Fuel boiling....
Fuel boiling.... This is one of the last problem I am facing. The fuel is too hot and is boiling in the bowl and is coming out of the nozzles. I can't figure is. The only other thing I can think of is to put in a spacer but I don't know if that is going to fit in my 95 f body. The really weird thing is that the carb is cool to the touch... and I can easily keep my hand on the intake so I don't know where the fuel is getting to hot... Makes no sense.
id think the fuel couldnt be boiling if your carb and manifold are not too hot to touch. is the fuel pump hot to the touch? maybe your fuel pump is aerating your fuel or there is a leak on the suction side of your fuel system causing it to suck some air? just some quick ideas
mani is hot but not hot enough to make me take my hand off, and I don't have fuel leaks. So where would the air be drawing from? Also what leads me to belive that the fuel is bubbling is because there is steam coming out of the vent holes in the carb
Last edited by stevecritt; Jan 21, 2013 at 08:26 PM.
Could your pump be heating your fuel way up? i always noticed my carb would be cold at the bowls and warmer twards the main body and i believed that was due to the cold fuel always drawing heat out. So theres a chance i guess your fuel could be boiling due to engine heat still since fuel boil points are pretty unclear when i looked online. If its not boiling maybe the pump is cavitating like from too small of a suction line or too restricted setup like 90* ells or something? I'm just throwin ideas here. Do you have a infared thermometer you can shoot the bowls and manifold and fuel line and stuff so your sure on the temps (it's my favorite tool in my chest lol) I thought my fuel was boiling at one time and causing a pressure drop so I added a thin carb spacer with no luck then changed the fuel pump to a new unit with no luck turns out my glycol filled gauge was te issue. But I didn't see boiling vapors like you
no infared gun. almost bought one the other day though... I suppose the pump could be heating it up, I would be shocked though, its a new aeromotive pump. I figured it has to be the fuel boiling because the car will idle all day with out it doing it but once I put the petal to the floor a few times my A/F gauge goes form 14, to 10... and when I stop I can hear the bubbling and the car runs terrible until it has cooled down.
Are you sure it isn't a stuck float/dirty needle valve causing the bowl to overflow? That would definitely cause you to go rich.
Probably wouldn't hurt to pull the carb off and look for debris in the bowls plus check all gaskets and mating surfaces.
Probably wouldn't hurt to pull the carb off and look for debris in the bowls plus check all gaskets and mating surfaces.
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I pulled the carb twice. It only happens under a couple hard accelerations. I can 5 - 10 minutes and it will idle fine. I mean when its doing it you can hear it... it sounds just like bubbling water. and steam is comming out of the carb.
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from what was said I would guess at the metal fuel lines under the car are being heated by the exhaust. I have a stock 2002 camaro and in the summer that thing can get hot as f*** under slow conditions and especially at hot idle when the radiator fans kick on which blows hot air down under the engine and across the exhaust further heating the air. If that air is passing across the fuel lines they will definitely pick up heat.
what you might be able to try is when you know the problem is happening, and the intake and carb are rather cool to the touch, operate the throttle on the carb and stick a finger down the throat, as the accelerator pump shoots feel the temperature of the gas. if it's hot then you know it has picked up heat from somewhere upstream. I don't think i've ever heard of a fuel pump heating up fuel, doubt it's that. If it's an external fuel pump then put your hand on it and see if it's hot. an in-tank pump certainly would not heat the fuel. you don't have exhaust pipes routed right under a metal fuel tank without a heat shield do you?
what you might be able to try is when you know the problem is happening, and the intake and carb are rather cool to the touch, operate the throttle on the carb and stick a finger down the throat, as the accelerator pump shoots feel the temperature of the gas. if it's hot then you know it has picked up heat from somewhere upstream. I don't think i've ever heard of a fuel pump heating up fuel, doubt it's that. If it's an external fuel pump then put your hand on it and see if it's hot. an in-tank pump certainly would not heat the fuel. you don't have exhaust pipes routed right under a metal fuel tank without a heat shield do you?
Mine was givin me the same problems early last summer. I'd romp it up to the limiter in last gear and then slow down and it would chug, go way rich, and die. I had plastic wrapping holding my needle and seat open. Like they didn't get it all off when they built the carb. So it was dumping loads of fuel in the engine. Never heard a boiling sound but it did smoke alot lthru the carb once it died.
Is this happening on both the primary's and secondary's or just on one end of the carb? Also, you said fuel is coming out of the "nozzles". Do you mean the accelerator pump nozzles/squirters?
If that's the case^^^^, I'd check to make sure your pump linkage has just a little bit of play (I don't know the exact spec) when its cold. If it's too tight when cold, it's posible that heat expantion is causing the pump arm to actuate the pump diaphram on it's own and is forcing some fuel out of the accelerator pump squirters once you've left off the throttle and/or shut the car off. I have seen that happen on a buddy's car in the past and it will cause the same steam/smoke effect coming out of the carb if there is heat in the motor.
If the fuel is coming from the boosters, check for stuck or misadjusted floats like was already suggested above.
If that's the case^^^^, I'd check to make sure your pump linkage has just a little bit of play (I don't know the exact spec) when its cold. If it's too tight when cold, it's posible that heat expantion is causing the pump arm to actuate the pump diaphram on it's own and is forcing some fuel out of the accelerator pump squirters once you've left off the throttle and/or shut the car off. I have seen that happen on a buddy's car in the past and it will cause the same steam/smoke effect coming out of the carb if there is heat in the motor.
If the fuel is coming from the boosters, check for stuck or misadjusted floats like was already suggested above.
So I've just found this Car Craft article and they state to adjust the linkage so there is zero slack.
http://www.carcraft.com/techarticles.../photo_10.html
That makes sense so there is zero delay in pump response. However, I would be sure the linkage isn't adjusted beyond "zero lash" and causing the condition I described above. Just a thought.
http://www.carcraft.com/techarticles.../photo_10.html
That makes sense so there is zero delay in pump response. However, I would be sure the linkage isn't adjusted beyond "zero lash" and causing the condition I described above. Just a thought.
This makes me even more confident that the fuel probably isn't boiling because I would expect the condition to exist in both bowls.....especially if the fuel is being heated before reaching the carb. I think you have a needle valve that is slightly hung open. The bubbling sound your hearing is likely just the residual fuel pressure being bled off into an already full fuel bowl after the fuel pump is shut off.....so it's being forced out the boosters. Turn your fuel pump on with the motor not running and I'll bet it gets a lot worse.
I would pull off the front bowl and pull out that needle valve assembly for a very thourough cleaning.......or better yet replacement. How old is the fuel you're running. Did this problem just start after leaving the car sit for an extended period of time? This **** fuel these days doesn't take long to varnish up and will stick a needle valve in a heartbeat. I went about three weeks without starting my car and had the same issue.
I was thinking about the boiling sound earlier today and thought gas doesn't boil like a tea kettle. If heated to that point it will f'ing explode first. It doesn't turn to steam either. Plasma maybe, but not steam.
It is possible you have multiple problems. You have a relatively new build, are you sure the noise isn't in the cooling system somewhere? Got all the air out and done a pressure test on the cooling system/radiator cap? I had a head gasket go the other day, could you be seeing coolant venting out the intake?
It is possible you have multiple problems. You have a relatively new build, are you sure the noise isn't in the cooling system somewhere? Got all the air out and done a pressure test on the cooling system/radiator cap? I had a head gasket go the other day, could you be seeing coolant venting out the intake?
