Weird problem

[Cptn. Haddock]

Hi there everybody!

I am new here tot his forum, since I recently bought a Honda CB 550 Nighthawk from 1983. It's my first bike, so obviously i'm very proud of it!

Although the bike drives really fine i have a strange problem and i can't figure out what it could be. After riding a while the engine looses power all at a sudden and then drops off. I cannot start it then again. Up to now it happened to me three times, all times after driving around 80 miles on a tank. I checked already a couple of things. Airfilter and all was totally clean, carburators were clean too, so was the fuel valve and filter. The spark plugs weren't really good, so i replaced them, but after that still had te problem.

Is there anyone of you who knows this problem? I thought it might have to deal with the amount of fuel in the tank, since it only stops running with less fuel in the tank and when i refill it it starts and i can drive again! It could also have to deal something with overheating maybe, because i didn't have any problem on highways yet, only when i was driving like 60 miles/hour for a while.

I checked the fuel valve as i said before, but it has something strange to me. When it is in OFF position, the engine still keeps running. Not as good as when i turn it in ON position, but is that an indication that the fuel valve is broken? a new one costs about 81 euro, so maybe i have to replace it and see what happens?

Anyway, a long story, but i hope somebody can help me! Now i have to go driving with a jerrycan of fuel in my backpack to refill everytime the bike stops. Not ideal of course!

Thanks in advance!

Jelmer

[Hangster]

Not sure about the 550s but on the 650 there is a fine mesh fuel strainer on the inside of the gas tank attached to the petcock valve (i'm assuming 550s havem too) ...there is a possibility that it has deposits clogging it a portion of the way up and not allowing the fuel to go through at a certain point ....to check that you'd have to drain the tank and remove the petcock valve but before you do that wait for more replies from more experienced folk as there may be someone who will know what the problem might actually be .

   Oh Yah    to the Forums

[Bumblebee]

After riding the 80 miles, how much fuel does it take to fill up again and what's the mileage? Completely empty tank or about 1-1.5 gallons down from full? Are you getting 20mpg or 50ish mpg? Also are you running with the fuel selector on RES or ON? Is there any fuel dripping from anywhere?

First guess without any more information is that it's probably not overheating. If it was overheating, you would feel the heat. At 60mph, there would have to be some pretty serious mechanical problems for an air cooled engine to overheat.

As for the running engine with the fuel selector at OFF: The fuel selector shuts the fuel off to the fuel line that feeds the carburetor float bowls. It does not stop the fuel going directly to the engine itself. When the fuel selector is set to OFF, the fuel flow from the tank stops. The engine will continue running until the fuel in the float bowl drops below the main jet pickup tube. Technically the residual fuel in the fuel line will also drain into the float bowl before the bowl starts to drain but you get the idea.
On my CB650, at idle on the centerstand with the selector set to OFF, it takes quite a while before the engine quits..long enough that I can start the engine, tie down stuff on the luggage rack, get a drink of water, go potty, put my crash gear on and it'll still be running. Range with the selector in the off position varies between about 0.2 and 0.9 miles depending on the throttle setting.

[Cptn. Haddock]

Hi again,

Thanks for your reactions! Today i went for a ride, started on full tank and did 70+ miles. Not a problem at all. Today the engine even started with 2 litres (how many gallon is that?) in the tank. That is the amount where it stopped earlier. I believe that when the engine stopped i couldn't start it with the fuel selector in RES position either (normaly its in ON position), but i should have to check that again next time the problem appears. I don't know how the european fuel is compared to american, but i tank Euro '95 here. There isno fuel dripping anywere, so it's not that i loose fuel that way. how far should i be able to drive on a full tank? The former owner told me that i could go 150 miles on the 12 litres...

thanks about the info about overheating (i don't believe in that then, it's not extraordinary hot) and the OFF position of the fuel selector. Never runned it so long in OFF position that i could do all the things you describe :)

greetz,

Cptn. Haddock

[Bumblebee]

2 liters is about 1/2 gallon. Based on a completely empty tank, 0.5-0.8 gallon is about where the reserve in the tank typically is on a Honda. IOW, you likely ran out of gas when it's in the ON position which is why it quit. It should start in the RES position for about 30-40 miles after that. Being unable to start in the RES position is typically a clogged in tank fuel filter or reserve pickup hole in the petcock hardware. It's easy to check that by pulling the petcock out of the tank (when it's empty lest you end up with a gasoline lake)

150 miles for 12 liters is about right. What is the mileage? IOW are you getting 150 miles or 70 miles on 12 liters?

[cmyers]

I had a similar experience recently on my '95NH750, still had fuel in the tank but the bike would not run in the RES position. As soon as I opened the tank I hear it suck air and the bike would crank and run, is it possible for the tank to vaccum lock and prevent fuel from flowing once it gets that low

[Bumblebee]

I had a similar experience recently on my '95NH750, still had fuel in the tank but the bike would not run in the RES position. As soon as I opened the tank I hear it suck air and the bike would crank and run, is it possible for the tank to vaccum lock and prevent fuel from flowing once it gets that low

Yes. There is a small vent in the fuel cap that lets air into the tank as fuel is used. If that vent is plugged and ther cap has a good seal, no air can enter the tank. Once the low pressure above the fuel counters gravity, fuel flow stops.

[flynrider]

Hey Cptn.,

   It does sound like you might have a venting problem.   Next time it dies, just open the fuel cap and try to restart.  If it's a plugged vent, the bike should restart and run for quite awhile longer (until the pressure in the tank gets too low again).   It's definitely worth a try, as this is a cheap and easy fix.   When working on bike problems, I always try the cheap solutions first

[Cptn. Haddock]

Hi there everybody!

I haven't been ont his forum for quite a while, because other things kept me busy for a while. Anyway thanks again for all the advice.

I thought for a while it was a venting problem too, but now i drive a little more the engine starts running better and i figured out that it runs out of fuel at let's say 85 miles. At least, thats without the RES tank, so to say. Then i can turn it into RES and it starts easy again. Anyway: i think it is a little bit too short distance, because with that I'm not going to make 150 miles on one tank.

another thing is that when i start the engine and rev it up shortly after that, it quits too. It looks like i drown it then, so i was thinking that maybe something in the egnition is not working quite well, so not all the fuel burns. that could also be an explanation of the higher fuel-use of the engine, couldn't it? Anyway: next week i hope to be ablo te replace a couple of parts and see if that works.

greets!

Cptn. Haddock

[detdrbuzzard]

if i am riding my 450 i start looking for a gas station at 80 miles. early nighthawks seem to have small gas tanks