Carb experts wanted!

mcgovern61 · Jan 27, 2010

I had my carbs rebuilt last spring and they came back working like a champ! Rode all summer til Fall without any problems (Except for that fact that the engine sounds like a diesel, but that is another story. I have a transplant engine going in soon, I hope.)

Last December as the bike was sitting for about 3 weeks, it decided to leak out the gas from the carbs into the intake manifold.

Not being a carb expert, is there something simple I should do to find the leak? I am assuming float needles and all that stuff, but have never worked on carbs. (Well, maybe once on my parents old '69 Ford LTD wagon, 390 engine. Ended up with a Cardo carb kit if you guys have ever delt with them.) :help:

Any help is appreciated! (Funny things is, I do not mind tearing down an engine to it's last bearing, but carbs have always scared me!) :nea: :smilie_happy:

dan filipi · Jan 27, 2010

I think you told me but I cant remember, was the petcock off?
Did the bowls actually go empty as if something drew the gas into the engine?

Rat · Jan 28, 2010

If it is just a stuck float, sometimes you can get lucky and fix it by whacking the bowl of the leaky carb with the handle of a screwdriver.

If that doesn't work, get a bigger screwdriver.

Gord (it has worked for me) Jones

mcgovern61 · Jan 28, 2010

dan filipi":32x6arj6 said:
I think you told me but I cant remember, was the petcock off?
Did the bowls actually go empty as if something drew the gas into the engine?

Dan, the petcock was closed and yes the bowls emptied from more than one.

mcgovern61 · Jan 28, 2010

Rat":1kfh9vql said:
If it is just a stuck float, sometimes you can get lucky and fix it by whacking the bowl of the leaky carb with the handle of a screwdriver.

If that doesn't work, get a bigger screwdriver.

Gord (it has worked for me) Jones

Gord, I like your style, "if it ain't fixed, get a bigger hammer!" :smilie_happy:

How do I tell which float might be sticking? BTW, I ran the gas out of the carbs to stop the leaking in my garage so I have dry carbs at the moment.

AApple · Jan 28, 2010

It's prolly a silly question, but that's all I know how to ask... :|
How can a stuck float allow fuel to be drawn out of the bowls, and down into the engine? :headscratch: I can only go by my experience with automotive carbs, so that's why I'm curious. On a automotive carb, if the float sticks down, it floods, but when you shut the engine off, there is no more fuel going in....the float being stuck will not drain the fuel bowl.
Not having ever seen the inside of a 'Wing carb(other than in the service manuals), it just doesn't make sense.
Now..I can see if the pet-cock is left "On", and the float is stuck, then it would overflow the carb, and run down into the engine, but....the bowl on the carb(s) wouldn't be empty when you start it next time.

Inquiring minds want to know! :laptop:

Joep · Jan 28, 2010

OKay here is how the carbs flow to the plenium.. liquid seeks it's own level... that being said ... a bad petcock that allows fuel to flow when off will allow gas to gravity feed into the carbs.. the carbs being lower then the gas in the tank will slowly feed up through the various jets until it spills into the the throats of the carbs.. with gas still being higher it will fow and drip into the plenium until the gas in the bowls equal the level of the tank.. then the gas will cease to flow anymore.. the effects are gradual and not like the old style cb tanks over the carbs.. which will run the tank to reserve level before stopping..

BigAndrew · Jan 28, 2010

mcgovern61":2lncccjl said:
Gord, I like your style, "if it ain't fixed, get a bigger hammer!" :smilie_happy:

:smilie_happy: Lol So true... A bigger hammer is always better :grin: or what i like to call it BFH (Big F'ing Hammer) :mrgreen:

AApple · Jan 28, 2010

Joep":88ddjcfy said:
OKay here is how the carbs flow to the plenium.. liquid seeks it's own level... that being said ... a bad petcock that allows fuel to flow when off will allow gas to gravity feed into the carbs.. the carbs being lower then the gas in the tank will slowly feed up through the various jets until it spills into the the throats of the carbs.. with gas still being higher it will fow and drip into the plenium until the gas in the bowls equal the level of the tank.. then the gas will cease to flow anymore.. the effects are gradual and not like the old style cb tanks over the carbs.. which will run the tank to reserve level before stopping..

I can unnerstand that.

The way I'm reading the problem, tho, is it is actually draining the bowls on "more than one" carb. That's what I'm having trouble unnerstanding.
Ya'll forgive me for being an idjit, but this is quite fascinating to me. I've been slingin wrenches and hammers on cars, trucks, and tractors for over 30 years, but bike logic is Japanese to me! :mrgreen:

dan filipi · Jan 28, 2010

It escapes me how gas could flow out of the bowls (and empty them) into the engine.
There is no pressure behind it so how could it flow out with the petcock closed.

Strange problem.
Have you tried to duplicate it?

Joep · Jan 28, 2010

Evaporating??? if the bike is in a warm enough area.. could cause gas to vaporise.. and you are right bowls should stay full unless the hoses for draining are connected to the plenium.. and they have sorry orings..on the drain screws.. or it is slowly draining else where.. (don't light a match anyone..)

RBG · Jan 30, 2010

My read is BAD petcock, tank full to or half way at least so fuel is seeping from tank to carbs and out into intakes due to bad float needles or floats sticking or set wrong..some easy checks. to see if all/which carbs are leaking. Take air box off..cut paper to fit in plenum and put it in flat to base..see where fuel is coming from by where the paper gets wet. You need to start with a dry plenum.

and/or pull the fuel line off the #3 carb and see if fuel will flow out of the line..with the petcock off and tank full..if it does BAD petcock..

Note if the guys who rebuilt your carbs didn't put new OEM float needles in that's most likely the prolbem old needles or non Honda replacements leak more often than not.

Oh and change your oil it's full of gas now!!!!

mcgovern61 · Jan 30, 2010

RBG":2r88lk13 said:
My read is BAD petcock, tank full to or half way at least so fuel is seeping from tank to carbs and out into intakes due to bad float needles or floats sticking or set wrong..some easy checks. to see if all/which carbs are leaking. Take air box off..cut paper to fit in plenum and put it in flat to base..see where fuel is coming from by where the paper gets wet. You need to start with a dry plenum.

and/or pull the fuel line off the #3 carb and see if fuel will flow out of the line..with the petcock off and tank full..if it does BAD petcock..

Note if the guys who rebuilt your carbs didn't put new OEM float needles in that's most likely the prolbem old needles or non Honda replacements leak more often than not.

Oh and change your oil it's full of gas now!!!!

Thanks for the tips and yes the oil is full of gas! I pulled the plugs and ran the starter, should have seen how much gas came out. I already ran the engine to give the bearings a good wash! :smilie_happy:

The engine is being swapped out anyway and the oil is coming out. All of the info presented gives me a place to start. :thank_you:

BTW RBG, welcome to the site!

RBG · Jan 30, 2010

Why engine swap? And PS where reinstalling the carbs run the throttle carbs along the outside of the frame makes take the carbs out and putting in Sooo much easier..because you can pull the carbs way out and get to the throttle linkage..

dan filipi · Jan 30, 2010

I had the understanding that the bowls EMPTIED themselves which is different than gas flowing from the tank into the engine from a leaking carb.

mcgovern61 · Jan 30, 2010

RBG":3dt2hxaa said:
Why engine swap? And PS where reinstalling the carbs run the throttle carbs along the outside of the frame makes take the carbs out and putting in Sooo much easier..because you can pull the carbs way out and get to the throttle linkage..

It is an '81 engine that was supposed to have 48K miles on it (and the bike, although I only bought it for the parts) but turned out by researching the title that it really had more like 169,000 miles on it. At highway rpm it raps real loud (sounds like a diesel), on cold startup it knocks until oil pressure comes up. During the initial oil changes when I first got it, I found sand in the oil. Good compression, 160's across all 4! Doesn't smoke and always starts.

The other main problem is that the '81 engine is in an '82 and gear ratio, wheel size and final drive cause the engine to run up at 6000 rpm at 70 MPH was is really loud.

mcgovern61 · Jan 30, 2010

dan filipi":1c58d7s5 said:
I had the understanding that the bowls EMPTIED themselves which is different than gas flowing from the tank into the engine from a leaking carb.

The bowls are (where) more than half empty as far as I can tell. The tank was at half before the gas drained.

Something else that has been happening that I didn't really think about, each time I get to the gas station and pull the cap, it sounds like it is under pressure or vacumm. There is a distinct quick hissing whenever I pull the gas cap after riding. Is it possible that the gas tank is under pressure? Or more likely vacumm.

When I emptied the gas out of the cylinders and ran the engine with the petcock closed to run out the rest of the gas, it only took half the normal amount of time for the carbs to run dry.

RBG · Jan 30, 2010

If the gas cap vents are plugged the tank will develop a vacuum after a few miles of riding..the cap is easy cleaned a dip in acid or CLR or even vinegar.

A little late for now but in the future you can screw in clear 1/4/" tubing into the bowl drains..tie them up above the carb lip ..turn the gas on and see what the level of gas in the bowls is..should be just below the lip of the bowl.

Note just thought is you cap is plugged that could stop/slow gas flow and keep you bowls lower than they should be while riding..1/2 full?? and when you stop slow leak of petcock and bad needles you get overflow into carbs?? At lesat that could explain it all??? I think

RBG · Jan 30, 2010

WOW just a major thought at least I think it's major..IF your gas cap was partially plugged it could starve you carbs and make the engine run like crap at high RPM's..as you described..cylinders cutting out due to gas storage would mark the engine run like it was out of synch at high speed..and could sound like a diesel..knocking as it would be out of balance????? worth a check before you swap out an engine with 160 compression numbers!!!!

Or this could be a brain fart???? what do you think Dan???

dan filipi · Jan 30, 2010

Anything is possible but since it had sand in it and Gerry says little metal bits are in the oil at every oil change, I'd say that engine is done done.

Carb experts wanted!

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