Topic: brown/tan goo coming from carbs...

[zzcoopzz]

Brown goo leaking from the air mixture screws at the bottom of 1977 CB750 F carburetors.

What is this?  Its like a weird sticky brown and tan goo that drips from my carbs.  Is it oil getting into my cylinders and somehow mixing with gas and leaking out. 

This is a very slow drip,  not enough to be a problem, but just enough to make a mess.

If this is a sign that I have an oil leak in my cylinders, then I guess its time to pull the engine and do a major overhaul.

Any thoughts?

cooper

[eldar]

How often do you ride thgis bike? If it has been a while, it could be varnished gas. If you ride often though, drain some gas right from your tank and see if there is an odd color. Could be rust or dirt in the tank.

[zzcoopzz]

I ride all the time.

this weekend I am going to clean the tank and coat it with "Kreem" (I've heard the pros and cons but am doing it anyway )

the tank has quit a bit of rust in it.  I have a pretty  major inline fuel filter and takes out all suit and specks but I'm sure particles still get through.

I'm not fully convinced that its just rust and gas for it has a sticky texture to it, very similar to honey.


I'm going to gut the engine anyway but would rather do it in winter then in the middle of the best riding weather here in LA.

if it is just rust and gas, awesome I'll just clean the cabs before each ride, makes no difference to me it only takes me about 20 minutes to do anyway.  The one thing about these bikes is that you sure get to know your carburetors on a very personal level...

Thanks

[eldar]

If you kreem, set aside about 1 - 2 weeks to do it right. The liner is where problems occur. It needs AMPLE time to cure fully.

Rust mixed with gas may be sticky but have you put in any additives?

[zzcoopzz]

no additives with the gas.

could it be that the gas and rust cooks down (almost like a good glaze sauce) from the heat of the engine, creating a sticky resin?  I think that would be my logical guess.

thanks for the Kreem tip.

I am in no hurry to get this done.  I might get a few more good rides in before I do it, that is if you suggest it takes a few weeks.  I'm assuming that's because I might have to use the liner cream a few times letting it cure each time.  from the instructions it sounds like I might need a few sessions with it.

[eldar]

If you have not gotten the kreen, do por-15. I have yet to hear anything bad about it. But if you have the kreem then wait till you are done riding. People that had good results say they have taken weeks to do the job and it works good then.

The cook down thing, I dont know. Seems like no, since gas evaporates. Have you noticed it actually dripping from the carbs or just the mess on the engine?

[zzcoopzz]

I don't see it dripping but I can see where the drip forms on the carbs.  its coming from that brass air intake screw that is seated under the carbs just before the carbs meet the rubber grommet that attaches to the cylinders.

coop

[eldar]

Hard to say but it could just be dirt that has worked its way into the screw areas but I guess I still think you should drain some gas and see if there is discoloration but it could be an over time build up too. Very hard to say. Either way if you think it is coming from the mix screws, replace the orings.

[bistromath]

When gas evaporates it leaves a sticky residue behind, which is usually brown or green. The same varnish that gets into your carbs when you don't drain them. When the bike is hot it will evaporate faster. When the bike is in the wind it will evaporate faster.

Bet you've got a slow leak from a pilot screw.

[zzcoopzz]

yeah, I need to rebuild the carbs pretty bad.  

I went back and looked at the bike and the goo smells like oil...  so I am in the process of taking the head off the bike.  I have quickly found out that you cant take the head cover off without removing the engine.  I am hoping that I can just rotate the engine by about 20% and get the head off that way.

even if this is unnecessary to remove the head it will make me feel like I have covered all by bases until winter when I strip the bike down and paint polish and rebuild from the ground up.

I figure if the head and carbs are right were they need to be then the rest of the season will be filled with open roads.

wish me luck and if you have any advice feel free to send it on.

thanks,
cooper

[littlebronco]

I've got what appears to be the same problem on a 75 750F.  I found earlier that oil was getting into the airbox via the crankcase breather, which, based on some research, may be pressure building up in the top end due to a leaky valve guide.  Not sure about this but I think I'm gonna end up with the engine apart for the winter.

[zzcoopzz]

so I decided NOT to take the head off until winter...  I think it's fine for now.  I called a buddy and he said the same thing that "bistromath" said about the slow leak out of the pilot screw.  I've been meaning to rebuild the carbs with new gaskets but haven't got around to it.

anyway thanks for all the help, and just to recap, gas and rust dust will cause a goo from evaporation and will leak out of a faulty pilot screw seal.

thanks again,

Cooper

[chippyfive50]

I hated the goo factor of Kreem, an on my most recent tank used a product called RedCoat from the auto parts store, much nicer, semi transparent coating. I did pay to have the inside of the tank professionally cleaned $30. I have no complaints, and it looks nice.

[DammitDan]

Where did you go to have it cleaned?  That might be worth it if it's less than $50 for me...

[chippyfive50]

My local "metal cleaner"  of course...  a friend told me.  American metal cleaning (cincinnati,oh) was the name of the place. I'm sure you can find someone in any decent sized city. I would look in the yellow pages though, a lot of these shops are LOW tech. Also, if you want to preserve your paint, ask ?'s and take precautions. have you checked the FAQ's and or greenspun thread for any good DIY methods???