48 IDA heat soak battle
 

hello to all
I will first say that I do not have a Cobra or GT40. But I am hoping some here may be able to shed some light on this issue, as I have been fighting it for a good 9 years plus, and seem to be "on my own" in the small circle of guys with similar engine/modifications.
So here we go. The engine is an air cooled Volkswagen type 1, 2165cc, running 91 octane, two Weber 48IDA, 40mm venturis, 60F10 x 115 air holders, F4 tubes, 165 main, 180 air, closed pump jet. Fuel pressure is 3.00psi metered by Malpassi Filter King regulator. Carburetors are mounted about seven inches above intake flange on head on cast aluminum manifolds. I have ~4mm thick fiber gaskets between Webers and manifolds. If we need to discuss other specifics in the engine, I'd be happy to.
The floats are set to 5.5mm above carb body/24.2mm drop to needle-valve tongue. Needle valves are 2.00.

The issue that came up about 9 years ago- out of nowhere I might add, is that after running the car sufficiently to warm intakes and get oil to 150-170F or higher, if I shut the car off and walk away for 15 min or so, once I go to restart it and set off, it runs as if the mixture screws are closed or that somebody swapped 50 idle jets in for my 60's. It will barely idle, and if I immediately drive off, it will buck and nosedive until I feel it pick up main circuit, at which point it will come on. After 15 minutes of normal driving, this goes away and the car will run strong again. It acts as if the float levels are much too low (when I first started setting 48's up on VW's in the early 1990's I learned through my mistakes what too low float levels cause).
An AFX AFR sensor is confirming it is very very lean when this happens. Asthe car struggles to idle, I am seeing 15.00+, and when throttle is crept open, it will spike 16.00.
I have read a lot about Weber fuel boiling here and on some of the Mazda RX7 and Porsche sites. It seems the common issue is the fuel will boil over during heat soak and dribble through nozzle in aux. venturi, (or acclerator pump nozzles) into intake throat, flooding the engine. I don't think, based on lean symptoms, I am experiencing this. But maybe I am so frustrated I am being blinded and not seeing the big picture. Again, no help from the VW world. Some have said they do not drive their cars as much as I do so they are not experiencing it. From what I have read here, it seems many of you have a better grasp on the Weber 48IDA, the fuel boil issue and remedying it.
Again, I am sorry for bringing in a problem from a non-Cobra/GT40 world, I I understand if this post is inappropriate.
I'm just looking for some help

Thanks and happy hoildays

What does your fuel feed line look like. How is it routed? What is your timing set at?

The fuel feed line is 8mm, pump is Carter rotary under VW fuel tank (front of car). So feed line is "under pressure" (I am assuming somewhere between 4.5 and 6psi), and it is not routed near exhaust or outflow of hot cooling air coming off heads/cylinders. It is routed in channel of body just above RR shock mount, about 12-15" away from closest header pipe.
Timing is 14 deg initital and 32 deg total.

Thanks

I don't know about vw but I run 2.5-3 psi at 38 deg at 2200 rpm,have you talked with jaycees they do bug stuff and are in the oc .

With an air cooled engine, it is entirely possible that the heat soak is greater than a water cooled engine especially with the long aluminum manifolds. However I would look initially at the closed pump jet as it does not give the fuel anywhere to go in the accelerator pump circuit and it may be dribbling out of the Accelerator Pump Squirters. Oxygenated (winter) fuels will also be more likely to percolate in the Float Bowls after shut down and drip out of the Auxilliary Venturies. Minor lowering of the Floats may help.

I'm going to take a ride down and go talk to Jack. I know they recently started making isolators to go between manifold and 48 base.
Most hot rodded VW on street don't like much more than 34-35 full advance, depending on chamber design/shape.
Thanks

I run them on my carbs from Jaycees, Like Rick suggested I lowered my float a little, bend the tab on the float .

Have you tried to run w/o the engine compartment lid? I remember some if the hot rodded VW engines I was around as a kid would run pretty hot & the compartment is pretty small. If it's an issue with heat, maybe more venting is needed?

Also drop psi...............;)

Over the lasts few years the fuel distillery company's have been reformulating the fuels to have lower temp boiling point.
Because of carburated engines being thing of past and fuel injection not effected by lowered fuel temp boiling point.
I guess there must be cost savings for fuel company's in this new formulation

Because of this today's formulated fuels tend to also be less dence meaning that your float levels tend to be higher because floats sink into fuel more meaning fuel levels need to be adjusted lower to make up for this less dence fuel.

Please excuse triple posting from my not to smart phone

Over the lasts few years the fuel distillery company's have been reformulating the fuels to have lower temp boiling point.
Because of carburated engines being thing of past and fuel injection not effected by lowered fuel temp boiling point.
I guess there must be cost savings for fuel company's in this new formulation

Because of this today's formulated fuels tend to also be less dence meaning that your float levels tend to be higher because floats sink into fuel more meaning fuel levels need to be adjusted lower to make up for this less dence fuel.

Over the lasts few years the fuel distillery company's have been reformulating the fuels to have lower temp boiling point.
Because of carburated engines being thing of past and fuel injection not effected by lowered fuel temp boiling point.
I guess there must be cost savings for fuel company's in this new formulation

Because of this today's formulated fuels tend to also be less dence meaning that your float levels tend to be higher because floats sink into fuel more meaning fuel levels need to be adjusted lower to make up for this less dence fuel.

Hey guys,
took a ride down to Santa Ana and saw Jack at Jaycee. Bought a set of his isolators and they're on. We'll see if they help. Thanks for everybody's tips and thoughts. I did lower fuel pressure to 2.5 as well.
I did run the car around for about 20 min, but ran out of time to keep testing. But carbs are somewhat cooler to touch afterwards.

Thanks again

Another option to consider is to switch the fuel pump. You can then shut the fuel off 1/2 mile or so from your destination, or just let it idle the bowls dry. Of course, you'll need to give the pump time to refill the bowls when you go to start itback up again.

Tim

Thanks Tim. As my car is set up now, the MSD CD box and the fuel pump are both "switched" (thru Bosch 40amp relay) through same toggle on dash, separate from ignition starting switch. (I did this for safety as my car has locking steering column- if I ever need to cut fuel/ignition, but keep steering....I can). But as it's set up now, if I kill the pump, I kill the MSD box too.
By the way, I want to compliment your write up on 48 IDA Webers on your website. I have spent the evening tonight finishing up what I couldn't read at work yesterday, then I re-read the whole thing. It is well written and probably the best explanation of what it takes to tune a 48 I've read, anywhere. I learned what I know from a lot of trial and error and from my grumpy ex boss, but there were a lot of holes that needed to be filled in. I've had 48's on my car since 1991 on various displacements and all kinds of state of tune and only in the last 18 months or so, have begun to unravel more than "just getting them close" (finally- emulsion tubes started to make some sense to me in 2012). Your write up, in the hour or so I've read it, clarified much more than my old boss, or any book has to date. Nice, nice work.

Rick mentioned it and I confirm it: a closed bypass valve in the pump circuit will cause dumped fuel into the carbs when they soak up heat after engine is turned off. Fuel expands and willgo out the only opening in the circuit: the pump jet.
Go to a .35 pump bypass and make your idle jet larger if a bog happens when accelerating.

I have to agree with Rick and Eljaro regarding the need to check the pump bypass or drain jet. When I first installed 48 IDA's on my car, I also had a post-shutdown flooding problem. The 48 IDA Webers were originally delivered with a zero (or closed) pump drain jet and several minutes after engine shutdown, I could hear and see fuel dripping out of the accelerator pump nozzle into the throat of the carbs. This occurred when the temperature of the carb body exceeded 140 F several minutes after engine shutdown while using available pump gas. I first tried adding an insulator below each carb but finally eliminated the problem by going to a 35 pump drain jet.

John

One of the things that is often overlooked and not mentioned is that the carb on an FE are canted towards the centerline of the engine. Those with Small Blocks don't have to contend with this. By design the carbs ARE intended to be installed "Straight Up". The canting affects the check ball in the bypass or "Exhaust" check valve in the bottom of the float bowl. Sometimes I have heard it said that lowering the fuel level a minor amount helps alleviate the dripping.

What Tim said. It will be a little effort to change from your current setup but it works.

The pump bypass valve in any Weber operates in same manner.

The ball "should" be unseated at rest, since it has to be raised from pump circuit pressure to seat.

http://www.poustusa.com/weber_carb_pages_pix/weberd.gif

That's why I run steel not nylon bypass valves.

Plastic balls seat faster and give a more responsive pump circuit, but they also are more prone to the above complaint.