Topic: Where is the leak coming from?

[coffee_brake]

I've been searching the forum and finding all kinds of great info, but not the answer to the source of my fuel leak.

1982 CB650 Nighthawk, I've rebuilt the carbs and put them through the ultrasonic, replaced all the gaskets and rubber bits including fuel rail o-rings and bowl gaskets.

I'm running a fuel filter and gravity-feed petcock, and the bike seems to be running out pretty well--at first.

After a mile or two, it begins to bog down, and fuel is coming from the middle of the carb bank. It seems to be coming from the accelerator pump area.

Having never dealt with an accelerator pump, is there something there I may have done wrong? I didn't think that diaphragm ever saw fuel...

When I first started the bike and put it through the gears on the street, it had a hanging idle that seemed to fix itself within 10 minutes. I took care to seat the boots and carb holders at each end, and they are still supple, so I was wondering if it there could be an intake leak from somewhere else. But after about 15 minutes, the bogging down began and when I dismounted I saw a considerable fuel leak. (As in, turn off the fuel and step away from the machine!)

I'm gotten tons of help here already using the search function, and many thanks to all the vets here for that. I'd love to find this last little glitch so this Honda can be put back on the street.

[shinyribs]

I'm not really up with the carbs on the 650's. If they are the same as the CV's on the same era 750's then I might have one small piece of advice for you.

The #2 carb that houses the accel. pump. There is an extra o-ring that goes between the bowl and the main body of the carb to seal that passage. The other three carbs don't have that passage/o-ring. It's easy to overlook. Maybe that's it?

Like I said, your bike may have totally different carbs than what I'm thinking about, so don't go pulling them off without further research. 

[coffee_brake]

Ok, I will concentrate on that area, then. Makes good sense to me.

I wonder where I would source a new o-ring?

[curemode2002]

+1 on carb number two

siriusconinc.com has them for our CB650's

The 750 carbs are pretty close just a bit of difference on the upper end the lowers like floats, floatbowl gaskets, etc... are the same from what I have seen.

[coffee_brake]

The Sirius site is down. Can't navigate it at all...

[coffee_brake]

The o-ring was present but a bit flat. I had a new one so I replaced it, but I'm still getting a leak. I've pulled the carbs; gonna swap floats from #1 and #2 and see if the leak follows the float.

Then I'm gonna swap float needles and check again.

Then swap bowl gaskets and check again.

These are non-adjustable floats.

After that, I'm running out of ideas.

[coffee_brake]

Float needle. It looked good but the leak followed it.

Now I have a screaming-high idle. 

[Don R]

The needles break in to their seat. i'd replace them all but if you don't put the good one back where it was.

[750K]

Make yourself a small wooden rack you can sit on a workbench or clamp in a vise tha the carb rack can attach to. It's much easier to troubleshoot a leak if you are bench testing rather than on the bike, you should be able to find examples of them if you search the site. I know I'm not the only one that has one, I run a small external fuel bottle that I hang above the rack when I need to set float levels etc. I made mine out of some scrap 2x4's and some 1/2" pine boards I had lying around, took 10-15 min. to put together. One ledge for the kehiens another for mikunis.

[harisuluv]

where did you get the o-rings, and what size are they.  did you replace the accelerator pump tubes? If so, with what and what size.

The accelerator tubes are not simply small pieces of hose.  They have restrictor tubes in them made of brass for pressure.

[coffee_brake]

To clarify, I'm no longer leaking fuel, one of the float needles that looked ok was actually malformed when examined up close.

Thanks all for good information, I appreciate it.

This bike and its "rebuilt" carbs were someone else's abandoned project. I managed to get it before the dumbas$ tried any hare-brained modifications. I only want to put it back to stock, no pods or jetting or anything like that.

The carbs had new float bowl gaskets and float needles, but I had to go back and replace the fuel rail o-rings. I sourced them from a reliable, long-time member of the DOHC forum, who knew what sizes I would need. His o-rings are high quality. The float needles and bowl gaskets, though...I don't know where they came from. I had a good float needle in my spares box, I tried it to see if it would work, and it did, so I left it in there. Looked a bit different but had the exact same dimensions.
No more leaking fuel, I tested it with the bowls off and the carbs held up level. A wooden rack is a great idea, much easier than rigging it up the way I did.

Instead, I have a very high idle now.

Harisuluv, the fact that I'm not sure what you mean by the accelerator pump tubes tells me you probably are "onto" the problem. Do you mean the tubes that run between each carb above the level of the fuel rail? These one are made of aluminum and I got new zyton o-rings for them, too.
Now, there is a third tube between each set of carbs, and it's open to the atmosphere. I assumed it was a vent. These one disintegrated when I took the carbs off the rack, I made new vents with clear plastic fuel line.

Thanks again for the help. It's sucking air from somewhere, I think, but not the boots or holders. Those are supple, snugged up tight, and pass the WD 40 test.

[harisuluv]

There are potentially three different connectors between each carb.

1. Fuel Tube (aluminum, easily identifiable)
2. Vent line (on earlier styles or some there is just a tiny hole, if you have a nippe then this is the vent line that uses a tube oem)
3. Accel pump tube.  At the bottom, usually fixed with clips on each end.

If you fixed your leak, it's a moot point.  If I experience racing idle and I know the settings are stock or have worked before, first thing I would do is check the air screws and adjust them.  Usually I can get the idle to come down after hitting the throttle.

(as a disclaimer there is an idle adjust knob which adjusts the idle, this of course is the first place to look, some people don't know about it or assume others have already tried it)

If you check my sig with the carb rebuild thread, you will find a link to my albums, where you can reference the pd style and the orientation of the different configurations, ie accel pump etc

[coffee_brake]

If you check my sig with the carb rebuild thread, you will find a link to my albums, where you can reference the pd style and the orientation of the different configurations, ie accel pump etc

I'm afraid I don't quite understand you. The carbs you did for Firstgenxxx look the most similar to the '82 Nightahwk 650's.

When I went through these carbs, I had just totally rebuilt my brother's '81 CB900 DOHC carbs. They were in fantastic unmolested condition, whereas my 650 carbs had some buggery done to them.  The linkages and accelerator pumps were identical, but the 900 carbs had a different vent than my 650.

One more bit of information: the throttle plates were sticking on this 650 in the worst way, I think someone bent the shaft. I did a LOT of work tweaking things back little by little. Now the throttle plates don't stick anymore, but I can't imagine that's related to the high idle.

How many turns out should I re-set the idle mixture screws?