cold/ first start for the day and fuse issues

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ROB650
Posts: 7
Joined: Sun Mar 10, 2019 1:09 am

cold/ first start for the day and fuse issues

Postby ROB650 » Wed Mar 13, 2019 11:44 am

Hi All.

I seem to battle a bit to start the bike from cold/ first start for the day.

bike is a 82 cb650 luxury custom, with VB54 carbs

find I need full choke, and twist the throttle about 6 times, it will start and then die out, ( I found opening the throttle makes it worse once it has started, )

also the revs don't seem to increased with the choke on- there is no fast idle on the choke?

I have rebuilt the carbs - taking my time to do so and used a keyster rebuild kits.

is this normal for these bikes?

also at the moment I have a very much dead electrical system, was riding along nicely, and as I pulled up to a stop the bike died- no dash lights - nothing. I fiddled with the fuses at the handle bar and for some strange reason, the dash lights came on and then died and have yet to come back.
I suspect I may have a dodgy ignition switch, but also cant seem to find the main 30amp fuse ?



many thanks

ROB650
Posts: 7
Joined: Sun Mar 10, 2019 1:09 am

Re: cold/ first start for the day and fuse issues

Postby ROB650 » Thu Mar 14, 2019 12:48 am

Found the fuse! Sometime in the past the solenoid fuse unit had been twisted around. Fuse was barely making contact, wired 8n a spade fuse holder and fuse- working all good now,

Now just the cold start problems

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GeorgeSweety
Posts: 354
Joined: Tue Aug 08, 2017 11:47 am
Location: UK.

Re: cold/ first start for the day and fuse issues

Postby GeorgeSweety » Thu Mar 14, 2019 2:49 am

Your description of starting your bike sounds exactly like when I start mine (82 CB650SC Nighthawk/Luxury Custom?), I found that I don't need full choke or it won't start. 3/4 choke is ok for mine plus 3 or 4 twists of the throttle, one push of the button and it fires up, leave it to tick over a couple of minutes before I give it any rev's or it'll just die, it just takes a few minutes to warm up.
If you haven't already then I would suggest that you go through the wiring connectors, unclip them all and give the contacts a light sanding with very thin strips of fine emery paper then a good squirt of contact cleaner and then blow them clean with compressed air (if available). Its better to do it in your shed/garage than at the side of the road. :wink:

ROB650
Posts: 7
Joined: Sun Mar 10, 2019 1:09 am

Re: cold/ first start for the day and fuse issues

Postby ROB650 » Fri Mar 15, 2019 5:09 am

Thank you for your reply.

I found I must use maximum amount if choke, and I gave checked the choke is indeed operating all the way closed at the carbs...

I also noticed I get a bit of backfiring into the carbs ,on carb cylinder no 1 only... and it only does this when cold, when warm idle and pick up is absolutely fine.

Wires and connectors are good, went through those i could find .

Also have new HT leads, sparkplugs, have set / checked valve gaps and compression.

It's just its such a bugger to start when cold- first start up.

I have to full choke and twist the throttle open quickly about 10 times, repeat about 3 or times before it will continue running to warm up, only then can I use a bit of throttle

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Volker_P
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Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: cold/ first start for the day and fuse issues

Postby Volker_P » Fri Mar 15, 2019 6:23 am

Welcome here! :D

Poor cold start is quite normal for a CB650. Choke is required quite long compared to most other bikes and it easily dies on the throttle without choke when cold, too. For sure you found out yourself, too... :lol:

ROB650 wrote:also the revs don't seem to increased with the choke on- there is no fast idle on the choke?


The fast idle activates on the last few cm when the choke is pulled. So your throttle should visibly move a little bit when you pull the choke completely.
This mechanism helps at least a bit and so it makes sense to have it working properly. There should be an adjustment screw somewhere in the depths between the center carbs.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

Katatonia
Posts: 17
Joined: Wed Aug 31, 2016 6:36 am

Re: cold/ first start for the day and fuse issues

Postby Katatonia » Tue Mar 19, 2019 11:14 am

I have the exact same issue, and so far no improvements has helped - i'm guessing it's just the nature of the bike.

But now i've run into a new problem. My bike only seems to run on 3 cylinders. And worst part is, i tried changing the plugs, rebuilt the carbs, adjusted the carbs etc. and that didn't fix it, it just made it jump from one cylinder to another. So there is no consistency in which cylinder doesn't run. Anyone got an idea of what could be the culprit?

Because it doesn't stay the same, my indicator says something electrical. Perhaps the CDI box?

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Volker_P
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Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: cold/ first start for the day and fuse issues

Postby Volker_P » Wed Mar 20, 2019 1:51 am

The CB650 ignition has two independent identical circuits for cylinders 1+4 and 2+3 with the plugs connected in series to one coil ( 1+4 to left coil, 2+3 to right coil). So in case of an electric issue typically both or none of each pair should fire. Anyway it is a good idea to check the cables and connections.

BTW, it is more or less normal that a CB650 starts on two or three cylinders and it takes up to a minute until it runs on all four. So not running on all four becomes an issue when the bike is warm but one or two headers are significantly colder.

As you had the carbs rebuild I could imagine that it is a good idea to start there.
In any case: first make sure you have a clean tank! :wink:
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues


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