We used to run phenolic spacers on our stock cars. That had to be the most oppressive environment possible and I never had a hot fuel problem. It helped to work in a machine shop where they had loads of FREE phenolic sheet. Bob
Just ordered a new intake, heat shield and spacer for my 305 Caballaro to fix the same problem. Too, my home delivery gas source finally switched over to ethanol a couple of weeks ago and that certainly didn't help the situation.
Hey guys just joined up to the wealth of knowledge available on this site. I have an interesting problem and it has dogged me since I got my car about 4 years back.. 1940 special delux 350 th400. my car will idle usually for about 40 mins to an hour or there abouts in cool temperatures 60f [eg parade traffic] then it stalls. the fuel filter is found empty of gas, there is gas in the tank. something is happening between the tank and the filter. the underbonnet temp near the filter was 167f. Temp at the back of the Edlebrock carb is 212f. My inlet manifold water outlet temp [cooling system] is around 200f. This problem is never an issue on open road only ever occurs when idling for extended periods of time. Car has vintage air conditioning. Mechanical 5 blade flexi fan Things I have so far done to assist fuel flow. Auxiliary autobest electric low pressure fuel pump. makes no difference still stalls eventually Cleaned out radiator to improve cooling. I dont believe the engine is running too hot, radiator does not boil and doesn't go above 220f at any time. Checked timing its 12btdc mild/standard cam Two thermocouples under bonnet to get area indications of temp to get above results. Fibreglass lined silicon tube to insulate fuel line from the outlet header and around fuel pump exit line where the bottom radiator hose otherwise comes in contact. The Copper fuel line is exposed for about 10" up the front of the block. When it stalls out it takes a minimum of 10 mins before fuel can succesfully be pumped back into the [clear plastic]fuel filter and then carb.[electric or mechanical supply]. Carb with phenolic spacer now eliminated as contributing factor based on no fuel in feed filter. Now in the process of adding an auxilliary 8"pusher fan to help at idle temps. Quoted temps are now in the cooler part of our generally mild winters. In summer the ambient gets up to about 86f with some days of high humidity. This issue is driving me nuts, especially at Beach Hop. Any solutions gratefully received. I guess under bonnet induction air during idle around 212F is not that good either and again thats a cool day. Thanks
If you stop going to those 'fast food' places, the problem may not arise. ha ha That insulator can only help. Good luck. Davo.
Working on this issue again today. Ambient temperature is 59f. After idling for an hour and 30 mins finally stalled out. Fuel pump temperature ended up at 158f. rough idled off and on from 155. My options are either direct a fan onto the fuel pump or disconnect the mechanical pump and run the electric only. what do you guys think. Id like to stay mechanical pump but it may not be an option in the tight 40 engine bay. I could insulate the pump more, but then the block temp may contribute anyway. on a an 86f ambient day this stall would occur much earlier. Cheers
Well Just my 2cents worth its the little things in life that will drive you crazy. I'm located in the desert so.west, Las Vegas 86 degrees would be a beautiful spring day so we have the sametemp challenges here also.I'm wondering if all else fails, you have as many of us rodders do so many parts that have been changed. Have you changed your gas cap. Yes I know simple thing but if it not vented and needs to be vented youll get enough gas to lite the thing off and go a little way but the suction side of the fuel pump will eventually get the tank into a vacuum situation and not be able to draw fuel from the tank. After sitting eventually the pressures will equalize and the cycle will start again. Also lowering the pressure in the tank will also lower the boiling point of the gas to the point it will start vaporizing in hi ambient temps. Does the cap make a swishing sound when you remove it? if so that's a clear sign you need a vented cap or its just dirt at the current vent. OH well just a thought and easy to check.nice car also. Hope you get it figured out.Just a little red neck test,remove cap,stuff a rag in the filler neck and go for a ride and see what the heck happens. It wount get you the best gas cap trophy at the shows but it might help you diagnose the gas cap issue if there is one.good luck.
A 33041 Wix filter and a return line to the fuel tank will cure your problem. It keeps fuel flowing through the system to keep it cooler.
Cheers chaps for the comments. I dont think the gas cap is an issue as the car would be more troublesome on the open road if it was starving for gas due to vacuum in the tank. Idling for an hour and a half... It gets warm in the summer here and if you get involved in Beach Hop Whangamata [ NZ's biggest hotrod and classic car festival by far. Look it up on the net. Billy Gibbons has been known to come down here for it]some of the parades and cruises involve upwards of 700 cars. moving at walking pace. Its no fun to stall out with 300 cars behind you waiting for you to sort your sh.....ff out. that Wix filter could be the go, that would mean your gas tank temp would rise a bit but due to surface area should not allow the fuel to get over hot... an oil cooler could be put in the return line to the tank to assist cooling. I like this idea. the mechanical pump would cope with this fairly easily I would guess the inline autobest auxiliary electric may struggle??? pumping enough fuel to the carb with a recirc to the tank from the filter. Carb needs about4-6psi Edelbrock 1406 as far as I can gather. My under bonnet temp at the carb around 212 means the engine bay is just too hot when the car is at any speed under 10mph. maybe an overdrive water pump pulley would assist as fan speed would be higher at idle..... 7 blade fan??? my radiator does have a shroud. I have thought about louvering my bonnet and removing the side cowels to see if that helps. I like the stock look of the body so I wont rush to make that change. You can imagine how hard / expensive it is to get 1940 parts over here [$1 NZ = 0.71 USD at the moment plus frieght plus sales tax @15%. Yes the cost of owning a unique car is worth it, Im not getting too wound up on the exchange rate] as I think my car may be the only 1940 special delux tudor sedan on the road in NZ. Body is stock it runs 1967 350 with TH400 and 70ish Camaro/Nova front clip. Thanks again for your comments I will work my way through this issue until I get the fuel temp down.
Didn't realise that Billy Gibbons came down to beach hop. Saw him wandering around at Marineland's show in Napier May 2009. Any way, perhaps ask yourself why the other 699 aren't having the same problems, that would rule out some of your possibilities. Late March in NZ isn't as hot as some may imagine. Start by taking side panels off. I know my flathead just runs so much better in the summer with complete bonnet/ hood removed, not just the side panels.
sheddynz, try the wix, if that doesn't fix it, I'd consider making myself a discreet fuel cooler can for parade days - its a half ass solution
The funny thing I'm noticing here is that for some reason, people seem to think that the problem originates in the fuel line between the pump and carb. In actuality, that's the least likely place for vapor lock to occur. That length of line is the only part of the fuel system that's under constant pressure. The higher the pressure in the line, the less likely it is to boil . A phenolic spacer certainly can help because it lowers the float bowl temperature, inhibiting percolation which causes the engine to load up due to excessive fuel entering the intake manifold. In that situation, it's not an issue with fuel delivery. You're getting it to the carb just fine. But after that the fuel expands due to heat and the fuel level goes high, percolating into the manifold. The problem of classic vapor lock typically originates in the line from the tank to the fuel pump. That section of line is always under a negative pressure so it can be thought of as a slight vacuum. On a normal carb/ mechanical pump set up, the fuel pump lowers the pressure in the line between the tank and the pump, atmospheric pressure forces the fuel from the tank to the pump. That's why it's also important to be sure you have sufficient venting from the gas cap. If the pump were capable of sufficiently lowering the pressure in that line, the fuel would boil at room temperature. The pumps are designed for moving liquid, not air so you get vapor lock. Sheddynz is experiencing classic vapor lock. He cant get fuel out of the pump and up to the carb. A spacer, aux. fans etc, will not fix the situation. In his case I would pay particular attention to the feed line from the tank, ensuring that it is not subjected to exhaust heat. This is why all modern automobiles run a fully pressurized fuel system with a return line.
I have got the wix filter with the bypass now. If I run a 1/4 " line back to my tank, will I need a fuel regulator or will the pump move enough fuel to keep the carb happy and cope with the 1/4 bypass return?.
Simply amazing! One of the most clearly, accurately written posts I've seen here for a while. Just a shame that more members here won't read and understand it. You and I must have had the same auto tech instructor. Just to repeat... Vapor lock problems exist on the vacuum side of the fuel pump, between the tank outlet and the pump inlet.
You won't need a regulator or have any trouble with volume. The filter only bypasses over a certain pressure. When the fuel level in the carburetor drops, the needle valve opens, the pressure in the filter drops so the bypass valve closes and all of the fuel goes into the carburetor until the needle valve closes again. It was used in many GM cars with large V8 engines and air conditioning. When you aren't using much fuel at idle, the fuel in the lines in the engine compartment gets hot. It usually remains liquid when it is in the line and under 5 to 6 psi pressure. When the needle valve opens, the hot fuel is dumped into an un-pressurized float bowl and it evaporates. Alcohol gas evaporates even faster. The return line allows flow back to the tank over the designed pressure to keep cooler fuel from the tank circulating through the filter. As long as the fuel tank stays cool enough you shouldn't have any problems. If the exhaust system heats the fuel tank or the road surface is very hot, you might have to do some modifications.
Atmospheric pressure is about 14.7 psi at sea level. A fuel pressure gauge measures the difference between the atmospheric pressure and the fuel pressure. The engine mounted fuel pump creates a lower pressure area and the atmospheric pressure inside the fuel tank pushes the fuel from the tank into the pump. On most vehicles, the fuel pump is lower than the fuel tank so the fuel also gravity feeds to the pump. When the line from the tank is removed, fuel will flow out of it. The fuel that is between the pump and the carburetor is under pressure until the needle valve in the carburetor opens. A hot liquid that is under pressure will evaporate when it enters the float bowl and the pressure drops. The bowl vent is inside air filter so it is at slightly less than atmospheric when the engine is running. The fuel on the output side of the pump that was hot and under pressure turns to vapor when the pressure drops. The pump isn't as good at pumping vapor and may not get enough liquid fuel to the carburetor before the engine stops running. When the engine stops running, the heat builds up quickly.
Thanks Engine man. I was trying to find detailed info on how this filter works, your explaination is great. Is there any other technical info for this filter / bypass available. Like does it have a pressure the relief opens up at, how is the pressure differential managed within the filter. Thanks
Ever wonder why modern, fuel injected cars generally have fuel return lines?? Hint: It's not because they are cheap.
Hey guys update, I know its been a while. I have done a fair bit of work on the Chevy since December last year. I wont go into it much other than inlet manifold blown gasket, wiring fire trying to find the leak with brake clean. fixed inlet leak and repaired wiring. New vacuum advance distributor , new coil and new TH400 vacuum modulator.. Now the fuel thing. The Wix filter and return line seems to have cured the vapor lock issue and it confirms it was happening around the fuel pump not in the carb. My under bonnet temperature on hot days ambient of 82F and long idling [parade traffic, jams etc] gets to around 180F. More recently I have had problems with surge after WOT and kickdown. Initially I was chasing torque converter or trans issues as it felt like the car was jumping from top to second. Today I blocked my Fuel filter bypass and all my problem has gone away no surging at all. The upshot is, I need to put an on-off valve on my fuel bypass line. Open for parade traffic and off for open road driving. I cant see any other way around it. I have a high temp switch set up now so that when my under bonnet temps go higher than 130F an auxiliary fan kicks in to help out [ it helps but not a lot]. If I had a solenoid valve on the ff bypass I could trigger it also from that circuit. I'm not sure about having a sv on the fuel line though. I guess my Auxiliary electric low pressure fuel pump isn't an issue from a spark risk [ the auxiliary electric fuel pump did absolutely squat for my vapor lock issues. I won't remove it but its basically redundant. I wouldn't recommend one based on my experience but also vapor lock issues as previously discussed can happen at different places in the fuel delivery so each to their own]. I will look into the SV option as I know Ill forget to turn the valve on and off at the right times.....
Sorry you're chasing your tail. You need to install a fuel pressure test gauge, stick it under the wiper so you can see it and drive the car. Return line or not the carb needs 5 psi. I'll bet that with the return line it's fine idling even if it's lower. Under throttle lower fuel pressure will cause you problems. You stated that you doubt the fuel cap to be an issue. Don't dismiss that without a test, you've tested more crazy crap than I've ever seen so test that too. There needs to be a way to let air into the tank just as fast as fuel leaves or ------- the fuel stops leaving the tank. If it stops leaving the tank it never gets to the pump. Parade duty has a few challanges that aren't quite with normal Hot rod thinking. First, at parade speed your tune and adjustments must dead on optimal for idling. DO NOT expect optimal drivability with that tune. I did many parades and it's important to do this. The optimal drivability has a goal of excellent performance and acceptable idle characteristics, that's not parade duty by a long shot. A pusher fan can help in parades but not as much as a good shroud will. If you've got the best shrouds and still running hot you probably need a bigger radiator that's more efficient at sheding heat. A pusher fan will limit airflow at highway speeds.
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