48 IDA leaking on Idle/shutdown

[Tom]

Hi,
I have new Spanish weber 48 IDA fitted to my 351windsor. They were tuned by a weber approved tuner and covered 0 miles since, just some starts ups.
I've had some fuel leaks due to needle valves but my supplier supplied me a set of new ones and hopefully that's cured.
With IVA now booked we let car do a few engine up to temps and fans kicking in just to check for leaks in all areas.
On the last check we noticed lots of fuel on the inlet manifold leaking from 3 carburettors after the engine was shut down, dripping pouring from the accelerator pump jet which it never has before.
Cleaned up and restarted and they continued to pour on idle.
Fuel pressure was 3psi which I've now lowered to 2 psi.
I let the car cool a bit and retried at at 2 PSI fuel pressure and all seems to be ok.
I'm worried about a reoccurrence when on its IVA test and obviously the fire risk.
Can anyone advise me on what can cause this?
Thanks
Tom

 

[JP Verweij]

Incorrect float height.
You'll need special measuring tools to set float height correct on a 48IDA.
The 48 IDA is very sentive for incorrect float height as it affects fuel mixture also.

I usualy set these up on a test bench at the recommended psi before Ill fit them to an engine.

 

[Frank Catt]

JP, You need to install the instant fuel pressure dump valve that opens instantly the ignition electrics are switched off , Frank

 

[Mike Pass]

As JP says - incorrect float height/ fuel level.
Setting the float/fuel level on 48IDAs is tricky as even the recommended *dry" method does not always guarantee that the fuel level is spot on. You have initially done the correct thing which is to set the fuel pressure to a sensible pressure so it won't push open the float needles so that is not the issue.
Here is a link to this subject on the Cobra forum.

48 IDA Float Settings - Club Cobra

I recently decided to check my fuel levels in the bowls since I still had some slight coughs and exhaust pops during the slow speed and cruise RPM

www.clubcobra.com

The fuel level is very important as it controls most of the carb functions. There are some good videos on Youtube which show how the emulsion tube works at different fuel levels. If the fuel level is too high it can cause fuel to spill over. The main problem is that you can't see the actual level of fuel in the float bowl unlike a Holley which has sight plugs or windows on the later models. If I used 48IDAs or IDFs I would drill ( and tap for a screw in plug) the carb top so I could "dip" the float chamber with a thin dowel and measure the actual working level. The correct level to be set can be seen on the video.

Cheers
Mike

 

[JP Verweij]

JP, You need to install the instant fuel pressure dump valve that opens instantly the ignition electrics are switched off , Frank

Frank, as a carb specialist. I don't install all the carbs I'll get regular myself. Most are installed back by the people who sent them to me.
I use a test bench with diesel fuel to check carbs up front and afterwards. It makes it easyer to check floatheight, accelerator squirt adjustments and leakage. I use it as a final control before carbs with a spec sheet are shipped back to the ones who sent it.
As I don't know what fuel setup my customers have, Ill have to make sure the carbs has no flooding & leaking issues when it leaves my shop.
All the carbs are set up "wet" by me.. Setting up "wet" saves time after install.
A flooding carb on first install can fill up an engine rapidly.... causing an hydrolock causing expensive failure. Thats why I "wet" test.

Only for just a few instances Ill alow a customers car to sit here for me to set up the carbs and if needed to modify the fuel system.
I have to many toys by myself that takes all the space..

 

[Ian Clark]

Hi Tom,

After determining that the carbs and associated plumbing and pressures are mechanically correct then you have to consider the possibility that heat soak after shut down is boiling the gas in the carb float bowls (it will find a way out, I know). Several things to consider especially while idling since no air is blowing through the engine compartment to reduce heat like when the car is being driven.

Cheers
Ian

 

[Frank Catt]

Following Ians comment, which I agree, is another of my crazy ideas for heat soak after a hot run on track. For a competition car running Webers, I have a drop on cover with a extractor fan, which pulls off all of the hot air from the top of the engine and cools the carbs entirely. Works great, and of course you can tell all of the other competitors its a ram air system foe enhanced performance, I nearly got lynched in the first time we said that , and scrutineers came and had a close look, then laugh , when they saw the real result.

 

[Mike Pass]

If you have a heat soak problem phenolic spacers may help. I am having some made for 44IDFs but the 48IDA ones seems be around still.
Cheers
Mike

 

[Richard Milner]

Remembering the hairy moments in the pits with fuel and 48iIDA’s when involved in racing P1001 back in the 60s, I had concerns about the risk of fire with the same Weber’s on my GTD. It was also irritating to stop to refuel after a fast run and have to sit for 20 minutes or so before the car would restart. Fortunately my car was re-engineered and developed for competition and road use by Frank, who continues to look after the car. On his advice his fuel dump system was installed and since then I have not had a single re-occurrence of the problem of starting nor with the Weber’s. Three pumps of the pedal and it fires whatever the conditions. - on further advice from Frank, I keep my hands off and rely on his extraordinary skills and knowledge to keep 804AJB at its best. My advice - listen to the man.

 

[Mike Pass]

For comparison of thermal conductivites

Copper 401 W/m/degree
Aluminium 247 W/m/degree
Phenolic plastic 0.32 W/m/degree - a bit better!

Also - the thicker the spacer the better.

Cheers
Mike

 

[Ian Clark]

Hi Frank, I always thought that ingenious not crazy A heat shield around the carburetors as used on the original racecars is also recommended along with insulating spacers. A lot of heat radiates from the headers, beneficial whether stationary or driving. Looks cool too...

Cheers
Ian

 

[Tom]

Thanks alot for all your replies.
I do think its very likely that heat is contributing alot to the problem. It would explain why more than one carburettor leaked at the same time.
At the moment the car is prepared for IVA so the top vent on the rear clip has a non vented panel on it so no heat from the exhausts can escape. But I will have to find a solution before the IVA .
What thickness do the phenolic spacers come in? Because I've opted for a 351 unfortunately the carb trumpets are close to the rear screen.
I'm also running an electric water pump as I thought it would help with the temps after shut down but obviously not enough ☹

 

[Mike Pass]

I have seen the phenolic insulating spacers in 6.5mm, 9.5mm and 12.5mm. If you are tight on space with your 351 these may be better - not phenolic but will have insulating value. They could be used singly or in double thickness.

Insulating Spacer 3mm 48IDA / 48IDF | Webcon UK Ltd

Insulating Spacer 3mm 48IDA / 48IDF

www.webcon.co.uk

If you have a blank plate in the rear clip there is no convection outlet for the heat. I would suggest that you have an IVA compliant grille to let the heat out. Hopefully you have a turkey pan to keep the exhaust pipe heat away from the carbs. A 9 hole grille after IVA will be good for heat escape.
Failing that an under 12v clip fan will help to direct cool air towards the carbs.
Cheers
Mike

 

[Tom]

Great thanks for the info.
I think were going to try and get a turkey pan made before iva as well as the spacers. I think 3mm to start a see how we get on with clearance.
Also how can I vent the rear panel to still be IVA compliant?
Are the fuel dump when ignition off devices available off the shelf? I tried some searches but couldn't find anything.
Many thanks
Tom

 

[Mike Pass]

External edges must be 5mm or more radius at any opening which will fit a fist sized metal ball. Edges rounded over with sufficient radius or covered with rubber edging. The usual suppliers will have IVA compliant mesh, rounded rubber edging strip etc. 9 hole vent panels with straight cut edges won't pass but the swaged ones may be OK if the rounded edges are of a big enough radius or if edged with push on rubber edging of a big enough radius. Louvred panels won't pass the radius test.
There is a thread on here about the fuel pressure dumping system or give Frank a ring - Google - Wealden Engineering.
Cheers
Mike

 

[Bob Putnam]

I use a test bench with diesel fuel to check carbs up front and afterwards. It makes it easyer to check floatheight

Be careful. Diesel is more dense than gasoline, and will effect (raise) the level of the float over gasoline.

 

[Mike Pass]

May be 5mm diameter. Check as I don't have the IVA manual to hand
Cheers
Mike

 

[JP Verweij]

Be careful. Diesel is more dense than gasoline, and will effect (raise) the level of the float over gasoline.

Diesel is less harmfull overtime as todays petrols are very aggressive. I use diesel as it also acts as preservation lube if my customers don't install their carbs direct after they recieved it.
I also test & set a few psi above factory setting as no gauge reads the same and my customers might have a different setting as their pressure gauge might not be as accurate as mine is.
I estimate the difference between density will be within the floatheight tolerance.

I do carb jobs for decades. I never advertise, its mouth to mouth customers sent other customers to me. Service by interest, and take that extra step.

 

[Tom]

So after your recommendations I've chose to carry out a few things and see if the problem is sorted.
The carb supplier has said they believe the floats are set correctly and its an engine or heat influence. (But who knows)
I've vented the rear panel
Had a turkey pan fabricated
Order phenolic spacers but only 3mm as the all the clearance i have but there is also extra gaskets due to the turkey pan.
I'm also going to check the ignition timing as i think it maybe to retarded which would increase head temps??
Tuner said its around 10 degrees advance which after searching the forum seems low. (Advice welcomed). The distributor was also locked out so I now have mechanical advance.
I've still struggling to find i fo on the fuel dump on shut off but would like to do that also. Would this require a return to the tank?
Thanks again for your help.

 

[Walter Williams]

SET YOUR TIMING AT TOTAL ADVANCE.. I BELIEVE NOT ENOUGH OR TOO MUCH CAN CAUSE HIGHER TEMPS ? THOUGHTS ANYONE ? 48 IDA'S LIKE TIMING . TOTAL ADVANCE 34 TO 36 ??? FEEL FREE TO CHIME IN ANYONE. AND LASTLY , I AM NOT A MECHANIC . I AM RUNNING 48IDA'S ON MY 347.

WALT