Topic: WTF ... main jet issue for 76 CB750

[cshanek]

I have been working to get one of my bikes road-ready on and off over the last few months, mostly electrical work, and noticed carb #2 was leaking fuel out of the drain tube when I tried to fire her up last week. I took them off today for cleaning and inspection and noticed that the threads of the main jet where protruding out of its aluminum housing (see attached pics).

So now onto the questions ...

• WTF ... how did this happen? I cleaned them 18 months ago and swear this was not an issue then.
• Is it a pretty safe assumption that this was the cause of my leak. The jet would not thread at all until I squeezed the degraded piece with pliers.
• Lastly, is my only option a new #2 carb? Any ideas or thoughts? JB Weld?

[MoMo]

It looks like it may have been JB welded at one time and the material disintegrated over time.  Looks like carb body time, or you could contact forum member Jim French.  He is in GA and does micro welding, saved me a couple times.   BTW, that is the main jet and emulsion tube not pilot....Larry

[cshanek]

Thanks, updated the thread. I will reach out to him.

[bryanj]

That on its own would not cause the carb to leak, there may well be other problems with that carb body. Myself i would try and source a complete new carb rack to clean and fit.

[MoMo]

Most likely the drain tube on the float bowl is cracked.  Another body or rack (as Bryan suggested would be the way to go).   Jim is quite talented but not sure if he'd be able to build up that area and rethread the interior of it.  JMF Precision Welding (at least I think that is the name of his business) in Georgia...Larry

[ekpent]

  I would consider micro welding a broken float post but that carb looks like a goner. I have fixed a cracked on that section before with the ole' 45 acp caliber pistol case trick before but that one looks too messed up to even try that.

[PeWe]

Easier to find another old carb or a even better, a complete set.
You have plenty of bike scrap yards in USA where you can find this for not much, right?

[setdog]

That looks like corrosion.  Tive heard the carb bodies referred to as pot metal, and they are a cheap alloy prone to disintegrate.  I think I also see a fair amount of pitting elsewhere on that carb body.  I too would look for a replacement set.  Maybe the difference in cost btw replace or repair is $50-100

[PeWe]

Carbs washed with acid?
An ultrasonic washer can do much harm in short time with wrong chemicals.

[cshanek]

All,

Thanks for the feedback. I was just going to JB-weld the damn thing, and clean all of the jets and components to track down the leak. Now I am leaning toward trying to find a good set online somewhere.

-Shane

[cshanek]

Other than Ebay ... any thoughts or opinions for best place to track down a old set of carbs? What about non-OEM replacement options (few I have seen run for about 1k).

[TwoTired]

Carbs washed with acid?
An ultrasonic washer can do much harm in short time with wrong chemicals.

Absolutely! 
Same is true for basic solutions, too, as some household cleaners can be. Best to use carb cleaners intended to save the parent metals.

Cheers,

[Bankerdanny]

Other than Ebay ... any thoughts or opinions for best place to track down a old set of carbs? What about non-OEM replacement options (few I have seen run for about 1k).

I see the proper vintage carbs on Craigslist all the time. You shouldn't need to spend anywhere close to a grand for a good set of used carbs.

[PeWe]

Not long time ago $100US for a set.

[pjlogue]

You can pick up a set off e-bay that is in decent shape for $100-$150.  You would have to rebuild them but then you would be good to go.  I would be hesitant to try and salvage your carb body.  Just too much damage to the body.  If something ate away that much of the body what are the internal passages like?

-P.

[cshanek]

I bought 2 sets from a local vintage Honda mechanic for $150. He even threw in new gaskets and fuel line. I also finally bit the bullet and purchased a 10L ultrasonic cleaner. I know they aren't magic, but I have been wanting one for cleaning parts for a while now. I will post picture this weekend.

[cshanek]

Alright, so here are some before and after pics showing the 2 sets I purchased and the one set I Frankensteined and cleaned with my ultrasonic cleaner. I still intend to go through and clean everything out with B12 and my carb brushes. I have 2 sets now.

[cshanek]

BTW ... anyone know what the "choke gate" numbers ("1 3" etc) are for?