Troubleshooting starting issue 1982 CB650

[renegi9036]

Apologies if this belongs in the technical forum...new member here

I've worked plenty on suzuki gs bikes and this it my first honda. I'll be tackling a 82' cb900 this winter, but the bike I'm currently working on (and it doesn't need much, I hope) is an 82 nighthawk 650.

Gal i bought it from claims it ran and rode until she plugged in the charger backwards and things stopped working.

So i go to work on it...30 fuse at the solenoid is blown battery reads 3v, is junk after a 24hr charge and i only get it to 8v.

New fuse, Fresh battery 12.9v, key in it powers up, all lights and do-dads work.

I go to start click, small ---, solenoid click small whir, rinse and repeat.

-Starter Solenoid Relay tests good...4-5 ohms across coils (ordered another one for $7 because why not?)
-Starter tests good (although, from the solenoid, I get about an entire 1v less (11.9 to starter when attempting to start vs 12.9 at battery...). I figure this should still be enough to do something, right? To crank? Educate me here please.

Additional and maybe not relevant info:

-Regardless of the run/kill switch setting, I am able to attempt to start the bike - Shouldn't I not be able to attempt to start if it is set to 'off'?
-I did clean up those nasty melted connections in the video

Here's a video of what its doing. https://youtube.com/shorts/qHDjQVIvLS0?feature=share

I'm a bit stumped. Any advice is appreciated!

[Volker_P]

Welcome here! ,

I do not get sound on the video so I do not know what it really does.

So lets try something different:

The starter should crank the engine when you bridge the two starter relay connectors by a thick cable. Does it?

If it cranks that way -and as it seems to click- the contacts inside the starter solenoid might be bad. Here is how I solved this issue some time ago:
viewtopic.php?f=4&t=4051&start=5 (this 30A main fuse there is not Honda )

The kill switch only affects ignition. On the other hand the clutch and neutral switches affect starter operation. But in this case you should not even hear a click. Basically you should never hear the click of the starter relay alone.

In case of insufficient battery power you should observe a blackout together with the click. So this is probably not your issue.

As you seem to miss 1V I would propose to open the starter and clean off the black stuff from brushes wear inside. Check if brushes are still moving and long enough.

If you only hear a fast spinning sound from the starter but the engine does not crank, you have a starter clutch issue (which is quite common) or missing teeth on a starter transmission sprocket.

[renegi9036]

Thank you for the reply! I followed all of your advice. Turns out, you can't use a 12ft jumper cable to connect a battery out of the motorcycle to their leads Although the battery was good and fully charged, there must be some type of degradation factor over that length of travel to a motorcycle, it just didn't quite have enough to crank even though 12.9v was read at the solenoid (and then the drop to the starter).

Installing battery directly on bike (needed to modify basket a bit) did the trick.

Also guessing in future if I test out of bike i need to use much shorter leads, which i didnt have at the time, which is why i used the car jumper cables.

I'll be here a while posting and reading! Few other things I'll need to tackle. Starter sproket teeth look good and only spin one direction, so that's good

[Volker_P]

Good to hear that you solved the issue.

Anyway at least for a cold engine it should at least crank weakly with reasonable starter cables, too.
So I suspect that something is wrong with your cables. Before you consider to cut them you could try again and check if something at these cables gets warm or even hot after a few seconds. Most suspicious is where cables are connected to the clamps.

[renegi9036]

Hmm interesting...I wonder if that's related to another issue I'm having (I can start a new thread too if that helps)

For starters, I have pd50 carbs on this bike and they look immaculate - 2 PO's ago someone clearly did some work on these, and replacing all gaskets and boots, etc....but....i don't believe these are the correct carbs for the 82' nighthawk 650?

Anyways, I'm experiencing an riding / fuel issue currently and need a schmidge of guidance troubleshooting. Bike is bone stock that I know of (other than those carbs if they aren't stock).

It's very difficult after the bike is warmed up and idling around 12-1500 to take off from first gear. What I've found works is actually using the choke about 1/2 way and giving it some gas to get it into first, up to about 4k rpm. Then, however, it kind of stumbles along...so i shift into second. While in second (or really any gear other than first), it moves along, but can really take off like a bandit with very little throttle! Almost like I'm WOT but I am nowhere near. All 4 exhaust headers are hot, so cylinders are firing.

Plugs actually show a little rich to fouled across all 4, all stock, air filter looks great. Plugs are hotter than the dickens after a short ride which, along with the surging, lead me to believe it's lean.

Any thoughts or guidance?

[Volker_P]

PD50 carbs should not fit the black cylinder head at all because of different intake spacing. A "clean solution" could be kinked carb boots but sometimes people force the carbs somehow into the boots. This is very susceptible to cracks and airleaks. If you take off the carbs be prepared to be unable to remount them reasonably!
The usual check for airleaks is to let it idle and spray starting fluid or brake cleaner on the carb boots and listen for changes in rpms.

Take off from idle requires choke when it is cold for a long time compared to other bikes but it should not be an issue any more when the engine is warm. Possibly the accelerator pump does not work properly.
Another option are the air cutoff diaphragms. Some carbs have it, others don't. You can remove the circular cover of the outermost carb to have a look. If there are diaphragms there are bores, too. One may block the bores to save splitting the carbs for diaphragm replacement (they are a expensive and hard to get as they are usually not included in rebuild kits). How to do so may be found in "forum links to common technical issues" in my signature.

CB650 plugs typically look bright, even a bit of white is still normal and all right. So I don't think your engine runs lean in general. Sounds like you have a significant carb issue.

[renegi9036]

Maybe it's all in my head and I'm just not used to riding these old Honda's (I've been riding old suzukis and yamahas for years with much simplier carbs )

Also, maybe I'm impatient with the warm up. It's 80 here daily and I don't need choke to start and idles 1200 straight away.

I did a test by taking airbox cover off and it seemed to ride better. However, I also took it on much longer ride, and after a while I was off choke completely. Getting going is still kind of funny, feel like I'm at 4k rpm to make sure she has some gas. I need to isolate one variable at a time.

Regarding carbs, they appear in order with correct boots, maybe someone also swapped engine? Here is a pic.

Capture.PNG (304.74 KiB) Viewed 20958 times

-air cutoffs exist (they appear new).
-accel pump also looks new and appears to operate normally (goes down a few milimeters with throttle)

[Volker_P]

Also, maybe I'm impatient with the warm up. It's 80 here daily and I don't need choke to start and idles 1200 straight away.

It is a fact that the CB650 requires much longer warm up to run reasonably without choke than most other bikes.

I did a test by taking airbox cover off and it seemed to ride better.

Which can be found reported by some people in this forum, too.

However, I also took it on much longer ride, and after a while I was off choke completely. Getting going is still kind of funny, feel like I'm at 4k rpm to make sure she has some gas. I need to isolate one variable at a time.

The CB650 is no low rpm torque monster so you really need some rpms to get off. In particular with the 50hp camshaft (which is however hardly found outside Germany). I can confirm that 4k rpm is kind of a minimum rpm level to feel something going on .

.. maybe someone also swapped engine?

For sure because the 1982 SC stock engine is black and carries a RC08E- engine number.
You seem have a 1979/80 silver engine with RC03E- engine number in a RC08 frame.
Nothing wrong about that, transmission gears are a bit different.

[fizzlebottom]

That's a weird one to see. PD carbs on a Nighthawk. If it works, it works! I'm wondering about the airbox though. Since the VB44 carbs have different spacing on the cylinder head side than the PD carbs, do they also have different spacing on the intake side?

[renegi9036]

That's a weird one to see. PD carbs on a Nighthawk. If it works, it works! I'm wondering about the airbox though. Since the VB44 carbs have different spacing on the cylinder head side than the PD carbs, do they also have different spacing on the intake side?

I believe it had a different airbox with it too, because the bike came with another/spare airbox

[fizzlebottom]

Well, if for any reason you ever want to change back to the VB44C carbs, then you'll also need the correct airbox and an '81-82 cylinder head to account for the different carb spacing. But I can't see a reason why you'd do that other than originality.

[Volker_P]

This looks like the PD carbs airbox.
Not really sure but I think I remember that the airbox side boots of the carbs are not exactly "coaxial". Which means turning them in the airbox by some angle would allow a certain adaptation of heigth and width.