Topic: 650 carb hazard, you'll want to see it.

[Hush]

OK so I've had a PITA carb problem, flooding/leaking etc the usual stuff and I cured it by buying another rack of carbs from wreckers, used one of the racks' floats and a bowl and hey presto carb problem solved.
But why did I have this problem in the first place?
This is the second carb float I have had to replace within a few months and both floats were punctured with a small wear hole in the very tip of them.
I wondered just what could be making these floats rupture and the answer will suprise you, inside the bowl Honda built a float hazard, a wee alloy ledge sharp enough to puncture the float after a long enough time of having the float drop low enough to hit/rub on this little razor.
"See the picture below, in the top left of the bowl you will see a small alloy ledge sticking out".
In the photos of the floats the small black dot in the very nose of the float is where it has been banging down and finally punctured.
It serves no useful purpose that I can find, it is just a casting error/fault/excess alloy whatever, if you have a dremil you can easily grind it off, I don't have a dremil but I do have a partner with a battery driven toe nail grinder which worked just as well. OK so I'm a dead man walking.
You may think this small ledge was there to stop the float dropping too low but if it drops that low then your pivot pin must have fallen out!
I'm just warning the 650 guys'n gals that this hazard exists, if you don't have leaky carbs and your floats are all perfect then you are lucky and this may be just something the older 79 650's have.
Anyhow you heard it here first! .................Hush.

[Hush]

Just me..........damn I'm special!

[Spanner 1]

Toe-nail grinders RULE !! Great detective work, Hush !
Can ya post a pic of the toe nail grinder !!??

[CBJoe]

My carbs are packed away in a box right now, so i cant check.

I'm not getting a clear mental picture of the ledge you speak of.  Is it in the top left of the photo?

Joe

[mtherrmann]

I just got done replacing my float valve...thought i had the problem fixed but i was WRONG!  This is good info, but i have one question.  Can this be done with the carbs still on the bike?  I am thinking of trying it and didnt know if anyone has done this?  Any other ideas as to why carb 2 would leak gas even after i replaced the float valve?  Also, it only seems to do it when the bike is on the side stand, never when on the center stand.

[Frankenkit]

Sure, if you're good with your hands, drain the gas from that carb bowl, *very carefully* unscrew the screws holding the bowl on (assuming you have tiny midget hands or a small child to assist) then look at it from there.  Good luck getting it back on, too.

[Spanner 1]

It's possible to remove the float bowl with the carbs. installed....a short stubby phillips screwdriver and an adult with hands the size of a 5 year olds helps ! But it is doable.
Once the bowl is off, put the bike on its side-stand and gently rotate the float upwards to see if it is rubbing on something or binding. Good luck..

[Hush]

Yes you can remove your floats while the carbs are on the bike still, it's a mission but many on here have done it heaps of times.
I replaced my cross head screws with allen (hex) key screws so it's easier everytime I have to remove the bowls.
mtherrmann: I'd guess your float has sunk, it's real hard to tell but to test it if you don't have any spare floats, just switch one of your carb floats that isn't flooding with the troublesome one, if the flooding follows the float you need a new one.
The problem will be worse when the bike is on it's side stand as the gas all flows to the one side and if the float is sinking it pulls the valve down too.
CBJoe: yes top left hand corner, that wee horse shoe looking thing is an alloy ledge, it maybe only relevant to older 650's like my 79.
Spanner 1 : no Jaffa won't let me show her toe nail trimmers on world wide internet.

[mtherrmann]

Alright, i changed float 1 and 2 with each other, got it back together, turned on the gas and gave it some choke.  I let it sit and idle for a few minutes, turn it off and went inside (while the gas and choke were still on and the bike was on it's side stand...i left it like this to see if i really fixed the problem, normally i turn the gas off when not riding)  I came back out and to my surprise, carb 3 was now dripping out the drain nipple   

After coming back out i immediatly turned the gas off, but one side note....I left the carbs on the bike to make the float switch.  As i was laying under the bike i could see from the float valve that gas would occasionally start to bubble and drip out.  It was never a ton, but it could for sure add up after 10-20 minutes of doing this.  Could my problem be a petcock issue, not a carb issue, and maybe the petcock...even when the fuel is off is still dripping a little fuel out into the carb bowels?  Even tonight after the fuel has been off it will still drip some gas from carb 2.

I honestly have no idea what could be causing this. Any help would be much appreciated.   

[Leaky]

Yes you can remove your floats while the carbs are on the bike still, it's a mission but many on here have done it heaps of times.
I replaced my cross head screws with allen (hex) key screws so it's easier everytime I have to remove the bowls.

Great idea Hush I'm gonna do the same to mine.

[mystic_1]

Once you've converted to allens, get yourself an extra long socket-driven allen wrench for a 1/4 inch ratchet.  Get the ball-end style if you can, they work even at a slight angle.

OR, find a cheap allen wrench of the proper size, and a cheap socket that the wrench fits into.  Cut the long leg off of the allen wrench and super-glue it into the socket.

This will make the job even easier.

mystic_1

[Hush]

Where were you Mystic when I was puuling my carbs for the first time last year? could have used that great tip.

mtherrmann:
(1) I'd drop the bowls off all your carbs (I know major PITA but worth it to fix the problem)
(2) check your floats, check the pivot pins (and give them a nice polish up with a steelo pad so they don't hang up/get stuck)
(3) empty your gas tank into a bucket ( you are looking for rust and cr*p) and dissasemble and check your gas tap.
(4) Check, clean, reassemble and cross fingers.

One thing though, these bikes hate idling for long periods and to pay you back with carbon up the plugs which will give you rough running until you take the bike for a really decent ride.
Get used to turning the gas tap off when you shut the bike down, make it a habit, "kill switch" "key off" "gas tap off", it's a mantra that will save you lotsa grief.

[TwoTired]

OK so I've had a PITA carb problem, flooding/leaking etc the usual stuff and I cured it by buying another rack of carbs from wreckers, used one of the racks' floats and a bowl and hey presto carb problem solved.
But why did I have this problem in the first place?

I don't have 650 PD carbs.  I do have 550 PD carbs.  The floats on those have a "down stop" tab on the float pivot, that rests on the pin pivot post of the carb body.  This tab can be bent so far that the float will bottom on the bowl when the fuel level is low.  These "Down stop tabs" are normally adjusted by the factory.  But, I've seen a couple bent too far, presumably by someone who didn't know what they were for, or thinking that the lower the flaot went, the more fule would flow through the float needle valve  (which is only true to a point).  I've never seen documentation that describes this adjustment.  But, it is not hard to figure out.  Measure the bowl depth from mounting surface to the deepest part of the float bowl.  Then let the float hang below the carb and bend the "stop tang" to where the float won't hit the bottom or any part of the bowl when the bowl is empty of fuel.

One thing though, these bikes hate idling for long periods and to pay you back with carbon up the plugs which will give you rough running until you take the bike for a really decent ride.

There may have been some truth to this statement for the earlier carbs with the air bleed screws and no accelerator pump.  But, the later carbs were engineered for minimum emissions at idle.  If they are adjusted properly, they should NOT foul plugs during idle.  Such large amounts of unburned hydrocarbons would cause it to fail emission tests.  This is precisely why the PD style carbs had the Idle mixture screws, to lean the idle mixture at peak levels, and then the Accelerator pump to make it rich enough to accelerate while twisting the throttle.

A bike with the PD carbs  should idle all day without fouling plugs.  (overheating due to no airflow over the fins is a different matter.)

Have you not found the leanest setting for the IMS at idle.  Or, have you just adjusted them for some estimated setting, or book value intended for use with the stock exhaust and induction arrangement?

Cheers,

[Hush]

From what I can see TT all the carbs have been set correctly, I had to adjust one very slightly but that carb has never given me any problems so can't be that.
With the float set at the correct level the nose hits that small alloy ledge and over a long period of time wears the tiniest of holes in the tip.
Could be that this is specific only to very early model 650Z models as no one has shown me any others like this.
As for carboning at idle, my old Honda mechanic backs me on this, the Honda service guys were told not to let the 4's idle for long periods as it would foul the plugs.
Again this could be specific to New Zealand conditions as we did not have to comply with emission controls here for many years after the U.S. and Canada, one of the reasons our bikes don't have the very undesirable " limiter cap" on the pilot screw.
This would have allowed our mechanics more room to enrichen the carbs, I'm not sure but I do know that our gas was like watered down lemon juice compared to the rest of the world for many years due to government legislation and we only got decent fuel in the last decade, one of the reasons our spark plugs and exhaust systems now last so much longer.

[TwoTired]

Maybe your carbs are different as I can't see them, though it seems unlikely.  But, all the SOHC4 carbs I have seen have two adjustments on the float assembly.  There is a fuel height tab and a hang stop tab.  Pictured below are my PD 46 carbs from my junker shelf.  Although earlier carb styles also had the hang stop.  If your carb do indeed have the hang stop, adjusting the hang stop tab would prevent your float from having wear issues rubbing on bowl protrusions.

I have to disagree about your NZ carbs being specific for your region.  It doesn't make sense that Honda would make an entire carb design for your limited market place.  If that were true then informatin you relay about carbs specific to NZ would be invalid for US models, and perhaps the rest of the world.  Far more likely is that your carbs have the same design features that allow it to run in NZ and the US so the same carb can be used in both market segments.

While I agree that earlier carbs with the air bleeds and no accel pump ran rich at idle, the newer carbs with the accel pump ran far leaner at idle.  With the 550, there was a dramatic difference between 76 and 77 models, even with no accel pump.  Same was true with the 750 76-77 model change corresponding to the PD carbs (with accel pump).  It is very hard to believe that these carb types won't work in NZ as well as they work in the US.

I will ask you directly, have you set the idle screws for leanest setting?  What setting have you chosen for your idle screws?

Cheers,

[Hush]

Yes TT the carbs are set at leanest setting I dare run with.
I see the adjuster tang you are talking about, it is possible that a PO reset this to get the float valve to drop lower for some reason?
As we are more interested in setting the cut off height on the carbs this would go unnoticed most of the time.
Something to be aware of anyway when next members pull their carb bowls off.

[Spanner 1]

Hush, the float ' low ' set tab would never come into play on a running bike as the valve would open way before the float would drop this far and top-off the gas level..is it not to stop the valve dropping-out in a dry bowl situation ?
Oh, wait I just read all the post thread...ah, I'll post anyway !