[JoshGelua]

Hello!

I bought a 1984 cb450 Nighthawk (Canada version, possibly the 1983 model) earlier this year. It started cold, worked great on a test ride, then I put it in storage for a few months (with little fuel, maybe 1 litre). The previous owner told me the carbs were timed very recently.

Last weekend, I installed new spark plugs (old were black and gunky), filled up about 5 litres of gas, and tried to start it with my other bike's battery(battery is dead). Still no start. It turns, turns, and turns, but it doesn't catch.


I spoke to a mechanic over the phone and they told me that they need to clean the carburetors. Additionally, they told me that my bike may have rust inside the tank and will not work on it unless I get it properly cleaned by a tank cleaner. This was over the phone. My bike does not have rust anywhere on the body, especially not in the tank (attached picture is a photo taken which I sent to the tank shop they referenced and they told me "there is definitely rust"). I disagree there is rust in the tank. However, I want to ask you all the same question you've probably been asked before. I know there are some forums that will guide me, but I believe my case is relatively unqiue enough to issue a new post. My apologies if you think otherwise.

Take a look at this photo that I sent to the tank shop. Do you see rust? He told me there is, but I don't see any!

Additionally, what else could you diagnose what is happening? Anything will help.

Thank you so much forum. I am really glad you guys are active here.

Best,
Josh

 

[markjs]

If you have an extra spark plug plug it in and turn it over with it on the head and check for spark (easiest thing to check), if not pull one. You can still have rust (or water) down in the tank. Today's alcohol gas attracts atmospheric water. You may need to clean the carbs, but I've had these down for years and gotten away with not, though it wouldn't hurt. These carbs are simple enough to clean yourself if you are careful and don't mix up parts. The hardest part is pulling and replacing them.

 

[JoshGelua]

If you have an extra spark plug plug it in and turn it over with it on the head and check for spark (easiest thing to check), if not pull one. You can still have rust (or water) down in the tank. Today's alcohol gas attracts atmospheric water. You may need to clean the carbs, but I've had these down for years and gotten away with not, though it wouldn't hurt. These carbs are simple enough to clean yourself if you are careful and don't mix up parts. The hardest part is pulling and replacing them.

I checked inside the rest of the tank, it is consistent with the colour of the tank in the pic I sent. I'll be sure to check the spark at a later date. Thanks for the advice.

Josh

 

[markjs]

I checked inside the rest of the tank, it is consistent with the colour of the tank in the pic I sent. I'll be sure to check the spark at a later date. Thanks for the advice.

Josh

Well it's work that's well worth learning to do yourself. Not only will it save you countless dollars (labor at bike shops is not cheap) you will learn about your machine and learn things that apply to other bikes. We're all willing to help you through and there is a wealth of info already posted here in how to stuff. Really none of it is that hard and until you get into complete engine teardown, few specialty tools are needed. Even then it's not bad, lots of guys who know nothing if they are slow, careful, pay attention to detail, have torn down and rebuilt these machines, it's really not rocket science, but it's fun and nearly endlessly rewarding. Welcome to motorcycles!

 

[J-T]

The up side here is you have identified two shops you want to never do business with!:twisted:

If it ran well a few months ago it's unlikely your carbs have gummed up so bad it won't even start.

Start with Mark's suggestion to check the spark. If you don't have any:
Warning, we give entry level Homer awards for this one: what position is your kill switch in?

If you have spark try spraying a bit of starter fluid into the air cleaner while cranking. If it fires, you have a fuel problem.

Another easy test: Remove the fuel line from the petcock to the carbs, open fuel valve. Steady flow of fuel?

If yes, with line re-connected and valve open, open bowl drains on bottom of carbs. Steady flow will tell you fuel is getting into the carbs.

If that doesn't do it, we can come up with more.

 

[markjs]

The up side here is you have identified two shops you want to never do business with!:twisted:

If it ran well a few months ago it's unlikely your carbs have gummed up so bad it won't even start.

Start with Mark's suggestion to check the spark. If you don't have any:
Warning, we give entry level Homer awards for this one: what position is your kill switch in?

If you have spark try spraying a bit of starter fluid into the air cleaner while cranking. If it fires, you have a fuel problem.

Another easy test: Remove the fuel line from the petcock to the carbs, open fuel valve. Steady flow of fuel?

If yes, with line re-connected and valve open, open bowl drains on bottom of carbs. Steady flow will tell you fuel is getting into the carbs.

If that doesn't do it, we can come up with more.

Actually the petcock trick won't work on a Nighthawk because it's a vacuum actuated petcock, but if you pull the vacuum line and apply suction fuel should flow.

 

[80cb400t]

You should be able to use your phone flashlight and creative angles to get a better look down the edges of the tank, any orange rust should be pretty obvious. One more test for rust is to get your tank nearly empty, remove it and tip it onto its side on a non abrasive surface, remove the petcock and examine the tubular fuel filter that sticks up into the tank for sediment and clogging. I'd start with the simple stuff though. You're also using choke right? These bikes aren't supposed to start cold with no choke unless maybe you're in AZ in summer.

 

[drydreamer]

Age old problems........there are some very good and inexpensive spark checkers out there, some being neon plug caps that will show ht passage and intensity in real world cranking and running conditions. Much safer than resting a plug on the cam cover ( no spark as its insulated ) or cylinder head.

You could of course attach 2 plugs to a metal strip with a flying earth lead, but that will meerly show ht in open air rather than "under pressure".

So, rule in or rule out ht loss first.

Its probably a fuel problem anyways but rule out things one at a time. Can the ign systems on these bikes die over nuight, or over a season, hell yes, they can and do sometimes.

Your bike stored in a nice clean dry tidy and probably heated garage ?

 

[JoshGelua]

You should be able to use your phone flashlight and creative angles to get a better look down the edges of the tank, any orange rust should be pretty obvious. One more test for rust is to get your tank nearly empty, remove it and tip it onto its side on a non abrasive surface, remove the petcock and examine the tubular fuel filter that sticks up into the tank for sediment and clogging. I'd start with the simple stuff though. You're also using choke right? These bikes aren't supposed to start cold with no choke unless maybe you're in AZ in summer.

Using choke yes. Won't start either way.

 

[drydreamer]

So do you have ht during cranking, at the plug internal electrodes ?

Rule ign problem in or out, then go from there, else just go round and round until you find/cure/trip over the problem. Be systematic and logical.