Topic: Why is the #4 carb always junk on a cb750?

[Geeto67]

So the emulsion tube threads in the carb body broke on one of my racks of carbs last night. I decided to rummage through the stock pile and almost all the racks of carbs I had #4 was consistently in the worst condition. In some cases it was the only one that showed corrosion, and in most of them it was complete junk. Anybody know why that is?

Also, is there another carb body that can be converted to be used as a #4 carb? Or at some point is it going to be difficult to find racks of cb750 carbs with rebuildable #4 bodies.

[flybox1]

contact harisuluv for fresh carb bodies.

[harisuluv]

Yes I have plenty of spares ready to go.  All I need is the casting number you want, I already know it's the #4.

[Geeto67]

I will reach out, but I am still curious as to why the #4 and not all equally or #1 (lowest carb when bike is on stand).

[evanphi]

I will reach out, but I am still curious as to why the #4 and not all equally or #1 (lowest carb when bike is on stand).

Longest time at highest point therefore potentially lowest fuel level therefore more evaporated gas and caked on ethanol and gunk?

spitballin'...

[ekpent]

Yes I have plenty of spares ready to go.  All I need is the casting number you want, I already know it's the #4.

All lined up like little tin soldiers ready to go to battle !!

[b52bombardier1]

That all sorta' makes sense. #4 on my 72 CB500 has a wobbly, loose feel in the carb body for its main jet even with a brand new o-ring on it.

I'm hoping a little JB Weld will tighten this fit up a little to eliminate the fatal amount of soot on this spark after less than ten miles. Heck, it's even a problem at idle.

Rick

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[Geeto67]

I'm hoping a little JB Weld will tighten this fit up a little ....

I think you are setting yourself up for failure on that one. Every time I have seen JB weld in a fuel rich environment the results did not end well. furthermore you don't want any tiny pieces to get sucked up into the engine.

[flybox1]

That all sorta' makes sense. #4 on my 72 CB500 has a wobbly, loose feel in the carb body for its main jet even with a brand new o-ring on it.

I'm hoping a little JB Weld will tighten this fit up a little to eliminate the fatal amount of soot on this spark after less than ten miles. Heck, it's even a problem at idle.

Rick

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you can sleeve the main jet post with brass tubing for more permanent fix if its cracked there.
If plugs are covered with soot after 10 minutes, are you sure its the main jet circuit doing the dirty work? 

[b52bombardier1]

I should probably start a new discussion and not hijack this conversation.

Rick

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