A Cars forum. AutoBanter

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.

Go Back   Home » AutoBanter forum » Auto newsgroups » Technology
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

weak ignition? (small engine)



 
 
Thread Tools Display Modes
  #1  
Old September 9th 06, 04:28 AM posted to rec.autos.tech
George[_1_]
external usenet poster
 
Posts: 42
Default 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  
Old September 9th 06, 01:37 PM posted to rec.autos.tech
jeffcoslacker[_113_]
external usenet poster
 
Posts: 1
Default 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  
Old September 9th 06, 02:08 PM posted to rec.autos.tech
jeffcoslacker[_114_]
external usenet poster
 
Posts: 1
Default 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  
Old September 9th 06, 02:37 PM posted to rec.autos.tech
George[_1_]
external usenet poster
 
Posts: 42
Default 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  
Old September 9th 06, 07:34 PM posted to rec.autos.tech
jeffcoslacker[_115_]
external usenet poster
 
Posts: 1
Default 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  
Old September 9th 06, 08:45 PM posted to rec.autos.tech
George[_1_]
external usenet poster
 
Posts: 42
Default 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  
Old September 9th 06, 10:56 PM posted to rec.autos.tech
Pop`
external usenet poster
 
Posts: 17
Default 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  
Old September 9th 06, 11:30 PM posted to rec.autos.tech
jeffcoslacker[_117_]
external usenet poster
 
Posts: 1
Default 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  
Old September 10th 06, 12:10 AM posted to rec.autos.tech
Steve[_1_]
external usenet poster
 
Posts: 3,043
Default 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

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

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


All times are GMT +1. The time now is 10:13 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AutoBanter.
The comments are property of their posters.