Gas POURING out of carb intake (positive it's not the float valves or petcock)

[Hasty]

Hey everyone glad to be part of the site! I bought my first bike (1983 Maxim XS400) recently and have been lurking the forums ever since, getting all the kinks worked out. It was running, albeit not perfectly, until a couple days ago when gas started just absolutely pouring out of the carb intake into the filter box whenever I start the bike.

Now, I've checked every relevant post I could possibly find and I'm as certain as I can be that it isn't the float valves, float seats, or petcock. I've cleaned the carbs 4 times since the problem started and used compressed air in a bucket of water to make sure that the floats themselves have no holes in them and that the valves completely seal (no bubbles coming from the valves when the floats are floating and air is pushed into the fuel intake). I also rebuilt the petcock with new gaskets and can leave the fuel line hanging without getting any drips out of it. This also seems to be unlike any posts I've seen in that the gas isn't just leaking a little bit, it is streaming out.

I'm at my wits' end trying to figure out why this just started and hoping someone can help. One possibly important detail is that I set my valve clearances shortly before this started happening. Could this somehow be caused by the clearances being off or by the head cover gasket being not totally sealed? Thanks so much in advance for any insights!

 

[Hasty]

Oh should also have mentioned that I have also adjusted the tab on the floats that presses on the valve. Bent it upwards (pushing the tab up towards the float valve so that it should take less gas to close the valve all way) a little more every time I took the carbs apart to clean them so at this point the float distance is even more than the 32mm mentioned in this post https://www.xs400.com/threads/setting-float-level.4774/

 

[BambinoFan]

Hi Hasty, welcome to the site! I'm new here too, after purchasing a 84 maxim. Thinking of taking the same path you did replacing gaskets and adjusting valves soon.

I believe the carburetor should have a fuel level check. Have you used this to check the fuel levels? Check 4-9 of the dohc manual.

 

[Hasty]

Hey Bambino thanks for the response. I wasn't able to find one of those gauges around here so I had just been going by dry float height. I'll try a DIY version like this (

) though when I get a chance and see where it is at

 

[tstidham]

I had a similar issue with just my left side carb while on the side stand, turned out I needed new float valve needles and seats. Also, I think the recommended float level setting is 26mm, despite what any manuals say. I set mine to that with two new float needles and seats and no leaks since. MikesXS.net has the needles and seats.
I'll add that in order to get my carbs to 32mm (like in the manual) i'd have to bend the hell out of the tab, where as 26mm require only a little tweaking.

 

[Hasty]

Thanks tstidham! I think changing from 32mm to 26mm would be allowing a higher gas level before the valves close which is why I went for the 32 (and then even more than that eventually). Could be that I just have to get new floats and seats like you did though. It seems like they are working as they're supposed to, but for the price it's probably worth replacing just in case.

 

[tstidham]

Thanks tstidham! I think changing from 32mm to 26mm would be allowing a higher gas level before the valves close which is why I went for the 32 (and then even more than that eventually). Could be that I just have to get new floats and seats like you did though. It seems like they are working as they're supposed to, but for the price it's probably worth replacing just in case.

I didn't need to replace my floats. The were still intact, no holes despite being the original, dreaded copped ones. I just bought a pair of new needles and seats, popped them in and set the floats to 26mm. Again, to get 32 mm would have been a lot of bending and it seemed wrong to be that far off. Maybe my bike got a set of xs360 spec carbs when it was sold or something but she runs great so I don't mind.

 

[Hasty]

Hi Hasty, welcome to the site! I'm new here too, after purchasing a 84 maxim. Thinking of taking the same path you did replacing gaskets and adjusting valves soon.

I believe the carburetor should have a fuel level check. Have you used this to check the fuel levels? Check 4-9 of the dohc manual.

I've checked the fuel level and I'm right in the 3-4mm range. I also adjusted the float tangs back to 26mm and tried hooking the gas tank up to the carbs when they were off the bike. Petcock on prime, they fill up, and then absolutely no leakage from anywhere. So I'm still pretty convinced that the needles and seats are fine because otherwise it should leak even when the bike isn't running right? I've still ordered some new ones just in case, but any other suggestions out there in the meantime?

 

[tstidham]

Hmmm, very odd. Those ports are supposed to let air into the carb and not have fuel in them. The one on the left,, with what looks like a jet in it (BTW, don't attempt to remove that, it's permanent) is the air bypass to feed the idle mixture and I think the other is to vent the bowl and diaphragm. Maybe you have a blockage in the idle mixture jet passages? So the vacuum attempts to pull fuel through it from the bowl but is too restricted so the the fuel gravity feed back out the air bleed holes? Or a blockage in the diaphragm passages? When I rebuilt my carbs, I had to use a single stand of multi-strand copper wire to clean out the pilot jet, emulsion tubes, etc, but I also removed the mixture screw and ran it through every passageway I could.

 

[Hasty]

tsidham I think you could be right about the fuel somehow not making it all the way through the idle circuit. The bike starts, but then even with a fully open throttle, the revs just get lower and lower until it dies then it won't start again until it sits for a while. So my thinking is that the gas isn't getting all the way to the spark plugs and is instead leaking out of the carbs. The last time I pulled them apart, I followed Houghmade's instructions from https://www.xs400.com/threads/bike-idles-fine-but-will-not-rev.6240/ (post #17) to clean the idle circuit. BUT as with all carb problems, it's definitely worth doing again to account for my own ineptitude so I'll pull them when I get a chance and this time take some photos as I go.
As a side note, I also replaced the spark plugs and closed up the valve clearances a bit last night and saw no change. I originally had the clearances all at the highest end of the recommended spacing from the manual, now they are more in the middle/low end

 

[tstidham]

Don't beat yourself up. I had mine apart three times. Once with just a spray cleaning, second time with the copper wire and spray cleaning and third because the needle seats were leaking. I use brake cleaner myself, seems to work better IMHO.

 

[JPaganel]

Don't beat yourself up. I had mine apart three times. .

Only three?

 

[tstidham]

You know, I'll bet your diaphragms are shot. They are opened via vacuum and maybe they're cracked or not fully seated and allowing vacuum to suck from from the wrong side of the fence, if you know what I mean.

 

[Hasty]

You know, I'll bet your diaphragms are shot. They are opened via vacuum and maybe they're cracked or not fully seated and allowing vacuum to suck from from the wrong side of the fence, if you know what I mean.

tstidham you just might have solved the mystery. I took a closer look at the diaphragms this time and wouldn't you know it, there's a tiny rip in one of them! I also picked up my new float needles today and had no idea that the top stems are supposed to be springy. My old ones must be so gummed up they've become one solid piece so I wonder if that could be contributing to the problem...
Got a line on a used set of carbs in town here that hopefully have intact diaphragms, otherwise I'll be placing an order to JBM Industries (it's just such a pain paying for shipping/customs to Canada).
Thanks so much for the suggestions tstidham, I'll update when I've got some new diaphragms

 

[BambinoFan]

Update request lol where are you planning on sourcing the diaphragms from? I'll likely have to pickup some myself. (Running revs on idle)

 

[Hasty]

Update request lol where are you planning on sourcing the diaphragms from? I'll likely have to pickup some myself. (Running revs on idle)

I ended up ordering from JBM Industries (http://jbmindustries.com/JBM_ORDER.html). Haven't gotten them yet, but it came out to like $97 CAD after conversion and shipping. I debated just getting a used set of BS34s from Kijiji, but it seemed like better value to get new parts that should last a little longer.

 

[BambinoFan]

I ended up ordering from JBM Industries (http://jbmindustries.com/JBM_ORDER.html). Haven't gotten them yet, but it came out to like $97 CAD after conversion and shipping. I debated just getting a used set of BS34s from Kijiji, but it seemed like better value to get new parts that should last a little longer.

$97.... for 1? Jeeze for a piece of rubber..

 

[Hasty]

$97.... for 1? Jeeze for a piece of rubber..

That's for 2 of them. I figured since it's not the exact same material as OEM, I'd be better off replacing both at the same time so there aren't any weird differences between the 2 carbs. $36 of that is also shipping which is part of why I always try to buy local if I can lol

 

[Hasty]

So I finally got the diaphragms in the mail on Friday (not JBMs fault it took so long, they shipped immediately. Just USPS and the border being slow). Installed those and the new float needles with no issue, set the floats to 26mm and....I still have the same problem
I gave the carbs 2 more thorough cleans while I was waiting for the diaphragms, all the passages and jets seem clear. It starts right away with no complaints, it's just this stupid gas issue. WTF did I do to this bike?

 

[Hasty]

Breakthrough! I realized that the only other way anything could get into the airbox was the hose connecting to the crankcase so I took that off to test and sure enough there is liquid bubbling out of the crankcase when I start the bike. It certainly smells and feels like gas which is what threw me off, so at some point throughout this process, gas must have overflowed into there and now it's too full of oil/gas mixture? Going to drain and refill the oil and see what happens.