carb heat???UPDATE

Posted By: bonefish

carb heat???UPDATE - 03/01/12 06:01 PM

UPDATED//////////// ////////////after about 20mi this is what happens.when i look at the sight glass at idle its perfect as far as level and no sign of bubbles.then when i rev it the bowl fils completly with bubbles like its boiling.but according to my IF therm. the bowl and all the lines including the itake man. all only at around 124 deg.,gas boils at 170.there are no apparent leaks in the system, this is the front bowl.i cant even make it to the trak.

//////////////got some clear hose and did the pump in the can trick,tons of air bubbles frome the pump.took the pump apart its like new and shows no sign of leakage,replaced all lines going from tank to pump.still tons of bubbles,what do ya think? mabey a crack in the pick up?

Posted By: StealthWedge67

Re: carb heat??? - 03/01/12 06:28 PM

There's no way the temp changes enough to boil the fuel just by cracking the throttle. There's got to be something else going on. It seems to me that is has to a seal somewhere that is allowing air to be sucked into the fuel bowl. Could it be sucking air through the accellerator pump diaphram? Just thinking out loud.

Does it do this when the carb is still cool?, or just after the motor is warmed up?

Posted By: sixpackgut

Re: carb heat??? - 03/01/12 06:32 PM

i would check for a blown power valve

Posted By: bonefish

Re: carb heat??? - 03/01/12 06:41 PM

no PV.it does this no mater what carb i put on here,ive tried 4.its got to be sumthin before the carb.i cant find a leak any where.ive insulated my supply lines and put a heat plate under the carb. (wheres the smiley of me pullin my hair out?)

Posted By: bonefish

Re: carb heat??? - 03/01/12 06:44 PM

Quote:

There's no way the temp changes enough to boil the fuel just by cracking the throttle. There's got to be something else going on. It seems to me that is has to a seal somewhere that is allowing air to be sucked into the fuel bowl. Could it be sucking air through the accellerator pump diaphram? Just thinking out loud.

Does it do this when the carb is still sool?, or just after the motor is warmed up?

this only happens after about a 20 mile drive.or if you let it idle for 20 mins. or so.im thinkin the same thing,my line runs thru my frame rail,mabey its a small undetectable leak thas suckin air?

Posted By: Dodgeguy101

Re: carb heat??? - 03/01/12 07:21 PM

Quote:

Quote:

There's no way the temp changes enough to boil the fuel just by cracking the throttle. There's got to be something else going on. It seems to me that is has to a seal somewhere that is allowing air to be sucked into the fuel bowl. Could it be sucking air through the accellerator pump diaphram? Just thinking out loud.

Does it do this when the carb is still sool?, or just after the motor is warmed up?

this only happens after about a 20 mile drive.or if you let it idle for 20 mins. or so.im thinkin the same thing,my line runs thru my frame rail,mabey its a small undetectable leak thas suckin air?

I know you may have already said, but I assume it is a mechanical fuel pump? I would think if you had a leak in the fuel line, it would drip gas somewhere. Fuel line pressure too high? Just throwing things out there, I read your other post, you have me stumped, and curious as to what it could be.

I can't remember whose site I saw it on, but there was a picture of the inlet, needle and seat of the "normal" valves vs a set he sold and it showed the difference in the air bubbles between the two, but with you saying it does it with all the carbs, can't be that.

What kind of tank is in the car? Is it possible it is sucking air inside the tank and aerating the gas in there first?

Posted By: bonefish

Re: carb heat??? - 03/01/12 07:28 PM

Quote:

Quote:

Quote:

There's no way the temp changes enough to boil the fuel just by cracking the throttle. There's got to be something else going on. It seems to me that is has to a seal somewhere that is allowing air to be sucked into the fuel bowl. Could it be sucking air through the accellerator pump diaphram? Just thinking out loud.

Does it do this when the carb is still sool?, or just after the motor is warmed up?

this only happens after about a 20 mile drive.or if you let it idle for 20 mins. or so.im thinkin the same thing,my line runs thru my frame rail,mabey its a small undetectable leak thas suckin air?

I know you may have already said, but I assume it is a mechanical fuel pump? I would think if you had a leak in the fuel line, it would drip gas somewhere. Fuel line pressure too high? Just throwing things out there, I read your other post, you have me stumped, and curious as to what it could be.

I can't remember whose site I saw it on, but there was a picture of the inlet, needle and seat of the "normal" valves vs a set he sold and it showed the difference in the air bubbles between the two, but with you saying it does it with all the carbs, can't be that.

What kind of tank is in the car? Is it possible it is sucking air inside the tank and aerating the gas in there first?

just a stock tank,the only thing that has changed is the filter befor the pump,i had a 80 micron filter befor and replaced it with a standard holley filter,mabey its to restrictive?

Posted By: Dodgeguy101

Re: carb heat??? - 03/01/12 07:50 PM

I'd say take the filter out, replace with just a line and see what happens. If it is a mechanical pump, the filter should be after the pump, if electric, I was told a 100 micron before and a 40 or so after the pump, but you will get differing opinions, but that is what I have and so far it works.

Posted By: Oyvind Mopar

Re: carb heat??? - 03/01/12 07:56 PM

It could be that your pump is cavitating because you have the filter before the pump. I would place the filter after the pump (like the factory did), to avoid this. Cavitated fuel could be foamy, but I never saw it. If you loose performance it could be due to the blocked filter and cavitation. My

Posted By: bonefish

Re: carb heat??? - 03/01/12 07:57 PM

Quote:

I'd say take the filter out, replace with just a line and see what happens. If it is a mechanical pump, the filter should be after the pump, if electric, I was told a 100 micron before and a 40 or so after the pump, but you will get differing opinions, but that is what I have and so far it works.

well i just came in,removed the pre filter,still does it.

Posted By: Dodgeguy101

Re: carb heat??? - 03/01/12 08:03 PM

Well, take the line you just stuck in place of the filter and run it into a can of gas, see what it does then. Lets trace the problem backwards.

Posted By: 383man

Re: carb heat??? - 03/01/12 08:56 PM

If you have any rubber fuel line I have seen them get dry and have cracks that suck in air but not leak fuel because its on the suction sde and very small. Ron

Posted By: bonefish

Re: carb heat??? - 03/01/12 09:00 PM

Quote:

Well, take the line you just stuck in place of the filter and run it into a can of gas, see what it does then. Lets trace the problem backwards.

thats a good idea,gunna have to wait gotta get my grand son from school.

Posted By: bonefish

Re: carb heat??? - 03/01/12 09:02 PM

Quote:

If you have any rubber fuel line I have seen them get dry and have cracks that suck in air but not leak fuel because its on the suction sde and very small. Ron

all newish steel line except a short peice from the tank to the pump,i just put a new peice there when i removed the filter.

Posted By: Dodgeguy101

Re: carb heat??? - 03/01/12 09:03 PM

Quote:

If you have any rubber fuel line I have seen them get dry and have cracks that suck in air but not leak fuel because its on the suction sde and very small. Ron

This idea has a allot of merit as well. I too have seen this happen.

Posted By: bonefish

Re: carb heat??? - 03/01/12 09:04 PM

Quote:

Well, take the line you just stuck in place of the filter and run it into a can of gas, see what it does then. Lets trace the problem backwards.

when i took the filter off, gas flowed freely from the line.

Posted By: Dodgeguy101

Re: carb heat??? - 03/01/12 09:16 PM

The filter you took out, was it paper or a mesh screen? If paper, change the filter. Or run the car without it for a little bit and see if it bubbles. I don't think you have a heat problem, it is sucking air somewhere, just not sure where.

Posted By: bonefish

Re: carb heat??? - 03/01/12 09:36 PM

Quote:

The filter you took out, was it paper or a mesh screen? If paper, change the filter. Or run the car without it for a little bit and see if it bubbles. I don't think you have a heat problem, it is sucking air somewhere, just not sure where.

i removed the filter,no diff. one more thing to look at.where the line comes out of the frame rail it makes a hard 90 to the line going up the back of the block,im gunna change that to a straight shot.we,ll see what happens but not till the first of the week,had to order a fitting.

Posted By: bonefish

Re: carb heat??? - 03/02/12 02:34 PM

one more thing,it has a Mallory 140 pump,could it mabey be suckin air but not leakin?

Posted By: Dodgeguy101

Re: carb heat??? - 03/02/12 04:22 PM

Quote:

one more thing,it has a Mallory 140 pump,could it mabey be suckin air but not leakin?

It could be trying to pull more fuel than that filter can handle. That is why I was saying stick the end of the hose ina can of gas and see if it stops doing that. That would tell you it was behind the pump. I don't think that fitting you are talking about up by the engine is going to make a difference, maybe less flow, but not causing the aeration. With it being an electri pump, I would say the problem is behind the pump. What size line do have feeding the pump from the tank thru the filter to the pump?

Posted By: bonefish

Re: carb heat??? - 03/02/12 05:33 PM

Quote:

Quote:

one more thing,it has a Mallory 140 pump,could it mabey be suckin air but not leakin?

It could be trying to pull more fuel than that filter can handle. That is why I was saying stick the end of the hose ina can of gas and see if it stops doing that. That would tell you it was behind the pump. I don't think that fitting you are talking about up by the engine is going to make a difference, maybe less flow, but not causing the aeration. With it being an electri pump, I would say the problem is behind the pump. What size line do have feeding the pump from the tank thru the filter to the pump?

all the lines are 5/16 to 6an.this is a prob. that has developed,this system has been working great for about 5 years.CORRECTION:3/8 pickupto 1/4 in. to 6-an

Posted By: Scamp408

Re: carb heat??? - 03/02/12 06:23 PM

Sounds like fuel in the bowls is getting airated. Whats your float level and fuel #. The airation could be from fuel rushinf from needle and seat.

Posted By: Dodgeguy101

Re: carb heat??? - 03/02/12 06:45 PM

Quote:

Sounds like fuel in the bowls is getting airated. Whats your float level and fuel #. The airation could be from fuel rushinf from needle and seat.

I would have to agree with you, but he had said it was happening with different carbs. We were working backwards thru the system trying to find the problem.

Posted By: Dodgeguy101

Re: carb heat??? - 03/02/12 06:47 PM

Quote:

Quote:

Quote:

one more thing,it has a Mallory 140 pump,could it mabey be suckin air but not leakin?

It could be trying to pull more fuel than that filter can handle. That is why I was saying stick the end of the hose ina can of gas and see if it stops doing that. That would tell you it was behind the pump. I don't think that fitting you are talking about up by the engine is going to make a difference, maybe less flow, but not causing the aeration. With it being an electri pump, I would say the problem is behind the pump. What size line do have feeding the pump from the tank thru the filter to the pump?

all the lines are 5/16 to 6an.this is a prob. that has developed,this system has been working great for about 5 years.CORRECTION:3/8 pickupto 1/4 in. to 6-an

So what did you change before this problem started?

Posted By: bonefish

Re: carb heat??? - 03/02/12 11:17 PM

Quote:

Quote:

Quote:

Quote:

one more thing,it has a Mallory 140 pump,could it mabey be suckin air but not leakin?

It could be trying to pull more fuel than that filter can handle. That is why I was saying stick the end of the hose ina can of gas and see if it stops doing that. That would tell you it was behind the pump. I don't think that fitting you are talking about up by the engine is going to make a difference, maybe less flow, but not causing the aeration. With it being an electri pump, I would say the problem is behind the pump. What size line do have feeding the pump from the tank thru the filter to the pump?

all the lines are 5/16 to 6an.this is a prob. that has developed,this system has been working great for about 5 years.CORRECTION:3/8 pickupto 1/4 in. to 6-an

So what did you change before this problem started?

heads and cam.im going to get some clear line and start at the pump filling a 5 gal can if no bubbles im going to do it at the reg and the the carb line.

Posted By: bonefish

Re: carb heat??? - 03/04/12 08:22 PM

bump