Fuel boiling, smelling gas... what to try first?

[TLC Whee]

Can anyone help me with this? I have a weber carb and just had the fuel line and filter replaced. After driving for a bit then turning the cruiser off, I can hear bubbling and boiling sounds right around the carb and can smell gas fumes. I don't see any gas dripping, though.

I did some searching here and see that this is a pretty common occurrence for the FJ40s. It seems that there are a lot of "solutions" available as well. I'm just curious what people think are the best to tackle/try first.

The mechanic was working on the carb because it was loose and in the process replaced the lines on both sides of the fuel filter. The old lines were rubber, but really stiff and starting to degrade. The new lines are rubber and seem softer.

So... Do I:
- replace the lines with metal lines?
- add a heat shield/wrap?
- get a carb fan? (i don't know if I have one... anyone have a pic so I know what I'm looking for? (I have a '76, so apparently it may or may not have had one)
- check the fuel pump (er... how? check it for what?)
- check the return line from the carb (again... how? for what?)
- something else?

Here's a picture of the setup

I think it's a vapor lock issue because I have all the standard symptoms (from what I've read): strong turn-over but no start when hot after sitting for a little bit, starts right up when cool, smell vapors & hear bubbling/boiling when off after running for a while.

Anyway, I'm excited as this will be the first actual work on this rig I will have done (other than taking all the seats out and cleaning it really well, which doesn't really count). Plus, my wife will really appreciate not smelling gas anymore. But I'm also a little nervous because I'm dealing with fuel issues and I don't want to royally screw up.

Thanks!

-Danimal

 

[desertpat]

What to do

My vapor lock problem is solved. I suggest that you:
Find another mechanic.
Replace the hose with steel and insulate the line especially over the head / manifold section - a heat shield there would also help.
Relocate the filter upstream and down low so it doesn't collect heat.
Good luck and thanks.

 

[bsevans]

You might want to reinstall the heat insulator between the carb and the intake manifold.

 

[1973Guppie]

warm the truck up really nicely, shut it off, walk the fuel line down from the carb to the tank and feel where it is hot and needs some shielding. Don't burn yourself, some gloves here will help. Check summitracing.com for a bunch of products under "heat", they have sleeves etc for lines that should help a bunch. I agree with the other poster on the filter, move that thing way back more towards the tank and a cooler spot, it is probably sucking heat.

Noah

 

[TLC Whee]

Do you guys think it's more likely the fuel filter is what's getting too hot vs. the rubber lines? I.e. if I just moved the fuel filter but kept the lines as-is? Or is it better to just do both at the same time: move filter & switch to steel?

I like the idea of figuring where the heat is "pooling". I'll try that, thanks Guppie!

One other thing: I've heard some people who had this problem and it was the fuel pump. What sorts of things would I check for with that? Just excessively hot pump? Leaks of some kind? Something else?

As for the mechanic, I'm frankly surprised. He's the guy everyone recommends for toyotas. I really don't want to doubt him as I figure I'll probably need to use him more. It's possible that he wasn't really able to replicate the problem and I didn't describe it well. Hrm.

One of the things I've learned in life is: ya gotta trust your mechanic or your screwed (figuratively and even sometimes literally). *sigh*

Oh, and thank you all! I'll get this licked soon! (and have a happy wife and garaged TLC all in one. Wheee!!!)

-Danimal

 

[brian]

plus one on moving the filter. that is a huge heat sink just sitting above the exhaust manifold.

i also have rubber line from about the same point as you, no issues with vapour lock.

the thing about rubber lines....if i have this righ....they do not collect as much heat heat what a hrad line would. what happens with the rubber lines is, they expand when the fuel gets hot, giving it room to boil, where as the hard lines will not expand making it much harder for the fuel to boil.

 

[Brian in Oregon]

If you smell fuel, it's not the fuel line getting too hot, it's the fuel in the fuel bowl(s) boiling and/or expanding to the point where they dump out onto the throttle shafts. If the latter, the fuel can capillary out the base of the carb through the throttle shaft tunnels and evaporate, or in severe cases, actually puddle on V-8 manifolds. On an I-6 thye might drip onto the hot exhaust manifold. Not good.

You can do a few things to resolve this.

First, put an insulating spacer under the carb. You can readily get various thickness 4-bbl spacers. A 2-bbl spacer is more difficult to find. Don't use the multi-plate insulators. They run the very real risk of cracking and/or warping the baseplate.

Run a heat shield under the carb. This is a very wide, long and thin plate. A secondary benefit is that fuel can drip onto it and evaporate, but hopefully that will be cured by other means. If you have to, you can make a very large heat shield that will parallel the valve cover and completely cover the intake and exhaust manifold area. Fugly, but they work. Thin aluminum plate works. Use a carb gasket for your base pattern and think of it like a giant thin carb spacer.

Lower the fuel level in the fuel bowls a little bit at a time. Do not set them so they 'weep' out the sight plug. Put the level below the sight plug. This helps with heat expansion of the fuel, followed by the fuel exiting into the main bore(s) and onto the throttle plates. This really helps. And it helps for off roading anyway.

Make sure you have adequate airflow around the carb when at idle. I discovered the two large CFM pusher fans I had on my pickup, while adequate for cooling, did not move enough air in the engine compartment. The air stagnated around the carb, causing boiling at low speeds and idle. I installed a regular flex fan on the engine and this fixed the airflow problem. The electric fans are now auxilliary fans. You might not have this issue, but it's worth mentioning in case V-8 owners read this.

It a good idea to insulate the fuel line and not run it over the exhaust manifold area. Run it to the side, away from the engine, and then back at the front, if possible. You can slip larger diameter fuel line over steel line to help insulate it. And you can get small diameter foam pipe insulation to put over rubber fuel line.

Open paper air filter elements are the worst offenders for gasoline vapor fumes. The fumes go right through the element and stink. An enclosed air cleaner is better. Plus if you run one with a snout, you can run a hose from it to a location in the front of the engine compartment to pick up cold air, which helps with power. (For every 10 degree reduction between engine compartment air and outside air, you pick up a 1% increase in horsepower. If your engine compartment is, say, 160 degrees (easy) and it's 80 degrees out, that's an 80 degree difference. You've just picked up 80 degrees divided by 10 degrees = 8 times 1% = a total of 8% more horsepower. You're providing a denser air charge. This is a well known trick among racers and was quite provable when we'd test it by checking ET with and without functioning cold air intake as the evening cooled down. It also has a cooling effect on the carb while driving, making it less apt to boil fuel (but not when turned off).

If you are running a 4-bbl, make sure the secondary throttle plates are SLIGHTLY open. If they are fully closed, you will not pull any fuel from the secondary fuel bowl. Unless you are constantly opening the secondaries (and with gas prices not everyone is a leadfoot), the fuel stagnates. It also heats up and can boil even when driving. This leads to sudden surges and stumbles as the air/fuel mixture becomes momentarily too rich. And it can lead to gummed up secondary fuel bowls. Sometimes the secondary throttle shafts stick closed, and performance falls on its face and you scratch your head and wonder why. (Obviously this refers to vacuum secondary carbs, not double pumpers for sticking, but the rest applies to both.)

For vapor locking, check the path of the entire fuel system. I had severe vapor locking on my 454 in my pickup. I put a fuel gauge in the line just ahead of the carb, along with a clear fuel filter to see what was happening. Five pounds fuel pressure, but no fuel. Classic vapor lock. Turns out that the factory routing of the fuel line was adequate for the original 350 (and probably those trucks with the 396), but my 454 has giant truck exhaust manifolds. They nearly touch the frame. And the fuel line runs along the inside of the frame, right under the lip edge. So for the entire length of the manifold, the fuel line was only about one inch away from it. Basically it was in an oven at hundreds of degrees. This is probably not an issue in your case, but with a V-8 Cruiser, it's possible for fuel lines to parallel headers, exhaust pipes, etc. But ANY heat hot spot can be an issue, so trace the fuel line anyway.

 

[Degnol]

An insulator like this one here......Part #2


GL

Ed

 

[TLC Whee]

An insulator like this one here......Part #2

Ed, is that a generic insulator or would it be specific to the carb I have (I'm assuming the latter).

-Danimal

 

[TLC Whee]

Pictures?

Brian,

THANK YOU! for all this detail. I'll need to read through it a few times to really grasp all the options. One thing seems clear to me: Among other options (of which there are clearly quite a few), I should consider rerouting the fuel line to the carb. I have two follow-up questions about that:

1) Can anyone post some pics of how they've rerouted the lines? I'd love some visuals to see what others have done. The fuel line attaches to the carb at what looks like a junction with an idential twin on the other side. If I route the line over near the wheel well, could it come into the carb on that other junction?

2) The other smaller line, which I'm assuming is the fuel return line (or whatever it's called)... should that be rerouted to? And if so, right along the fuel line or a different path?

Thanks,

-Danimal

 

[Degnol]

Ed, is that a generic insulator or would it be specific to the carb I have (I'm assuming the latter).

-Danimal

I believe you can fit that insulator to any of the '70> 2bbl carbs. You might have to trim the heat shield a little if it interferes with your linkage. I'm sure you can find a used one somewhere. I sold a real nice one for like 10-15.

Ed

 

[Brian in Oregon]

Well, here's what I'd do if that was my setup....

Looks like you are running a mechanical fuel pump. So you need to get to it on the other side of the engine...

If possible, and most are set up that way, I'd switch sides on the inlet fuel bowl. Then run a fuel hose to the LH fender. At the fender you could run a steel line back to the firewall, across the firewall, then down alongside the RH fender. Or run segements of steel lines joined by fuel hose, whichever is easier for you. You could swap the fuel bowl out if need be for a fuel bowl with the inlet on the RH side. A rear fuel bowl off a 4-bbl carb would work in that position, for example.

The small line is not a fuel return line. It's for your vacuum advance on your distributer. Leave it alone.

EDIT: I put on my reading glasses. I thought that was a Holley 2-bbl, but it obviously isn't. Still, see if the fuel bowl inlet will swap over.

 

[TLC Whee]

Next step: insulator

Well, I finally got around to moving the fuel intake line to the carb. Apparently that wasn't it. The line now runs pretty cool but I can still smell gas vapors. I should have figured it wasn't the line, but it was an easy step to rule out.

So the next step, I suppose, is a heat shield / insulator.

Is that something specific to the type of carb?

Oh and any leads on a cheap insulator for my Weber carb setup (picture at the top of this thread) would be much appreciated!

Thanks, all!

-Danimal

 

[grant5127]

By the looks of the exhaust manifold.... the heat riser might be stuck in the closed position..... can cause excessive temps on the intake and carb...

 

[Fuzzy Logic]

X2 on the heat-riser thing, the heat can even cause cracks in the intake under the carb time to up-grade to a header Cruise-on, Fuzz

 

[cruiserjunktion]

I would move the filter and reroute the fuel line.

Check out the areas circled in yellow.

Your fuel line has direct contact with the valve cover.

This will cause vapor lock.

My filter is just before the fuel pump.

 

[TLC Whee]

By the looks of the exhaust manifold.... the heat riser might be stuck in the closed position..... can cause excessive temps on the intake and carb...

Grant,

Can you help me understand how I'd diagnose this? I can take some closer-up pictures, but I'm not really sure what I need to look for. What exactly is the heat riser? (there I go... showing my uber-newbie-ness. *grin*)

Ya know, the previous owner never said anything about fuel vapors, which could mean that he just didn't want to say, or that this is a recent development. If the latter, then perhaps there's an easy (or relatively easy) fix.

BTW, it's definitely not fuel boiling in the fuel line. Since I rerouted that, it stays nearly cool to the touch even after running for a while. The boiling/vapor is coming from the carb most certainly, or at least really really near it. hehe.

Thanks everyone! I'll lick this eventually!

-Danimal

 

[snailwagon]

Move the filter before the fuel pump. Unrelated to vapor lock much, but it you knock chunks loose in your gas tank, they can kill your fuel pump. I still have very mild vapor lock when it is over 110F outside. When the vapor lock was bad, I had a bamboozled heat riser. Every 10 seconds or so I could see the fuel bubble inside the carb. I've also insulated my fuel lines since then. Look underneath the carb and down to the exhaust manifold. You will see a little valve looking thing there. This is the outside of your heat riser valve, It should move when hot.

Figure out where that smell is from. Is your gas tank pressurized when you remove the cap?

 

[grant5127]

Grant,

Can you help me understand how I'd diagnose this? I can take some closer-up pictures, but I'm not really sure what I need to look for. What exactly is the heat riser? (there I go... showing my uber-newbie-ness. *grin*)

Ya know, the previous owner never said anything about fuel vapors, which could mean that he just didn't want to say, or that this is a recent development. If the latter, then perhaps there's an easy (or relatively easy) fix.

BTW, it's definitely not fuel boiling in the fuel line. Since I rerouted that, it stays nearly cool to the touch even after running for a while. The boiling/vapor is coming from the carb most certainly, or at least really really near it. hehe.

Thanks everyone! I'll lick this eventually!

-Danimal

# 62 in the pic...it's been known to stick in the closed position.. sometimes one can grab the end of shaft # 63 with vise grips and check if it'll rotate.. or deflector plate # 12 will break-off and fall down on # 62 causing problems also.....a disassemble may be required for inspection......

 

[Liam]

i have the same set up, but the only time it seems to be not getting gas is when it sits for a day....
It takes a lot of pumping and cranking in order to turn it over...

Is this the same issue??