Topic: '77 cb550 tuning issues.

[ATZ]

I know tuning these PD style carbs with new exhausts is tough, I have gone through a many things but I'm going to try and explain everything to you guys and see if you can help me out, I'm really backed against a wall here and don't know what to try. I had an earlier post if you would like to read that as well. http://forums.sohc4.net/index.php?topic=102548.msg1185738#msg1185738

So from the beginning then...

I picked up an all stock '77 Cb550K last fall accept the PO had put on an aftermarket exhaust (see attached photo) The bike started when I got it but didn't run the best. It held on to RPM when I opened throttle. I didn't think to much of it because I had assumed the PO had jetted accordingly with the new exhaust. Turns out the PO hadn't done any work. The stock mains and idle jets were still there and the needles were in the stock positions.

So I went to work trying to get the bike running properly:
I set the ignintion timing
Adjusted the valve tappets
Checked the Cam chain
Cleaned the Carbs thoroughly
Bench synced the carbs
Tried to vacuum sync them but couldn't get consistent readings on the gauges
Set the float height to 14.5mm (which seems perfect)
Checked for air leaks thoroughly

mostly the basic tune up stuff.

I then learned that the bike probably wasn't jetted correctly. I tried upping the idle jets, upping the main jets but still the bike would not run properly. It could barely hold an idle and had a very inconsistent throttle. I took suggestions from you helpful people on this site and still I couldn't master it.

As of now, I have 105 mains, the needles on the second to last notch and 42 idle jets. The bike is still struggling. It may in fact be worse then when I got it. I have some knowledge of tuning but I have never tuned a four stroke or a four cylinder cycle.

I am just hoping you guys can give me some insight. My last post kind of went dead so I thought I would try again. I am out of ideas and nothing seems to be working. Any other suggestions would be much appreciated. My only thought now is to buy a set of stock pipes and see if going back to the stock carb set up will work out. I am having a hard time finding a pair. I really wanted this bike to be on the road for spring and summer but no luck.

Any ideas? Anyone with a set of stock exhausts willing to trade for an aftermarket?

attached is a photo of the bike, the plugs and here is a link of it running http://screencast.com/t/PWmzp27fy

Thanks ahead of time.

[ATZ]

here is the bike

[lucky]

The bike looks good!!! I would be proud of it.

About your problem.
I am trying to build a database.

The accelerator pump system and needles HAS TO WORK.
Check with engine off. air filters off. look into intakes with a flashlight.
turn the throttle a few times while you look and make sure a squirt of gas is coming out of the nozzle of each carb.

Please always include the following:
Year 1977
TYPE of AIR filters???
TYPE of exhausts.
idle jet 42
needle position. (adjustable)
main jet 105's

Floats should be set at 12.5mm not 14mm
But check your manual.

If all else is ok I would put in the 42 idle jet as suggested by others.
Put the clip on the needle in the middle groove and choose a mainjet the next step up from stock. That will get it going. IF all else is right.

And we still do not have a report back from you on the accelerator pump and nozzles.

After hearing the whole story and seeing that others have tried to help you on another extensive thread (three pages long)!!! here is what I would want to do.

I would start back at the very beginning.

First you bought the bike and you knew nothing about it.
Adjust the slack out of the cam chain (by the book!!)
Ad just the valves the correct way.
Then do a compression check and report back what the results are.

See carburation is the LAST step in the tuning process.

But starting a new thread and going all through the story is not going to get you where you need to go.

This needs a complete work up from SQUARE ONE.-LUCKY

[Frostyboy]

There's a bit of deja vu in your 1st post for me. When I bought my 550 it was a dog at low speed & if I put a passenger on the back I was never sure if I could actually get going at all from a standing start, let alone a hill start.
After tuning things a number of times I decided maybe a compression test was in order. The results were staggering. 40lb; 40lb; 40lb; 40lb.
I pulled the head & couldn't find a thing wrong with it. Put it all back together &  investigated valve timing.
It turns out the PO had put in a hot rod camshaft. Once I threw that in the bin & fitted a standard cam, everything came good.
I don't have the PD type carbs on mine & from what I've read here they do require knowledge to get synched correctly, however maybe you should check how good the compression really is before you go altering too much in the carbs.
Just tryin' to help 

[TwoTired]

Have you checked the timing advance?
Checked the compression?

[dave500]

that must have been some long overlap cam owen?thats why some engines have a static compression ratio of 12:1,to make up for all the overlap and early/late opening/ closing timing.

[Frostyboy]

that must have been some long overlap cam owen?thats why some engines have a static compression ratio of 12:1,to make up for all the overlap and early/late opening/ closing timing.

Sure was Dave, inlet valve finally closed 45º ABDC. I never did rev it high enough to find out where it might've worked.