Topic: Fuel Flowing from Carb Drain Lines?

[rkeaton]

I'm still trying to get this '80 CB750-F going that I recently bought.  Got the main fuse hooked up and yesterday was able to get it to turn over.  I had to use some starting fluid but it only took a few tries til she cranked up.  Not bad considering it's been garaged for the last 5+ years.

So I figured fresh gas would be a good idea.  I disconnected the fuel line between the shutoff valve and the carbs and drained out all the old gas - three gallons of it.  Then I added a gallon of fresh 91 octane.  I was all ready to give her a crank so I reconnected the fuel line and opened the valve back up.  Then I heard a sound, and looked down to see fuel pouring out of all four carb drain lines.  What the hell?  Why would it be doing this?  

[mtr]

Stuck floats?

[my78k]

My guess is the 5 yrs of gas has turned those carbs into a varnish filled mess! The floats are likely stuck (as mentioned) and the jets are probably plugged solid.

Save yourself alot of headaches and tear into them and clean clean clean!

They may seem scary but they arent that bad at all! Just remember to pull the idle jets and make sure you get em properly clean with carb cleaner and compressed air. When you are done you should be able to see day light through them.

If you just want it running and not worried about winning any shows you should neet need to break them apart totally. They can be left on the carb rack and still cleaned. If you aren't comfortable do them one at a time to avoid mixing pieces and then you can use one of the others as a guide to put them back together.

Dennis

[Hush]

Yup, what he said.
The old fuel was holding the floats up, when you drained them they tipped forward and now they are jammed down therefore flooding.
You can drain the bowls again and try to get them clear that way or as most on here would say, remove the bowls and give her a good clean out.
5+ years of old gas would have left some nasty crystals and rubbish in there, you will thank yourself for doing the dreaded carb clean later as it's just about obligatory when starting an old SOHC4.

[rkeaton]

This explanation makes sense - even though I know nothing about carbs   I was planning to take a whack at cleaning them anyway, since that's all I hear people talk about when it comes to old bikes.  I guess I'll have to move that up to the top of the list. 

Can you point me to any good links that might walk me through it step-by-step?  A "carb cleaning for dummies" type of thing? 

[1974CB750rider]

Go to the autoparts store and buy a gallon bucket of carb cleaner. It comes with a small parts bucket that you can put the jets in and soak them. If you pull 2 carbs at one time apart pull the jets out of each and put them in seperate baggies as well as the floats. Then you can submerge the two carbs you have a part into the bucket. Let them soak for at least 2 days. Then submerge the small parts into the bucket. After you get those back together do the same with the other 2. You can do this without pulling the carbs off the mounting bar. I'd replace the airfilter while your doing this prerferabley with a K&N.

[my78k]

One word of caution on dipping them is I am not sure if the 80 has an accelerator pump. If it does I speak from experience that the diaphragm and carb cleaner don't get along so well!!

Check the FAQ for some carb cleaning tips or PM bob wessner...he is a bit of an expert! He was one of the guys I harassed early on...

Dennis

[rkeaton]

This should get me started.  Thanks, guys.

[rkeaton]

I'm finding it very difficult to remove the carbs from the bike.  I loosened all the clamps front and back and the rack won't budge.  Seems like if I could get the airbox out or at least moved back it would be easier but that won't budge either.  Any suggestions?  Again the bike is a 1980 CB750-F.  Thanks.

[my78k]

Two words...BRUTE FORCE! Just kidding...a delicate touch is better in the long run.

I am not as familair with the DOHCS but, on my 78 750  you had to pull the airbox off. In that case I had to remove the two bolts up top holding it on and then basically finesse the boots so that they folded inwards and pull the box to the left side of the bike. It can be done but be patient, be careful not to crush the clamps and bend them too much out of shape.

It certainly can be done but it does require patience and when you get frustrated stop and have a cold one. Don't just yank or you will find your self needing new clamps on top of everything else.

Dennis

[Zaipai]

When taking off the air cleaner, just make sure all the screws that hold it down some maybe hard to see. Also the gas and time may have fused the boots to the carbs, what I did was use a small flat blunt tool, and pry up the boot and squirt some carb cleaner in there and let it sit for 1/2 hour and then I was able to rock the carbs up and down then they came off. Be careful you don't want to muck up the boots..

GL with the carbs, and he's right, 2 days of soaking should do it. It sucks but it works.

[rkeaton]

Success!

After getting everything disconnected it just took a lot of wiggling and gentle prying.  Then once they were loose I had to deal with disconnecting the throttle cables which was kind of a #$%*.  But eventually I was able to slide them out.

Now all I have to do is figure out how to take them apart.  And how to clean them.  And how to put them back together.  And how to put them back on the bike correctly

[my78k]

Remember that you do NOT need to totally disassemble them. Turn them up side down and pop the float bowls off. Pull the jets and clean them...soak the bowls and scrub the crud off. Clean the emulsion tubes and make sure that the floats are free and set to the correct height. I wouldn't spend a ton of money on rebuild kits until you know that the bike runs and is decent. I have fixed up a couple of really cruddy bikes and in most cases I required NO new parts.

Dennis

[rkeaton]

I wouldn't have known that, Dennis.  Thanks.  I'll get into them tomorrow and see what I'm dealing with.

[Hush]

Emulsion tubes are the long brass tubes with off set holes in them like a flute, probably the main jets are attached to their ends, I use some medium guage fishing line to poke them all clear.

[rkeaton]

So I just pulled the float bowls off this morning and was surprised at the lack of "crud".  Am I wrong or are they looking fairly clean?  Remember that this bike has been sitting for over 5 years with a full gas tank.

And assuming those brown things are the floats (reiterating here that I know nothing about carbs) then the floats are not "stuck" as some had suggested.  They are swiveling completely freely on their hinges.

I have not pulled the jets off yet.  Going to do that now.  So bottom line, I'm still trying to figure why fuel was flowing straight through them after I changed out the old gas with new.

[TwoTired]

Check the stand pipes in the bowls for cracks.

Check for a leaky float that has liquid inside it.

[rkeaton]

No cracks in pipes or floats with fuel in them.  I pulled the jets and they, too, look surprisingly clean save for a tiny bit of crud here and there.  Holes are not plugged at all. I'm soaking them in chemical dip right now anyway.

[rkeaton]

Maybe I'll just do some cleaning and then throw it all back together and see what happens.  I kind of hate to do that, considering what a pain it will be to pull it all apart again if they're still leaking.  But I don't know what else I can do with them apart.

[rkeaton]

*bump*

Any other ideas before I re-assemble the bike?  I don't feel like I really found the problem and there wasn't much cleaning needed.

[Zaipai]

I guess the next step is to be sure that you have a good seat with the needle valves and the floats are at the correct level and then put it back together and see.. Wait to do the air box until you see if it happens again. You may have fixed the problem the moment you cracked them open and not even know what the problem was.. Some times its trial and error.

[rkeaton]

I'm hoping that's what happened.  As for checking that floats are at the correct level, I'm hearing that phrase mentioned a lot and don't really know what it means.  I guess I'll have to figure it out if it comes to that. 

Gonna try to use the remaining daylight to put it together but wouldn't you know the Braves @ Dodgers game just started on ESPN...

[Zaipai]

I'm hoping that's what happened.  As for checking that floats are at the correct level, I'm hearing that phrase mentioned a lot and don't really know what it means.  I guess I'll have to figure it out if it comes to that. 

Gonna try to use the remaining daylight to put it together but wouldn't you know the Braves @ Dodgers game just started on ESPN...

It refers to the distance between the top of the float to the bottom of the carb, I think.. I would have to look it up as I know almost nothing about carbs myself, just what I learned rebuilding mine and what I gleamed from here.

Dude, first thing I did was put a TV and cable in the workshop.. Think you need that so you can watch the game AND work on the bike.. Ad a beer and oooooohhh thats living man!

[Green550F]

Don't for get to check the overflow tubes! I had this issue and I found the tube had a crack that was so straight that it looked like a seam!

[my78k]

I would doubt that it magically fixed itself (sure it is possible but unlikely).

I would strongly suggest you save yourself some time putting it back together only to pull it off again. Pull the float pins and make sure the floats are moving freely and not cracked etc. Have a good look at the valve seats too.

After you button it up put it on the bench and use an alternative tank and connect it and see if they over flow. Atleast that way you will atleast save the time it takes to put them back on and take them off again if the problem isn't fixed.


Dennis

[Hush]

I'm not sure but the 82 model CB650 I owned had a set of very fine petrol filter screens under the float valves, (they are the wee pointy things that the floats (brown square things) are attached to) once you remove the pivot pin (axle) you can lift away the floats and just check if there is a set of screens in there.
I would guess that as your bike sat for 5 years with gas in it, the float valves got so used to being in one place and with a build up of crystals and petro-chemicals they need a decent clean, just clean the with a clean rag and push the wee tips at the end in and out a few times to make sure the tiny springs are not stuck.
After that I can't see why all your carbs would leak at all, the float height is probably correct as when you got the bike it wasn't spewing gas out of them eh?
Once you drained them and added new gas you probably created a whole new set of problems.

Edit: Don't under any circumstances play with or try to remove the grey slotted screws at the ends of the bowls, they are set when tuned and if you play with them you will need a bit more help from the forum.
You have the one's that were made specifically to be "eco-friendly" so the nice people at Honda fitted them with a very small range of adjustment so you could not enrichen them and pollute the earth.

[Hush]

Just a tip, the way your photo has the carbs they are #1 #2 #3 #4 and only #2 has the booster attachment on it so don't try fitting it to any of the other carbs.
You can dissasemble that booster as well if you want, inside you will find a spring and rubberised plunger system, note how it comes apart and especially where the spring goes, (I put spring on wrong side of diaphram and bike did not like it).
Also remember to "aim" the wee drain screws out to the sides, #1 #2 should face towards left and #3 and #4 should face out towards the right side of the bike as you sit on it.
This will help when you go to drain the carbs in the future and can't understand why the screws are unreachable.
Something I would definately do if you are going to keep this bike is replace the stock carb bowl screws with Allen/hex key screws, so much easier to remove with an allen key when the carbs are back on and you need to access say just one carb float/jet.....OK I'll leave you alone now...