Leaking carbs

After cleaning out the carbs and replacing both float springs on my girlfriend's bike because they were leaking (Maxim 400), I still they still leak (very slow drop between the bowls from somewhere... So how should I tackle the problem now? I took the carbs off and held them level below the tank with the fuel line attached and the petcock on prime, but then it wouldn't leak! I know the petcock doesn't leak when set "On", but I didn't test it to make sure it flows freely when set on "prime".

 

could be the fuel rail seals.

 

have you considered joining xs400.com ?

I agree with bendoza. how are the bowl gaskets?

 

The bowl seals looked fine. I guess for the $5 though, I should of put new ones in when I first took 'em apart.

 

Could be the fuel o-rings on the fuel rail.......

 

Is the fuel rail that connection tube between the carbs that carries fuel from the lefthand carb to the right side one?

 

Yes.

 

With regards to the HSC 32 Carbs on a '82 XJ750J Maxim , there are 3 fuel rails with 2 o-rings each....total of six.....

the fuel rails are the connecting pipe between the carbs....

 

I just realized that these are vacuum carbs, so it won't suck in fuel, even on "prime", right? That would explain why the fuel is not flowing into them when I've tried this off-the-bike leak test, right?

 

No, the fuel should flow on prime - it bypases the vacuum. Vacuum operates only the ON and RES portions.

Make sure you have enough fuel in the tank, I believe PRI uses the top fuel line (the same as ON) and won't pick up from the bottom of the tank.

 

I realized I was wrong after I typed that. But still, the fuel does flow out when set on prime, but once I hook up the line to the carbs, it doesn't.

At this point, barring a better idea, I'll dismantle the fuel rails and take a look at those 0-rings.

 

i think prime takes from the bottom which is why you have no reserve if you (because your dad insists that pri stands for primary) run on prime. found that out the hard way

 

I'm not sure we're all talking the same thing here. When you have the petcock on PRI, fuel will flow into the carbs.

......UNTIL....

Until the float bowls have filled up and the float valves close. Once the carbs have taken all the fuel the floats will allow, the fuel flow will stop regardless of the petcock position.

Does that make more sense?

 

Yes, makes perfect sense. But for some reason, the fuel was NOT flowing into the carbs when set on prime. Maybe the bowls were already full and thus had stopped the fuel from flowing in, but I couldn't see a leak either, like I had seen when on the running bike.

 

To check if the bowls are full, just loosen the drain screw on the bottom of the bowls. Fuel should flow in the top from the tank as it flows out the bottom through the drain. You know you should have set the float levels using the clear tube method anyway, right?

What you do next depends on a lot of things. First, is there truly fuel in the bowls or not? And beyond that, where is it leaking from? There really aren't a lot of places to leak...

Past the drain screw.
Past the bowl gasket.
Past the fuel rail O-rings.
Overflow the bowl and run out the carb throat.

Different fix for each of the above.

 

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Agreed. Dude, save yourself the aggravation, buy the rebuild kit and get rid of all 30 year old rubber. They're all bad or hard and crumbly and near bad. Not worth risking a fire under yours or your girls ass. I broke my carbs 3 times replacing different seals and orings each time. Replace float needles, float bowl gaskets, fuel rail seals between the two carbs and I imagine you have one or two on the elbow as well, and fuel mixture o rings. Then set your floats to whatever specs xs400 s call for. Also, you'll probably find some gunk in the elbow or rail which might be contributing to your fuel not flowing, which you might want to consider a fuel filter if you don't have one already. Anyway, that's my experience so far with old carbs. Good luck.

 

I think I have this problem....how can I fix it?

 

be ready for a more labor-intensive job----a LOT of times the bowl-drain screws are frozen and you have to drill/heat/extract them and replace. Some models have an o-ring in there, too, others do not. Just be aware in advance