Topic: 1976 CB550F Petcock Question

[marwax]

Just recently bought a 76' CB550F and the PO said the petcock needed to be replaced. I do notice a slight gas smell in the garage even with the petcock left off. How do I go about checking if this needs to be replaced or repaired?

Also, took the bike out for a short ride today and noticed it starts up fine with the choke on, but as I take the choke off, it stalls. I can ride the bike, but have to leave the choke on half way or it will stall when I come to a stop. Is this a carb issue? This is my first motorcycle and just starting to learn about it, so any advice helps!

[goldarrow]

Most likely the rubber orings and seals around the petcock need to be replaced, carbs likely need good cleaning and adjustment, but we need more info about the bike.  3k miles tune up recommended.

[Stev-o]

Turn the petcock off and disconnect the fuel line at the carb.  Have a cup handy, fuel may come out, let it drain. Then, empty the cup, dry it out and place the fuel line in it overnight and see if the petcock leaks. 

It is not normal to ride with the choke on, this is most likely a carb issue, possibly clogged jets. 
If you are not comfortable rebuilding them, forum member Harisluv offers this service.

The 550F is a fine bike, it was my first SOHC.   

[heyitsrama]

Also check on the fiber-washers inside the petcock. I don't see why a rebuild would not fix the issue. have and pictures?

[Duanob]

Welcome to the club!

If you have to leave the choke on, its more than likely a vacuum leak. There are o-rings between the intakes and the head that dry out and crack. They are the same exact size (30.8m) as the o-rings used on the valve adjustment caps so buy lots of them, they are cheap. Also check the intake boots for cracks as well.

If you have a 76 you should have the petcock that has two drains pointing straight down. you can buy a rebuild kit that consists of an intank filter as well. It's pretty much just the filter, a 2 hole rubber gasket and an o-ring. They usually run about $30.

[Scott S]

 The '76 petcock was a one year design. It has a tapered "cone" inside that controls the fuel flow. It is essentially not rebuildable.
 I searched for a LONG time, but your only choice is a genuine Honda replacement for about $100. The same year 750 uses a petcock with the same thread size but it only has one fuel outlet. It's only a few bucks cheaper and you'll need a tee, so I just went with the 550 unit.

[marwax]

Hey everyone, thanks for the replies!

I am going to tackle cleaning/rebuilding the carbs and repairing or replacing the petcock this weekend. This will be my first time doing either though. I found these tutorials on cleaning carbs:

http://www.bikebandit.com/community/guides/how-to-clean-out-or-rebuild-your-motorcycles-carburetor
http://www.instructables.com/id/Cleaning-a-Carburetor-in-8-Easy-Steps/

Is it necessary to synch the carbs after cleaning them? Not sure if this is something a novice like me would be able to do.

Scott - are these the correct ones?
http://www.ebay.com/itm/251391664898?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
http://www.ebay.com/itm/231098015839?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I will try to upload pictures tonight or tomorrow.

[Stev-o]

Yes, you'll need to bench sync them after a rebuild - search for the procedure on this site [the custom Google box, not the search at the top right of the page.
A vac sync after you get the carbs back on and running is a great idea, you'll need the tool though.

[Scott S]

 Yep, those are the correct petcocks.

[Duanob]

We have all been there. it's not rocket science. Get a table with a white sheet covering it to lay the cabrs out on. White is easier to see small parts that might get dropped. Make sure you don't mix and match from one carb to the other. I usually do one carb at a time. You don't have to remove the carbs from the rack that's a PITA to get back together at least on your first try. remove the main spring, that makes life a lot easier. When taking to bowls off remember there is a leaf spring/jet holder, they can be fragile and break easily. The main jet pulls out, the pilot jet unscrews. The float jet has a screw holder but pulls out. Once you remove the main jet you need to remove the emulsion tube( needle jet) above it. I use a piece of coat hanger with a 1/8" bend and push it down from the venturi. Get yourself some guitar strings or a carb cleaning wire kit. Canned air also helps. Have a small bucket with some form of cleaner to dip and scrub. Make sure the floats are set to 22mm. Rock the carbs back and forth to you can see the float tang just touch the float needle without compressing it. That's when you take the measurement from the carb base. Replace all rubber pieces when removed. The bowl gasket can be a slight beyotch but use a bit of gasket in a tube to hold it in place and make sure it doesn't pop out and get pinched. Also shake the carbs a bit to make sure the flaots aren't stuck when tightening the bowls.

Then when you're done with the lower carbs you can start on the upper carbs. Remove the cap srews. Loosen the linkage cap nut 8mm socket I think. Remove the 6mm socket bolt that holds the arm to the linkage. You should be able to pry the arm from the linkage and pull the arm up and out with the slide. This is where tiny parts can go flying. try to hold all the little parts in the arm so you know what sequence to put them back together. It kind of makes sense but if you've never seen the assembly before you might get confused. There are two tiny screws holding the slide to the needle holder. remove and twist the holder 90 degrees to pull out. you now have access to the needle and clip to see what position it's in. I would take some 0000 steel or brass wool and clean the needles. Put the clip in the stock position and reassemble. I use a magnetic screw holder and long #2 philips bit to get the screws at the needle holder started. It takes a bit to put it all back together and you might think WTF did I just do!?! but you will get it.

One day you will be able to do this all in your sleep.  let us know if you need any help.

ps. are there no vacuum diaphrams in these carbs.

[Duanob]

The '76 petcock was a one year design. It has a tapered "cone" inside that controls the fuel flow. It is essentially not rebuildable.

Actually two years on the F model. Same with the tank which is a PITA trying to find one