Carb Leak- A real head scratcher

[crozell]

Hey guys,

I have a '79 with original carb. Having issues with them leaking. I have replaced the float and seat and confirmed they work using a pressure test. Float high triple checked to specs (25.7mm). Submerged the floats to confirm buoyancy. With the bowl off I can manually shut the fuel off by lifting the float (no fuel leaks), but when I reassemble the bowl fuel continuously flows from overflow. I have adjusted the floats to 23mm and the same problem... I have messed around with the float drop and it does nothing.

I wish I could make a clear bowl to see what exactly is happening....

I feel like I am missing something. Any thoughts?

[DiverRay]

Do you have the fuel going to the fuel "T", and not the vent "T"? Fuel "T" is close to the bowl, vent "T" is a little higher up the carb body. Is it just one carb? If so, check for free movement of the float when installed. Sometimes the bowl gasket can keep the floats from working properly, and need to be trimmed a little.

[Socer4m]

howdy crozell,,,these carbs are very finicky,,,,do not drive with leaky carbs, the oil will thin and destroy your rings in no time. Anyway,,,
1. pop off the carbs, reclean the jet area with spray carb cleaner,,,jiggle each one to see they are not hanging up, blow cleaner through every hole front and back
2. hold upright and blow through the carb gas inlet, no air should go through, if any does narrow down which carb float is not closing,
3. also hold upside down and blow through both inlet hoses and air should go through easy
4. there are those that do the technical tests,,,,but blowing through the two inlet gas hoses can narrow down the problem carb, carbs quick
5. float height doesnt matter to much as long as all four carbs are the same, use a mm scale from the top of the carb to the bowl top edge, tons of info on the search area
keep us informed, I am guessing one or more floats is hitting the gasket or the post rod is not smooth causing the float to stick.....
Mike in S.Diego and Pa.

[crozell]

Thanks for the reply Ray. Yes, it is connected to the fuel "T." When I apply suction to the fuel T, the needle will seat and it will hold pressure. All the carbs are leaking...

[jkorn]

I have replaced the little shut valves that the gloat's open and close every 30 years or so. Maybe try that. I’m original owner of my 79 and have had those carbs off and on so many times. Mostly for cleaning. Jeff

[Larrym]

Uhh....Next step?



One way to know f'sure the fuel level in the bowls is where it is IRL instead'a hoping/trusting that just setting the float height to the right height above the gasket surface wurky. Likely they're NOT leaking but actually overflowing. BTDT. щ（ﾟДﾟщ）

Need the cut measurements on the 2x4? Where to get the 10mm fittings to swap out with the bowl plugs? How to bend the bailing wire so it holds the sight tubes/lines securely? (O_o)7

STEAL/misappropriate the cookie sheet from your or a friend's kitchen and NEVER fess up to it!! (⊙ᴗ⊙)

[cajun31]

Are you still running the original petcocks? If so have you rebuilt them lately. The diaphragms may need to be replaced. As you are probably aware the vacuum shut off is built into each petcock. As was stated these carbs are finnicky. Are they leaking while on the center stand, if you still have one, or when you have it on the side stand? Sounds like you need to check to make sure the floats are moving freely on the float pins. Have you replaced the float needles. In those carbs they are the needles without the viton tips on them. If I were messing with the bike I would just go back through the carbs to verify everything is right with them just to make sure there is nothing (crud) in there interfering with anything. Spraying carb cleaner through every orifice followed by compress air.

Stupid question time. When you set the float heights were the bowl gaskets removed first?

[Larrym]

ORANGE ALERT!!! (⊙▂⊙)

When you state, " I have replaced the float and seat".....

Did they come with the carb kits/boxes shown here-



PLEASE say you din't install the jets what came too! (/へ＼*)

(Or Norrrrrrrr!)

[skids]

(snip)Have you replaced the float needles. In those carbs they are the needles without the viton tips on them.(snip)

79 models should be the same as 78 model carbs and the float valves were metal to metal to shut the flow. Not viton tipped.

[crozell]

Thanks for the feedback guys! currently the tank and carb is off the bike, using the tank to run fuel to the carb while on the bench. Petcocks have been rebuilt and functioning properly, ie- no fuel is flowing when in the "on" and "res" position. The needles and floats are from a cheap amazon kit (don't shoot me), but since they have a good seal as confirmed by pressure and manually, i have ruled them out. I guess "overflowing" would be better term than "leaking." I have done the clear tube method to confirm fuel height but since they just overflow the bowl and I can't get a reading.

I need to replace the float rods next to rule that out....the more I think about it, I wonder if the new gaskets are causing an issue since the floats seem to work fine with the bowl off but issues when the bowl is back on....?

[Larrym]

" I have done the clear tube method to confirm fuel height but since they just overflow the bowl and I can't get a reading."


Yup. BTDT. (っ˘̩╭╮˘̩)っ

No way you'll get the cheepee needles and seats to wurky at the 25.7 mm setting. (⊙︿⊙)

While the carbs are inverted...
RAISE the float levels up/higher offa the surface like yur tryin' to raise the Titanic. (｢ ⊙Д⊙)｢

Records show I FiNaLlY got my levels correct with height settings ranging from 27.06 mm to 26.05 across all carbs.

WUT a Bother,eh?! (⩺_⩹)

[crozell]

here is a clue-

When carb is upright and I pull suction from the fuel inlet, air flows freely. If i keep the suction hose connected and invert the carb (simulating the float bowls rising) I get complete suction....when I position the carb back upright, air flows freely again. So it appears the float bowl and valve are operating correctly, why then does it continue to overflow the carb?

[Larrym]

Floats, prob'ly the brass ones, right? (ー_ーゞ

I took the trouble to clean/polish all the green "patina" offa them so they'd be as close to the real OEM weight as possible. (º～º)

STILL, when using the "Amazon" aftermarket parts and set to 25.7 mm (Triple checked...) the float-and-aftermarket-needle-and-seat allowed the fuel level to be WAY higher than it should be....even overflowing on #3 carb. (゜-゜)

The individual components of the needle "pin" and internal "spring" are just that far off from OEM that this just happens. It WON"T perform like the OEM. Close enuf foar hand grenades/horse shoes doesn't cut it in this situation. (--_--)

I did get them to finally "work" and usable but by setting the float height WAY higher. High enuf to get the darned thangs to do their JORB. (ｏ´_｀ｏ)

You CAN see/check if the aftermarket bowl gaskets rub on the sides of the floats and then cut-to-fit. ( ⚆ _ ⚆ )

[Socer4m]

oops, maybe I had it backwards,,,,when the carbs are inverted and blowing through the fuel inlet lines there should be no air flowing as the needle is hopefully seated,,,,when upright and blowing the needle is up, not seating and air should blow freeely,,,,its been awhile since I pulled carbs,,,,anyway, one way no air, the other freely blowing air. Usually I can hear which carb is a problem with a slight wind sound on the non seated float. Float height between 23-25 mm when measured to top of float and bowl edge shouldnt matter as long as all four are the same......also check oil for gas, put a stick in the filler and smelll the oil or try to light it...if any gas smell, or it ignites easily also DO NOT run the bike,,,,need to change oill or wait until the carb problem is settled then change oil......keep us informed,,,yes, carbs are a nuisance until right, then they go good for a long time.............Mike in S. Diego and PA.

[Larrym]

Well....befOaR I disappear into the real wurld and drop off the XS11 radar anuther 10 years or so? (⊃‿⊂)

I want to make my position on this matter plain. (ㆆ ᴗ ㆆ)

When the repair manual states the float height needs to be XX mm (depending on the year/make/model) above the metal surface the gasket sits on, it assumes that the needle/seat are the OEM installed by the factory or newly purchased/installed OEM parts.
(　◜◡‾)

But if you have installed parts from the aftermarket kits pictured in this thread? (⊙︿⊙)

The "adjust the float height-assemble the carbs-install on the bike" is NO LONGER VALID. (っ˘̩╭╮˘̩)っ

The aftermarket needles/seats are mechanically different from the OEM and do NOT adjust the fuel level to the same degree. Sadly, it's not like I could recommend a new "rule-of-thumb" height to use as not only are these aftermarket parts different from OEM, they also vary widely between themselves. Like the consistency of the quality control in each set of needle/seat just wasn't part of the manufacturing process. (つ﹏<。)

To be plain, when one buys these kits, the person MUST opt-out of the "adjust the float height-assemble the carbs-install on the bike" or repeat the cases histories shown here-

https://www.google.ca/search?lr=&sca...ih=342&dpr=1.5

The NEW normal for owners choosing to install these aftermarket needles/seats? （´＿｀）

Each float must be adjusted to whatever height it needs to be using some form of Real World observation/measurement/verification of the actual fuel level in the float bowl. Each one. No exceptions. ヾ( ･`⌓´･)ﾉﾞ

That is, of course, assuming that the owner wishes to have his bike running like the Super Bike it IS. ╭(* _ *)╮

And what if you've installed the jets from the aforementioned Orange Boxes? （´-`）. ｡oO (Hmm...)

There's a whole list of negative symptoms waiting fOaR you to experience directly and personally. (◔_◔)