Cafe Racer Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
69 Posts
Discussion Starter #1
Like the title says, my 74 cb 550 won't stay running with out the starter engaged. It fires right up once you hit the starter but will die the very second you let go. Example, hit starter, motor starts, hold starter, motor keeps going, let go starter button, motor dies. Bad things. Also, I dunno if this is unrelated. But while all this is happening moving the throttle up/down does not change the engine speed what so ever.

I have cleaned out the carbs extensively. Before so the motor wouldn't start. I've set the points gap and timing, though the gap may be off as the specs and my feeler guage didn't really speak the same language. I haven't gotten around to checking valve clearance.

I currently have no air filter/air box on right now. I have a 4-1 exhaust that i removed the cone off of to repair the baffle. I am indeed using fresh gas. I have replaced the points and 3 of the spark plugs, one I can't get to too very well and I'm -still- waiting for a spark plug wrench. But i do have blue spark from every wire.

Also, the bike will not start without half throttle and choke.. sure this has something to do with this.
 

·
Registered
Joined
·
854 Posts
my guess without seeing it would be that it is getting way to much air. no box and no baffles...the air box will help meter the air into the engine and keep your lean/rich mixer in a good mood. also without any baffles there is no restrictions on the exhaust. i would wait till you get the box back on and then make sure the carbs are sync'ed and your air screw is set.
 

·
Registered
Joined
·
5,782 Posts
You have an electrical problem that needs to be addressed before you can go much farther. The bike should not die when you let off the starter button, so your ignition hot lead to the coils is hooked up wrong. Possibly in the headlight shell or under the tank. You will need to have a wiring diagram and start chasing it down.
It should run at idle and rev up and down with out having an airbox or baffle. It probably won't run cleanly, but it should still run. It could be related to the wiring problem or the carb passages aren't clean.
I would start over again to set a base line by replacing all 4 plugs, setting the points gap and timing, adjusting the valves(you are going to have to do it sooner or later, anyway),change the oil and filter, pull the carbs and all the jets and metering devices and clean them and their passages(not very hard with the airbox off.
Good luck,

Ken
 

·
Registered
Joined
·
69 Posts
Discussion Starter #4
Thanks alot for the responses. I will indeed start all over. I've had the carbs with me at the shop everyday now cleaning the jets, soaking, blowing air through it, they look great imo. Tuesday I should finally have that damned spark plug wrench so I can get that one plug. And I'll go on an spring for 4 more plugs. I've been using NGK because at me shop, all hondas must have ngk.

I've got wiring diagrams out the wazoo so I'm-a tackle that tuesday as well. I hope it's under the tank wires as the tank is still not back on. I'm not very fond of taking the shell off.
 

·
Registered
Joined
·
69 Posts
Discussion Starter #5
Well, took a stab at the wiring thing, didn't have much time for much else. But what I can say is that the wiring diagram confuses me. I'm used to working on cars where most wires goto the same point. So on the diagram I am trying to trace the hot lead to the coils. But the diagram connfuses me.



I gather that the hot wire is the black/white wire but looking at the diagram it doesn't have much to do with the starter button. I may be making things harder but I uno, any help would be great.
 

·
Registered
Joined
·
2,740 Posts
If you follow the red/yellow wire out of the starter button, you'll see where it connects into the start magnetic switch (commonly called the starter relay). The start relay applies 12vdc to your starter motor when activated. The green/red wire travels off the starter switch travels to your clutch switch and the ssm unit. If the clutch is not closed, then it keeps the starter button from operation. It does this by not allowing a gnd connection to your starter button. (all green wires on hondas are usually ground).

Now the question is - why doesn't the motor keep running. When the starter button is released, the black/white wire maintains. The 12vdc to the coils through the start/stop switch (called emergency switch on diag). The black/white wire should have 12vdc on it while the ignition switch is on. To test for this, locate the black/white wire hooked to the coil (under the tank) and unhook it, turn on the ignition switch and using an ohm meter check for 12vdc between the black wire and ground (touch anywhere on the engine for ground). If you get 12vdc - then you don't have an electrical problem. If you don't see 12vdc then check on the other side of the emergency switch for 12vdc and follow the diagram to find where the 12vdc is (follow the black wire to the voltage rectifier. An easy test of the black wire is to see if your horn works while the ignition switch is on. This will tell you if your getting 12vdc on the black wire.

I'm thinking the 12vdc on the black/white wire will exist - otherwise the engine would not have started and run in the first place. Which gets us back to a mechanical problem or a coil type of problem. Check each coil with a spark plug to ensure your getting fire - if that's ok, then your electrical should be ok and you need to look for a mechanical reason for your problem.
 

·
Registered
Joined
·
69 Posts
Discussion Starter #7
Well crap, based on what you said I must have a mechanical problem. I do have spark coming from each wire. I guess I'll just start from ground one and see if I find anything.
 

·
Registered
Joined
·
5,782 Posts
If you kick the bike over with the kickstarter, do you get spark? It could be that you have a carb problem such that the bike runs because the starter motor is spinning it over fast enough.

Ken
 

·
Registered
Joined
·
69 Posts
Discussion Starter #9
Hm, I never thought about checking for spark with the kickstarter. I'll get on that today. I'm still wanting to be doubtful that it's a carb problem as I cleaned the crap outa them, but I think i'm gonna spring for a rebuild kit anyway.
 

·
Registered
Joined
·
2,740 Posts
Its a process of elimination, got spark - then check for gas, got gas then check for other reasons why the motor is not spinning. If the plug looks wet then your getting gas into the cylinder. The kick start to check for spark is an excellent suggestion. Some of these problems can be a head banging exercise. Keep us posted.
 
1 - 10 of 10 Posts
Top