(Another) Vapor Lock Question

[70 sport WA]

Yes, another one. I've read about it for years, taken in the knowledge, but never really experienced it and thinking that some feedback based on my circumstances might be helpful.

I've got a 2100 carb and have had the Bronco for about 18 years. Never runs hot, meaning it's typically at 180 degrees in most situations...even in 100 degree parade (5 mph) driving several miles. Maybe gets to 190. Since last tuned, it was at about 3200 altitude.

A few days ago went up a trail outside Albuquerque. About 5500 altitude. Decent grade, going slow, a bit rocky but nothing terribly challenging. Only went a couple miles in, about 90 degrees out, and coming back flat + downward grade it just wanted to stall out a lot and had to restart many times. Temp gauge 200-205. Still not bad, well within operating range.

Again, doesn't seem to be an overheated engine. Have I ever really been on a trail in this rig since I've owned it? No. Deep snow (10 inches), across town in TX panhandle in FWD yes, but flat and performed extraordinary. Driving up a mountain in WA to a ski at high altitude? Yes. But warm weather in mountainous terrain no.

So I let it cool off a bit and things got better, but just enough to get me out. And in city driving after leaving, when things really cooled down, was just fine. And driving since has not been a problem, so I don't believe there is a chronic issue with the carb or fuel delivery.

I'm thinking it's not engine temp but rather a fuel issue. Either carb isn't tuned properly for the altitude or there's some vapor lock going on.

So...let's say I check for an in-line filter and get rid of it (beyond the one that's at the carb.) Then I check to make sure that no lines are near exhaust. Assuming the mechanical pump is functioning properly. Assuming that the tank and fuel are clean (tank was replaced a few years ago.) Maybe replace the fuel filter at the carb as a precaution.

Not trying to throw money at problems, but looking for improvements when I go out again, thoughts on the following in addition to the few things listed above:

1. Re-time the, well, timing? Easy enough and will try.
2. Re-tune the carb? Easy enough also.
3. Get an electric fuel pump? A decision.
4. Some insulation on the lines where there might be heat issues. OK.
5. Get a non-import, Carter mechanical fuel pump. Worth a try? Hasn't been changed since I've owned it.

Any other approaches are welcome. I've got time, lol. I know it could be a myriad of issues, but again other than the obvious carb failure/issues that demand a rebuild (in my case about every 7 years, but it otherwise works fine right now.)

Thanks.

 

[blubuckaroo]

The two things that contribute to vapor lock are temperature and altitude. If you have both, you can be in trouble.
If you look at the instructions on a box of cake mix, they tell you that baking takes less time at higher elevations.
That's because water boils at a lower temp at higher elevations.

Vapor lock is the point that fuel boils. It's lower at higher elevations.

 

[70 sport WA]

The two things that contribute to vapor lock are temperature and altitude. If you have both, you can be in trouble.
If you look at the instructions on a box of cake mix, they tell you that baking takes less time at higher elevations.
That's because water boils at a lower temp at higher elevations.

Vapor lock is the point that fuel boils. It's lower at higher elevations.

I'm thinking it's my problem for this very reason. In another recent thread about vapor lock, you indicated:

"I ended up putting an electric fuel valve back in front of the rear axle, and ran the fuel line outside the frame rails. That fixed the vapor lock problem."

This your thought in this instance?

 

[jckkys]

The phenomenon is actually called "vapor pressure". If you search that term you'll find some great descriptions and explanations. Since the problem occurred when descending it doesn't sound like vapor lock. I would look at the fuel pickup filter in the tank.

 

[70 sport WA]

The phenomenon is actually called "vapor pressure". If you search that term you'll find some great descriptions and explanations. Since the problem occurred when descending it doesn't sound like vapor lock. I would look at the fuel pickup filter in the tank.

Interesting, I have two fuel tanks and I should switch to the other to see if it made a difference.

 

[blubuckaroo]

Vapor lock can happen even when the engine isn't running hot.
It doesn't matter if the car is going down hill.
It's the fuel turning into vapor before it can get to the fuel pump. The mechanical pump can't pump vapor.

Once My Bronco, with trailer in tow, vapor locked on a blind curve. It was in a very bad place for traffic. I opened the hood and poked a hole in a bottle of water with my pocket knife. I squirted water on the pump and the fuel line going to it. The Bronco started right up and got me off the road to a safe place.
This is when I found out that putting in dual exhaust put the exhaust pipe right along the same path as the fuel line. I ended up moving the fuel line to the outside of the frame to block it from exhaust/drivetrain heat.

 

[70 sport WA]

This is when I found out that putting in dual exhaust put the exhaust pipe right along the same path as the fuel line. I ended up moving the fuel line to the outside of the frame to block it from exhaust/drivetrain heat.

First think I'm going to check is the fuel line route...thanks(!)

Another question coming to you, another thread, about transmissions...

 

[jckkys]

If fuel isn't getting to the carb power goes away. True, but a truck going down hill doesn't need power, it has gravity. The fact that your engine ran after a stop is consistent with the dirty pickup sock scenario. Once the engine stops running, the crud drops off. The engine now runs. Some times it takes a long drive to plug it up again, but it will. When this happened to me, it took weeks to figure it out. Cleaning out the tank is a PITA, but it fixed the problem.

 

[the74bronco]

Yes, another one. I've read about it for years, taken in the knowledge, but never really experienced it and thinking that some feedback based on my circumstances might be helpful.

I've got a 2100 carb and have had the Bronco for about 18 years. Never runs hot, meaning it's typically at 180 degrees in most situations...even in 100 degree parade (5 mph) driving several miles. Maybe gets to 190. Since last tuned, it was at about 3200 altitude.

A few days ago went up a trail outside Albuquerque. About 5500 altitude. Decent grade, going slow, a bit rocky but nothing terribly challenging. Only went a couple miles in, about 90 degrees out, and coming back flat + downward grade it just wanted to stall out a lot and had to restart many times. Temp gauge 200-205. Still not bad, well within operating range.

Again, doesn't seem to be an overheated engine. Have I ever really been on a trail in this rig since I've owned it? No. Deep snow (10 inches), across town in TX panhandle in FWD yes, but flat and performed extraordinary. Driving up a mountain in WA to a ski at high altitude? Yes. But warm weather in mountainous terrain no.

So I let it cool off a bit and things got better, but just enough to get me out. And in city driving after leaving, when things really cooled down, was just fine. And driving since has not been a problem, so I don't believe there is a chronic issue with the carb or fuel delivery.

I'm thinking it's not engine temp but rather a fuel issue. Either carb isn't tuned properly for the altitude or there's some vapor lock going on.

So...let's say I check for an in-line filter and get rid of it (beyond the one that's at the carb.) Then I check to make sure that no lines are near exhaust. Assuming the mechanical pump is functioning properly. Assuming that the tank and fuel are clean (tank was replaced a few years ago.) Maybe replace the fuel filter at the carb as a precaution.

Not trying to throw money at problems, but looking for improvements when I go out again, thoughts on the following in addition to the few things listed above:

1. Re-time the, well, timing? Easy enough and will try.
2. Re-tune the carb? Easy enough also.
3. Get an electric fuel pump? A decision.
4. Some insulation on the lines where there might be heat issues. OK.
5. Get a non-import, Carter mechanical fuel pump. Worth a try? Hasn't been changed since I've owned it.

Any other approaches are welcome. I've got time, lol. I know it could be a myriad of issues, but again other than the obvious carb failure/issues that demand a rebuild (in my case about every 7 years, but it otherwise works fine right now.)

Thanks.

I just have been fighting this same issue. I was told either reduce heat or increase fuel pressue. I live at 5,500ft and it has just started to get into the 90's. Ran great when it was cold, but now once I get up to temp the engine stumbles and dies at idle. I have a quick fuel carb with the sight window. I could watch my fuel boil and eventually disappear from the window. I moved the fuel line to the outside of the frame rail (was right next to my exhaust), and installed a phenolic carb spacer. First test drive today proved no issues and my engine ran a little cooler as well. time will tell if this is good enough of a fix.

 

[68rustbucket]

If you have a metal line going from fuel pump to carb, insulate it. Get some spark plug wire insulation. That’s what I used on my stainless steel line.

 

[70 sport WA]

If you have a metal line going from fuel pump to carb, insulate it. Get some spark plug wire insulation. That’s what I used on my stainless steel line.

I do have only (bare) metal line going from fuel pump to the carb...I'll get it insulated. Good idea.

One other question: Maybe dumb, but how about idle speed adjustment? I started up the rig and moved the screw in a bit, while it was cold, and it ran much better/smoother. Maybe that was enough to put things over the edge when things got a little warm?

Stalling at a red light happened to me the other day, twice, coming home and after sitting in a drive through for several minutes. I think that I adjusted it down a few weeks ago (don't ask why) and that could be part of the problem?

 

[LSharpNM]

What you described is not vapor lock. With vapor lock, the engine will die and not restart until you wait around for a while for things to cool off (5 minutes+ usually). Then it will restart and run like nothing ever happened.

However, vapor lock is commonly an issue in this area, and properly installed electric fuel pump is all you need to cure it. Everything else is just a band-aid.

 

[jckkys]

I think you stumbled into a fix. Increasing the idle speed moves more air through the radiator and circulates more coolant. There's more fuel moving through and so less likely to boil. The fuel line actually looses heat to the frame, so I don't find that to be a problem. The only thing I would look for is an inline filter between the tank and the pump. That's an invite to vapor lock.

 

[70 sport WA]

What you described is not vapor lock. With vapor lock, the engine will die and not restart until you wait around for a while for things to cool off (5 minutes+ usually). Then it will restart and run like nothing ever happened.

Great comment, thanks. What happened in the city probably wasn't...but maybe it was the issue at the trail last month. Took minutes to restart then. My mucking with the idle speed last month couldn't have been helpful.

I'll hook up the vacuum gauge and check things. I haven't yet. (I did screw in the fuel mixture screws and backed them out 1.75 turns...I think that I mucked with them last month, too. Again, don't ask because I actually don't remember why.)

I've ordered some fuel line insulation and (as mentioned by jckkys I'll put in new fuel filters at the carb and between tanks/fuel pump. The latter can't hurt and are cheap.

I'd check timing but I don't have a pointer. I need to investigate that or simply hook up the vacuum and adjust the dizzy a bit one way or the other to see if there's much difference. No points--an Accel drop in unit.

 

[LSharpNM]

Great comment, thanks. What happened in the city probably wasn't...but maybe it was the issue at the trail last month. Took minutes to restart then. My mucking with the idle speed last month couldn't have been helpful.

I'll hook up the vacuum gauge and check things. I haven't yet. (I did screw in the fuel mixture screws and backed them out 1.75 turns...I think that I mucked with them last month, too. Again, don't ask because I actually don't remember why.)

I've ordered some fuel line insulation and (as mentioned by jckkys I'll put in new fuel filters at the carb and between tanks/fuel pump. The latter can't hurt and are cheap.

I'd check timing but I don't have a pointer. I need to investigate that or simply hook up the vacuum and adjust the dizzy a bit one way or the other to see if there's much difference. No points--an Accel drop in unit.

Careful, don't start just making adjustments without knowing what you are doing. Putting fuel filters between the pump and tank is a bad idea, and will only exacerbate and fuel delivery/vapor lock problems you are experiencing. There should be nothing other than a fuel strainer in the tank between a mechanical fuel pump and the fuel.

If you think you have vapor lock problems you need to get a quality low-pressure fuel pump (The carter rotary vane pumps are excellent and inexpensive, but they are noisy) and install it as close to the tank as possible, and as low as possible (preferably completely below the bottom of the tank). With an electric pump you will want a coarse, screen-type filter on the suction side and you can put a finer filter on the output side. With an electric fuel pump, you will probably want to run a fuel pressure regulator as well.

Regardless of whether you have a mechanical or electric fuel pump, you should use as much hard line as possible, avoid tight bends, and keep the fuel lines away from the exhaust and other sources of heat.

 

[70 sport WA]

Careful, don't start just making adjustments without knowing what you are doing. Putting fuel filters between the pump and tank is a bad idea, and will only exacerbate and fuel delivery/vapor lock problems you are experiencing. There should be nothing other than a fuel strainer in the tank between a mechanical fuel pump and the fuel.

Thank you for the response and my bad; I wrote, "new fuel filters at the carb and between tanks/fuel pump." That was just wrong. I have an existing fuel filter between the fuel pump and carb--before the filter at the carb. That comment didn't help, my apologies.

I have a hard line between the fuel pump and carb. I will put a heat sleeve around it this weekend.

 

[jw0747]

If you decide to install an electric fuel pump, keep its mounting location far away from all heat sources.

 

[nvrstuk]

... and mount that electric pump as close as possible to the tank. Electric pumps don't "suck" or create as much vacuum lift as mechanical pumps... same for EFI pumps...