Thanks Roger. I did pull the float bowls off and check inside before I fitted it. I gave it all a thorough flush out with carb cleaner. All was well inside. Not sure if I will need to change the main jets yet, but at least I know what size these ones are.

Well good for you. Run it for some bit of time and take a close look at your plugs the proper way after that. The great thing about Holleys is they are easily adjustable just about every which way. With the full kit there are many options. The bad thing is they very likely need to be checked/adjusted every which way for optimum performance. Pretty much the same as any other carburetor. Don't settle for out of the box. Likely much more to be had. Mileage, power, all of it.

Hi guys. Thanks all for your awesome input. I have finally solved the problem. It was the carburettor all along. I put on the new Holley and straight out of the box it idled. It idles smooth now, the bouncing vacuum gauge is steady, pulling about 15/16 HG, just got to set the floats now and reset ignition timing and idle mixture. As we say in the UK.....' I'm well chuffed' 😀😀😀
Thanks again everyone for your help👍👍

Try a green pump cam after you get your Holley on ..   ; )



"Came too close to dying to stop living now!"

I will still suggest opening up the Holley to determine that everything is as it should be prior to installation. You can record jet sizes, check the floats, check/clean orifices, and all the other little things that need to be known (should be known) while you're at it. If adjustments are necessary later you will already know where you stand before going any further.

Of course maybe you are just lucky. I'm not. I don't know if I'm any smarter after doing this stuff for over 50 years. But I do know I am less ignorant. Learnt that the hard way.

When someone says, "Well did you check this and then this while you were doing that?", it is best to already have the correct answer. Working for a tough Service Manager at a Ford tractor dealership taught me that a long time ago. Doesn't make you feel good if you don't. The right answer always holds up, even if you are working alone which is my usual situation these days. "Dammit! I knew I should have..." then "Now I have to..."

Easier, not harder, to do it right in the first place. 

Had one other very good boss later on who was the same way. Always made absolutely sure of what was actually happening during a project. And could prove it. Very good lesson to learn. 

Having the information and not needing it is better than needing some information and not having it.

Edit:
Even worse yet. Needing some information, not having it, at the same time not even knowing you need it. That's the ignorance part I try to avoid. A lot of struggles get easier or disappear altogether when the right information is had and applied. 

Thanks guys. I don't like Edelbrock carburettors at all. I bought it because it was easily available . I scored a brand new 600cfm Holley on eBay for a great price. I've just picked it up from the seller. I'm gonna install it tomorrow.
My set up should be identical to yours then Dave 👍👍👍

I have worked on three brand-new Edelbrock carburetors in the last few years. They all had been installed on very well done rebuilt Y-Blocks. None of them performed well out of the box, no matter how much tuning. In each case nothing left to do but take them apart and find out what was going on.

Each of them was a mess inside. As if they had been merely assembled from the necessary parts with no consideration of any adjustments or settings. One had the floats stopped only by the top of the carburetor. One of them had machining debris in the bowls. The closest to being somewhat usable would still sting your eyes and give you a headache even when tuning with the back end of the car hanging several feet out the garage door and a big fan blowing on the radiator. None were close to having the right jets and rods for the application.

If you have not already done so I suggest getting the proper (for your model) carburetor calibration kit from Edelbrock, study and follow the instructions closely. Then you will know just what you have and what to do if/when more needs to be done.

You absolutely cannot assume anything about your carburetor. Any brand. New or old. Especially new these days. Get the right stuff, set it up right, and enjoy life with no mysteries. 

I have about the same setup that you have Mike. A 312 with Isky E4 cam, Pertronix ignition, but a 600 Holley. I installed the cam 2* advance putting it at 106*, giving it 180lbs compression. Idles at 800 rpm with a standard transmission. I found that it runs best advancing the timing a lot more. I recurved my distributor to run 22* initial with 14* mechanical to have a 36* total. 16-17" vacuum. Runs incredibly well. DaveV

SE Wis

Thanks. I emailed Isky and they confirmed intake lobe centreline is108. I'm happy at 106. I think my problem is carb related, I can hear it spitting and gurgling down the Venturi, it's not a smooth flow of fuel and air. The car runs absolutely spot on apart from idle. Thanks for your input 👍👍

Mike,
My Isky data shows Intake open 22 deg BTDC and close 58 deg ABDC. That would put the intake centerline at 108 deg ATDC. Depending on your accuracy you're real close and because your reading is close you must be fairly accurate. If your reading is perfect you are 2 deg advanced which is fine. This is assuming your intention was to determine the intake center. With the compression
readings your getting my guess is that you are a bit advanced. I don't think your cam position is your problem.