Coil Output Voltage Question (Poor Mileage Troubleshooting)

[Steel Toed Tank]

I have a poor mileage issue. depending on how I ride I get between 27 - 34 mpg. Sometimes worse.

I had a very crappy air filter/intake from the PO on it last season, and since my plugs looked great and the electrical and ignition systems checked out with minimal voltage drops and resistances all in spec, I figured my issue HAD to be the intake.

So this season I installed the proper airbox and filter but my mileage never changed.

I weigh about 340 lbs so I figured maybe THAT would account for the bad mileage, but other big guys on here with bigger bikes than mine get WAY better mpg than me.

So if everything checks out and is up to proper spec, what could the issue be?

I remember way back when reading a thread where the guy was chasing his tale trying to figure out why he was running rich even though everything else he could check was right where it should have been.

In the end he replaced his coils with dyna greens and his issues vanished.

I searched high and low for a way to check coil output voltage but aside from 'checking for spark' the old fashioned way or buying expensive lab equipment I couldn't seem to find a way.

I didn't want to just replace things that otherwise tested perfectly fine, and it seemed my size was the last obvious cause I could find for poor mpg.
My bike starts instantly, hot or cold, choked or not, and accelerates smoothly with no stumbles or flat spots, so the coils HAD to be good right?

A few days ago a friend of mine found this device at a very remote garage sale, and grabbed it for me for $10!

So I have tested my coils and the results are 5kv from the left coil and 7kv from the right coil.
I should add here that I tested this unit on two cars with a known coil voltage output spec and they both tested perfectly.

I know the accel and dyna coils put out 35kv, but despite my forum searches and scouring BassCliff's site, I can't find what the OEM coils should be putting out.

So finally we get to my question, what is the stock kilovolt output of an OEM coil?

 

[Steel Toed Tank]

A little update.

A little update.

When I first ran the test the engine was hot.

I tested it again cold and got 12kv from left coil and 14kv from the right one.

After a 10 minute trip to warm it up it's back to 5-7kv.

I know I need new coils, but still wondering what spec kv is supposed to be.

 

[Steel Toed Tank]

Somebody has GOT to know what the coil output voltage is supposed to be.

 

[koolaid_kid]

You should be at least 20 Kilovolts to the plugs. You are way too low.
Have you tried trimming the coil wires to remove corroded copper?

 

[Steel Toed Tank]

Oh yeah, that stuff is all tip-top.
Trimmed up the plug wires and tested my resistance and voltage when I cleaned and greased my harness last spring,
then I did it all again this spring as I had unacceptable voltage drops in the harness.

I should mention that the bike gets parked inside the garage too.

The resistances and the other voltages are all right where they should be.

Also the readings I get are identical from both wires from a single coil.

 

[Badooka]

STT,
Did you try ohming your wires? They can go bad as well.

 

[Steel Toed Tank]

Yup, all the resistances are great.

The coil test results from the instructions on BassCiffs' site are all exactly where they should be.
Everything tests perfect according to the site, but the site doesn't cover what the output voltage should be.

Nothing anywhere tells me what the output voltage should be, lol.

Only instructions I can find anywhere say to remove a spark plug and see if the spark is blue or white, weak or strong, etc.

While not as bright white and snappy as my sled or car plugs, the sparks on my bike are still strong looking.



Either way I now know for sure that I need new coils, thanks to this tester.

 

[almarconi]

Worn needle jets (they are in your carburetors) can contribute to poor gas mileage. They will make your mid range real rich which I would imagine is where most of your driving occurs. There are many factors that could cause poor gas mileage, I think its funny how you have convinced yourself that the coils are the problem.

 

[koolaid_kid]

Yup, all the resistances are great.

The coil test results from the instructions on BassCiffs' site are all exactly where they should be.
Everything tests perfect according to the site, but the site doesn't cover what the output voltage should be.

Nothing anywhere tells me what the output voltage should be, lol.

Only instructions I can find anywhere say to remove a spark plug and see if the spark is blue or white, weak or strong, etc.

While not as bright white and snappy as my sled or car plugs, the sparks on my bike are still strong looking.



Either way I now know for sure that I need new coils, thanks to this tester.

I have never seen a manufacturer publish the output voltages of their coils.
If it has proper voltage the spark should be bright blue.

 

[Steel Toed Tank]

My car ones are supposed to be 45-50kv, they test at 48kv.
I got that number under the specs of the replacement product page.

Same with the Accel and Dyna coils, they sometimes use "30-35kv output!!" as a selling point.

The spark looks great, I mean without doing this test I would never have suspected the coils.
My plugs are always light tan like coffee with a good amount of cream in it, never dark or fouled or crusty.

I seriously doubt stock output is supposed to be 12-14kv, then dropping to 5-7kv, lol.