Topic: let try this again without the hostility - Help with odd carb leak please.

[timdhawk]

1978 cb750 k8
The carb in question in this video is #3. It only does this on #3 carb. Im not familiar with the parts terminology where its leaking. It only does this when I push the start button with no throttle. The motor is a fresh rebuild and the carbs are 100% gone through and rebuilt last year. I had the motor and carbs running (roughly) in a test stand about 6 mo ago. Now everything is in the bike and Im trying to get it ride ready. I noticed this leak when trying to trouble shoot it not firing after running a battery down while trying. It will turn over and a time or two almost caught and fired. I need to recheck my pilot screws but this leak has me a little concerned. Can anyone shed some light on this for me? Please ask if any you need any other info. Any help would be greatly appreciated.

Gas

[TwoTired]

...'Cause it's confused about what bike it is?
...'Cause you twisted the throttle and the accel pump squirted raw gas into the carb throats?
... 'Cause the accel pump circuit is leaking?

[timdhawk]

bump - with edits!

[mrrch]

Did you twist the throttle while turning it over? Are your accelerator towers shooting a good stream of fuel when you twist the throttle? I know when they are partially plugged they tend to dribble rather than squirt.

[TwoTired]

The vertical tube is the accel pump squirt jet.  It should be full of fuel ready to squirt into the carb throat when the throttle is twisted.  It could be cracked or buggared, too.  Were the exits rodded out?
The horizontal tubes at the carb mouth are air jets. One is for the pilot circuit (the left one, I think), the other is for the mains emulsion tube cavity.  The mains emulsion tube cavity fills with fuel at a level determined by the bowl float.  If the bowl is way too full, it may weep out the air jet at that location.

I can see that carb was bashed hard enough to break off some of the casting at the entrance mouth.  That can't be a good sign. 
How can you/we be sure there isn't more damage to that carb?

Cheers,

[scottly]

That is no leak! It's a drop of fuel laying under the tube that gets sucked up into view on the intake stroke, then drops back down.
With your carbs, you can easily check the fuel level in the float bowls with clear tubing on the drain nipples, and opening the drain screws. 

[timdhawk]

First thing- I had a very bad day today. If anyone read 2 of my posts before i pulled my head from my ass and deleated them - i apologize to those individuals.

Now:
mrrch - no, no throttle twist just start button. I also don't notice any fuel squirting in from any of the the towers when I do twist the throttle. I thought they only squirted when you opened up the throttle hard - like with a hard acceleration.

TwoTired - You're one the apology applies to. If you don't know why - we're both good! = ) Thanks for the definitions. I do have clear tubing in place for a bowl level check and 2, 3 and 4 are all good - within a mm or so of the top bowl lip. #1 is on the low side however. The carb breakage is a PO thing, so yes there could be more than meets the eye. I did go over everything with a fine toothed comb during the rebuild and everything seemd to do what it was supposed to do back then. Its been over a year since I rebuilt them so the memory is a bit fuzzy.

I think the carbs are coming off again and getting a re-going over with some adjustments where needed and triple checking that all passages are clear.

Thank you.

[scottly]

When I hear a motor almost catch and start, the first thing that comes to mind is retarded ignition timing. I would do a static timing check....

[scottly]

Hey Tim, it looks like the relay is going to get pretty close to Billings in a week or so. Get that puppy running so you you can meet Godzilla!!!  

[KingCustomCycles.com]

+1 on ignition timing.

[timdhawk]

Scottly - I am SOOO trying to get this thing running ASAP!!!!!

Okay, double (triple) checked ign. timing. I have the Dyna S. I did the static check 2x on 1-4, and 2-3 and timing marks line up as per Dyna directions - far right advance mark lines up with fixed mark on case for both. I may have been off by a degree or less, but no more than that.

timing set correctly, spark on all plugs...
With these reults are we back to it being a carb issue?

[TwoTired]

If you blot/dry the fuel away from the damp area, does the puddle return?

I don't think this is a cause for a non-running engine though.  Maybe something to scrutinize if it persists or that particular cylinder exemplifies a problem different from others.

Verified spark at the plug tips?
Got compression on all cylinders?
The plugs get damp with fuel using choke?

Methodical approach has always worked for me.  If you force the correct physical conditions, the engine must run.

[scottly]

An easy test is to spray a shot of starting fluid into each carb throat, and hit the start button. If the motor starts, then dies after a second, that indicates you are not getting fuel into the motor.

[timdhawk]

This was a surprise to me. Why would I have this crap in my bowls after a very detailed and thorough cleaning and rebuild? My carbs have sat on the motor without gas in them for upwards of 4 months and were clean at that point as well.
Another issue: the first time I put gas in it last week all bowls filled with gas (I did clear tube trick for float level). Overnight he tube fell over and all the gas drained out. When I tried to fill it again the next day only bowl 2 filled and the other three would not no matter what I did. When I took it apart today there were no obvious obstructions!!! WTF? Can these carbs "vacuum lock" up or something like that?

[cameron]

so.. I am like the most ignorant guy here.. but heres the deal:

1 - I really think your engine would start with one carb MISSING if everything else was right.
2 - if you are only filling 1 carb with gas.. you have upstream problems.
3 - was it YOU who 'cleaned and rebuilt' those carbs?
4 - when you say "no obvious obstructions" you should probably tell us exactly what was UNOBSTRUCTED.  .. . because otherwise we cant help you. AS it is, you are saying "something is wrong, and I looked but I cant tell what!". Something obviously IS obstructed. And it is probably something obvious. Start from the tank and work your way down

5 - If you force the correct physical conditions, the engine must run.

[timdhawk]

so.. I am like the most ignorant guy here.. but heres the deal:

1 - I really think your engine would start with one carb MISSING if everything else was right.
2 - if you are only filling 1 carb with gas.. you have upstream problems.
3 - was it YOU who 'cleaned and rebuilt' those carbs?
4 - when you say "no obvious obstructions" you should probably tell us exactly what was UNOBSTRUCTED.  .. . because otherwise we cant help you. AS it is, you are saying "something is wrong, and I looked but I cant tell what!". Something obviously IS obstructed. And it is probably something obvious. Start from the tank and work your way down

5 - If you force the correct physical conditions, the engine must run.

Cameron - downtown Seattle's my old stomping grounds!
1 - correct! It should start if all else is correct but theres the rub - something isn't and i can't find it. I seem to chase down one Gremlin only to find another.
2 - in a vaccum you're right.  But I'm using a brand new plastic auxillary fuel tank and on monday, all 4 filled just fine. monday night they accidently drained empty (clear plastic tubing fell over from float level check). On tuesday, with nothing else being different from monday - now only one carb fills up.  -  Gremlin!!!
3 - it was me who cleaned and rebuilt the cards. BUT - 4 months ago they worked fine enough to get the motor to run and idle (roughly). they only difference between then and now is they were drained of gas and sat empty on the bike. Now all this trouble.  -  Gremlin!!
4 - "no obvious obstructions" means that upon removal, tear down and inspection of the #1 carb, there was nothing found that would have prevented the carb from filling with gas. No blockages in the jets or other passage ways. And no blockage of the fuel passage way from #2 carb into #1 carb either.  -  Gremlin!! (maybe i just found the name of my project: Project Gremin, or Gremlin Bait!)
5 - in the normal world that would be true, but apparently in my world of gremlins and unicorn tears, the magic isnt happening that way!

[TwoTired]

The white stuff in the bowl is corrosion.  Water got in there somehow, possibly with the ethanol.

I would at least clear the pilot jets, and ensure the float pivot freely and the float valve operates.
If the corrosion also occurred within the passageways in the carbs, then you are looking and another carb clean including rodding out the pilot circuit and and the air jet passageways to the mains emulsion tube.

Next time you drain the carbs, try to get some WD-40 inside or fill them with kerosene so they won't oxidize again.

[Danno]

I can't tell from the picture but if it is white like two tired says it is water or alcohol  but if it is green it most likely is a tank additive or cleaner I have taken carbs apart that looked like they had frog eggs in them
but as everyone else has said that engine would run at least half hearted idle even if one was getting no fuel
as already stated look for a plugged passages 
ultrasonic cleaners can help with that a lot and you can also use stabil and sea foam when you let it sit
the point is do something unless of course you enjoy carb pulling and cleaning more than the rest of us do

[TwoTired]

... but if it is green it most likely is a tank additive or cleaner ...

Green is often copper oxide, or verdigris from the breakdown of the copper contained in the brass amalgam/alloy.

Ethanol can be oxidized to acetaldehyde and further oxidized to acetic acid, depending on the reagents and conditions.

Leaving acids in contact with most metals will stimulate a reaction which we observe as corrosion.  The color of the corrosion is dependent on the base metal.

Ethanol in our fuel is far less harmful if it is constantly being replaced with newly manufactured blended fuel.  The government studies leading to its approval were flawed by not not taking into account storage and stagnation within vehicles.

Cheers,

[timdhawk]

The white stuff in the bowl is corrosion.  Water got in there somehow, possibly with the ethanol.

I would at least clear the pilot jets, and ensure the float pivot freely and the float valve operates.
If the corrosion also occurred within the passageways in the carbs, then you are looking and another carb clean including rodding out the pilot circuit and and the air jet passageways to the mains emulsion tube.

Next time you drain the carbs, try to get some WD-40 inside or fill them with kerosene so they won't oxidize again.

Thanks. I am going through all the carbs again to make sure none of the corrosion is contributing to my issues. I also may have found one of the culprets however. On the accel. pump diaphragm - the mickey mouse ears portion - the inlet and outlet holes were obstructed.

[bollingball]

Tim it gets old taking the carbs on and off. Here is a cheap and easy test stand. You can see it pivots so you can do most every thing on the bench. Put your aux. tank on and check fuel issues. Turn it back and check floats. I have modified it with a lock to hold it in position.

[bollingball]

Also it is a lot easier to set up the choke fast idle cam and the accelerator pump on this stand If you don't set these two thing up correctly it will be a lot harder to start cold trust me on that.


                         Ken