Topic: 1973 cb500, missing on one cylinder

[toyolla86]

so i've been troubleshooting my bike ever since i bought it.
i have gotten it to run and will drive down the street but its missing.
found that one exhaust tube is cold enough to touch after running.
i managed to get spark to that cylinder, but its still not firing.
i am getting fuel to the carb, but not sure if the fuel is getting to  the cylinder.
have not done a compression test yet. i guess i should've done that already. lol.

my heart says its a fuel/carb issue.

anyone care to help me out with this problem.

[cmonSTART]

I don't really have any good thoughts for you.  It sounds like you're off to a pretty good start.  Check all the tune up items and such and a compression check is always good to do just so you're certain the engine is strong. 

Did the bike sit for a while before you bought it? 

[Greggo]

Pull your carbs and clean them twice as good as you think you'd have to...then see if it runs. 

[toyolla86]

cmonSTART- hey (nice name btw haha) yes this bike sat for over a year. i have found 3 significant problems with it so far that i have been lucky enough find and fix.

Greggo- ughhhh. i cleaned the stupid carbs once. it started and i was really happy. and i am thinking the same thing. take the carbs back off AGAIN and clean them out again. they are not easy to get off or back on.
the one carb in question is the cylinder farthest to the left when riding the bike. im thinking about just trying to get it cleaned out while still on the bike. what do you think.


also in my throttle, it sometimes feels like something is sticking and then pops loose. and the bike all of a sudden roars up to 4k rpm's. when the bike is not running  i cannot replicate the symptom, which makes me think that this separate issue may be harder to find.

[cmonSTART]

also in my throttle, it sometimes feels like something is sticking and then pops loose. and the bike all of a sudden roars up to 4k rpm's. when the bike is not running  i cannot replicate the symptom, which makes me think that this separate issue may be harder to find.

Personally, I would look into this ASAP.  Stuck throttles can be a serious problem. 

[toyolla86]

yeah you may be right.

i want to say its valves, but i can literally feel it in the throttle when it pops free.
maybe it only does it when the system is under vacuum, and its holding one of the flutter valves shut.

[Greggo]

Greggo- ughhhh. i cleaned the stupid carbs once. it started and i was really happy. and i am thinking the same thing. take the carbs back off AGAIN and clean them out again. they are not easy to get off or back on.
the one carb in question is the cylinder farthest to the left when riding the bike. im thinking about just trying to get it cleaned out while still on the bike. what do you think.

I think if you can get to the jets (clean EVERY little hole with fine wire, or guitar string) you could try that.  Also, try to blast some air thru the idle adjustment screw hole (one of mine was blocked and I had no idea)

[toyolla86]

i need to get a diagram of these carbs.

[thrutheframe]

  These two issues could easily be related.  The throttle linkage could be sticking or improperly connected to the #4 carb.

[lucky]

Wow ....I don't know where to start.

Oh, Get a workshop manual now. Not kidding.

OK... The sticking malfunctioning throttle.
If you do not get that solved it could get you killed.
Take the tank off and CAREFULLY observe the throttle as it is opening and closing.
Check the cables from throttle to carb. IT could have a broken strand and that strand that is broke is getting hung up.
Remove the screws on the throttle housing and inspect the throttle cable as you open the throttle. The cable almost never breaks at the carb because the cable is pulling in a straight line.

CSI will not come investigate and find out after extensive investigation that your throttle had a broken strand and was hanging up. The newspaper story will just say," motorcyclist killed." LOL...lol

Next
QUOTE:
"i managed to get spark to that cylinder, but its still not firing."
i am getting fuel to the carb, but not sure if the fuel is getting to  the cylinder. "

"my heart says its a fuel/carb issue. "

Leave your heart out of this. Engines have no heart.

First the spark. Take a clamp on timing light and clamp it on to each spark plug wire while it is idling that will tell you for certain if it is "getting spark".
Make sure the timing light is showing a consistent  spark.

If not Install NEW points and condensors. You cannot adjust old points.
I do not want to take the time to explain all of that right now.

To properly work on the carbs they must be taken off of the motorcycle.
Otherwise you will strip screws and frustrate yourself to death.

You do NOT need to take the carbs all apart.
But you will need to remove the float bowls with a #2 phillips screw driver.
You need to make sure the idle jets are clean.

You did not tell us if the bike will idle correctly.(doubt it, since you said Cylinder #1 was cold.)

There are no  "flutter valves ." Those are called butterfly valves.
Sometimes butterfly valves are used as a choke to cut off air.
Sometimes butterfly valves are used as a throttle and control vacuum.

Also: When members suggest cleaning the idle jet with a guitar string it has to be the right size guitar string. The smallest steel guitar(electric) is .009 thousandths so if the hole in the jet is smaller than .009 it will not work. So if the jet number (stamped on the jet) says #25 that is .25mm and if you go to google and type in mm=inches you will get a conversion chart that will show you how many thousandths that is.
It is ??.....009 thousandths! So that would not work unless the jet is larger than a #25(.25mm) right?

See what i mean?

[lucky]

i need to get a diagram of these carbs.

Get a workshop manual and it has drawings,pictures, and words.
Put the cell phone away.LOL...lol..lol

[Duanob]

Pull your carbs and clean them twice as good as you think you'd have to...then see if it runs.

I'm with Greggo on this one. My guess is your pilot jet is plugged. It's a very tiny orifice that you can barely see through but it needs to be clear. they get plugged pretty easily. But a good cleaning of the entire carb assembly never hurts. Sometimes 3rd time is a charm.

[Deltarider]

I managed to get spark to that cylinder

Are you sure? Have you checked and double checked?

[toyolla86]

it was pretty sunny out when i checked the spark. should've done it in the shade. but im pretty sure it has spark.

the bike actually idles pretty strong. when i start it to test something, i have to turn it off cause it wont die on its own anymore. haha.

one thing about the throttle sticking issue. its not sticking open. it is sticking like it wont open and then it does open. and it operates fine after that.
also to give a little more info since Lucky mentoined carb#4, i did accidentally break the little tab that connects from carb 3 to carb 4. (each carb is connected by a thin piece of metal, yeah that part... i broke it)

ok so i guess ill be taking the carbs back off again.
is it bad to spray carb cleaner in the carb body after taking out the float and all the little thingy's. or is there still some rubber up in there that can get ruined.

[toyolla86]

ok,
so i cleaned out the #1 carb (the one that wasnt firing).
now its firing at idle (or should i say all cylinders are getting hot as hell while idling).
i take it out for a spin and its still missing.

-one more issue i found... the valve cover is leaking oil just above the #1 spark plug. i dont know what its called but you take it out and it looks like a journal that sends oil to the head to keep everything lubed. there are two O-rings that need replaced. i wouldnt think that this leak is causing a misfire.

I am going to see if eBay has a manual for me.

its crazy how at idle i can take the rpm's way up and it does fine, but under load, all of a sudden something is causing a miss.