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Help starting '83 Honda Nighthawk 550

6.8K views 11 replies 6 participants last post by  Nab the Nightowl  
#1 ·
So, after 20 years of motorcycle dreams, I finally took the plunge and bought one last April despite not knowing anyone with a bike to learn from.
The fellow I bought it from told me he had trouble starting it after winter, and had drained the gas and got it running after some coaxing on fresh gas.
Good to know, but it fired right up for me the first couple months. I was actually impressed for a 35yo bike that had clearly been neglected recent years. Choke full open always, but these bikes are known for that.
Anyway, after a few months it got harder to start - more cranks, and eventually more and more throttle too.
Eventually I had to push start it to ride, and that involved keeping the revs over 3k until it had warmed up or it would stall out.

New to all this, I thought it was the battery and had it tested at a shop, but they said it was ok.
Also pulled outside plugs and checked spark - weak but there. New plug wasn't any better.

Front brake seized and I was done for the season - August or so.
Heartbroken.
I bring her in for the winter. Hit youTube and the Clymer manual.

Pilot jets - gotta be.
After many videos, think I've got this, and spend a Saturday ripping out the carbs.

Cleaning them, I didn't want to do any un-needed disassembly so I didn't take off the top cover or vacuum cylinder. The screws to the float bowl were hard enough to get off and expensive to replace ($13!) I also didn't remove the float or check the float needle, as the bowls were all filled with gas when I drained them prior to removal, so I assumed they were letting fuel in fine.
I was actually surprised how clean they were inside after some of the videos I had seen, but sure enough, the slow jets and even main jets were all quite gummed up.
Soaked all those in carb cleaner, and cleaned the outsides and linkages etc being careful not to get any plastic or rubber parts wet, especially the diaphram on the vacuum cylinder as I knew it would distort them.
Blew everything out with compressed air.

Something I'm still not clear on is the jets - obviously the main jet interacts with the needle on the vacuum cylinder to modulate that fuel draw, and the smaller one provides a small constant source, like a pilot light on a water heater. So is the small one that can't be removed for starting, or interacts with the choke, or what? Why can't it be removed? I blew air in this one, but no carb cleaner for fear of getting it in somewhere it shouldn't, and didn't check it for blockage.

Because even when I got it all back together, it still won't start.

While I had the carbs off, I also lined up all the butterfly valves to be level - before the first was low, second high, last two level. By eye, but way closer than they were.
Was that a bad idea?

Also, the mixture screws were similarly off - so like an idiot I reset them to manual specs without writing down were they were, although I did at least take a picture which gives me some clue.
I assumed these had been adjusted to compensate for the clogged jets or out of whack butterfly valves, or it was all related and best set back to "factory" now that I had cleaned it all out.
Also I didn't actually pull the mixture screws and clean out that passage - could this be the blockage that's preventing adequate fuel mixture?
I suppose I should have known what I was doing more, but felt quite confident after it all going so well until it didn't work.

Now I don't know what to do - I was considering pulling the carbs again and fulling disassembling and cleaning them better. Am I on the wrong trail? I assume compression and spark are adequate considering it could be push started, although the head gaskets are leaking slightly and are one my list assuming I can get her running again.
The battery still feels flaky to me - it coughs promisingly right after it's been on to charge - but I think the shop would be keen to sell me one if that was it.
Or have I just thrown it all out to the point a professional needs to look at it?

Thanks so much in advance, and sorry for the length.
 
#3 ·
Ya, I agree with Eye. Most of the time these old Hondas need a good, thorough carb rebuild to make them right again - break the carbs down completely. Carb cleaner and compressed air are your friends. Not only do the jets need to be cleaned, but all the internal passages in the carb bodies as well. You also need to put new rubber parts in - get some cheap rebuild kits with new o-rings and bowl gaskets. All of the dried up o-rings leak a bit of air or fuel past and that all adds up. Also check closely and make sure your intake boots are still soft and in one piece.

I use an old muffin tin to keep my carb parts straight, and like I said compressed air is your friend!
 
#7 ·
Sorry I didn't report back sooner, but right after my last post I did take everything completely apart and run a bunch of cleaner and air through every orifice.
Much to my dismay, I didn't find anything clogged, worn, or damaged. Nothing suspect at all.

Discouraged, I never put them back in.

But it was nice out yesterday, and I need my baby back.

Is there anything I should check while I've still got the carbs out?

Is it worth putting fresh gas in the tank?
Think I bought it in August and put fuel stabilizer in around October. It was premium so no ethanol.

Other than that and charging the battery, any tips/tricks for getting it started indoors?
 
#9 · (Edited)
Everything lights up and it turns over, but even freshly charged I can only crank it a few times before it sounds really tired, and it never feels like it gets quite enough pop, if that makes sense.
But I took the battery to the local dealer and they tested it and said it was fine.

I could push start it before but even then I'd have to keep it above 2200rpm until it warmed up, so I was so sure it was the idle jets...
 
#10 ·
Just an update for future riders with a similar problem...

So, after my second, more exhaustive rebuild/clean/inspection I put the carbs back in, charged the battery, changed the fuel to fresh premium, but no go.

Still hoping it was the battery, I got a multi-meter and confirmed that it does charge to over 13v, but tapers off to ~12.4v over the next 6 hours.
Then, trying a load test on the battery (which it passed), after about 25 seconds of cranking, it started!

The idle was a bit high (~2200), but encouraged by this victory, I rebuilt the front brakes (an adventure in itself).

Unfortunately, I haven't been able to get her to start since.

I've checked all 4 spark plugs and tried boosting it with a fully charged car battery, but really don't know what else to do, except take her outside, try to push start her, and bite the bullet and take her to the shop.
 
#11 ·
Battery and Honda

I have a bunch of Honda Motorcycles and having a battery that will take a charge is absolutely necessary. If you do not want to get a battery because a shop said it was OK is fine with me, but the way you describe the bike starting after you took measures like kick starting it makes me think otherwise.

I have a rule of thumb for batteries and that is checking a battery after it sets for two days. A strong battery at rest that will let your bike run well needs to be showing 12.6 volts. If it shows 12.4 it may start the bike but the bike may not run well. I have had many occasions where the bike will actually start and not run well on 12.4 volts or so. Remember how old your bike is. there will be losses of voltage due to voltage drop alone. Old bikes have voltage drop period, and worse if neglected.

Here is what I do to check out problems with motorcycles. BTW, jumping a bike with a car battery could cause all kinds of problems. Use a small charger for motorcycles that puts out from .75 to 1.5 amps I do use a car battery that is fresh and strong, but I hook the battery directly to the motorcycle by running an inline fuse on one jumper wire, the + wire [and NEVER through the motorcycle battery]. You can start with 10 amp fuse and maybe go to 15. I have actually used a 5 amp when diagnosing wiring problems. Better to blow fuses than smoke wiring and risk a fire. A brand new battery will usually show 12.6 or 12.7 volts. A battery showing 12.4 is on its way out, and a battery showing 12 volts is dead for all practical purposes

Dan's Motorcycle "Batteries" This gentleman gets more into the practical aspects of things and has an excellent site for repairing old bikes
 
#12 ·
Interesting... I'd love for it to be something as simple as the battery.
As hesitant as I was to boost it with the car battery, you'd think that would provide ample juice if the battery was fading, especially with both freshly charged, but electricity and especially batteries are a mystery to me.

Talking to my neighbour last night, he said his 1100 Honda did the same thing and it was the CDI box, which he couldn't find a replacement for and thus sold his bike.
I can find both identical and supposedly compatible Nippondenso CDIs on eBay for $100+, but it sounds like I shouldn't be getting a spark if it were the CDI. But if it controls the timing couldn't it just be firing at the wrong time?

Neither are returnable, so... any thoughts on which would be a better investment (battery, CDI, or visit to the shop)?
Pride is on the line re: the shop visit.