Topic: Choke problems

[chstr1]

HAPPY NEW YEAR FROM MINNESOTA!

I bought a 78 CB 550 last spring and enjoyed riding all summer.  My only complaint has been that the bike is impossible to start when the engine is cold.....even if the temp is 80 degrees out.  The guy I bought it from never told me, so I spent a good deal of time figuring out how to get it started.  Choke out, choke in, some throttle, no throttle etc. but no success.  Finally I pulled the airbox, and spryed some carb cleaner into the chamber.  Pow...instant start.  Being cold it quit right away, so did it again and gave the throttle a rev.  Once warmed up, it rode and started like a charm.  I continued to do that for a week or so, but knew this couldn't go on. Since then, I have used a piece of cardboard to cover the air intake and it starts every time.  Once warm, I replace the filter and put it back together.  Of course that means pulling the air filter every morning and having to mess around doing what the choke should be doing for me.

I had it started last week, temp was about 20 degrees but the same proceedure continued to work.  I have taken the choke cable off the handle bar, pulled the gas tank off, and see that the bar where the choke mechanism is located.  When I pull the choke handle out, I can see the bar moving about a quarter turn, probably no more.  The clip that the cable attaches near the carb seems loose but still the bar moves.

I am new to biking, and the 550 was purchased for the benefit of learning to ride safely.  So far that has been accomplished.  But although I can tell a carb from a coil, I don't consider myself handy enough to start pulling a whole bunch of lines and doing a carb rebuild.  However, I expect to sell the bike this next summer, and would like to know that the person who is getting it will have a bike that starts properly. 

Anyone tell me if there is a fix I can do that won't require a transplant?  I have been reading the forum for several weeks and am amazed at the knowledge base here.  Therefore I thought I better join up and see if there was some help out there.  Thanks- Chstr1

[750goes]

not really used to cold climate conditions, but does the bar you are talking about have any more movement left in it when you have pulled the choke cable all the way out..you could be trying to start the bike while only using half choke, which may not work well until warmed up.
the clip that is near the cable and bar should be firm but not overtight..
this may solve some slack movement in the cable and possibly give you full choke conditions for that cold start...
there are sooooo... manyyyyyyyyy...... other things that could also be involved in stopping the bike from starting straight up from cold..
I'm sure there will be heaps more information coming..

[chstr1]

It's really hard to know if there is more potential movement.  It is pretty hard to get to.  I may try getting a needle nose down in there and see if it will turn more.  The temp here is not a factor as the problem was occurring all summer, which we actually do get for a few months.

[750goes]

check this thread it sounds like this may help

Re: 77/78 750 carb/choke questions
« Reply #7 on: December 29, 2005, 07:20:07 PM »   

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   If your idle isn't increasing when you pull the choke knob all the way up it may be that the cable has slipped or is set too low. There is a small clamp that holds the cable just above the activating arm (middle rear of the carbs) and if the cable is not set correctly in this clamp then the choke will not work properly. On my carbs, the idle speed doesn't begin to rise until the choke is more than half way engaged.

[STLrocker]

to see if your choke is fully closing, all you need to do is pull the air box and look in the carbs. when you pull the choke on, you should see the butterfly valves in there close. if they close all the way, its working right. if they dont move, or only close part way, you may need to adjust or see if there is a bind somewhere.

if the choke is working properly you may have a slight clog in your carbs or it may be a general tune up issue. it would be a good idea to do a full tune up anyway if you havent done one since you've owned the bike. i had a kz1000 a while ago that did the same thing for a while. after pulling the carbs and cleaning them out, it was good as new.

[scondon]

    A trick that works, much like spraying carb cleaner, is to set the run switch to the "off" position and then hit the starter while twisting the throttle. Then put the run switch to "on" and the engine should start. Do this with the choke pulled out. This "primes" the cylinders with gas for easy start.

if the choke is working properly you may have a slight clog in your carbs or it may be a general tune up issue. it would be a good idea to do a full tune up anyway if you havent done one since you've owned the bike.

I'll second that. When I got sick of carrying a can of carb cleaner/starter fluid around I finally tuned the bike and pulled the carbs to clean the slow jets. It seems to be a common problem with these type of carbs that the press-in slow jets become clogged fairly easily.

It's really hard to know if there is more potential movement. It is pretty hard to get to. I may try getting a needle nose down in there and see if it will turn more. The temp here is not a factor as the problem was occurring all summer, which we actually do get for a few months.

   A long screwdriver should suffice. Pull the choke lever up and watch the arm raise(back of carbs), then try and push the arm up further using the screwdriver.

[chstr1]

I took it down a little further today; was able to get to the butterflies and they seemed OK and moved when I pulled the lever.  I noticed two of the rubber intakes were not tight at the point of the carb.  The metal band was not in the grove that seals the intake.  I can't help but wonder if that was negating the choke by letting in air.  When time permits, I will clean and lube it up good and put back together to see if I have made any improvement.  If not, I think it will be time for the tune-up suggestion.

Any other suggestions? It would be nice to do anything I can before putting everything back together.  Thanks!

Here are picts of one butterfly open and closed.  Do they seem to be closing enough?

[Bodi]

Not closed. Fully closed you should only see that metal disc completely flat blocking the entire carb opening.

[Gordon]

Definitely not closed.   The first time I looked at the pictures I thought you had accidentally posted the same one twice.

[chstr1]

Well certainly answers that question! Any idea what would cause them to not fully close? I cannot manually push them any farther closed.

[750goes]

Sounds like that damned cable is either badly/loosely adjusted, or maybe needs some lubrication... you know where you said it was loose.

stick your fingers in the carbie throats  - one throat at a time while pulling & pushing (gently) on the choke cable to see if it reflects any movement in the valve closing over or if they are STUCK .. if the cable has full movement and little or no movement in the throat valves, then the cable needs to be adjusted, if they do move only slightly and under a bit of strain on the cable, then they are stuck/gummed up/ need a clean etc....

keep at it.....

[damn_yankee]

Loosen the clamp that holds the choke cable above the carbs. Then pull and close the cable with the knob at the other end. You should be able to open and close the choke all the way - then adjust the clamp and tighten. If the cable will not open any more it may need lube or replacement.

Good Luck-

[chstr1]

I found something new when trying to get those butterflies to close.  It appeared that something was obstructing them from moving fully closed so as I looked at the throttle cable, it looks like there is some kind of adjustment screw buried by the choke cable.  So when I turned the throttle about 15 degrees or more, and manually pushed the butterflies, they closed fully.  I think it has been a loong time since those butterflies closed all the way.  However, I think the cable is OK and will move once I have it hooked back up again.

So, do I make an adjustment in the throttle cable by the choke, or do I make a large change in the idle screw?  When I inserted a screwdriver in the idle arm adjuster, I was able to close the butterfiles, but wouldn't that give me too great an increase in idle if I changed the screw tension? It would be easiest, because I don't know how to get down into the choke and throttle cables very easily.  It is an awfully tight fit down in there.