Topic: 1978 CB550 Keihin PD46A Carbs

[JD]

Hello, hope you can assist me ive been searching the web for assistance on how to set up my Carbs,  Ive been out for a run today for about half an hour, on returning back to the house i was looking over the bike and spotted that cylinders 3+4 seemed to be hotter than 1+2, so much so that the exhaust headers on 3+4 had a nice blue tinge to them and 1+2 where still gleaming stainless steel.... but after carrying out a very quick touch test number 2 cylinder was so cold that i could keep my finger on the header after just 3 min's of the bike being shut down.... where as the other pipes were still to hot to touch....i removed the spark plugs and number 2 was quite white compared to the other plugs which were wet and black, so i swapped the plugs around and number 2 is still the same.. so i can only think its a carb problem but the manual i have does not cover the PD46A carbs... i need information on all the measurements and settings to restore factory setting so i can begin from scratch, at the moment im running the bike with a MAC 4-1 and individual air filters .. help would be greatly appreciated.

cheers JD

[Honda550k]

Check to see if you're firing on cylinder 2. To do this you simply remove the spark plug from the engine. Plug the spark plug wire to the spark plug and hold the spark plug to the frame. Make sure that the threaded part of the spark plug is touching the frame then hit your starter button.

[Bankerdanny]

If the other plugs are wet and black then you need to adjust your idle mixture screws to lean out the mixture a bit. The problem is I don't recall which direction is leaner in the PD's

[JD]

Honda550K, Thanks ive checked them all and their all firing nice, clean spark, Bankerdanny thanks ill try that today if i can find some information on the correct settings.

[busa]

Try fully closing idle mixture screws right in the bring them all out 1 and 1/2 turns out  thats what infor i got from keihin in glasgow  uk

[JD]

hello guys thanks for all info, as usual this web site is an amazing source of information, ive now got my 78 CB550 K3 cafe racer running perfect... it seemed to be a multitude of different things,,, first the ignition timing was slightly advanced,, then the air mixture screws all set up different now all set 1.5 turns out,,, and then i purchased a set of carb synchronizers,, set them up, ran the bike and.... wow .... they carbs were way out, spent about an hour setting them up(oh on the PD 46 A carbs the adjustment screws are inside the carb bodies) and now she runs like a dream im so chuffed to get this sorted as my next step was to strip the engine and check the piston rings etc...

[busa]

top job  well done mate

[scottanderson76]

hello guys thanks for all info, as usual this web site is an amazing source of information, ive now got my 78 CB550 K3 cafe racer running perfect... it seemed to be a multitude of different things,,, first the ignition timing was slightly advanced,, then the air mixture screws all set up different now all set 1.5 turns out,,, and then i purchased a set of carb synchronizers,, set them up, ran the bike and.... wow .... they carbs were way out, spent about an hour setting them up(oh on the PD 46 A carbs the adjustment screws are inside the carb bodies) and now she runs like a dream im so chuffed to get this sorted as my next step was to strip the engine and check the piston rings etc...

Hello, I have the same setup basically and I was curious if you have a pic of the adjustment screw you used to sync your carbs?  Any help would be greatly appreciated!

[Bankerdanny]

Scott, the screws are under the caps at the top of the carbs. In order to synch you have to remove the tank. It's a slotted adjuster with a nut around it to lock in place, similar to adjusting the valves.

The #2 carb is non-adjustable, so you synch the other 3 to match it.

There's actually really good video on synching the 77-78 CB550 I used when I had mine in 2011. I don't have access to YouTube from work, but if you search you should find it.

[scottanderson76]

Scott, the screws are under the caps at the top of the carbs. In order to synch you have to remove the tank. It's a slotted adjuster with a nut around it to lock in place, similar to adjusting the valves.

The #2 carb is non-adjustable, so you synch the other 3 to match it.

There's actually really good video on synching the 77-78 CB550 I used when I had mine in 2011. I don't have access to YouTube from work, but if you search you should find it.

Thanks Bankerdanny!

[scottanderson76]

Scott, the screws are under the caps at the top of the carbs. In order to synch you have to remove the tank. It's a slotted adjuster with a nut around it to lock in place, similar to adjusting the valves.

The #2 carb is non-adjustable, so you synch the other 3 to match it.

There's actually really good video on synching the 77-78 CB550 I used when I had mine in 2011. I don't have access to YouTube from work, but if you search you should find it.

Thanks Bankerdanny!

Ok I watched the video but they guy hooks up those brass tubes to a spot on the carb inlet.  I do not have these on my carbs so where do those tubes go?

[Bankerdanny]

Look at the picture of the PD46 from my '77 K in my hand in this thread, post #5. The synch port is the screw visible top of the output throat. http://forums.sohc4.net/index.php?topic=88743.msg995816#msg995816

[scottanderson76]

Look at the picture of the PD46 from my '77 K in my hand in this thread, post #5. The synch port is the screw visible top of the output throat. http://forums.sohc4.net/index.php?topic=88743.msg995816#msg995816

Is this what you are talking about?

[Bankerdanny]

Yes

[scottanderson76]

Yes

Booyah! Thanks, just wanted to make sure.

[JD]

hey Scottanderson76 sorry i didnt reply sooner been away working but i see Bankerdanny has sorted you out .... good luck its amazing the difference the carb syncing does mine runs perfectly now ... any issues let us know.....