Carb leaking fuel (2 Viewers)

[Beehanger]

Hey guys,
At the last line of defense here with firing this thing up. Rebuilt motor and whole project coming to this point. Carb was leaking upon initial firing yesterday, snd I think had a vacuum leak as well. so I rebuilt the carburetor again and it’s still leaking. Vacuum leak is resolved though. When I remounted I sued gaskacinch on all surfaces. there’s definitely still a leak coming from the middle gaskets as shown in the photo, and maybe the mounting gasket as well, but just redid them All a second time . what am I missing here? I’d there a ball there or something it could be leaking from?


I can’t tighten s*** down any more besides maybe a little more on the mounting bolts, but not much. I went to almost 20 ft fbs.

Ideas on resolving this leak? Mechanic friend thinks if I run it at idle temp for a minute it could figure itself out.


See video for more detail: Video Jan 03 2024, 4 42 31 PM.mov - https://www.dropbox.com/scl/fi/43hb0lf1wdhzp6dp5pj3u/Video-Jan-03-2024-4-42-31-PM.mov?rlkey=ia678dn0ergz5qcmdtiryafef&dl=0
Dan

 

[Beehanger]

Edited photos

 

[Beehanger]

I’m also leaking a little out of the throttle shaft.

Could the leak abate as it’s running?

 

[kirvesmies]

@Beekeeper , i haven't kept up on your carb session too thoroughly . but i do recall advising you not to use a file on your mating surfaces. what did you use? from these pics n your description, that's where your the issue is. yeah, i know, not the answer you want.

 

[Beehanger]

@Beekeeper , i haven't kept up on your carb session too thoroughly . but i do recall advising you not to use a file on your mating surfaces. what did you use? from these pics n your description, that's where your the issue is. yeah, i know, not the answer you want.

It’s leaking in a spot I never used a file on, I replaced the gaskets last night as pointed on the arrow. Weird!

 

[klinetime574]

Are you sure the float isn’t stuck down? I don’t see how those two gaskets would allow a fuel leak. I had fuel dripping like this and as a result my engine would not start because it flooded the engine. Float was full of gas and sunk down which over filled the bowl.

 

[Mark W]

What doe the fuel level in the bowl look like (via the sight window)?

Mark...

 

[Beehanger]

Are you sure the float isn’t stuck down? I don’t see how those two gaskets would allow a fuel leak. I had fuel dripping like this and as a result my engine would not start because it flooded the engine. Float was full of gas and sunk down which over filled the bowl.

The sight window shows it up about 3/4 of the way up the window. Just rebuilt it and adjusted float to stock spec (bending the metal on it), although it was "hanging down" at a 45 degree angel when I installed it, I think that's normal right?

Also, If it was overflowing where would it leak from? overlfowing as in its over the level of the float resevoir?


My vacuum gauge is reading 10-11... indicating a major leak somewhere. There's no way its the intake or exhaust gasket as I just redid them and machined them. Could a leak at those gaskets drop my vacuum? Could a faulty diagram do so as well?

Thanks,
Dan

 

[klinetime574]

Yeah the float will hang down when holding the assembly as if it were installed. The fuel in the bowl should be halfway. Might need to pull the air horn off and recheck the float gap where it contacts the needle and seat. I used a paper match stick because I remember reading that’s about the right thickness. I don’t have specs on hand otherwise I’d quote them.

I’m not sure exactly where it would leak from but I feel this is a problem worth investigating. I will have to check some old pictures to see if anything sparks an idea.

A leak from your intake could drop the vacuum reading. The secondary diaphragm wouldn’t affect idle vacuum. I wouldn’t worry about vacuum yet if it is running. Fix the fuel leak and then investigate the vacuum.

 

[Beehanger]

Yeah the float will hang down when holding the assembly as if it were installed. The fuel in the bowl should be halfway. Might need to pull the air horn off and recheck the float gap where it contacts the needle and seat. I used a paper match stick because I remember reading that’s about the right thickness. I don’t have specs on hand otherwise I’d quote them.

I’m not sure exactly where it would leak from but I feel this is a problem worth investigating. I will have to check some old pictures to see if anything sparks an idea.

A leak from your intake could drop the vacuum reading. The secondary diaphragm wouldn’t affect idle vacuum. I wouldn’t worry about vacuum yet if it is running. Fix the fuel leak and then investigate the vacuum.

It's definetly leaking out of the secondary diaphgram (this is the arrow pointing to those two gaskets with the spacer correct?) Not sure why it would leak there if the float was overflowing. Could a vacuum leak at the base of the carberator where it mounts to the insulator create the idle vacuum issue?

Thanks,
Dan

 

[Beehanger]

@Pin_Head

If you woudl kindly take a look at this thread. could a stuck needle valve or incorrectly sized check ball cause the secondary diaphragm leak shown in the photo? Or perhaps a faulty float adjustment as @klinetime574 is mentioning?

Last idea is there's another opening under here that isn't the secondary diagram gaksets leaking after all.....



Thanks,
Dan

 

[Pin_Head]

I don’t understand why you say that your “secondary diaphragm” is leaking. Leaking what? There is no gasoline anywhere near it and there is no vacuum in it until you floor the accelerator pedal.

Your major problem seems to be an intake vacuum leak. The reason for the gas seeping out from the primary shaft is because liquid gas is dribbling out of your primary main nozzle on to the primary butterfly so that the engine can run at idle speed with such a big vacuum leak. Fix the manifold vacuum problem and the leak will go away. You know the drill: block off any hose connection to the intake and spray carb cleaner around every possible connection and mating surface to find the leak. Also make sure that the bottom of the manifold right under the carb is not cracked.

The float adjustment is not the cause of your manifold vacuum leak.

 

[Beehanger]

I don’t understand why you say that your “secondary diaphragm” is leaking. Leaking what? There is no gasoline anywhere near it and there is no vacuum in it until you floor the accelerator pedal.

Your major problem seems to be an intake vacuum leak. The reason for the gas seeping out from the primary shaft is because liquid gas is dribbling out of your primary main nozzle on to the primary butterfly so that the engine can run at idle speed with such a big vacuum leak. Fix the manifold vacuum problem and the leak will go away. You know the drill: block off any hose connection to the intake and spray carb cleaner around every possible connection and mating surface to find the leak. Also make sure that the bottom of the manifold right under the carb is not cracked.

The float adjustment is not the cause of your manifold vacuum leak.

Apologies, for the secondary diaphragm confused with the two stacked gaskets above the carb base. I can see it dripping from there. Has to be the gasket leaking or a pinhole crack. I get like one drop every 60 seconds. I’m assuming the cause is the same, though, a large vacuum leak either at the base of the carb or elsewhere. Will scout it out

Best,
Dan

 

[mattressking]

Bowl vent plugs, sight glass or feed line is leaking. Dry off then inspect, very simple.

Don't use any gasket sealer on a carb, period. This includes the mating surfaces.

 

[Beehanger]

Bowl vent plugs, sight glass or feed line is leaking. Dry off then inspect, very simple.

Don't use any gasket sealer on a carb, period. This includes the mating surfaces.

If these were leaking would it go through that gasket stack or elsewhere?

 

[Beehanger]

If these were leaking would it go through that gasket stack or elsewhere?

How can one fix a bowl vent plug leak?

 

[Beehanger]

I don’t understand why you say that your “secondary diaphragm” is leaking. Leaking what? There is no gasoline anywhere near it and there is no vacuum in it until you floor the accelerator pedal.

Your major problem seems to be an intake vacuum leak. The reason for the gas seeping out from the primary shaft is because liquid gas is dribbling out of your primary main nozzle on to the primary butterfly so that the engine can run at idle speed with such a big vacuum leak. Fix the manifold vacuum problem and the leak will go away. You know the drill: block off any hose connection to the intake and spray carb cleaner around every possible connection and mating surface to find the leak. Also make sure that the bottom of the manifold right under the carb is not cracked.

The float adjustment is not the cause of your manifold vacuum leak.

Just turned the starter over for a while with no ignition, the leak is coming from the top arrow in the previous photo.

Float bowl was totally emtpy when I came back to the shop this morning. Doesn't leak when running.

Vacuum leak confirmed at carb base to insulator. ordering new carb from city racer llc, the japenese made one.

 

[Beehanger]

Fuel leak has stopped. I put deflon on fuel fitting and a little bit of RTV on the gold ball on underside of float bowl.

I Put carberator back on with a small amount of RTV between it and gasket over insulator. Couldn't get tighter than aout 7 ft/lbs before old studs started stripping. Still hunting and rough idling. Vacuum flucatautes between 11-14 HG. RPM flucruates between 1200 and 700 RPM on its own, strange! trying to diagnose what this is. Could an untuned carberator cause running issues like this, or do vacuum leaks behave in similar ways? Could it also simply be a faulty carb or does the 11 Hg reading still strongly suggest a leak?

Im not convinved its an carb- to intake leak anymore, especially considering the RTV and no more fuel leaks.

Would love people's take, going to do more trouble shooting. One thing im thinking is that since im using stock fuel cutoff solenoid instead of the aftermakret one that came with the chinese carb- this could cause an issue with fueling.

 

[Hokie LX]

Vacuum should be closer to 20Hg when there are no leaks on a healthy engine. When I rebuild my carb last year mine was 20-21Hg. Also I agree on getting rid of the RTV under the insulator when you put the cityracer carb on. That's just asking for trouble.

The CR carb is going to be a better bet than your chinese carb.

 

[mattressking]

You’ve got massive intake leaks, which means manifold gasket and subsequent leaks that connect off the intake manifold. You need to spray each item with carb cleaner, etc to test for idle changes then fix the leaks. You also need to verify fuel cut solenoid clicks reliably.

The carb may have faults but without working knowledge and having verified internals, none of us can tell you if it is another culprit.

Please verify:

1. How did you confirm all 6 cylinders are firing
2. How did you verify timing is correct and what did you set to
3. What plug gap did you set every plug
4. What accessories are using vacuum and how did you verify each is not leaking.
5. You still haven’t listened regarding RTV, don’t use it.
6. Fuel lines won’t last with Teflon tape, it will degrade and fail, you need to fix the leaks with the correct gaskets. The nipple you RTV’d shouldn’t leak as it is a pressed aluminum plug, it’s just the lowest point, so you likely had a leak from fuel inlet, bowl vents, sight glass.