If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
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 |
Ads |
#2
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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
|
|||
|
|||
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, |
#8
|
|||
|
|||
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 |
#9
|
|||
|
|||
weak ignition? (small engine)
>>>>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. The mechansim is actually on the camshaft, not the crank. When the cam is below a certain speed, a tab moves onto the back of the exhaust valve lobe so that the exhaust valve lifts partway through the compression stroke and reduces compression dramatically. Once the engine starts, the tab moves out of the way and the exhaust valve stays closed on the compression stroke. Here's a manual for the K161 (7-horse) and k181 (8-horse) engine families: http://www.kohlerengines.com/common/..._593_f_all.pdf |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Recommendations for Jeep Mechanic near Edison, NJ | [email protected] | Jeep | 1 | July 30th 06 07:10 PM |
rec.autos.makers.chrysler FAQ, Part 1/6 | Dr. David Zatz | Chrysler | 5 | June 8th 05 05:28 AM |
rec.autos.makers.chrysler FAQ, Part 1/6 | Dr. David Zatz | Chrysler | 5 | May 24th 05 05:27 AM |
rec.autos.makers.chrysler FAQ, Part 1/6 | Dr. David Zatz | Chrysler | 3 | February 18th 05 06:34 AM |
rec.autos.makers.chrysler FAQ, Part 1/6 | Dr. David Zatz | Chrysler | 4 | February 2nd 05 06:22 AM |