700 double pumper on a road car

[MilesnMiles]

There is an alternative, although il,probably get flamed for suggesting it:
http://www.streetrodderweb.com/tech/ins ... arburetor/

I fitted the 750 version to my 340 car the night before driving it 300 miles to the Nats. It has mechanical secondaries and is a modern version of the Thermoquad without the hassles of the older 1970s carbs.

Immediately got 14" of vacuum at idle whereas my nearly new Holley 670 could only produce 11.5" of erratic idle despite my best efforts.

I've tuned the pump shot and squirter and it takes off really smooth and idles good.
Cost me $300 bucks to the door inc shippimg and taxes.
Meantime, do take note of Dave and others advice regarding getting timing right first.

[dustymopar]

I'll end up having bore wash and destroying my engine

There is an element truth there. Vac secondaries are controlled via the velocity in the primary venturi, as the RPM increases as does the velocity creating a stronger vacuum signal to operate the secondary diaphragm.

In a heavy manual car with a stock motor, DP carb and slow gears you could mash the throttle in 4th and risk washing the bores - you would be insane to do that but it could occur. With a Vac carb, the secondaries are not likely to open in that scenario.

You have a light car with I would guess reasonably tall gears, then a DP is absolutely perfect. In my opinion the 700 is also a good compromise between air / fuel delivery and throttle response. Like others, I have always used DP's and wouldn't consider a Vac.

My

[GJUK]

Thank you all.

I'm not sure that I trust my car to get to Doncaster having broken down again the other night. Car was totally flooded could only start it with the throttle wide open.

I might try and nurse it to Doncaster though. Will have to see, maybe he does home visits?

Jon

[Blue]

It's nothing you can't sort out yourself, methodical approach, one step at a time.

[GJUK]

It's nothing you can't sort out yourself, methodical approach, one step at a time.

I am waiting for the dizzy plate and spring to be available - Turnip is moving shop and they're in the back of his van I understand.

[Les Szabo]

Jon I'll give you an example of what happened to me once on the way home from a Race Meeting when I used to drive it there and back.....everything all ok and I then notice the temperature going down excessively, straight away I knew it was overfuelling, so stopped in a layby, carb apart, blew it out, checked and reset the float levels and all ok, never touched it again apart from jet changes, however it was already sorted on the PV side and things....could be similar prob, or a gasket, needle seat sticking etc....but yes get the timing sorted first then attack the carb, perhaps a member who is close to you can help you set it all up and explain what and why they are doing what they are if your not sure.

[db]

The main thing you need is patience!
Dave Rob has put together a great guide on here somewhere on setting up timing, then setting up carburation.
You can't generally fix these things by throwing money it them, time is what they want, just like kids!
I knew nothing of these magic arts when I joined the MMA, now I'm almost competent!
Read Daves posts, do everything methodically, don't take short cuts or miss anything out.
If you're really bored all my experiences are detailed in my Belve thread (it's very long now!)
I started out with a 750 vac carb then moved to a 750dp. I was so impressed I've now bought an 850dp to try

[GJUK]

Thanks Guys, most helpful.

I saw Mick on Sunday (with the red/orange dart) and advised that I will be kidnapping him shortly to help with just this

Turnip is going to get me one of these dizzy control bases and springs soon from there I think I will get the carb rebuilt and make sure everything is sorted.

Will keep you all posted.

Thanks

Jon

[Pete.S]

With blue it just needs timing sorting or ignition sorting, the car runs a lil fat. And it's mech secondaries.

Mick will put you in right direction...

[GJUK]

I've just bought a timing light and taken my holley carb haynes manual away with me for some light reading while in Copenhagen.

I should be a timing expert on my return!

[Dave-R]

Hope it is the type of light you can dial the advance degrees into....

[GJUK]

Hope it is the type of light you can dial the advance degrees into....

Nope, I assume you read this off the crank markings?

[Pete.S]

Hope it is the type of light you can dial the advance degrees into....

Nope, I assume you read this off the crank markings?

You can Jon just with a dial back it's easier not a necessity.

[Les Szabo]

Without a dial in timing light that you can set to say 34 deg and then check for the zero mark you'll need to put timing tape on a stock damper to check total timing readings unless you got an aftermarket damper thats marked up to be sure its right from your initial setting + what the dizzy is set to put in at a certain rpm.

[GJUK]

Thanks Pete.

Without a dial back timing light you'll need to put timing tape on a stock damper to check total timing readings unless you got an aftermarket damper thats marked up to be sure its right from your initial setting + what the dizzy is set to put in at a certain rpm.

I've not looked it the car has any other marking other than TDC. Hope it does, can't find any timing tape on ebay or the likes, expect its another £30 purchase from real$$steal