several discussions around the FE fraternity recently regarding fuel delivery and the things that interfere. You might look over at Jay's place for one that's going on at present. My own answer, going back to flathead days, is to use an electric fuel pump---or even pumps.
Also consider: If you have headers, you may want to ceramic-coat them to reduce the level of heat they give off. The thin steel header pipe combined with large header surface area permits a lot of heat to be released under the hood.
If you run exhaust manifolds, make sure the H-pipe is a heavier construction, to slow the release of heat under the hood. Also, earlier exhaust manifolds lack the heat fins of the late pickups. The earlier exhaust manifolds likely radiate less heat under hood than the later ones, though they do get stressed a bit more.
If you are running a factory iron intake, or an aluminum intake with exhaust crossover active, you may want to plug them (if interested, ask about good methods on plugging them). Keeping the intake manifold cool is becoming more necessary as gasoline is becoming less tolerant of 1960's era fuel pressures.
I wonder whether it would help to run a fuel pressure regulator and electric pump which allows increasing the fuel pressure a pound or two. The carb may need to be recalibrated, but, depending on where on the engine the fuel is actually boiling, there is a chance it might help.
Insulating the fuel line under the hood, both before and after the pump, might help a little. As mentioned above, an insulating carb spacer can help.
All just guesses, but things I've pondered.
This message has been edited by daveshoe22 on Sep 7, 2013 10:33 PM This message has been edited by daveshoe22 on Sep 7, 2013 10:31 PM
Years ago , I remember people using clothes pins on fuel lines to act as heat sinks to get rid of the heat. A cooler thermostat would also be of help. Cleaning and flushing the cooling system can't hurt. If your not running antifreeze this is also a mistake, as the antifreeze helps to conduct the heat out of the motor. In addition, running no thermostat will cause the fluid in the system to circulate faster which causes a loss of heat transfer. Lots of different situations, depending on a lot of different factors concerning the engine. Radiator condition can also cause heat build up. The old caustic acid flushes did a great job of getting rid of the rust but did a number on radiator hoses and caps. Would cure a lot of problems though , by getting rid of rust and other things causing loss of heat transfer. Phenolic spacer would really help in your instance, but may not be the cure to your problem. Flushes sold these days are a poor substitute for the old caustic acid ones of years ago but would most likely help. If, you decide to use caustic acid as a flush, just remember you have to neutralize the acid by then running with something like baking soda . And don't forget to have a new radiator cap handy. Possibly new hoses.
If it's in the fuel line, then you have to look at the routing, paying attention to proximity to objects radiating heat and either relocate the line or insulate it.
If the boiling is occurring in the carburetor, then you have to make sure the carburetor isn't getting heat soaked. The approach here is to use the factory aluminum spacer that has coolant running through it or an aftermarket phenolic/plastic spacer. If you use an aftermarket aluminum spacer with just the thin carb gaskets, you will be no better off.
An electric fuel pump will not cure the issue of fuel boiling in the system. The cloths pin trick doesn't work since wood is an insulator and will not pull heat from the line.
You also have to make sure that if you have a heat riser, the valve is functioning properly and is fully open as the engine warms. Also, if you have a thermostatic valve air cleaner, that the valve is fully open once coolant reaches operating temp.
clothes pins dont work? try and tell that to my...
September 8 2013, 10:28 AM
Old jeep. When I bought it I thought the same thing so I removed them. Sure enough summer hit and I had major issues with vapor lock. I put the clothes pins back on and never had another issue with vapor lock. So while it isn't a pretty fix it can work.
As for an electric fuel pump the point is to run higher pressure and regulate down at the carb as well as having a return fuel line. This does two things 1.) the higher the pressure the higher the boil point 2.) keep the fuel circulating to keep cooler.
I struggled with vapor lock for years - 428, headers, in a tight mustang engine bay. Tried all the usual tricks: phenolic spacer, insulating fuel lines, etc... Finally decided to fix the problem for good.
Electric fuel pump (with return line), bypass fuel regulator, 8AN lines. Totally fixed my problem. I can now idle in traffic and at any outside temp.
If you decide to go this route let me know and I'll get you my parts list.
Plumbed everything with 8AN to carb and 6AN return. Completely solved my vapor lock/fuel boiling issues. Also, wired in a fuel pump relay that detects tach signal. Automatically shuts off if engine dies so it won't pump fuel all over in the event of an accident.
Vapor lock is going to happen on the suction side of the pump
September 8 2013, 7:01 AM
On older vehicles it is common to see rotten fuel hose between the tank and the pump. Any leakage can result in vapor lock type symptoms, ie the truck won't run.
Also common is dirt in the fuel tank, causing blocked fuel flow.
The problem is not under the hood. Opening the hood and waiting a few minutes will seem like it affected the problem, but you could also just wait a few minutes without opening the hood and achieve the see results.
"...not under the hood..." Gee whiz, Royce, that's a bit dogmatic isn't it? A suction-side leak, by definition, isn't a vapor lock. A vapor lock is caused by gasoline turning to vapor and thus not pumping properly. What you're describing, prior to the pump, would be better spoken of as a starvation situation.
And I'd offer that it'll be necessary to do some hands-on exploration to find out where the problem is!
One is to prevent carburetor icing on the cool, damp days. The other is to keep the carb from getting too hot and boiling the fuel. The heat from engine metals is higher than the coolant temp. The heat situation is worse with an aluminum intake.
My "Vapor Lock" was infact leaking soft hose on the suction side of my RobbMc Pump.
Without starting a flame war, replace any short pieces of rubber hose on the suction side of a mecanical pump if it feels hard or has cracks. Those hoses can leak and pull air into the system that lowers the already too low modern gases vapor point,what you end up with is a froth in the fuel bowl when the needle/seat opens.
at about 140 degrees. When heated it looks stable but as soon as you agitate it, it gets all bubbly. I saw this on a video where gas was heated on a hotplate in a pan with a thermometer. Even though it was just sitting calm in the pan at temp, as soon as it was stirred it stated to boil. Very interesting. I would look for your heat source. It should be fairly easy to find. Headers or undercar exhaust. reroute fuel line or install some reflective heat shields. As others have said too a carb spacer should help keep the carb cooler. Good luck,
I had this happen to me one time in a 95 E150 van, climbing up off the Hoover Dam at 10 mph, 120* heat, EFI 351. The fan clutch had quit, thus no air moving thru the engine box, thereby letting the fuel lines get too hot and the gas turning to vapor. Had me stumped til a park Ranger drove up and asked what happened. When I told him I had no idea, he told me to just let it sit awhile to cool down then it would be fine. He was dead on right. I changed the fan clutch the next morning and washed the radiator fins out at a car wash.(had a pin hole leak in the upper tank that allowed a slow buildup of crud in the fins along with the years of bugs that didn't help the airflow) Never had any trouble after that.
Maybe it's not technically vapor lock. I don't know. What difference does it make what it's called if your engine won't start?
You need to keep the fuel lines, carb, and fuel pump cooler in any case.
I'm sure most of this has been mentioned above. It'll likely take the cumulative effect of several small changes to fix the issue.
1) Is the exhaust crossover in the intake manifold blocked?
2) Good phenolic or wood carb spacer. As tall as you have room for.
3) Heat shield in addition to carb spacer. I believe Holly sells a spacer/heat shield combo.
4) Insulate fuel lines.
5) A cooler thermostat could help, at least in the summertime.
6) I believe it helps to shim the back of the hood up at the hinge (with washers) to allow heat to escape in low speed city driving and at traffic lights. I think this doesn't help at higher speeds and may even hinder airflow in that situation.