Topic: Nighthawk 550...more electrical problems

[Laminar]

I finally got around to working on the Nighthawk and I can't get it to start. I'm pretty sure it's an electrical problem.

It's to the point where it will occasionally pop and sound like it's running until I let off the starter button, at which point it ceases to do anything.

The battery's good, I have good power straight to the coils, and the carbs and fuel lines have been recently cleaned out. There is compression on all four cylinders and the timing is set correctly. I see spark on all four cylinders, but it's a tad weak on cylinders 1 and 4 (same coil).

The biggest thing I noticed is that with the engine off I see the tach needle jump with the turn signal. I can hear a hiss or buzz from the coils when the turn signal blinks.

I took a Dremel and sanding drum to all of the grounding surfaces at the coil to make sure the ground is good. I have the yellow wire going to cylinders 2 and 3 and the blue wire goes to cylinders 1 and 4. Color on top, black and white on bottom. I took a light piece of sandpaper to clean off the pickups on the crank sensors.

All of this started after about a 45 minute ride in the rain led to stuttering at about 5000rpm. I'm not sure what to do next. Grab a new set of coils?

[Alan F.]

Maybe you could run a new positive lead directly from the battery to the coils?  Maybe they're not getting enough voltage to produce an adequate spark?

Could you measure the voltage the coils are getting now?

You should be able to measure your coils with an ohmmeter, across the primaries of each coil you should get a similar reading, and across the output leads of each coil you should also get similar readings,  if there is infinite resistance across any of these points...you've found the fault you're looking for.

-Alan

[Laminar]

I already performed the relay mod so I have 12V straight to the coils from the battery turned on via a relay. I measure very little drop between the battery and the coils.

Just to clarify - you're suggesting that for each coil, I measure resistance between the terminals where the colored and black/white wires connect, and then measure resistance between where each of the two plug wires connect?

[pikeymick]

Were you able to get it running again?

[Laminar]

Nope, not yet. I bought a set of replacement coils on eBay that turned out to be DOA, so I sent them back. I bought a replacement CDI box but that didn't change anything.

I'm open to suggestions.

[pikeymick]

Hmmmmm, have you run a compression test?

[Laminar]

Hmmmmm, have you run a compression test?

Yep. Equal compression on all 1, 3, and 4, and 2 was about 10 pounds below them.

[750goes]

check for adequate fuel flow..
is there fuel in all bowls?
after cranking are the plugs wet ?
is the off/run/off switch positioned correctly?

[pikeymick]

You have spark so it's not the kill switch, you have fuel, so it's not the carbs... Try this. Open the vacuum ports on the intake rubber mounts and spray some carb cleaner or starting fluid in there, crank over.

What about flopping your coils and spark plug wiring so that 1&3 and 2&4 are on the opposite setup that they are on now.

[Laminar]

check for adequate fuel flow..
is there fuel in all bowls?
after cranking are the plugs wet ?
is the off/run/off switch positioned correctly?

1. Petcock cleaned, fuel line cleaned, fuel seen flowing through filter
2. Equal fuel in all four bowls
3. Don't remember
4. Yes.

[Laminar]

I just redid the compression test and got this:

1: 60psi
2: 120psi
3: 150psi
4: 120psi

The fact that the compression numbers changed this drastically between my first test and this one tells me that something funky is going on. Maybe I had the choke on before or maybe I screwed the tester in tighter this time. Either way, this current test doesn't look good.

The plugs were mildly damp after cranking, I wouldn't call them wet. They were more sooty than anything.

I need to put a little oil in #1 to see if that improves compression. If not, I'm assuming this means I have to pull the top end apart for the third time and make absolutely certain that the tappets are bled correctly. PITA.

[pikeymick]

How many miles on it?

[pikeymick]

But I don't think one low cylinder would keep it from running... I was low on two and they were the only two that worked, and I could still ride it haha.

If it won't start there must be some other complication going on...

[Laminar]

How many miles on it?

25,000. I put 5,000 of those on this past summer.

[Laminar]

I realized last night that the low cylinder (1) was the one I was squirting carb cleaner into to see if it would fire (it didn't), so the carb cleaner probably just washed the cylinder walls of oil, causing low compression in that cylinder. I put a little oil in it and saw a 30psi jump.

My money's still on spark. Maybe I'll try swapping the coils from my '76 onto it.

[pikeymick]

Phew! That's good to hear! Good luck with the coil swap!

[kirkn]

Hmmm......  all this started with a ride in the rain leading to a stutter at/above 5000 rpm?

That sounds like water contamination on a wire somewhere.  Pretty straightforward.

And now it won't start at all.  But you never really said - do you have spark at all four plugs?  The simple test - laying the plugs against the head and seeing a nice fat blue spark when you crank it over?

Swapping coils?  I'm not sure that's going to work, nor tell you much.  A '76 is a point-type ignition and that Nighthawk will be an electronic ignition.  Do the coils interchange?  Point-type ignitions function differently than electronic type.

Carbs?  Compression?  That all doesn't seem to follow from a simple rain-induced stutter....

Seems like you're running all over on this one.  Time to track down one item at a time...   

Kirk

[Laminar]

Hmmm......  all this started with a ride in the rain leading to a stutter at/above 5000 rpm?

That sounds like water contamination on a wire somewhere.  Pretty straightforward.

You'd think so.

And now it won't start at all.  But you never really said - do you have spark at all four plugs?  The simple test - laying the plugs against the head and seeing a nice fat blue spark when you crank it over?

Yes, spark at all four wires.

Swapping coils?  I'm not sure that's going to work, nor tell you much.  A '76 is a point-type ignition and that Nighthawk will be an electronic ignition.  Do the coils interchange?  Point-type ignitions function differently than electronic type.

The coils appear the same, all the way down to the wire colors coming in. I figured it was worth a shot.

Carbs?  Compression?  That all doesn't seem to follow from a simple rain-induced stutter....

Seems like you're running all over on this one.  Time to track down one item at a time...   

I'm open to suggestions for which one item to check, as I've checked every one item at a time I can think of.

[w1sa]

It sounds like you've got a coil ground short (similar to points that don't open properly).

I haven't got a circuit for your bike, but looking at a '84 750 N'Hawk, the 2-3 coil ground (yellow) completes the Tacho circuit via each 2-3 pulse generator/coil firing. That yellow wire also connects to the tach thru a common connector that includes the common harness ground for instrument and blinker lights.
So, I'm thinking along the lines, that during the 45 minutes of riding in the rain, water has got into that connector (or other) and created a short between the yellow wire pin (2-3 coil ground) and the harness ground pin. It would also explain why your tach pulses as the blinker operates i.e. blinker ground acts as ground for tach.

That could (I think) cause your coil firing to be weak on those two plugs, as you indicate.

Probably worth checking anyway!              

[Laminar]

Very interesting. I'll take a look at this this weekend!

[Alan F.]

Just to clarify - you're suggesting that for each coil, I measure resistance between the terminals where the colored and black/white wires connect, and then measure resistance between where each of the two plug wires connect?

Sorry man haven't been back to your thread in a bit. Here's some reading to clerify measuring coil windings... http://forums.sohc4.net/index.php?topic=59101.0
Best of luck.
-Alan

[Laminar]

Going nuts with the multimeter.

Coil/Primary/Secondary

2-3/2.8ohm/14,250ohm

1-4/2.8ohm/13,850ohm

The Clymer's manual says specs for the coils are 2.8ohm primary and 13,600-15,500ohm secondary. I saw roughly 5,000ohm in each of the spark plug wires, which is right on.

I pulled each spark plug out and confirmed that it was either wet or damp after cranking, and that if laid against the engine it produced a spark when cranking.

I have compression.

I have spark.

I have fuel.

I have air.

That's all it takes, right? So WTF am I missing?

[w1sa]

Are the sparks bluish or yellowish?

Also, a faulty spark unit/connection may affect ign. timing. Is it possible for you to check the timing with a strobe while cranking?

[Laminar]

Are the sparks bluish or yellowish?

Also, a faulty spark unit/connection may affect ign. timing. Is it possible for you to check the timing with a strobe while cranking?

I tried a replacement CDI box but that didn't change anything.

Sparks are blue/purple.

BUT I'M SO CLOSE. IT FIRED.

It managed to sustain itself once I let go of the starter button, but only for a few seconds. Doing that a bunch of times let me on to the fact that exhaust pipes 1 and 4 were too hot to touch and 2 and 3 were ice cold.

I put the multimeter to the 2/3 coil and it tested identical to the 1/4 coil, so I know the coil is good. The wires also tested good. I tested each spark plug in its respective wire and saw a spark.

The battery's charging now (5 minutes of cranking will wear it down pretty quickly) but once it's up again I'm going to swap the coils to see if 2 and 3 suddenly start firing.

It wants to run but it won't keep going on only two cylinders like that. I'm considering a new set of spark plugs as that'd be a cheap and easy fix that would help anyway.

[750goes]

maybe timimg for 2/3 is out of whack somewhere ??