For my early 1990's Johnson outboards 6hp, 25hp, and 115hp, I use an adjustable gap spark tester set to 7/16, if it jumps it, then I set it to 3/4 to see if it does it, if it does it is good. I'm told by the forum that the spark must snap and be blue, two things which I have never seen yet. Maybe they are testing them at night (see blue?), and how I'm supposed to hear a snap with the starter turning is a mystery to me. ANYHOW, is this OTC 6589 a more accurate tester, see the review from Amazon posted below.
OTC 6589 Electronic Ignition Spark Tester
http://www.amazon.com/gp/product/B0050SFVO2/ref=ox_sc_act_title_3?ie=UTF8&psc=1&smid=ATVPDKIKX0DER
Most Helpful Customer Reviews
42 of 46 people found the following review helpfulProfessional Mechanic here
By EAGLESOAR1 on May 7, 2013
Verified Purchase I own an automotive repair facility that employs 3 other technicians and I have been using spark testers for over 30 years and I have tried them all:
1. The plastic encapsulated ones (not reliable or accurate)
2. The "In Line" type - NEVER - NEVER USE THESE!!
It only takes around 10,000 volts to "light" those up - but today's cars need upwards of 50,000 volts so you'll have a "light" but not enough volts to fire the spark plug.
3. I have had 2 OTC 6589's in my box for 20 years - they ALWAYS work AND tell the TRUTH!
Yes, I have played around with the others and ALL OF THE DIFFERENT STYLES OF THE FIRST 2 I LISTED HAVE CAUSED ME TO MISS A DIAGNOSTIC. (Hence - cost me productivity time & money) But, when I am in doubt, I grab my OTC and PROVE IT! I NO LONGER USE OR ALLOW IN THE SHOP ANY OTHER SPARK TESTER THAN AN OTC.
When I am diagnosing a V-6, V-8 or V-10 motor, I use 2 of these at the same time - one on each side of the motor. Sadly, I dropped one and it being porcelain - it broke (just like a regular spark plug would) So I just ordered 2 more today to keep in my shop.
By the way--- the KD 2757 that "LOOKS" the same as the OTC one DOES NOT!!! They changed the design and it is now "plastic encapsulated" and not as accurate. (Same design as the KD 2756)
Yes - the OTC is more expensive but this is truly a case of " YOU GET WHAT YOU PAY FOR!"
Update:
Something I forgot to mention - the clips on these are as heavy duty as they could make them with the amount of material they have to work with.
I don't use the clips on the tester itself (yes, they break)
I use a 3 foot jumper wire I made out of common "lamp cord" with alligator clips on each end. (it's flexible, heavy duty and rated for 25 amps)
(also see: Kastar Hand Tools (KAS1138) 2 x 30' Magnetic Retractable Test Leads - 10 amp rating)
I clip one end of the jumper wire to the spark tester clip and the other end to the CLEAN Negative post on the battery - not any metal on the engine itself.
If you don't "KNOW" that you have a good ground (rust, corrosion, bad ground from battery to engine block) then you could make a false diagnostic not due to the spark tester operation but because you didn't have a good ground path for the current.
Whenever I am testing electrical, I NEVER ground to the frame or body - I always run a jumper wire to the battery negative post - and make sure the negative battery post is clean!
OTC 6589 Electronic Ignition Spark Tester
http://www.amazon.com/gp/product/B0050SFVO2/ref=ox_sc_act_title_3?ie=UTF8&psc=1&smid=ATVPDKIKX0DER
Most Helpful Customer Reviews
42 of 46 people found the following review helpfulProfessional Mechanic here
By EAGLESOAR1 on May 7, 2013
Verified Purchase I own an automotive repair facility that employs 3 other technicians and I have been using spark testers for over 30 years and I have tried them all:
1. The plastic encapsulated ones (not reliable or accurate)
2. The "In Line" type - NEVER - NEVER USE THESE!!
It only takes around 10,000 volts to "light" those up - but today's cars need upwards of 50,000 volts so you'll have a "light" but not enough volts to fire the spark plug.
3. I have had 2 OTC 6589's in my box for 20 years - they ALWAYS work AND tell the TRUTH!
Yes, I have played around with the others and ALL OF THE DIFFERENT STYLES OF THE FIRST 2 I LISTED HAVE CAUSED ME TO MISS A DIAGNOSTIC. (Hence - cost me productivity time & money) But, when I am in doubt, I grab my OTC and PROVE IT! I NO LONGER USE OR ALLOW IN THE SHOP ANY OTHER SPARK TESTER THAN AN OTC.
When I am diagnosing a V-6, V-8 or V-10 motor, I use 2 of these at the same time - one on each side of the motor. Sadly, I dropped one and it being porcelain - it broke (just like a regular spark plug would) So I just ordered 2 more today to keep in my shop.
By the way--- the KD 2757 that "LOOKS" the same as the OTC one DOES NOT!!! They changed the design and it is now "plastic encapsulated" and not as accurate. (Same design as the KD 2756)
Yes - the OTC is more expensive but this is truly a case of " YOU GET WHAT YOU PAY FOR!"
Update:
Something I forgot to mention - the clips on these are as heavy duty as they could make them with the amount of material they have to work with.
I don't use the clips on the tester itself (yes, they break)
I use a 3 foot jumper wire I made out of common "lamp cord" with alligator clips on each end. (it's flexible, heavy duty and rated for 25 amps)
(also see: Kastar Hand Tools (KAS1138) 2 x 30' Magnetic Retractable Test Leads - 10 amp rating)
I clip one end of the jumper wire to the spark tester clip and the other end to the CLEAN Negative post on the battery - not any metal on the engine itself.
If you don't "KNOW" that you have a good ground (rust, corrosion, bad ground from battery to engine block) then you could make a false diagnostic not due to the spark tester operation but because you didn't have a good ground path for the current.
Whenever I am testing electrical, I NEVER ground to the frame or body - I always run a jumper wire to the battery negative post - and make sure the negative battery post is clean!
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