Fuel leak question

[Eljaro]

My Webers have always leaked and are one of my main concerns right now.
The pump bypass does not help, I tried that out with the smallest one possible (0.35) and only got a bog when accelerating. The phenolic spacers helped some but did not totally do away with the problem.
When I stop the car the Webers are cool. After a while they get really hot from the engine heat. They get so hot that the fuel trapped in the conduit between the pump plunger and the pump jet starts boiling (you can hear it !) and drips out of the pump jet. And it can be quite an amount.
The float level has no effect on this because the pump circuit gets the gasoline from the bottom of the bowl as has been said here, and if you lower it too much you can get fuel starvation when taking fast and tight turns. This problem has nothing to do with the fuel level and fuel supply by means of a bypass, lowering fuel pressure or letting the fuel bowls empty some before shutdown.
The only way to get around this problem is to get the hot air out of the upper engine bay.
Maybe a flexible duct drawing air between the Webers and with an exhaust fan infront of the engine or behind it or a 12 Volt computer fan behind each side vent in the engine compartment and have them come on when you shut down the engine. This way you remove the hot air that is trapped under the hood.
The aluminum Webers heat up fast with the hot air trapped under the hood and slowly exiting through the scoop.
This can be done elegantly with a relay and a timing circuit so the fans come on automatically and shut off after 10 minutes.
What I do now and what really helps is to open the hood when I stop and the heat gets out fast and does not soak up the Webers. No dripping this way.

[carmine]

My starting instructions on page 1 works every time. Never open my hood to cool and i can start instantly with stinking hot and heat sinked engine.
That tip given to me by a good friend in the arrow space industry

[priobe]

Still looking for a solution to resolve the leaking problem, I decided to open the carb.

Well it seems as though the fuel level does have something to do with the pump jets. By looking at the pump piston where it receives its fuel there is a hole at the fuel level. This hole is either used to feed or bleed back if the level gets too high.

Either way if the fuel in the bowl expands it can then fill over to the backside of the piston, which will then seep past the piston.

The inclinded intake also has and effect because the hole is positioned toward the higher level of the fuel.

Adjusting a lower level on the float will only effect the timing engagement of the main jet. I will begin test how low the level can be with running into a lean spot.

Any feed back is welcomed


On a side note, on the right side there is a chamber that is not used for anything. By opening a hole at the bottom will increase the volume that the chamber can hold. The added fuel might be enough to keep the fuel cold to not heat up to the point of boiling and creating pressure.

[priobe]

Here is the top view

[priobe]

ok,

After receiving a goodnights sleep, I was able to come up with an idea. As Eljaro mentioned that the phoenlic spacers did help alittle with the fuel boiling.

Eljaro,
I am curious to hear how much of a difference did the spacers make?

If the spacers made a significate difference then this just might work. Here we go...


Instead of using spacers or even with the aid of spacers creating a shield that mounts to the 4 mounting bolts of the carb. This shield will be elevated just underneath the carb body below the cam, shaft, spring assembly. My thought is that the fuel must be getting the heat from the intake , which in turn passes it to the carb body.

I will try to provide a diagram for better explaination.

Any thoughts ? Comments?

[carmine]

Priobe: Been there, done that.

The alluminum heat shields you discribed i made last year. Helps about 10%.

When the hot engine is shut down the main bulk of the heat is actually traveling from the heads through the intake runners of the head and up through the intake runners of the intake and into the throttle bores of the carbs and then is trapped there buy a closed throttle plate. this traped heat in the ruunners and throttle bores then heat soakes into the carb body.

[priobe]

Carmine,

Well scratch that idea. Anyway, I think I will try to slip a piece of heat barrier material below the carb body between the intake just to see the results.

If that is the case then it will have to be adjustment of the fuel level. If what you are saying is correct, then all setup should recieve the pump jet problem. Is this limited to only the BBor do the SB have the same problem.

Rick do you have the same problem.



What do you think about added fuel in the bowl to raise the boiling point, ie increasing the volume of fuel?

[priobe]

Carmine,

Have you tried keeping the throttle plates opened to see if the boiling over still exist.

If your theory is correct the throttle plates will only contain the heat when closed. By keeping them open should release the heat.

[carmine]

Priobe : I have been wanting to prove that theory out for a while but everytime i have thought of it i would forget when i got back from my run.
This forgetting part of my life seems to be getting worse with age.

Its cold up here in Canada right now and our toys are in storage.

This gives us lots of time to think about problems but not be able to do anything about them.

I would really appreciate you trying that test out and please let us know what results.

Regards Carmine.

[priobe]

Not a problem.

The follow ing test I will perform are:

1. heat barrier ( 1500 degree cloth) between Carb and intake
2. Keep throttle plates open after shutdown
3. lowering fuel level to verify at what adjust boiling stops.

[jimf]

From what I read in this thread, it seems that a lot of the heat transfer is via hot air coming back up from the cylinder heads through the intake ports, through the manifold, coming to a stop at the throttle plates in the carbs......I wonder what the effect would be if, after the engine was shut off, one was to hold the throttle plates open and allow the air to pass through the carbs untill the engine cooled. Maybe the venting of some of the hot air would be enough to stop the heat transfer to the carbs and boiling the fuel. This should be relatively simple to do if it would change the situation. Has anyone tried this???

[priobe]

jimf,

This is one of the test I will perform that was mentioned in the previous post.

Do you too have this issue with 48 IDA on a BB w/ 10 angled intake?

[jimf]

Dooo...guess I should read a bit more carefully....your right it has been suggested....my set up is not yet installed and when it is it will be flat not angled. I have been glued to any thread that is about 48 IDA's.....learning as much as possible before installation. One thing I see over and over again is the heat problem, so I am most interested in its solution.

[priobe]

okhere it goes...

I trired the heat shield underneather the carb - does not work
I tried opening the throttle plates - does not work

I also noticed that if you watch it from shutdown it take approximatly 3 min. to strat to drip and it begins from the progression holdes.

What I did notice that made a huge difference was changing my bypass to 55.

I also played with my jetting to work with the 55 bypass (you can do that you know) and it made a 90 percent increase for the better.

I also used a F-11 emulsion tube and it runs beautiful from 2500 - up

My idle circuit is almost there it is definitly drivable and enjoyable but get a pop eveyone and awhile.

i also noticed that you should not even think about trying to tune for 14.7 it is too lean. At least in my situation.

if you can get your idle at 15.1 then off idle to 13.0 - 13.5 and level off at 13.8 cruise you will love these webers. I am able to get my cruise at 14.0 but it seems it is alittle to lean. When I see it at 13.5-13.8 it is loving it.

I know I will need to lower my bypass to about .45 or 50 and hopefully it will take care of the slight gap on acceleration.

Again, this is my situation my tuning and this is what works for me.

I will hopefully take the car out on a long drive Saturaday.

But back to the drawing board from the leak, but at least it is only a slight drop now.

[carmine]

Priobe : thanks for the results.
What venturi size are you running?

[priobe]

I am running a 40 mm venturi.

However, as many have mention (Inglese and others) by moving up to a 42 mm you will only have to adjust your mains. I think differently I think more than likely you will have to rejet your mains stack as well as idle slightly, as Ejaro is experiencing.

My ultimate goal is to go to 42's them remove them all together ( no choke) just to to see what will happen.

Another item I dont understand is why would one increase the 48 to 51 to only put a choke back in it. You will then reduce the 51 back to what ever the choke is.

An I know the throttle body is not beveld like the choke but the 37 mm choke that many were running were probably more resticted than what ever turbulance the no choke would deliver.

Just my .02

[carmine]

Priobe;
The reason you would open to 51 is so you can put in a slightly large venturi and still have a tapering bell shape bellow the choke diameter.
This taper allows the signal strength to increase on the augsillery venturi as the air speed increases
With a large venturi and no taper at the bottom half of that venturi the car would have a tendancy to fall flat on its face when the mains are being asked to come on and get stronger.
A smaller air corrector would help also when venturi is larger with less taper.

[jimf]

Priobe; Since holding the throttle plates open and allowing the hot air out did not seem to work, it sounds to me like the heat is soaking into the carbs via the physical connection with the manifold and the manifold to the heads and block. The alterations you have made are partially compensating for the problem but the problem still remains and that is the heat soak. So how can the heat soak be eliminated or stopped. I think that Eljaro is on to the answere with getting the heat out of the engine. If a person had one of the electric water pumps and electric rad fans, one could set it up so that after shut down the water pump kept pumping and the rad fan could be set to reverse and blow out the rad untill a preset temperature or time period was reached and then both of them shut off. Even if having a reversable rad fan is not possible then having a regular one continuing to run after shut down along with a electric water pump should make quite a difference to the amount of heat that gets removed from the engine compartment.

[priobe]

Jimf,

I dont think the computer fans will make much of a difference. But that is just my thoughts.

If the heat is building up and heat soaking the carb then why doesnt it happen to the 289 motors and 302/ 351?

I am not saying that what I have done will solve the problem but it seems to work in my case and my jetting has never been better.

Its funny because unless you listen for a couple of mintues, you would not know it is even happening in my motor. It happens so slight that when it leaks the heat from the throttle plates evaporate the fuel so it never sits on the plate.

I am curious if someone with a SB motor would listen to the carbs after shutdown to see if this happens to their motor as well.

I also have to mention that I did adjust my float level. Many might not agree with the way I did it but again it works for me.

I measured the tang in relation to the float bracket and measured the tag at its highest point. When the carbs would leak the measurement is .197. I then readjusted the tang to .220.
When I made this change and started playing with my elmusion tubes the motor actually ran better. Keeping my mixture at cruise at 13.8 target was what the motor wanted.

I did not concern myself with power because that is easy to tune.

I would like to to hear and see more people submit there A/F reading rather than giving general terms as runs good. I think we ( weber community) have made great success with the help of CC, and the knowledge that Ejaro has provide.

I think we have reached a point with these webers that we need to know what is happen in the cumbustion chamber and what the motor wants, rather than just giving it jets.

The wideband is just a tool, and with out knowing what the A/F should be it is a useless tool. Many article state that A/F ratio should be between 14.7 to 12.5 but I have noticed that the poping thru the carb happens at 14.7 and 15.0.

[Rick Parker]

The wideband is just a tool, and with out knowing what the A/F should be it is a useless tool. Many article state that A/F ratio should be between 14.7 to 12.5 but I have noticed that the poping thru the carb happens at 14.7 and 15.0.

14.7:1 -15.0:1 is very lean and will cause popping out of the carbs. Look at some of the dyno charts that are here and on other sites. They will often indicate the A/F ratios at respective RPMS. You are on the right track aiming for 13.8:1.