Honda Cb450 NH engine problem?

[Exabes]

Dear Forum members,

I recently took of the back wheel of my honda cb450sc Nighthawk '85. This because of my valve being broken. So i took it off, took it to a shop and they fixed it. Afterwards i reinstalled the wheel and i started driving, everything seemed to be just fine in the beginning.

After a few miles i noticed a loss in power in the lower rpm's. When i opened up the throttle after switching gears it was stumbling a lot and i dint get any power. I had to open it up a little, wait a few seconds for the rpm to go up a bit and then i regain full power like always. This became worse after i turned around and headed back home. All of a sudden, again after switching gears, in the low rpm's the stumbling got worse and i couldn't get through the "dead" point and the engine turned off by itself. Not knowing what to do right away i waited and called a few people trying to get some help. After a few minutes i fired it up and it worked again but still with the stumbling in the low rpm's. This repeated a few times till i was almost home and decided to walk the last bit.

I noticed at home my chain was rather loose, i think because of nog checking it a few times properly after i changed the back wheel. The chain now is very nicely tensioned. Then i checked my air filter which was like new (i just bought the bike so i don't know a lot about the history of the bike except it always stood inside and the guy who owned it before me treated it very good, everything looks very good and well maintained). Also of course i checked random little things like amount of fuel, deadmans switch, contact and my bougies. The bougies looked rather used and i ordered new ones on which i'm still waiting.

At this moment i can't get the bike to start at all, with choke or without. The bike is always inside and it only stood still for about 2 weeks with a flat tire. So there is not a lot that could have changed after the flat tire but i can't figure out what the problem is.

Does anyone has a clew? All tips are more then welcome, i'm checking everything i can.

Erik

[ariwhiteboy]

Have you run through Laminar's How To Diagnose a Bike that won't Start thread?

[Laminar]

What's a "bougies"?

My first thought is fuel flow problem, it could also be an electrical issue. Run through the aforementioned thread.

[SirSeanSean]

What are "bougies"?

+1

How good is the seal on your carbs to the air box and to the engine?

[Exabes]

Excuse me, bougie means spark plug. I'm dutch, kinda went with the idea of that item having the same name in both languages. The complete air intake looks perfectly fine. I'll go through the manual posted before! Thanks, if there are more suggestions, everything is welcome!

[coffee_brake]

Sounds like you ran out of fuel.

Especially if it quit, then it sat for a few minutes, then it started up again for just a little while longer.

You can check if there is fuel in the carburetors by turning the drain screws on the bottom of each carb. If no fuel comes out, then you know this is why the engine quit running.

[SirSeanSean]

Is your petcock switched to On or OFF? I did this once before. I got a mile down the rode and then had the same problem you had.

[Exabes]

i have it opened up, and there still is gasoline left in the tank. Not a awful lot but it should be enough i guess.. Next step is renewing the spark plugs and fill it up all the way, see what happens. Thanks.

[coffee_brake]

Not the tank. Forget the tank. We're talking about the carbs. Is there gasoline in the carbs?

[Exabes]

I see. I checked the carbs. On one side (left) gasoline came out, on the other side i didnt get anything. After draining i tried to start to get new fuel in the carbs, but this didnt do anything. Both carbs are drained now. I assume that on starting the bike new fuel gets in the carbs or am i wrong? The petcock switch is on "on".

[coffee_brake]

I think you have a vacuum operated petcock. This means that you have two hoses coming out of your petcock. One is for fuel, and the other one is for vacuum.

Do you have two hoses on your petcock, and are they hooked up to the carbs? Are they kinked up?

For a vacuum fuel feed system, fuel goes into the carbs when the  motor is turning.

SOME petcocks have "on," "reserve," and "prime." If you have prime, you can use it to prime the carbs, just remember to turn it back to "on" once the bike is running.
If you don't have prime, you get fuel into the carbs by making the  motor turn over.

It might take a few tries.
Don't burn up your starter. For every ten seconds of trying to start the motor, let the starter cool down for at least 5 minues.

You did not have fuel on one side. Some causes for this may be 1) a stuck float. The float is in the bowl on the bottom, and when the fuel level gets low, the float moves and a valve lets in more fuel. If the float is stuck, the carb can't get more fuel. Sometimes you can carefully hit the bowl with the plastic end of a screwdriver, and the float will un-stick itself. Worth a try anyway.

2) there is a fuel rail between your two carbs. It seals with o-rings. This rail can conceivably become clogged. Let's look for other causes before we mess with this, it involves dismantling the carbs.

3) the fuel line is made of rubber and decomposes like all things made of rubber. If the fuel line is old, it can flake and fall apart on the inside, cutting off the flow of fuel. Similarly, if the fuel line is kinked up in the middle it can stop flow. Finally, if there is a fuel filter and it gets full of funk, it can stop fuel flow.

4) Is fuel getting out of the tank? If your fuel tank is all rusty inside, the place where it goes into the petcock might be clogged up.

Remember that just because you hear fuel sloshing around in there, doesn't mean there's enough fuel to run. Try starting the bike with the fuel on "reserve" or fill the tank with fuel and try again.

One more thing: try starting the bike with the gas cap open. If the vent in the gas cap is clogged, fuel cannot flow into the carbs.

And do, read the thread linked earlier, it is an excellent way to help you find what's wrong.

[Exabes]

Thanks for the tips! I do have a petcock with 2 hoses to the carb. One is surrounded by some sort of spring, and there is a rubber one. There both not kinked up. On the petcock i have "on", "off" and "reserve". I gently hit the bowl with the floater, started with petcock on reserve with the gas cap open.

The engine dint start, but i reopened the drain screws and now a fair amount (and as far as i could check also the same amount) came out of both carbs.

Does this exclude some failures in the carbs?

I ran through the thread posted before, about analyzing starting problems but with no success.

My next attempt is going to be filling up on gas, install 2 new spark plugs and try again, or is this not the right thing to do?

Thanks once more for helping me out! it's really appreciated!

[coffee_brake]

If there is fuel in the carbs, there is enough to run the bike.

Yes, check the plugs, but know what you are looking at. I do not think the bike would quit starting because of plugs. It usually would run rougher and rougher and then stop running, if a plug suddenly went bad. Plugs do not suddenly go bad, but sometimes they can become so dirty that it is best to replace them. Make sure you gap the new plugs according to the specifications for your bike!

If you have fuel (and you do), then next to check is spark.

This is how to check spark. This is what forum member Laminar wrote, and you can find it in the link posted in reply # 1 above:

8. Spark is easy to test. If you're strapped for time, remove a spark plug, keep it connected to its respective wire, and lay the threads of the spark plug against the fins of your engine (this provides a ground for the plug). You can also get spark testers at auto parts stores for $5 or less that have a clip at one end and a post for the spark plug wire at the other. With the kill switch turned on, crank the engine and watch for a spark. If you see no spark, skip to 9. If you see a spark, that doesn't guarantee that you have a spark when starting. When the engine compresses the air/fuel mixture in the cylinder in preparation for ignition, the mixture now bridging the gap between the spark plug's electrodes has a much higher resistance than that of the open air you just tested the plug in. If the plug is mildly fouled or if you're not getting enough voltage from the battery/coils, the plug may fire in the low-resistance conditions of open air but not in the high-resistance conditions of the cylinder. If you think that your spark may look weak and you're unsure of the plugs' histories, replace them with new properly-gapped plugs (typically $2.50 each at an auto parts store). If you have a strong blue spark on all cylinders, continue to step 10.

If this doesn't make sense, let us know. But you are essentially pulling off a spark plug wire, putting a plug in the wire, and grounding (earth) the plug to the top of the engine. Don't touch while you push the starter botton. You should see a spark in the gap of the plug. Do this on both sides. This is how you can check for spark.

[Exabes]

I checked the spark, your explantation was very clear. On both cylinders i have clear blue sparks going on.
All the other electrical parts seem to work fine as well (lights, starting, parking light, break light)..

[Exabes]

I also went through the fuses, everything is in good shape there as well.

[Laminar]

I see. I checked the carbs. On one side (left) gasoline came out, on the other side i didnt get anything. After draining i tried to start to get new fuel in the carbs, but this didnt do anything. Both carbs are drained now. I assume that on starting the bike new fuel gets in the carbs or am i wrong? The petcock switch is on "on".

This strikes me as odd - why was one carb without fuel? If fuel flow to one of the carbs was restricted, that could certainly cause your issues.

[coffee_brake]

I don't know. He's got spark on both sides, he now has fuel on both sides, but no go.

Are you SURE the kill switch is on?

All I can think of, is that maybe Exabes emptied the carbs of fuel when he was checking them, and there was no fuel when he tried to start it.

What's left?

[Laminar]

Battery?

[coffee_brake]

Wouldn't hurt.

Exabes, batteries may seem good but they can actually cause a lot of weird problems. Can you try jumping off your bike? You can jump it off from a car, just make sure the car is NOT running when you do it. You can jump it from another bike, too, and bike can be running.
Or, can you take the battery in to a local auto parts place for testing? We do that often here in the States....

[Exabes]

Well actually i replaced the battery 3 or 4 months ago. When i bought the bike it stood still for a while (this was 6 months ago) before i started driving it. The the battery died and now i have a new one in there for a few months. I certainly could check it, but since i also have experience with a not so good battery, this one seems proper. Still now after all this hustle i can try to start it and the start engine will turn with the same speed as usual. Levels in the battery are also good. I could try jumping it of a car yes, got to fix one first so that may take a few days.

[coffee_brake]

It is probably not the battery, but it is certainly worth checking.

Batteries can fail unexpectedly, and early. I have had a battery that was bad out of the box. Others here have had batteries fail within 6 months, with no warning.

You just need a good car battery to jump from, the whole car doesn't have to be in running order.   You can carry the car battery to the bike.

The last place that comes to mind right now is the kill switch on the right handlebar.
Does the 450 have a clutch lockout switch (the bike won't start if the clutch lever isn't pulled in), or does it have a sidestand lockout switch (the bike won't start unless 1) it is in neutral with the sidestand down, or 2) it is in gear with the clutch pulled and the sidestand up)? Sometimes these switches can get dirty or short out, and cause such symptoms.

Is the bike in neutral?

who knows if the 450 has sidestand or clutch lockout switches?

[Brittles]

It would be a good idea to pull the tank, remove the petcock and clean the filters. There should be a filter in the tank and another one in the petcock. Do you have a service manual? How's the inside of the tank look?

[Laminar]

The last place that comes to mind right now is the kill switch on the right handlebar.
Does the 450 have a clutch lockout switch (the bike won't start if the clutch lever isn't pulled in), or does it have a sidestand lockout switch (the bike won't start unless 1) it is in neutral with the sidestand down, or 2) it is in gear with the clutch pulled and the sidestand up)? Sometimes these switches can get dirty or short out, and cause such symptoms.

Is the bike in neutral?

who knows if the 450 has sidestand or clutch lockout switches?

Yes on the clutch switch, no on the sidestand switch. Those would disable the ignition and prevent spark, but since he saw spark, they shouldn't be an issue, right?

[jerjohn]

There is a black wire with a white stripe with pull apart connectors in the headlight bucket. This is the connection for the cut off switch, check to make sure that it is connected (happend to me). Also check the ground wire that connects to the side of the bucket. These are connections that just slide on and come loose over time.

[Exabes]

I took off the headlamp unit, and like you said, there were wires unlinked. 2 black ones with a white stripe (male plugs) 2 orange ones and a light blue one (female plugs). I made a picture of it so it's more clear. I re-attached the black ones with a orange and the blue one, and the engine worked again!! But, now both my front  flashers are always on. At least the engine started AND i did not have the same problem that the rpm goes down when you open the throttle a bit. Ive been going trough the service manual and didn't find anything about how the re-attatch the cables. After it ran once, i took off the cables again like i found them, and after that the bike started without any problem.. So i don't know if this can be the whole problem but at least the engine runs. Now i have to get the cables connected in the right way. Weird thing is there are 2 black wires (male plugs, coming out of flash pipes) and 3 females plugs undone..
(See picture)
http://s1158.photobucket.com/albums/p609/Exabes/?action=view&current=unlinked2.jpg