Boiling Fuel

oj · September 28, 2012, 03:55:58 PM

I been dealing with an interesting problem. The underhood heat is boiling the fuel off in the carb. The carb has a glass sight window and you can watch it happen.
When i shut the engine off there isn't any problem but when it sits the temp in the bowl rises and it is pushing fuel out the squirter! I would have thought it'd come thru the booster but it is dribbling out the squirter. It is a dominator carb and i can watch it happen.
I put the temp gun on it and the bowl reads 147degrees, i can see it boiling inside at that temp.
I've added a phonelic spacer, we'll see how that changes things. I believe the heat is affecting fuel pressure as well. When the engine gets close to 200deg it changes how well it runs and the fuel presure jumps to above 9psi and can overwhelm the needle and seat.
I don't understand all i know about that, the regulator is attached to the hard lines going into the carb so there is air all around the regulator, the fuel line comes up from the frame in front of the cylinder head and runs rearward to the regulator - it is stainless braid and air around it too. I believed the fuel pressure spike to be something in the fuel pump bypass, i took it apart last night and give it a clean bill of health. This work was done before i became aware of the heating affecting the fuel. I think the heat and fuel pressure spikes are connected.
Hot rods, there just isn't anything normal about them, is there!

BFS57 · September 28, 2012, 08:57:14 PM

Hello;
Welcome to my world!!!! I have this problem and it seems as though anything I try does not work!
I put heat shield on my fuel lines, nothing, I added a fuel regulator set to 4 lbs, Nothing! It seems like when I see my temp gage get to 180 deg, it's like someone flipped a switch! Car runs rough, idle goes down my temper flares!
I have heard that an electric fuel pump might help. I have heard that a regulator with a fuel return line might help! WHAT'S A GUY TO DO???
It's the ethanol in the fuel for sure!!! I even got some non ethanol fuel and it did seem to help but the $4.40 a gallon was not helpful.
All I can say is I have a 32 Ford (the problems are on my 57 Chevy) that does not seem to have this problem!! What the heck!!

Bruce

wayne petty · September 28, 2012, 09:55:53 PM

i know that i have said this several times.. i just don't recall who i posted it for..

gentlemen... magnets inside the fuel tank bottom... attract any sediment that many fuel systems are plagued with..

take a look at what happened when i drop a tiny neodyneum magnet into the bottom of the of my translucent plastic drain tray..

i pushed it with my finger.... and WOW....

this crud gets in the fuel mechanical pump check valves...

it gets in the electric fuel pump bypass valves ... it gets in the fuel pressure regulator seats .. it gets in the carb needle and seat...

this almost invisible sediment allows needles and seats to leak fuel through..

its so small it will pass through everything except for Fuel injection type fuel filters....

i have fought this problem for decades...

super magnets either in the tank bottom.. or big speaker magnets stuck to the bottom of the tank work really well..

i buy ring/washer shaped super magnets and actually stick them over the inlet fitting on some fuel filters..

when the fuel pressure drops do to the sediment holding the
needle and seat open.. or allowing the fuel pressure to flow backwards thru the fuel pump... its going to boil in the fuel lines.. as the fuel pressure drops..

BFS57 · September 29, 2012, 08:29:28 AM

Hello;
According to what Wayne said that if you use fuel filters for fuel injection that this crud will at least be cut down or out? Can someone use a FI filter for a carbureted car?
I don't feel that sticking magnets everyplace will completely help. I know for a fact the Ethanol gas has a much lower boiling point than the good ol gas we used to buy.
My 32 Ford has pretty much the same engine and trans as my 57 but the 57 seems to have this problem and not the 32. Same carbs (1406) fed from a mechanical pump, the pump on the 32 is a name brand unit while the pump on the 57 is a no name brand. I did install a regulator after the pump on the chevy while the 32 has a direct feed line right next to the engine from the pump.

so o o o tell me why does the chevy have this problem and the 32 doesn't?

Bruce

oj · September 29, 2012, 09:05:10 AM

Quote from: "BFS57"Hello;
According to what Wayne said that if you use fuel filters for fuel injection that this crud will at least be cut down or out? Can someone use a FI filter for a carbureted car?
I don't feel that sticking magnets everyplace will completely help. I know for a fact the Ethanol gas has a much lower boiling point than the good ol gas we used to buy.
My 32 Ford has pretty much the same engine and trans as my 57 but the 57 seems to have this problem and not the 32. Same carbs (1406) fed from a mechanical pump, the pump on the 32 is a name brand unit while the pump on the 57 is a no name brand. I did install a regulator after the pump on the chevy while the 32 has a direct feed line right next to the engine from the pump. so o o o tell me why does the chevy have this problem and the 32 doesn't?

Bruce

The heat is trapped in the '57 while the '32 lets the heat escape.

When testing to get the carb sorted out i had the idle ckt too lean and the temp went to 200ish, the power steering acted funny as well. I now think the power steering fluid was boiling in its' lines as well.
The car has new fuel tank, electric fuel pump, scintered bronze filtter from Earls and holley regulator. I put the fuel tank in about a year ago and drove the car with the other engine and mechanical pump. These problems are from the new engine.
I am considering a bypass style fuel system so that fuel will flow continuous and that would keep all but the carb inlet lines cool. I could run a line back to the inlet of the pump and test it for a while and consider adding a return to the tank.

wayne petty · September 29, 2012, 10:10:53 AM

sorry there are SO many choices in fuel filters.. both aftermarket and OEM to work with..

i went individually through the AZ catalog to spot various ones with fittings that might work..

this is while you await others replys to see about magnets..

one way to tell.. last time you have the float bowl off or open.. was there any red stain on the bottom..

this is the fram HPG1

this is the AC Delco GF62C... there are several versions available USED ONLY... unless you spot one on ebay..
they come off sevilles and eldorados with fuel injection starting in 76 and ending somewhere in the early 80s.. these would be the versions with the 3/8 FIP inlets and 3/8 inverted flair female adaptors already installed...
every parts store in the country stocks the element.. as its the same for ford fuel pump mounted fuel filters..

this is an FF745... fits a LOT of fords... has 5/16 inlets..so you can push a hose on. clamp it...

these are filters i grabbed that have 8mm, 9mm or 10mm fitting inlets.. i have not personally tried these.. i use the 3 above on various applications .. but most people are afraid of the 8MM inlet size.. since i install them on the inlet side of the fuel pump.. i have not had a problem until they start to clog...

G6377

FF855

FF703 with 8MM inlets

FF756 with 9mm inlets

FF751 with 10MM inlets

FF776 with 10MM inlets

FF744 with 10MM inlets

sorry for commenting back in.. before others had a chance..
but now there is more to discuss...

ethanol attracts moisture.. also is hard on the non stainless sections of your fuel system.. kinda removes the galvanizing as i understand.. current gasoline is formulated for FUEL INJECTED cars. its also formulated to operate at higher fuel pressures.. they just barely care about carbed cars..

best of luck.

enjenjo · September 29, 2012, 12:07:34 PM

Quotecurrent gasoline is formulated for FUEL INJECTED cars. its also formulated to operate at higher fuel pressures.. they just barely care about carbed cars

This is the key in a nutshell. Back in the carburetor days fuel was blended for a lower vapor pressure, particularly in warm weather. In the late 60s, with emission controls coming, engine operating temperatures started to rise to reduce emissions. This caused vapor lock problems, so the manufacturers started using a return line to reduce fuel temperature. It was effective, but only while the engine was running.

By the 90s, most cars were fuel injected, and using pressures from 15 psi up to as much as 90 psi, so vapor pressure was not as big a problem, and the oil companies stopped blending to keep it low. Cars than never had problems in the past started having fuel boiling problems.

If you don't have a return line, installing one will help. Some fuel pumps are configured for a return line, if yours is not, you can install a regulator between the pump and carburetor that has a return provision. Weatherhead also has check valves, pn 63x4, 63x5, or 63x6 that are reversible and adjustable, that can be teed in between the fuel pump and carburetor to act as a return line, and still maintain the fuel pressure needed. A insulated spacer between the carburetor and manifold is helpful, you can buy premade ones for most 4 barrel carbs, others may need to be custom made, I usually use Phenolic plastic to make them.

Fuel lines can also have a big effect on heat retention. Rubber is bad, it holds a lot of heat. Most braided is bad, it is just rubber with a metal overbraid. If you want braided, use teflon with a metal overbraid. Steel is good, aluminum is better. an inline cooler is also helpful, Flexilite makes some nice ones.

Fuel boiling in the float bowl after shutdown is generally not a problem, as most float bowls are vented. If the vent is plugged, that may be a problem. Fuel coming out of the accelerator pump squirters, is fuel trapped in the pump well, and not much can be done about that.

I like the Fram G3727 type fuel filter. It is available everywhere, and uses a 10mm Oring fitting on both ends, and is adaptable to 3/8" inverted flare tubing.

oj · September 29, 2012, 02:01:17 PM

Quote from: enjenjo
Quotecurrent gasoline is formulated for FUEL INJECTED cars. its also formulated to operate at higher fuel pressures.. they just barely care about carbed cars

Fuel boiling in the float bowl after shutdown is generally not a problem, as most float bowls are vented. If the vent is plugged, that may be a problem. Fuel coming out of the accelerator pump squirters, is fuel trapped in the pump well, and not much can be done about that.

I watched this happen, fuel coming out of the squirter. The thing about that is it'll empty the float bowl. I watched a continuous dribble of fuel run from the squirter into the venturii. As the pressure pushed fuel up the accelerator pump passage more fuel from the bowl would enter the accelerator pump in a continuous cycle until the float bowl emptied.
I thought it was very interesting.
It also explains a lot.

Rrumbler · September 29, 2012, 04:53:17 PM

Along with some of these other suggestions and ideas, I would consider getting a carb heat shield and a phenolic spacer to try to shield the carb from the radiant heat from the engine and the direct heat transfer from the manifold. Summit has a whole pile of them to select from.

GPster · September 29, 2012, 09:36:46 PM

My '80 Jeep CJ7 with the 258 six has one with the line back to the tank. One of them could help you make a quick try at that fix. Maybe with that kind of heat the gas sitting in the line between the pump and the carb is developing enough pressure to keep dribbling gas into the carb every time the carb float drops because of evaporation in the float chamber. The mention about the float chamber being vented brought something to mind. If your carb would happen to have been made for a marine application and given to you by mistake it would have a different float chamber vent than an automotive carb. GPster

Arnold · September 29, 2012, 11:58:57 PM

Quote from: "enjenjo"
Quotecurrent gasoline is formulated for FUEL INJECTED cars. its also formulated to operate at higher fuel pressures.. they just barely care about carbed cars

This is the key in a nutshell. Back in the carburetor days fuel was blended for a lower vapor pressure, particularly in warm weather. In the late 60s, with emission controls coming, engine operating temperatures started to rise to reduce emissions. This caused vapor lock problems, so the manufacturers started using a return line to reduce fuel temperature. It was effective, but only while the engine was running.

By the 90s, most cars were fuel injected, and using pressures from 15 psi up to as much as 90 psi, so vapor pressure was not as big a problem, and the oil companies stopped blending to keep it low. Cars than never had problems in the past started having fuel boiling problems.

If you don't have a return line, installing one will help. Some fuel pumps are configured for a return line, if yours is not, you can install a regulator between the pump and carburetor that has a return provision. Weatherhead also has check valves, pn 63x4, 63x5, or 63x6 that are reversible and adjustable, that can be teed in between the fuel pump and carburetor to act as a return line, and still maintain the fuel pressure needed. A insulated spacer between the carburetor and manifold is helpful, you can buy premade ones for most 4 barrel carbs, others may need to be custom made, I usually use Phenolic plastic to make them.

Fuel lines can also have a big effect on heat retention. Rubber is bad, it holds a lot of heat. Most braided is bad, it is just rubber with a metal overbraid. If you want braided, use teflon with a metal overbraid. Steel is good, aluminum is better. an inline cooler is also helpful, Flexilite makes some nice ones.

Fuel boiling in the float bowl after shutdown is generally not a problem, as most float bowls are vented. If the vent is plugged, that may be a problem. Fuel coming out of the accelerator pump squirters, is fuel trapped in the pump well, and not much can be done about that.

I like the Fram G3727 type fuel filter. It is available everywhere, and uses a 10mm Oring fitting on both ends, and is adaptable to 3/8" inverted flare tubing.

I went pretty crazy trying to figure out this problem once ..as it was related to venting.There was a tang on the throttle linkage that opened the vent..tang was somehow gone.

Harry · September 30, 2012, 02:16:26 PM

What about using an intake manifold with no heat risers, or blocking off the heat risers.

papastoyss · October 01, 2012, 11:07:55 AM

I agree w/everything Enjenjo said w/ the exception of the fuel boiling in carb bowl after shutdown. I have had this happen on my own rods. It may be a geographic thing since temps are usually warmer "down south". This is more prevalent w/Eldebrock carbs due to the fuel being closer to the manifold heat than in Holley carbs. A 1" phenolic spacer & a couple of gaskets sandwiched w/ aluminum shields will usually cure this in our area.