Topic: '73 CB500 Petcock and fuel lines

[ProudGecko]

I know that this topic has been discussed many times, but I couldn't seem to find a good answer to my question...but first a bit of explanation (see the attached photo for further reference).

When I got my bike it was obvious that the PO had altered the stock fuel line setup.  My guess is that he didn't understand how the petcock works (admittedly I didn't either until searching these forums).  The front (reserve side) outlet was blocked with a stubby hose and a bolt.  At first I thought he had the reserve blocked off but after tearing my petcock apart I realized that it didn't work that way.  So I've been reading that both outlets need to be feeding the carbs, but I have no clue how the lines are supposed to be routed now.  There are two right angle nipples on the inner carbs (red circle) but they didn't have any hoses connected.  Instead the one line coming from the petcock was attached to a T (blue circle) that ran a line to two other T's(green circles).  The second T's (green circles) where connected directly to their corresponding carbs.  Then there are the mysterious lines running between the two left carbs and the two right carbs (yellow circles).

How are these things supposed to be setup?  Between the rusty tank, plugged petcock and filter screen, and plugged up inline filter I know that my bike is being starved for fuel.  I've fixed all of those issues but now I'm not sure how to run the hoses.

Thanks

[dustyc]

This help?
http://forums.sohc4.net/index.php?topic=23614.msg242641#msg242641

[TwoTired]

The red circled nipples are bowl vents.  These had hoses that route in front of the swing arm pivot.

Originally, the 500 had two fuel lines connected to the petcock.  One went to the 1-2 junction the other went to the 3-4 junction.  These are green circled.

The yellow circled hose is a bowl vent connector.

Cheers,

[TwoTired]

Another thing, the T in the fuel lines was used in production on CB550s that had a single outlet petcock.

What carbs do you have there?  CB500s had 627A or B.  By 1977, the CB550F (069A) used the single outlet petcock and the inline T.


Cheers,

[ProudGecko]

Well I'll be darned, my carbs are from a 550F.  They have 069A stamped on them.  I wonder what else is from a 550F, and I also wonder why things were changed.  I know that the side covers are, they have the 550F logo.

Will the 550 carbs affect anything?  Will running the dual outlet petcock with one outlet blocked off hurt anything?  Would it be better to remove the inline T and run two separate fuel lines?

[TwoTired]

Will the 550 carbs affect anything? 

Sure, if they are still in factory setting.  They were set up from the factory for and engine that breathes like a 550 with a stock 4 into 1 exhaust and stock air filter set up.  If they haven't been modified, they probably don't run right on the 500 (with unspecified exhaust and air filter).

Will running the dual outlet petcock with one outlet blocked off hurt anything? 

Can't imagine what, if so. (Unless it's a sense of neatness, and sloppy bothers you.)

Would it be better to remove the inline T and run two separate fuel lines?

Potaytoe, potahtoe

Are you having a fuel feed issue?

Cheers,

[ProudGecko]

The exhaust is an aftermarket 4 into 1 and the air filter setup is actually a 550 setup (purchased by accident) that replaced the pods put on by the previous owner. I just rebuilt my carbs though and used CB500 rebuild kits not realizing that mine were different.  Everything looked the same and the jets were the same size so I there shouldn't be any problems correct?

[SteveD CB500F]

The 550 jets are physically the same size but the jet number (the size of the hole) is different for the 550 to take account of the 4-1 exhaust (amongst other things)

See carb specs here

Better still, read the whole Carb FAQ thread...

[ProudGecko]

What I meant to say is that the jets that came out had the same number stamped on side as the ones that I put in.  Now the real issue is going to be the fact that my exhaust (and preferably the intake too) is different from stock.  I guess I'll have to do some reading then lots of tinkering to get the everything tuned correctly. 

Thanks for your help.

[TwoTired]

The CB500 should have #40 slow jets and #100 Main jets.  The 069A from the factory had #38 slows and #98 mains.  The slide needle was 2nd groove from top on the 069A.  I understood the middle position was used for the 627B.  But, I don't have documentation for the latter.

With the new exhaust, let you spark plug deposits and engine performance be your guide.

Cheers,