Topic: Honda CB550 Petcock

[LLG47]

Greetings!

I've owned a 1974 CB550 for a few years now and I'm working through the process of getting it running. I had the carbs rebuilt, and purchased a replacement tank as the other one was hideously scaled with rust.

This new tank has a hole on which the petcock is screwed on, rather than bolted on with 2 screws. I have read on this thread that it came from one model of one year, the 76' supersport. The guys at Honda ditched the design because it was evidently irreparable and prone to damage from any rust or particles in the tank.
         It can be found on eBay:
http://m.ebay.com/itm/Honda-CB-550K-550F-550-F-K-CB550-NOS-petcock-1975-76-/232068102484?_trkparms=aid%253D222007%2526algo%253DSIC.MBE%2526ao%253D1%2526asc%253D20150519202348%2526meid%253D6b938ff85d9c4db2b75944ce34589a4e%2526pid%253D100408%2526rk%253D1%2526rkt%253D1%2526sd%253D231995364905&_trksid=p2056116.c100408.m2460)

..... buuuuut, I don't want to buy it. First, it seems to be horribly designed and will not last long. Secondly, it's $96 + shipping (for a petcock!), And thirdly, I cannot be sure I can find a new one again as they seem very rare. I bought the tank not knowing I would be faced

I had heard though, on other threads that a CB750 petcock can be had and fit the tank exactly like the original with the easy addition of a T splitter in the fuel line. It can be found here:
http://m.ebay.com/itm/Honda-CB750K-CB750F-CB-750K-750F-Petcock-19mm-CB750K-75-76-CB750F-75-76-CB550-77-/221171456740

My question is for you experienced and versed men of Honda motorcycles, can they actually be used interchangeably. I thought they could at first, but the ad for the cb750 petcock says it has a 19mm thread, and the one meant for the tank says 20mm according to the seller if you look at the links.

I am on no schedule, but I'd like some direction on this issue. I can help with any extra information you may need.

Thank you for your advice,

Lawrence

[Scott S]

You'll only save a few bucks and be adding an additional place for fuel to leak but, yes, you can use the single outlet petcock and a T.
 Make sure the tank is spotless for those type petcocks. Debris gets between the body and cone and scores it, causing leaks.
 Personally, I'd spend the $100 and get the correct one and be done with it.

[calj737]

I am pretty sure I have a used, correct one too if you want to experiment. The same one I have on a 550 has worked perfectly since originally installed, and now some 40 years later.

[mj1176]

I went through the exact same thought process with mine; trust me, just buy the new one. there really isn't any other good option for less money, and they aren't as fragile as people say. They're definitely rebuildable, you just have to be more gentle with them than others, in terms of making sure you don't dick with it too much and not risking any fuel contaminants going through it since it's more prone to scoring where the valve seats.

[LLG47]

Thanks! I think I should just take the past of least resistance and buy the correct one, it's a shame it costs so much, but I suppose it's rarity and the demand for it that does that.

Cheers,
Lawrence

[Gene]

You could put out a feeler for a used one - I picked up one for 50 bucks a few years back. But hell, if I could have gotten the new one I probably would have bought it.

[Duanob]

First, it seems to be horribly designed and will not last long

Funny! All of mine have lasted 40 years and after cleaning them and new gasket and sock filters they will probably last at least another 10-20. What's your definition of long lasting? I think it's a pretty good design, it gives plenty of fuel flow at high RPMs. The sock filter does a fairly good job keep crud out of the carsb and you should always keep your tank innards as clean as possible anyway.

[Scott S]

It's only the '76 model with the cone that's a bad design. Even Honda said so. The other styles last and are rebuild able.

[Gene]

It's only the '76 model with the cone that's a bad design. Even Honda said so. The other styles last and are rebuild able.

Yes, the plastic cone, if damaged at all, will constantly leak.  Mine was that way when I bought the bike, didn't know it at the time til I realized it was impossible to turn the petcock all the way off. Ever. Trick is, keep the tank and fuel clean so it doesn't get scored. Which is what we want anyway.