Topic: Loss of Power in a 1982 Honda Nighthawk 650

[Cyprusice]

I recently picked up a 1982 Honda Nighthawk 650 with a 4 into 1 exhaust and K&N RC-2362 clamp on airfilters. I noticed when i bought the bike that it had a lob to it when it ran. I adjusted the valves to .003 on the intakes and .004 on the exhaust and this took care of the problem. However it has a problem that I just cant figureout. Now granted I am a novice when it comes to both small engines and motorcycles so be gentel with me. 

Every so often the bike will just lose power as if it were running on less than 4 cylinders. For example last night it was sitting in my garage idling (1050 rmps) like a champ for 15 mins when it just suddenly died. So I tried to start it again, which it did but it was rough starting; when it did start it sounded funny, kind of like it wasn't running on all cylinders. So I drove it up and down my driveway (400 yards) and gave it hell in 2nd gear a few times when it just suddenly came back and was running like it normally does. This sudden loss and regain of power has happen when driving down the road two or three times before. One of these times it would not start again until I let it sit for 30 mins, and even at that it started very rough, normally it start great.

I have not ran a upper cylinder lube like BG44K through the bike yet as mentioned in one of Hondaman's posts, I have replaced the sparkplugs and done valve timing as i mentioned earlier. Could this be a problem with my carbs? I have also herd mention of the timing advance, but even after looking at my Haynes manual I cants seem to find where it is and how to adjust it. To me it seems to be a problem with either the fuel or ignition systems... I will be receiving a official Honda service manual today in hopes it will be more descriptive, yet I decided to post here to see if any one has experience with this problem and could save me time in my search.

Also I didn't notice that the fuel \ reserve switch on the tank is missing its filter. I am going to replace that as well, but thought it may help to know that when posting your responses.

Thanks.


On side note completely not related to the issues above I have a few more questions.

1. What is the best motor oil to use with this bike?
2. What is the best fuel grade to use with this bike?
3. Any unusual tips I should know about this bike?
4. Tips for the battery charging system?

[Cyprusice]

As to not open a can of worms I am going to change my motor oil question to as long as I use a API-SJ oil I should be fine... correct...But that the lest of my problems, any help with the larger issue would be greatly appreciated. Thanks

[Gordon]

Can you narrow the problem down to specific cylinders?  This will help a lot with figuring out what's wrong.  Try to reproduce the problem then start pulling spark plug leads.  The ones you pull that don't affect the running are the problem. 

So far from what you describe it sounds like it could be either a fuel delivery or ignition related issue, but I'm leaning towards ignition. 

[Cyprusice]

Thanks for the advice I will try that method to try and norrow it down to a particular cylinder.

[Gordon]

If you narrow it down to a pair of cylinders (1/4 or 2/3) then there's a decent chance that it could be ignition related since each ignition unit/coil combo controls one of those pairs of cylinders. 

It doesn't mean it's definitely not a carb/fuel problem, but it helps steer you in a particular direction. 

[Cyprusice]

whats your thoughts as to a possible timming advance problem?

[Gordon]

whats your thoughts as to a possible timming advance problem?

Doesn't sound like a timing issue to me. 

As for your question about fuel grade:  87 octane (PON, the octane rating method that's used in the U.S.) is what it was made to run on.   

[martino1972]

how about a weak connection on a wire somewhere...

let it idle,start wiggling wire harnas etc. to see if it reacts on it........wiggle ignition key a bit,kill switch.....see if any are sensitive.......


just a thought....

[jeepster]

Are the K&N filters replacing your airbox? Didn't know you could run "pods" on the Nighthawk. Did you have to rejet?

[WFO]

Download the manual if you don't have one..

http://forums.sohc4.net/index.php?topic=17788.0

I have a 82 nighthawk and the PO used castrol 10W 40 so iam just staying with what she likes and what makes you think the charging system is suspect? but to start the process start off with a fully charged battery reading atleast 12.6 ( settled ) then proceed to troubleshoot if it's any lower than that maybe a new battery to start things off.

[MrZxp]

Every so often the bike will just lose power as if it were running on less than 4 cylinders. For example last night it was sitting in my garage idling (1050 rmps) like a champ for 15 mins when it just suddenly died. So I tried to start it again, which it did but it was rough starting; when it did start it sounded funny, kind of like it wasn't running on all cylinders. So I drove it up and down my driveway (400 yards) and gave it hell in 2nd gear a few times when it just suddenly came back and was running like it normally does. This sudden loss and regain of power has happen when driving down the road two or three times before. One of these times it would not start again until I let it sit for 30 mins, and even at that it started very rough, normally it start great.

Firstly, I would not let a bike (especially an air cooled one) idle for 15 minutes without a decent airflow across the engine finning. Heat buildup can cause all manner of strange symptoms....

As to your problem, it sounds to me like fuel starvation, as if some gunk from your tank has made it's way into your fuel lines/carbs - you have maybe pinpointed this as a potential problem later on in your post... the fact that there is no filter on the fuel pickup from the tank....? One of the first things I ever did was to get an inline fuel filter... after ensuring the tank was squeaky clean of course!

Cheers, Phil

[Hush]

Cheers Cyprusice, I owned the exact same bike up until a few months back, the gas tank gave me the biggest headache, constant build-up of rust flakes.
It could be the shape of the tank which is quite unique to that model but I had to remove it for cleaning heaps of times and like you the in-tank filter was long gone.
Also as someone else mentioned, I wouldn't let her idle for 15 minutes, that's way too long for an air cooled bike, you run the risk of fouling your plugs which will give an indication just like you describe.
If it was my bike I'd clean out the carbs, you will find these strange little orange plastic petrol filters actually inside the carbs, mine were clogged to death with rubbish.
Removing the Custom carbs is not such a hard job as it is on the older "Z"' model I have now.
The tank, I would possibly fit an inline filter if you can't replace the in-tank one.
Apart from that I found the 650 Custom to be quick and once cleaned out, reliable.
Best of luck.................Hush.

P.S. if your front brakes start binding and wont release there is a tiny tiny pin hole in the bottom of the master cylinder that you must keep open, mine tried to trow me over the bars when brakes locked.
 
 

[Cyprusice]

To All,

Thanks for the loads of advice and tips! I am so glad that there is a forum for such a great bike. I think that I have found the main problem that has been hindering my riding experience thus far, but like all older bikes that have been sitting for some time there is normally more than one problem. However this issue seemed to resolve my intermittent loss of power and poor starting idle. When I finally got the offical service manual in the mail this Saturday I read through their troubleshooting flowchart in the back (which is pretty handy) and it led me to either the fuel delivery system or ignition system which I was suspicious of as well as some of you had been. However based off its symptoms it pointed more to the ignition system than the fuel system. I think this was mostly due to the intermittent quality of the issue. The book pointed to a few items to check and one of them was the spark advancer unit behind the pulse generator. So I took off the cover and the generator after marking its setting and found the spark advancer to be sticky and in need of a good cleaning and lube. After putting it back on it moved smoothly and freely. So I used my timing light to re adjust the pulse generator to the books specs and took her for a ride. I have yet to experience another unexpected loss of power (park advancer not advancing) or poor cold start (spark advancer not resetting back to original position after shutting off). I have taken all of your advice and will no longer let bike idle for 15 mins don't want to hurt her. As far as jeepster's post yes they are replacing the air box. I did some research on it and it turns out that it does not meet pollution control regulations being it is an 82 and 79 is what i believe is the cut off. They are a tight fit and apparently had to be modified a bit to let the choke cable pass between them. It looks like all the hoses that use to run into the air box now run into the holding tank (box) that sits below where the air box would have then drain out the house that the holding tank has running to the ground. I was not the one who put the K&N air filter on the bike so I cant tell you if they had to rejet the carbs but from what I have read so far no rejetting is necessary for the mod, but like I said I am not sure on that. You would want to research that further if you plan on doing it. As far at the fuel tank filter. I have ordered a new in tank one and should see it soon and will be cleaning out the tank and when it arrives. Last think I need is that rust sucking through my carbs.   Form my recent repair experiences and i have educated myself enough to now know this bike has a few modifications. A four into on exhaust, clap on K&N air filters, and an oil cooler attached where the horn use to be. If any of you have any information or opinions about these mods please let me know. I would like to know if they are ok for my bike or if I should try to revert back to stock. Thanks for your help! 

[cb650]

Depends what you like.  I put 4-1 on most all of mine.  And have 2 with uni filters.  If it running good now and you like it leave it.  Youll spend a bunch of money to get all stock parts. Especially the exhaust. When you put the fuel filter in clean out the tank.