79' cb650 carbs

If it's broken or just needs tweaked

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jaynesm
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79' cb650 carbs

Postby jaynesm » Tue Feb 03, 2009 8:45 pm

hi,
i have been working on the carbs to my 79' cb650 for a while now but can't get them running right. i have been trying to avoid buying the carb rebuild kits as the cost 40$ a piece and don't include the air cut-off diaphragms (i'm guessing these will need to be replaced as well). as far as i can tell, these carbs were only made for one year and finding parts for them is extremely difficult and expensive. does anyone know if any later models have carbs that will fit a 79'?
thanks for your advice
-mike

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Volker_P
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Re: 79' cb650 carbs

Postby Volker_P » Wed Feb 04, 2009 1:52 am

Welcome here! :D
The '79 is special in some parts, however did you check whether you have the air cut off diaphragms at all? At least the later models just have the covers, but there is nothing below. :wink:
Anyway, other piston type carbs (numbers starting with PD5 or PB5) should also fit, however the CV carbs (number starting with VA4 or VB4) have a different spacing and require a different cylinder head (or cranked carb boots). Maybe even someone here likes to have the rare '79 carbs and offers you a swap.
Are you sure that you have a carb problem? They must really look bad and worn to be responsible for completely unacceptable running. What did you try so far?
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

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Re: 79' cb650 carbs

Postby cb650 » Wed Feb 04, 2009 9:01 am

80 carbs will work. 650's didnt go with the CV carbs untill 81. Soos has used 750 carbs on his.
Did you clean the tank out?!?!?!?!

soos
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Re: 79' cb650 carbs

Postby soos » Sun Feb 08, 2009 5:49 am

cb650 wrote:80 carbs will work. 650's didnt go with the CV carbs untill 81. Soos has used 750 carbs on his.

Yeah the PD50 a/b are compatible('79/'80) cb650 carbs.

And i'm with you on the carb rebuild cost on these.
Astronomical.

There are options, some more straightforward, some not so much.

If changing carbs, you should at the least be familiar with reading your plugs.


There are 3 options I have found so far.


One, My favorite on looks, functionality, cheapness of a full rebuild, and availability.

CB750 carbs.

But beware, there are 3 main distinctions to the cb750 carbs.
"sandcast" carbs, with 4 individual pull throttle cables.
Haven't tried them, heard they can be a nightmare to synch, would sell them for the "sandcast" prices of late as well.

'71(?'70?) to '76 carbs.
Excelent choices.. The only interference is the return cable hanger on the carb assembly.
It contacts the head, and prevents the carbs from wanting to seal in the stocker cb650 boots.
This can be remedied by cutting it off, or as I did, bend the snot out of it to give about 1/2" more room so the carbs can mount up.
I wanted to keep the push cable on that setup.
They are a near perfect alignment compared to PD50 carbs, but the motor side of the carbs is larger OD, so fitment is assisted GREATLY by new carb Isolators.
But if you heat the boots, it's not too bad.

And then there is the '77/'78 cb750 carbs.
AVOID THESE, unless you want the same air cutoff diaphragms, and accel pump $$ to replace in the future.

The cb750 carbs fit nicely, however very loosly in the PD50 carb spaced airbox.
I had to find smaller clamps to tighten down enough for a good seal.
It worked though, quite well at that I might add.
Those carbs are prone to leaking, but with new gaskets, and in particular the rubber tipped float valve needles, they are pretty darned reliable.




Option 2) Kawasaki ninja 600cc (mine are '84's) carbs AND carb isolators(rubber hose bits between the carbs and the motor)
I stress the carb isolators because without them this setup would not be possible.
The ninja carbs actually almost identically mimic the '81/'82 cb650 carb spacing.
But the Kawasaki ninja carb boots have a offset to them that allows the head and carb spacing differences to be overcome.
It's not perfect, but like the cb750 carbs being tight on install, these have their quirks being mounted.

Have found that tilting the airbox side down as far as possibly, and lining the bottom of the motor side in the isolators, then pulling while twisting the carbs to a level position If i do it in a nice fluid motion, they pop in perfectly.
If the motor side lineup challenge wasn't enough, the airbox to the kawasaki carbs is a feat in itself. I am going to mod my spare airbox to help things align better.
I used CV cb650 airbox boots in a '79 cb650 airbox to help with the offset difference. They work, but it's more work on this side of the carbs to get a good seal than the motor side.

I am currently running a set of Kawasaki Ninja carbs.
I LIKE THEM.


option 3) CV carbs from a '81/'82 cb650 bike.
However, as with the Kawasaki ninja carbs there are offset differences compared to the stocker PD50 carbs.
Again the Kawasaki ninja carb isolators come into play here.
Without them this firment is impossible.
Have not run this combo, but when mocjing it up on my '79 motor it fits and has just enough clearance to fit.
Have not tried to mount up to the airbox, as the CV cb650 carbs I have are not in working order(never really were)





Overall, the Kawasaki carbs are reliable, easy, and the rebuild I did to them has entailed a whole $12.00 for a few float needles.
I plan on using them on my daily driver.
The 32mm venturi(cb650 PD50 carbs = 26mm) works well with my setup.
bored, head job, dyna2000 as far as motor mods.
These on a stocker cb650...
I would imagine they would be run, but as well as it does compared to how they do with my motor is setup?
Dunno.


The 750 carbs.
You can't beat them if you want to add a classic touch to your bike.
The side choke lever wins hands down over the cb650's prone to break choke cable system...
As well as a 2mm venturi gain.
You can also do things like adjust your needle clip position.
I have ran these my cb750 carbs on stock motors, and my bored out one, and it's a gain on both rides.
With the correct manipulation I would bet they would at least perform at the level the kawasaki carbs do, if not better.

Going with the 650 CV carbs and the kawasaki carb isolators(I think the years '84-'90 used the same part # for this.)
Well they would probably look more period and origional to the bike with these. But again I don't have a working set of these carbs so have no idea the full scope of exactly whats needed to get them to work.



If you want more details on my experiences, I can post a few links, and answer any Q's you have on my past carb experience with different carbs on a cb650.

I love my '79cb650.
I also love tinkering/upgrading/improving performance.
Having enough cb650 parts to make another bike(and then some) helps with mods/mocking up...




l8e
-=≡ Soos ≡=-

jaynesm
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Re: 79' cb650 carbs

Postby jaynesm » Mon Feb 09, 2009 9:09 pm

hello,
thank you all for the warm welcome. i've found a few options for carbs:
1. carbs from a 1980 honda cb650, if i can't get these i also found:
2. carbs from a 1973 Honda CB750
3. carbs from a 1978 CB 750 ( soos- i know you told me to avoid these but the seller is local and if they are running would it be worth it?)

the bike runs well while choked but will not run while off the choke (unless it is at 5000 rpm or more). i have cleaned the carbs several times, set the floats, checked engine compression, spark, and timing (as much as possible). i replaced the float bowl gaskets with o-rings which worked but they are a few mm taller than the originals. i don't know if that would be enough to throw off the carbs.
i got the o-rings from a place in Denver, CO called "Rocket Seals"- thought i would mention it because they have an amazing selection of seals and if they don't have one they can make it for you- it's hard to find these places anymore.

thanks for your advice on this

buzz
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Re: 79' cb650 carbs

Postby buzz » Mon Feb 09, 2009 10:54 pm

if his idle (pilot) jets are clogged, would using full choke cause enough vacuum to start drawing fuel through his main jets? could that be the problem?
when i bought my bike, the rust in the tank had completely clogged the idle jets. it would only start with full choke, full throttle. i had to replace the jets. all the cleaning in the world wouldn't have fixed them.

jaynesm
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Re: 79' cb650 carbs

Postby jaynesm » Tue Feb 10, 2009 12:11 am

i've gone through all of the jets and cleared them all. it took me all the time and cleaning in the world.

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Re: 79' cb650 carbs

Postby cb650 » Tue Feb 10, 2009 10:07 pm

Interested in see in the seals from rocket. Been there for other things and thought they were aholes. FYI on my 80 couldnt get the carbs right and tried a set of 79's and no problem. Not that any year might be better just sometimes one set is beyond repair with out a major overhaul.
Have run across that with the 81/82 carbs also.
Did you clean the tank out?!?!?!?!

jaynesm
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Re: 79' cb650 carbs

Postby jaynesm » Wed Feb 11, 2009 5:52 pm

will the carbs off of a 1978 cb 750 will even fit?

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arcangel
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Re: 79' cb650 carbs

Postby arcangel » Fri Feb 13, 2009 10:18 pm

jaynesm wrote:i've gone through all of the jets and cleared them all. it took me all the time and cleaning in the world.


Did you clear the inlet ports the tiny holes in side of the carb next to butterflys I beleave they are in a dimond shape like below they lead in side the carb and connect to the carb bowls?

'
' '
'

Mine were clogged I thought I got them clean but no dice.
If cleaner won't come out some where they go when you spray cleaner through the holes they are clogged and must be cleaned I had to sue a wire to unclog mine . you have to be careful not to enlarge them or erratic or unreliable performance will result
hope this helps.
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jaynesm
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Re: 79' cb650 carbs

Postby jaynesm » Sat Feb 14, 2009 12:41 am

i cleared those out too and also had to use a small wire to clear them. they made a huge difference in how the bike is running but it still has to be choked.

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Volker_P
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Re: 79' cb650 carbs

Postby Volker_P » Tue Feb 17, 2009 3:40 am

If it runs fine above 5000rpm but needs choke below even when really warm, your idle jet/channel system may still be not really free or the carbs are heavily (easily visible) out of sync (Or maybe you have no air filter installed).
If you can fix the float bowls with the stronger seals without any gap to the carb this should play no role. The carb bowls also have a small overflow tube at the center release bolt. It also serves as a vent and possibly could cause trouble if blocked while the needle still is down.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

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arcangel
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Re: 79' cb650 carbs

Postby arcangel » Wed Feb 18, 2009 10:36 pm

Have you tryed using starter fluid ?
after you start the bike spray fluid in to the breather while the bike is running have some on else turn off the choke while you are intermittantly spraying starter fluid if the bike runs fast with the choke off it is a fuel delivery problem.
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Volker_P
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Re: 79' cb650 carbs

Postby Volker_P » Thu Feb 19, 2009 2:46 am

Well, if it runs fine above 5000rpm there should be basically enough fuel in the carbs, the problem rather seems related to the transition to the idle circuit with the mains almost closed.
Possibly one can change needle positions in the '79 carbs and these are too low.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

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arcangel
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Re: 79' cb650 carbs

Postby arcangel » Thu Feb 19, 2009 8:31 pm

Ya sounds right.
I just thought if you get it to idle with the spray you know it is delivery problem. the needle positions or the cloged ports still look like the problem to me.
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