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Author Topic: !978 CB 550 Choke  (Read 2992 times)

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Offline Fandan

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!978 CB 550 Choke
« on: August 02, 2018, 08:25:38 AM »
Hi everyone


I seem to be having issues with my choke when staring my bike. No matter if I open my choke all the way or just a little the bike the bike screams at 5000 rpm when I start it. I have to play with the choke to get the bike to idle properly. The bike is alway parked indoors and with the heat wave we're having th bike isn't cold.
I told my Mechanic who did all the work on the bike and he seems to think its common. I think there is something wrong.

Thanks
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Offline Bankerdanny

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Re: !978 CB 550 Choke
« Reply #1 on: August 02, 2018, 09:33:35 AM »
Your mechanic is an idiot. Now is a great time to learn to fix these relatively simple bikes yourself.

Does your bike have the PD series carbs with the choke knob at the handlebar by the speedometer? If it does the there is a fast idle cam built into the shaft that controls the carbs that opens the carbs a little to boost the idle speed when the choke is on. But it should only boost by a few hundred RPMS, not a few thousand.

Does it idle properly when the choke is off?
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Tews19

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Re: !978 CB 550 Choke
« Reply #2 on: August 02, 2018, 06:52:30 PM »
Fandan, is it possible to get a video of a cold start up?
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Offline Fandan

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Re: !978 CB 550 Choke
« Reply #3 on: August 04, 2018, 09:32:33 AM »
Hi Danny

 Yea I'm getting that feeling..lol

Correct my choke is at the handlebars by the gauges.
yes after a few seconds I'm able to play with the choke and the bike beings to idle properly

Thanks
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Offline Fandan

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Re: !978 CB 550 Choke
« Reply #4 on: August 04, 2018, 09:37:51 AM »
Hi Tews19

Yea I'll get you a video today hopefully it starts, it died on me yesterday while riding had to kick start it.

Thanks
 
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Offline Fandan

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Re: !978 CB 550 Choke
« Reply #5 on: August 05, 2018, 04:45:18 PM »
Hi Tews19

I attached a video of my bike on a cold start. Sorry for the quality it's dark in my building's underground parking.
It's difficult to see but the RPMs jump to 5000 as soon as you start the bike (choke is fully open) after a few seconds you can lower the choke and the bikes idles normally but often I have to play with the choke or the bike dies.

Thanks again!
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Offline Bodi

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Re: !978 CB 550 Choke
« Reply #6 on: August 05, 2018, 05:22:02 PM »
Bit confusing. You close the choke for starting, fully open is when the engine is warmed up and will idle with no choke.
The choke knob/lever closes choke plates just before the throttle slides, causing high vacuum at the throat and sucking a lot of fuel into the engine... a cold engine doesn't vaporize fuel very well and this makes for a mixture rich enough to fire. Some (ie your) carb banks have a cam mechanism to increase throttle when the choke is applied... that means you don't have to stand and work the throttle to keep it from stalling. Once the cylinders warm up a bit the fuel spray is vaporized fully and it doesn't need the added fuel from a choke.
Probably the choke idle cam is now misadjusted. There's an adjustment in there, not sure how it works on your bike. But this problem suggests that the slide adjustments were done wrong in a carb sync attempt: it is way easy to do that so the choke cam is off... whereas changing the choke cam setting is not a common adjustment. This can cause trouble with the throttle, either it is unable to open the slides fully or the idle adjustment doesn't work properly (or both).
Anyway, there is a spec for the choke idle cam setting in the service manual, usually a gap between cam and actuator with choke open (off). The RPM should be maybe 3-4000 with choke almost fully closed (the engine will probably choke out and die with it 100% fully closed when warm).
« Last Edit: August 05, 2018, 05:26:28 PM by Bodi »
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Offline Fandan

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Re: !978 CB 550 Choke
« Reply #7 on: August 05, 2018, 06:14:02 PM »
ok, you're saying when I'm pulling up the choke lever to "full-on"  I'm closing the choke
And pushing down the choke is fully open?

Thanks for all your info!!

Take care
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Offline robvangulik

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Re: !978 CB 550 Choke
« Reply #8 on: August 05, 2018, 10:51:53 PM »
Quote from: Fandan on August 05, 2018, 06:14:02 PM
ok, you're saying when I'm pulling up the choke lever to "full-on"  I'm closing the choke
And pushing down the choke is fully open?

Thanks for all your info!!

Take care
That's why it is called the choke, you are shutting the air out   ;D
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Offline Scott S

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Re: !978 CB 550 Choke
« Reply #9 on: August 06, 2018, 06:23:48 AM »
 Those carbs have an adjustment for the choke. There's a fast idle cam down on the carbs that can be adjusted. The choke cable itself also has an adjustment,  but it's more for fine tuning.
 Look for a service manual for the '77-78 models and it should cover it. I have it at home somewhere and can snap a few pics, but by the time I do that and get them uploaded you can probably find it online.
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Offline 2wheels

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Re: !978 CB 550 Choke
« Reply #10 on: August 06, 2018, 07:18:34 AM »
If your 550 is anything like my 1978 750 F then what you are seeing is similar to mine.

When i am starting mine i pull the choke knob out all the way.  Then push the starter button, or kick start.  It usually fires up right away.  Then the engine will rev up to over 4000 RPM.  So i quickly , but smoothly, push the choke back down a little.  Until the RPM drops to about 2000 RPM.  For the first 60 second i have to keep my hand on the choke to keep the RPM stable.

I allways thought this was normal for the PD42 carbs.  But i am not sure about this.
It is very different then the older versions of our bikes.
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Offline Bankerdanny

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Re: !978 CB 550 Choke
« Reply #11 on: August 06, 2018, 08:46:03 AM »
I wonder if the carbs are set up with the slides too high. The slide height is what you adjust as part of the synch process. The fast idle cam doesn't lift the slides enough on its own to push RPM's that high.

For the PD series carbs the #2 slide is non-adjustable, so you can use it as a reference for a bench synch to make sure the slide height is correct when the throttle is closed.
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"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Fandan

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Re: !978 CB 550 Choke
« Reply #12 on: August 06, 2018, 10:05:18 PM »
thanks, everyone!

Scott S, I have the Clymer manual for my bike I will take a look.

LOL robvan makes sense...

thanks again Danny

Take care guys!
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Offline flatlander

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Re: !978 CB 550 Choke
« Reply #13 on: August 06, 2018, 10:45:04 PM »
get the proper honda manual here: http://manuals.sohc4.net/cb550/
then, take the clymer off your workbench and carefully place it in the next paper recycling bin or put it somewhere else that's far away from your workshop.

joking aside, you can use the clymer to cross reference things with the honda manual if you really want but it contains a few flaws, misses a few things and doesn't really add anything. so why bother with it?
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Offline Bankerdanny

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Re: !978 CB 550 Choke
« Reply #14 on: August 07, 2018, 06:00:18 AM »
Quote from: flatlander on August 06, 2018, 10:45:04 PM
get the proper honda manual here: http://manuals.sohc4.net/cb550/
then, take the clymer off your workbench and carefully place it in the next paper recycling bin or put it somewhere else that's far away from your workshop.

joking aside, you can use the clymer to cross reference things with the honda manual if you really want but it contains a few flaws, misses a few things and doesn't really add anything. so why bother with it?

LOL.

Seriously though, download the various sections of the factory manual that are available via the link at the top of the forum home page. There are supplements for the 77-78 K model specifics like the carbs. I have them downloaded to both my laptop and tablet for easy access in the garage.
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"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline flatlander

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Re: !978 CB 550 Choke
« Reply #15 on: August 07, 2018, 07:13:57 AM »
ha danny, i tried to formulate it in a politically correct way. hope you appreciate the effort as it doesn't happen often  8)
of course, you could also use the pages of the pamphlet to light your bbq!
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Offline Fandan

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Re: !978 CB 550 Choke
« Reply #16 on: August 07, 2018, 02:11:57 PM »
ok I get it the Clymer was a waste of money.. :'(

Should I look in part 2 (engine) of the service manual to help me troubleshoot the choke issue?

Thank again
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Offline Bankerdanny

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Re: !978 CB 550 Choke
« Reply #17 on: August 07, 2018, 06:43:31 PM »
Quote from: Fandan on August 07, 2018, 02:11:57 PM
ok I get it the Clymer was a waste of money.. :'(

Should I look in part 2 (engine) of the service manual to help me troubleshoot the choke issue?

Thank again

Waste is probably too strong, but it is not as helpful or comprehensive as it should be.

I'm not sure that the factory manual will help you. I would start by removing the carbs so that you can observe the position of the slides with the throttle closed and what happens when you close the choke.
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"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline TwoTired

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Re: !978 CB 550 Choke
« Reply #18 on: August 08, 2018, 11:19:46 AM »
I haven't seen a climber manual that has any details of the 78 PD carbs.
So, it's not a blind leading the blind sort of thing.  It's a blind and brain dead leading the blind sort of thing.

Cheers,
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