the plug is installed. But, a new > coil costs $75, which is a kind of expensive experiment. > > To test the coil, I made a 10:1 voltage divider (with a HV 10M > resistor), and looked at the spark plug voltage with a scope. With the > plug not grounded, I see a 4-6KV pulse. When the plug is grounded, this > drops to about 1KV. I get the same 1KV when the plug is in the cylinder > (no fuel). > > Questions: > - Is above consistent with a 'weak' coil? > - Is there another way to test that? > > > And, any other thoughts would be appreciated. > > G 75 psi compression doesn't sound like enough for a gas engine to run....usually around twice that... -- jeffcoslacker ------------------------------------------------------------------------ jeffcoslacker's Profile: http://www.automotiveforums.com/vbul...?userid=219638 View this thread: http://www.automotiveforums.com/vbul...d.php?t=617196 http://www.automotiveforums.com |
#3
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weak ignition? (small engine)
jeffcoslacker Wrote: > 75 psi compression doesn't sound like enough for a gas engine to > run....usually around twice that... I seached on a lawn equipment site I post on sometimes...the consensus seemed to be a small engine won't run very strong below 120 psi, and probably wouldn't start below 90 psi...new compression spec on that motor is probably around 160 psi. -- jeffcoslacker ------------------------------------------------------------------------ jeffcoslacker's Profile: http://www.automotiveforums.com/vbul...?userid=219638 View this thread: http://www.automotiveforums.com/vbul...d.php?t=617196 http://www.automotiveforums.com |
#4
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weak ignition? (small engine)
On Sat, 9 Sep 2006 05:37:25 -0700, jeffcoslacker
> wrote: > >George Wrote: >> I have an old tiller with a Kohler single-cylinder 4-stroke engine. It >> lost all power (over about 30 secs), and now won't start. Since then, >> >> - Replaced spark plug. (Which does spark, when grounded to the >> head.) >> >> - Points look OK. >> >> - Compression looks OK (75 psi). >> >> - Cylinder is getting fuel (plug gets wet, and exhaust smells.) >> >> - Carb float valve works, and float seems OK. >> >> - Coil resistances look OK. >> >> - I cranked it in the dark, and didn't see or hear anything bad >> around the coil. >> >> I wonder if I have a weak spark when the plug is installed. But, a new >> coil costs $75, which is a kind of expensive experiment. >> >> To test the coil, I made a 10:1 voltage divider (with a HV 10M >> resistor), and looked at the spark plug voltage with a scope. With the >> plug not grounded, I see a 4-6KV pulse. When the plug is grounded, this >> drops to about 1KV. I get the same 1KV when the plug is in the cylinder >> (no fuel). >> >> Questions: >> - Is above consistent with a 'weak' coil? >> - Is there another way to test that? >> >> >> And, any other thoughts would be appreciated. >> >> G > >75 psi compression doesn't sound like enough for a gas engine to >run....usually around twice that... This is a 7 hp pull start, and it has some sort of compression relief to reduce the starting effort. It works off the crankshaft speed. I figured it out once, but I don't remember the details. G |
#5
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weak ignition? (small engine)
George Wrote: > On Sat, 9 Sep 2006 05:37:25 -0700, jeffcoslacker > > wrote: > > > > >George Wrote: > >> I have an old tiller with a Kohler single-cylinder 4-stroke engine. > It > >> lost all power (over about 30 secs), and now won't start. Since > then, > >> > >> - Replaced spark plug. (Which does spark, when grounded to the > >> head.) > >> > >> - Points look OK. > >> > >> - Compression looks OK (75 psi). > >> > >> - Cylinder is getting fuel (plug gets wet, and exhaust smells.) > >> > >> - Carb float valve works, and float seems OK. > >> > >> - Coil resistances look OK. > >> > >> - I cranked it in the dark, and didn't see or hear anything bad > >> around the coil. > >> > >> I wonder if I have a weak spark when the plug is installed. But, a > new > >> coil costs $75, which is a kind of expensive experiment. > >> > >> To test the coil, I made a 10:1 voltage divider (with a HV 10M > >> resistor), and looked at the spark plug voltage with a scope. With > the > >> plug not grounded, I see a 4-6KV pulse. When the plug is grounded, > this > >> drops to about 1KV. I get the same 1KV when the plug is in the > cylinder > >> (no fuel). > >> > >> Questions: > >> - Is above consistent with a 'weak' coil? > >> - Is there another way to test that? > >> > >> > >> And, any other thoughts would be appreciated. > >> > >> G > > > >75 psi compression doesn't sound like enough for a gas engine to > >run....usually around twice that... > > This is a 7 hp pull start, and it has some sort of compression relief > to > reduce the starting effort. It works off the crankshaft speed. I > figured it out once, but I don't remember the details. > > G See if it will start with a dry plug and the air cleaner removed. Let me know. I did see Kohler has a compression release, I was wondering if you figured that into the compression reading... Your spark, fat and blue or thin and yellow/white? -- jeffcoslacker ------------------------------------------------------------------------ jeffcoslacker's Profile: http://www.automotiveforums.com/vbul...?userid=219638 View this thread: http://www.automotiveforums.com/vbul...d.php?t=617196 http://www.automotiveforums.com |
#6
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weak ignition? (small engine)
On Sat, 9 Sep 2006 11:34:40 -0700, jeffcoslacker
> wrote: > >George Wrote: >> On Sat, 9 Sep 2006 05:37:25 -0700, jeffcoslacker >> > wrote: >> >> > >> >George Wrote: >> >> I have an old tiller with a Kohler single-cylinder 4-stroke engine. >> >> It lost all power (over about 30 secs), and now won't start. Since >> >> then, ... >> >> Questions: >> >> - Is above consistent with a 'weak' coil? >> >> - Is there another way to test that? >> >> >> >> >> >> And, any other thoughts would be appreciated. >> >> >> >> G >> > >> >75 psi compression doesn't sound like enough for a gas engine to >> >run....usually around twice that... >> >> This is a 7 hp pull start, and it has some sort of compression relief >> to >> reduce the starting effort. It works off the crankshaft speed. I >> figured it out once, but I don't remember the details. >> >> G > >See if it will start with a dry plug and the air cleaner removed. No. Tried that, early on. >I did see Kohler has a compression release, I was wondering if you >figured that into the compression reading... No - that was just a raw reading while I pulled it. >Your spark, fat and blue or thin and yellow/white? I'd call it violet and thin (watching it in the dark). It's not inspiring, but it is there. (That's spinning the crank with a drill.) G |
#7
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weak ignition? (small engine)
George Wrote: > On Sat, 9 Sep 2006 11:34:40 -0700, jeffcoslacker > > wrote: > > > > >George Wrote: > >> On Sat, 9 Sep 2006 05:37:25 -0700, jeffcoslacker > >> > wrote: > >> > >> > > >> >George Wrote: > >> >> I have an old tiller with a Kohler single-cylinder 4-stroke > engine. > >> >> It lost all power (over about 30 secs), and now won't start. > Since > >> >> then, ... > > >> >> Questions: > >> >> - Is above consistent with a 'weak' coil? > >> >> - Is there another way to test that? > >> >> > >> >> > >> >> And, any other thoughts would be appreciated. > >> >> > >> >> G > >> > > >> >75 psi compression doesn't sound like enough for a gas engine to > >> >run....usually around twice that... > >> > >> This is a 7 hp pull start, and it has some sort of compression > relief > >> to > >> reduce the starting effort. It works off the crankshaft speed. I > >> figured it out once, but I don't remember the details. > >> > >> G > > > >See if it will start with a dry plug and the air cleaner removed. > > No. Tried that, early on. > > > >I did see Kohler has a compression release, I was wondering if you > >figured that into the compression reading... > > No - that was just a raw reading while I pulled it. > > > >Your spark, fat and blue or thin and yellow/white? > > I'd call it violet and thin (watching it in the dark). It's not > inspiring, but it is there. (That's spinning the crank with a drill.) > > G I think I'd put a new points and condensor in just for laughs and see where that gets you... -- jeffcoslacker ------------------------------------------------------------------------ jeffcoslacker's Profile: http://www.automotiveforums.com/vbul...?userid=219638 View this thread: http://www.automotiveforums.com/vbul...d.php?t=617196 http://www.automotiveforums.com |
#8
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weak ignition? (small engine)
George wrote:
> I have an old tiller with a Kohler single-cylinder 4-stroke engine. > It lost all power (over about 30 secs), and now won't start. Since > then, > > - Replaced spark plug. (Which does spark, when grounded to the > head.) > > - Points look OK. > > - Compression looks OK (75 psi). > > - Cylinder is getting fuel (plug gets wet, and exhaust smells.) > > - Carb float valve works, and float seems OK. > > - Coil resistances look OK. > > - I cranked it in the dark, and didn't see or hear anything bad > around the coil. > > I wonder if I have a weak spark when the plug is installed. But, a > new coil costs $75, which is a kind of expensive experiment. > > To test the coil, I made a 10:1 voltage divider (with a HV 10M > resistor), and looked at the spark plug voltage with a scope. With > the plug not grounded, I see a 4-6KV pulse. When the plug is > grounded, this drops to about 1KV. I get the same 1KV when the plug > is in the cylinder (no fuel). > > Questions: > - Is above consistent with a 'weak' coil? > - Is there another way to test that? > > > And, any other thoughts would be appreciated. > > G First of all, read this carefully: http://www.gotfusion.com/tutsTD/ask.cfm Then, learn the difference between multi-posting and cross-posting and DO IT RIGHT! Jeez, |
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