Want more power???

[Pete in PA]

I've done this to many bikes I've owned in the past but I don't remember it waking the bike up this drastically. Never any problems, no burnt out coils, ignition modules, pick up coils, nothing. Seems to be a Honda thing with resistors in the sparkplug caps and in the sparkplugs.

 This applies to the 91-03 Nighthawk but also The 80's NH'S and really any bike.

There are 2 coils for the 4 cylinders, so there is a waste spark on the other cylinder. 1+3 and 2+4 are paired.

On the outside (1+4) sparkplug caps, each one has a 5000 ohm resistor in it. You pull the cap off the plug, look inside with a flashlight and you'll see a straight slot for a screw driver.  turn this out and you'll get a spring, the resistor, and the screw.

Go find a rod, all thread, something of the same diameter and cut a section the same length as the resistor. I used a cutoff wheel in my Dremel.

Put that piece in to replace the resistor and reassemble. Do the same for #4. cap.

Now on the 80's NH'S and other bikes there might be a resistor in every cap. Just have to check.

The DPR8EA-9 sparkplug calls for a .032-.035 in. gap. It's capable of a .044 in. gap and maybe more. The ground electrode needs to stay level. It can't come in at an angle or the spark will just track up and away from the tip of the ground.

I set mine for .044 in.

I havent checked but if a DP8EA-9 (no R for resistor) plug is still available you can cut another 5000 ohms X2 out of the circuit.


Don't start talking voltage, spark duration, Why it's there (RFI, EMP, interference), etc.

Just try it. Bike starts easier, more power everywhere but especially midrange to rev limiter.

Of course completely reversible if you want to...You won't.

This mod is similar to one on my 2 Chevy Cruzes. Even on them no problems or interference for 100k miles. Since they are turbos you can't get as drastic, they get spark blow out if the gap is too big.

[Larry Fine]

1+3 and 2+4 are paired.

Actually, 1 and 4 share one coil, 2 and 3 share the other one.

[Pete in PA]

1+3 and 2+4 are paired.

Actually, 1 and 4 share one coil, 2 and 3 share the other one.

Hmmmm...Well that doesn't work with only 1 and 4 having a resistor.

2 and 3 are different inside the caps. Can't get them apart as far as I can tell.
Maybe there are still 2 resistors I missed.

[mollusc]

I replaced my wires and it made a huge difference.  I believe they all have resistors.

[Pete in PA]

Took bike apart again and found the 2 straight boots (2+3) Can not come apart to remove the resistors.😡😡

So I put the resistors back in but left the plugs gapped at .044 in.

Haven't test rode yet, but since half of the plugs still had the full resistance should be fine.

I'm going to go get resistorless (DP8EA-9) plugs. Auto Zone shows them in stock.

[Pete in PA]

I replaced my wires and it made a huge difference.  I believe they all have resistors.

Just the wires using the same caps at both ends?

The resistors are in the boots at the spark plug end.

[mollusc]

No, I replaced wires and caps with aftermarket ones.  But since it would make no sense for only one of each pair to have a resistor, either they all have them or they don't.

[draser]

Hmmm... the physics of this says it doesn't make much diff in the high voltage that gets to the plug, the current is so small that the voltage drop on the resistor is not much. You're feeling the bike more lively... but my NH in stock form is as lively as I want it to be, with standard gearing that keeps the revs high I can pass no problem in 5-th, and so on...

Unsure about increasing the gap, what is the benefit? That requires more HV from the coils and changes the spark timing. The engine was built to work optimal with the stated gap.

Another comment from the "hot rod books"... they (hot rodders) modify the plugs by shortening the ground electrode and reshape down it to create the required gap - that will expose the spark to the mixture and have some benefits. Never tried it but makes sense.

[Pete in PA]

Test ride went fine as I figured, same power. I will get the no resistor plugs for it. Too much stacking of resistance with the waste spark system. Two 5k ohm resistors, two 5k ohm  resistors in plugs.

Why does it work: larger gaps = bigger spark = better burn = more power.

[Pete in PA]

In the Honda manual they list sparkplug gap as .030-.040 in. At .044 I'm only slightly large.

If anyone knows where to get resistorless straight plug caps that screw onto the plug wire like these do let me know.

[Willie]

If anyone knows where to get resistorless straight plug caps that screw onto the plug wire like these do let me know.

I'm in need of new caps too and figure I'd replace the wires while I'm at it.
Can anyone recommend a vendor for either or both?

[Pete in PA]

A lot of NGK caps on Ebay, as to a particular vendor no idea. All seem to have resistors, unknown if you can get to them.

 I'm assuming wire can be bought by the foot and you cut to length and assemble.

Ive never changed caps or wires on any bike I've owned, never had a problem. Having an actual wire in the wire helps. Never understood old car wires why they didn't use real wire.

You can cut a smidge off both ends and reassemble.  There can be corrosion from water especially if it's an older bike.

[draser]

Why does it work: larger gaps = bigger spark = better burn = more power

Right... but a larger gap will require a slightly longer time for air to ionize and spark to occur, hence timing will be retarded some = less power.

[Willie]

I'm embarrassed to admit that, although I noticed the slotted head inside OEM caps, I never thought to look inside one. Thanks Pete for bringing that to my attention. I'll be substituting rods for resistors in the near future.
Now about buying replacement caps....am I correct that the 700 requires (2) that come off at an angle and (2) that are straight? That's what it looks like to me.

[Larry Fine]

Not required, per se, but what best routes the wires.

The shop manual probably has a drawing showing it.