Starting/idling issues. (Arm chair mechanic here)

[Nathan]

Hello! I wanted to get into the world of wrenching and took upon an 85 cb700 with 22,000 miles as my first project. Project indeed... I bought it as a pile of parts and worked my way through videos, forums, and of course the manual.

I have done it all on this bike. I rebuilt the engine from the ground up, every bolt, every torque value. And now I have found myself with a "functioning?" Nighthawk.



However, it doesn't work, and here is the issue. When I start the bike it cranks and runs until I stop pressing the starter button.

After a summer of work and many dollars spent, I am sad and happy with this outcome. However I would like to solve it, and get this beauty up and running.

So, with the issue relatively laid out, I will go into depth below. I would immensely appreciate it if you read it all the way through, and give any suggestions at all. While I wait for comments, I am going to go through some other threads on the forum and see what I can see.


Firstly, let me structure this post.
1. I am going to go into an overview of my current problem.
2. I will dive into all that I have done to the engine/bike/wiring harness afterwards.
      I hope these two will give the experienced mechanics a way to put two and two together, where I cannot.

Beginning with an overview of my current problem. So, my 85 nighthawk won't idle. I get the starter motor to turn on via the starter solenoid, I am getting gas through the petcock, and through the carbs. When I do the starting routine; Clutch, kill switch set to "on", and then press the starter button (no choke more on that later..) it will fire up, UNTIL I release the starter button.

    I can, however, open the throttle just a tiny bit before releasing the start button and then release the starter button and I can keep the engine running.  I can even rev it up, but again, after I stop giving it throttle, it dies. 


I have two main suspicions for this:

1. Some component in my ignition system is bad (cdi, coils, spark plugs, pulse generator).
2. My compression is under performing. It is sitting at 125 psi (A cheap 20$ compression tester from amazon) The specs are supposed to be 175 psi +_ 30 psi so I am 20 under spec.

      Ignition system:

Going deeper into the faulty ignition system I have found that I do have spark on every cylinder, and the spark is descent to my untrained eye, kinda blue kinda white.

I have tested the resistance on my pick up coil terminal and the ohm values from the white and yellow leads are 367 ohms (6 ohms out of that initial 330 300-360 ohm range) and from the other white wire and the blue wire is 363 (3 ohms out). First question I would like answered, are these upper and lower bounds absolute? I am a mere 6 and 3 ohms out, does that make a difference? (This will come up again very shortly)

I have tested the resistance on the coils' terminal, the 3 prong white connector with the blue,yellow, and black/white wires. Resistance readings are as follows:
      blue to black/white: 2.8, good (spec is 2.8 +_10%)
      Yellow to blue: 5.6 bad
      Yellow to black/white: 2.8 good

I have also taken off the two black and white wires, the yellow wire, and the blue wire from the coils. Testing the "blue wired" terminal to it's counterpart black/white wire terminal on coil 2 (right most when on bike) I get 2.8 good,
Testing the "yellow wired" terminal to it's counterpart black/white wire terminal on coil 1 (left) I get 2.6 good. (The difference with the wires on vs off is weird to me but I am but a noob)

So with nothing inherently wrong but the resistance on b to y I go further in the manual; testing the resistance of the spark boots while attached to the coils ( think this is the secondary side as referenced in the manual? Idk)
      On coil 2 with the spark plug boots in I get a restiance of 26.2 k ohms (spec is 16.3 to 21.7 k ohms) so that is bad.
      On coil 1 I also get a bad 25.4 k ohm reading.




So, there it is, the coils seem to be bad thus the ignition system is not working right. But wait... there's more?

I go deeper and take of the spark boots and test the actual coils themself, when I stick my probes in the holes were the boots used to be attached and test for resistance I get very respectable resistance values of 15.62 k ohms on coil 1 and 15.45 k ohms on coil 2. In spec of the 14+_ 10% k ohms (a.k.a 12.6-15.6 k ohms). 0.02 k ohms is not much to worry about I think.

Okay so if the actually body of the coils are in spec, then what about the actual spark boots? Well I am not sure what values are in spec of not, but I did them anyways and found something interesting. The two "L" shaped boots (both being the bl/w wired boot) are sitting at a resistance of 1.3 m ohms and the two straight shaped boots are sitting at about 5-7 k ohms.          In case it is needed, I jus stuck one prong on my multimeter into the spark plug entrance end (actual boot) and then one end into the wire where it would screw to the coil terminals)

So, it seems the coils are bad with the boots on but fine with them off. expect for the blue to yellow ohm value on the 3 piece connectors. (Because you can't get a reading just from the primary tab things on the blue and yellow wire terminals on the coils.) I know that is messy sorry about that.
And it seems that the pickup coils are good because they pass spec. Which makes me think the ignition system could be faulty, but more than likely it is the compression which I will get into now.



        Compression:

So, yes I have bad compression. This might be an immediate answer to my starting issue. Without descent compression and thus vacuum ability by the piston, I will never be able to draw in enough air/fuel to start the bike. So, this could be the answer and I am simply too naive to accept that bad compression would be the reason for the bike not being able to idle.

But something in me tells me it has to do with the ignition system. How can I rev the bike with bad compression? Wouldn't it not start at all? And all 4 cylinders are firing as evidence of my semi hot exhaust tubes on each piston. SO it just seems like there is a feedback loop that I am missing that is the cause of this.

The bike instantly dies when I let off the starter button. There is no struggle it just stops. Not like a hard stop, but it just stops.


I do believe it is the rings as I put a bout a table spoon of oil in one of the cylinders and the compression shot up to about 200 psi. So I think that rules out the valves. I did lap the valves, and I did put test for leaks by putting gasoline on them while closes with no springs on them and they did okay-ish.

I did try to keep the rings in the correct orientation while putting the cylinders over them (120 degrees apart and all that) but stuff definitely could have goteen turned around in that process) I also put a descent 45 degree cross hatch in each cylinder with a hone, so maybe I went to far, but I really don't think I did. I spent about 20 seconds with the hone in each cylinder going at hight speed on my drill. So I don't think I could have opened the up much with a 220 grit hone at only 20-40 seconds. I think it is the piston rings as I didn't replace them and the bike originally had about 22,000 miles.




Now, I will go into what all I have done with the bike. One thing might also be a very large red flag for it working AND from a restoration stand point...

So, I have replaced the starter chain with the upgraded chain. I have been through the carbs and they are all clean with some new jets where needed (ebay carb rebuild for 700 with good reviews) and the correct two turns out of the pilot screw. I also have a new air filter and oil filter. Oil is getting all around the engine and through the air cooled radiator at the front.

I have replaced all gaskets including head gasket. I have also replaced most oil seals with the correct oem ones.

Some things to note, I have not attached brake lines or even the clutch line to the slave master cylinder. I did not want to attach these until the bike ran, just in case I have to take the engine out again. (Which is looking likely for new piston rings). I know I am in neutral.

Could there be something with the clutch line actually being installed and thus the clutch actually being fully disengaged that would prevent the engine from running? I don't think so, but maybe I am wrong. When I rev the engine the back wheel does turn a bit which is weird to me, but idk. I know I have the clutch dogs and everything in place.

Here is the red flag, I have an aftermarket gauge in which everything works except for the rpm gauge. I have the yellow wire on the wiring harness connected to the rpm wire on the gauge but I still don't see any movement when I "run" the bike. I wonder if this is a link to the 5.6 ohms out of spec on my blue to yellow resistance check on the 3 piece white connecter as mentioned above.

I don't think there is a relay or anything in the original gauge cluster, but I could be wrong and this could actually be the reason. Not sure.

With that, there are only 4 other things I can think of.

1. I am missing that little small air duct that is under the seat and is like a funnel for the air filter.
2. I haven't fully tested the rectifier or alternator. But I hooked up my multimeter set to dc voltage on the battery, and when I was "running" the engine I saw it jump to about 13 volts, meaning it is charging, I think...
3. The coils are bad, but also the cdi could be bad, not sure how to test cdi. There are no cracks in it or anything, and all terminals are clean.
4. Maybe I have a stuck float and the engine is being flooded, but I don't know how to check that. And I don't think that is the case as when the bike is "running" no leakage is occurring at the carbs. I have taken out the sparks and they do all have carbon on them, and some of them were kind of wet, but I think this is because I had flooded the engine once when I used the choke for too long. Which I am now not using it.

So, there we go. My very messy and jumbled plea for help on my nighthawk, again anything helps. And thank you for spending your time to read all of this! Looking forward to some responses.

[Larry Fine]

Welcome to the forum. That's a hell of a first post!

The symptoms suggest the carbs, since you can keep it running with throttle.

Could it be as simple as setting the idle-speed adjuster?

[Nathan]

Hi Larry! Thank you for replying. I am 99% sure I set the idle screws correctly. Tighten them down, and then two turns out? I will definitely check them though as that would make my day if it that is the case.


I do have a couple of questions I sort of poked at in my Original post, but I would like to list them out clearly. Simply because you are right, that is a long twisting and winding post and I think a clear list of questions would greatly benefit me and whoever is reading this. This is actually the first time I have posted anything in any online forum, so I apologize if my formatting or anything else is a bit weird.

Anyways, here they are:
1. Would me using an aftermarket gauge affect anything? As far as I am aware, the rpm wire in the bike's wire harness is yellow, and serves two purposes. One is to read the pick up coils (or whatever they are called) and the other is for the ignition coil. This is my most important question because I have a bad ohm reading involving that yellow wire that I listed somewhere in my original post. So, I think maybe it is linked and possible being amplified through my not stock gauge cluster.


2. A more general question. Why did my wheel spin when I applied throttle to baby the engine and keep it running? I am in neutral so I am off put by this. It did not spin fast at all. Very slow. Maybe a rotation in 10 seconds.

3. How big of a deal is low compression? I know it is quite severe especially for power output, but in terms of idling? Just so people don't have to poke around: idle specs are about 140-200 I am at 125 psi. Haven't done a leak down test yet.

[Nathan]

Oh! I will say the spark plugs to seem to have black soot or carbon or something on them. Just a thin layer I can wipe off with my finger. I think that means engine is "running" rich. So maybe I set the idle speed screws to spec, but that is not what is needed. Which means I am off to replace the oem ones with ones that don't have the limiter. So I can muck around with them more easily while on the bike. Which would also help with actually getting the idle in that 1,000 rpm sweet spot when I do get it working.

[Larry Fine]

No, I mean a single idle-speed adjuster knob (if there is one) or screw, not the four idle-mixture screws.

1. If your wiring is correct, no. Could you have the starter wire connected to the wrong side of the starter button?

2. Because in neutral, the oil still provides some rotational drag between the input and output gear shafts.

3. It is said that what matters is no more than a 10% variance in compression readings among the cylinders.

[Nathan]

Ahh yess I do have one singular knob. It was one of those things where I just kind of forgot about it. Let me go look and play around with it. And look in the manual of course.

Also, I just have to say I should have been on here a long time ago. I don't want to over ask questions, but this is awesome having someone knowledgable to talk to. No one in my family is mechanically inclined, and I can read through forums and videos as much as I want, but getting a response to your very own questions feels much better and concrete.

With that, I am off to look at the knob, and recheck the starter button wire.

[Nathan]

WOAH. I just turned the single idle adjuster knob in some because I think the engine is running rich as previously stated. And it idled for like half a second or so! I am going to test it more, but I am simply excited there is actual progress.

[Nathan]

Yep it is idling. Not sure at what because the gauge still not working. But yeah easy fix apparently. Will post more later asking about other stuff as I still have quite a few questions regarding wheels, suspension, and general motorcycle practices.

[Larry Fine]

You're welcome. Electrical is my specialty, but I have done just about everything at least once.

Let us know how it progresses.

[Larry Fine]

Just to add, you should need 'some' choke (enrichener) when it's stone cold, but should be able to idle without it in three to five minutes. I always wait until it's warm enough to carburete cleanly without it to start riding.

[Nathan]

Okay so the bike is idling pretty well. I am now coming back here to ask you with your electrical knowledge, if I ended up making a dumb purchase. So, I bought an aftermarket gauge that is marketed as a " Motorcycle Mechanical Odometer Speedometer Engine Speed Universal Cafe Racer" It is also (or it is also using) an "Inductor rotating speed" as it's "rpm" wire.

Now, on the nighthawk there are 5 wires running to the rpm gauge, two are for the light being the y/white wire and the ground wire. And 3 are running to the actuall tachometer unit. These three are a yellow wire, a black/brown wire, and of course a ground wire.

I believe the nighthawk is measuring it's rpms using a pulse signal to measure rpms and it is carried through that yellow wire. My aftermarket gauge has a wire for rpms and so I connect the two. I believe the bl/br wire supplies power to the unit and so I connect that to the "live wire" on the gauge. (I would send a photo, but I am not sure how)

With these wires plugged in this way, everything on the gauge works, but not the rpm dial. So, I wonder if it is because the nighthawk uses pulse signals and the gauge uses "Inductor rotating speed" signals it is not working. Maybe I need to search for an "Inductor rotating speed" gauge. Or spend a lot of money on a functioning nighthawk cluster.

[Nathan]

Also, when I start the bike and I have the alternator cover on there is this loud screeching noise. When I take the cover off and start the bike, there is no noise.

Also when the cover is off I can see the alternator body (the copper coils on the outside of the spinning part of the alternator) sort of turns and then stops because idk why. So, I think that is just friction from the alternator connected to the starter chain holding it in. But I think that wanting to twist acts on the screws and the cover making a screeching noise. It is really weird how it is set up. Like the outside coils the pick up coils I guess they are called, are touching the screws and touching the cover.

Which makes sense as they are stationary and the spinning fan thing inside of those coils is the one that moves, but I am just confused and wonder if this is a common problem or I need some tupe of electrical grease to lube something inside of the alternator.