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GT40 Tech - Fueling, Electrics, & Engine Cooling Petrol, Electrons, & Water

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Old 3rd April 2017, 02:51 PM   #1
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48 IDA Weber fueling issue

I previously had a random backfire issue with my car that disappeared. Today it returned with a vengeance, and it appears to be due to "overfueling" ? as shown in video 1.

After switching the engine off there was a large pool of fuel sitting on top of both butterflies as shown in video 2.

With my IVA test rapidly approaching, any advice on how I can resolve this greatly appreciated.

010 - YouTube

011 - YouTube
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Old 3rd April 2017, 04:57 PM   #2
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Re: 48 IDA Weber fueling issue

Fuel pressure should be low ~ 2 or 3 lb max.
There is fuel dribbling from accelerator pump nozzles at idle, that should not be occuring...possible pressure, float level to high, missing parts in pump circuit, debris in that circuit.
To prevent residual fuel pressure flow after shut down you should have a restricted by-pass in fuel line pressure side back to tank to kill fuel pressure immediately on shut down
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Old 4th April 2017, 03:48 AM   #3
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Re: 48 IDA Weber fueling issue

....or

Have a fuel pressure gauge visible from the drivers seat and run the engine with the pumps off till the pressure has dropped to zero.

Brian.
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Old 4th April 2017, 08:50 AM   #4
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Re: 48 IDA Weber fueling issue

Quote:
Originally Posted by jac mac View Post
Fuel pressure should be low ~ 2 or 3 lb max.
There is fuel dribbling from accelerator pump nozzles at idle, that should not be occuring...possible pressure, float level to high, missing parts in pump circuit, debris in that circuit.
To prevent residual fuel pressure flow after shut down you should have a restricted by-pass in fuel line pressure side back to tank to kill fuel pressure immediately on shut down
I have Webers on my Pantera race car and I would agree with Jac on the fuel pressure. Any more than 3.5 psi and mine will start 'dribbling'.

I fought for months trying to keep a consistent pressure. It would vary for seemingly no reason at all.
I went through 4 of the Holley regulators. They all were the same.
Although I kept getting assured by 'those who should know' that the Holley regulators were the right thing to use, that regulator did NOT work for me.

What solved my problem was using a Aeromotive fuel pressure regulator
This one: Aeromotive A1000 Carbureted Bypass Fuel Pressure Regulators 13224 - Free Shipping on Orders Over $99 at Summit Racing
And then adding a return line to the fuel tank.
My fuel pressure is now rock solid and I've had no more issues.

FWIW,
Kirby
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Old 4th April 2017, 02:00 PM   #5
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Re: 48 IDA Weber fueling issue

I'm not a Weber expert by any means, but what eliminated that problem for me was a combination of the following:

Fuel pressure as mentioned above,
Using a return line instead of a dead head,
Making sure the floats were adjusted properly,
Phenolic spacers to minimize heat soak into the carbs, and
Turning off the fuel pump 30 seconds before shutting off the engine.

Good luck with your IVA test. If you can't do all of the above, at least do the last one, even if you have to run the carbs dry. That will fix it for sure.
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Old 4th April 2017, 03:30 PM   #6
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Re: 48 IDA Weber fueling issue

I had exactly the same issues. It turned out to be a mix of different things. First I found that the timing advance and retard was sticking on the MSD distributor. I could have cleaned it but it was easier in my case to just switch it. This stopped the backfire that had been appearing and disappearing.

Next the fuel pressure was too high. I had a fuel pressure gauge in line but it would stop working with the heat of the engine. I found one of these to work much better (no oil inside):

Hot Rod Chrome White Face 1.5" Fuel Pressure Gauge 0-15 PSI Amazon.com: Hot Rod Chrome White Face 1.5" Fuel Pressure Gauge 0-15 PSI: Automotive

I found that the engine would stall when it got hot and the fans would turn on in traffic. What was actually happening was the fuel pressure was too high and it was over coming the needle valves and flooding the engine.

I switched the pressure regulators for some new malpassi regulators. Once I took the old ones apart I realized that they had come undone inside and probably were fine if I had put them back together right! With the new regulators on the pressure was a perfect 3psi and no more stalling. The timing properly set with the advance and retard working sorted the backfire and now everything is running reeeeeally sweet! I also found the idle mix can be adjusted with the fuel pressure correct. The other key point is the float levels. I knew these were set right as I had sent the carbs away to be rebuilt.

I am by no means an expert, but these symptoms are exactly the problems I had!

Good luck,

Karl
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Old 4th April 2017, 03:38 PM   #7
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Re: 48 IDA Weber fueling issue

This may be of use: Cobra/GT40 options14
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Old 4th April 2017, 10:48 PM   #8
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Re: 48 IDA Weber fueling issue

Here's a really good article on system design.

How To Build The Proper Fuel System For Carbureted Motors - Chevy High Performance Magazine

However, I would agree the right pressure for your webers is in the 3-5psi range.
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Old 4th April 2017, 10:59 PM   #9
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Re: 48 IDA Weber fueling issue

Hi Cliff, I found that 5 could be too much. I had 4.5 and 6 and had issues, but 3 was perfect. Just my experience with Webers. Redline suggest 2.5 to 3

IMPORTANT THINGS TO KNOW

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Old 5th April 2017, 03:43 AM   #10
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Re: 48 IDA Weber fueling issue

Hi,

Thanks for all the replies. I have a redline set up with a pressure gauge, think I set it around 3-4 psi although I suspect the gauge is not that accurate.

Think I will initially lower the pressure to see if that makes any difference, just need to get it through the test before going through all the points raised.
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Old 19th May 2017, 02:07 PM   #11
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Re: 48 IDA Weber fueling issue

Good thread!

Found this Automotive fuel pressure regulator, which seems tailored to Webers:

Low Pressure Carbureted Regulator – Aeromotive, Inc

Low Pressure Carbureted Regulator
Our new Ultra Low-Pressure Regulator features a completely unique valve, designed to support high flow at a very low pressure. Intended for multiple smaller carburetors, such as the classic Weber, Mikuni, Dellorto, and the Solex.
-Adjustable from 2-5 PSI
-Ideal for small carburetors
-(1) ORB-06 inlet port and (2) ORB-06 outlet ports
-1/8″ NPT gauge port
-Clear anodized finish for a subtle look
#13222

Wonder if anyone has any experience with it??

Chuck
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Old 19th May 2017, 03:41 PM   #12
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Re: 48 IDA Weber fueling issue

Quote:
Originally Posted by CESLAW View Post
Good thread!

Found this Automotive fuel pressure regulator, which seems tailored to Webers:

Low Pressure Carbureted Regulator – Aeromotive, Inc

Low Pressure Carbureted Regulator
Our new Ultra Low-Pressure Regulator features a completely unique valve, designed to support high flow at a very low pressure. Intended for multiple smaller carburetors, such as the classic Weber, Mikuni, Dellorto, and the Solex.
-Adjustable from 2-5 PSI
-Ideal for small carburetors
-(1) ORB-06 inlet port and (2) ORB-06 outlet ports
-1/8″ NPT gauge port
-Clear anodized finish for a subtle look
#13222

Wonder if anyone has any experience with it??

Chuck
Very interesting Chuck, one of the criticisms the tuner I took the car to was that my pressure regulator went from a 1/8th NPT regulator outlet to a dash six fuel pipe. He felt in no uncertain terms the 1/8 npt outlet would restrict the flow, although I know a number of people running the same set up.

It appears your pressure gauge would be more than acceptable as it has a dash 6 outlet. Have to see how things go, could be my first upgrade, if the car ever gets finished.
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Old 19th May 2017, 06:06 PM   #13
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Re: 48 IDA Weber fueling issue

Quote:
Originally Posted by CESLAW View Post
Good thread!

Found this Automotive fuel pressure regulator, which seems tailored to Webers:
Bingo, we have a winner. Nice find Chuck.
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Old 19th May 2017, 08:12 PM   #14
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Re: 48 IDA Weber fueling issue

These are the regulators I got :

://www.merlinmotorsport.co.uk/p/malpassi-filter-king-regulator-large-v8-85mm-black-fprv8-npt

Malpassi Filter King, they are working great for me.

Regards

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Old 21st May 2017, 06:49 AM   #15
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Re: 48 IDA Weber fueling issue

Quote:
Originally Posted by KarlWood View Post
These are the regulators I got :

://www.merlinmotorsport.co.uk/p/malpassi-filter-king-regulator-large-v8-85mm-black-fprv8-npt

Malpassi Filter King, they are working great for me.

Regards

Karl
Hi Karl,

That is what I have at present, there are some who think the 1/8 NPT outlet in my case into a Dash 6 petrol pipe is to restrictive.
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Old 21st May 2017, 03:05 PM   #16
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Re: 48 IDA Weber fueling issue

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Originally Posted by dallas_ View Post
Bingo, we have a winner. Nice find Chuck.
Ordered the regulator and the necessary fittings from Pegasus. Will report further once I get it installed.

Chuck
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Old 21st May 2017, 03:50 PM   #17
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Re: 48 IDA Weber fueling issue

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Originally Posted by CESLAW View Post
Ordered the regulator and the necessary fittings from Pegasus. Will report further once I get it installed.

Chuck
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