In addition to Tim's good advice there is a lot of information on line on how the vacuum tank works. Its a simple and usually trouble free device and its worth spending a little time understanding how it works.
Vapor lock is not so easy, one of the problems in diagnosing it is that it does not occur all the time. You can drive the car in hot weather and convince yourself you have fixed it only to find that it comes back when the conditions are "right". I have restored 2 633's and the second one incorporated all that I had learnt from the first. On its maiden run of about 2,000 miles it performed flawlessly only to vapor lock on a long steep climb on the last day. A wet rag on the carburettor and vacuum tank had it going quickly but up to then I thought I had the dreaded vapor lock issue beaten. I have since fitted the standby electric pump and it could be a while before I get to test it under actual vapor lock conditions.
29tons,I hope you update the forum with progress on you 626.

29tons, in response to your question about the vent, the owner of the twin six had drilled a hole in the top plate of the carburettor float bowl, soldered a standpipe that was routed up a short distance, discharging below the engine. It was not very tidy but the car was a driver not a show car.
The twin sixes have the carburettor mounted in the "V" between the cylinders with the exhaust manifolds running closely along each side making a heat shield a virtual necessity for any significant driving and although our 1929 cars are not as bad I believe that the heat shield is the first line of defence. It can be done neatly but would not suit a show car.
Another method I have used when touring in hot weather is to make spacers that lift each side of the hood a few inches so that air is directed into the engine bay over the top of the radiator instead of being heated passing through the radiator.
This does not look good when driving but in hot weather some drastic measures are needed.
I have driven my 633 in 100 deg plus weather with lots of kerosene in the fuel, a heat shied, hoods raised and it still vapor locked when stopped at traffic lights.
I have now fitted an electric fuel pump that delivers fuel directly to the carburettor bypassing the vacuum tank. It is only for use when needed, I have not yet had the opportunity to test it when vapor locked.

The car in question is a 1929 626 and strangely the Packard parts list for that model does not call for insulation on the exhaust pipe although it is specified for other similar models however I have fitted insulation to my 1929 633 (which is identical). I am sure it helps but I think the main problem is radiant heat from the manifold to the vacuum tank due to the close proximity of the tank to the manifold, hence the need for a heat shield..
I once had an interesting conversation with the owner of an early twin six (they are notorious for vapor lock) and he had tried many things and found the best improvement was fitting a vent to the carburettor float chamber. He stressed that it had to be at least 1/4 / 3/8" dia tube to be effective.
As a matter of interest, hold you ear to the vacuum tank when the car is hot and you will hear the fuel boiling inside, this does necessarily mean it is vapor locking, it is the very low boiling point fractions boiling off. But it shows how close these cars are to vapor locking with a little more heat.

This sounds like classic vapor lock, a subject that has been discussed many times before on this and the AACA forum.
In warm weather I need to leave the hood open on my 633 if the car is to be restarted in a short time otherwise under hood heat vaporises the fuel making the car hard to start.
Fitting a shroud around the vacuum tank to shield it from radiant heat from the exhaust manifold reduces vapor lock on these cars. This works best if it is made from polished stainless steel.
I find that adding kerosene to the fuel helps, others have reported that diesel has the same benefit.
I wonder whether the fuel filter you have fitted is restricting the fuel flow given that there is a very low pressure by gravity feed from the vacuum tank to the filter, this might be adding to the problem. I rely entirely on the sediment bowl for filtration and have never had a fuel blockage issue in over 20 years.

Mal,
Thanks for the explanation, an interesting project. I hope you keep us posted.
David

Mal,

It would be interesting to know a little more about your speedster project. I am guessing the rationale is to use up a collection of parts that are not sufficient to build a complete car.

But the idea of building a car with sporting pretensions using truck sized components and huge unsprung weight is intriguing. Still Packard had a go at this with the 626 & 734 speedsters.

However regardless of whether you use the 1929 or 1936 engine they both are best at no more than about 2000 rpm. If the car is to have a sporty feel it would be better to be able to rev feely at much more than this. I doubt that either engine could be modified to do this without wrecking it.

If you make it as light as possible with a high ratio diff it will go well enough and look good.

I hope you keeps us posted on the project through to completion.

If you find a suitable sediment bowl, please post the details, I have 2 / 1929's and one has the original pot metal sediment bowl that is warped and needs 2 cork gaskets between the bowl to seal and the threads are not the best. I would like to replace it.

To your question about the sediment bowl, I purchased a reproduction glass bowl filter with built in shut off valve from Henry Yeska at Hershey many years ago, it fitted the outlet of the vacuum tank on my 1929 perfectly. I don't know if they are still available of whether Henry is still in business, perhaps others can advise.
The same filters units were probably available from other suppliers but I have never been able to find them, I could also use another one.
There are other reproduction glass bowl filters available from other suppliers such as Vintage Car Parts in UK but they do not incorporate the shut off valvehttp://www.vintagecarparts.co.uk/search?query=fuel+filter.

Pat,
There is a small area under the front seat on the 126" 5 passenger , 133" 7 passenger model open tourers. Its about 3" deep at the front of the seat tapering down to about 1" deep at the back so there is not much room. It is accessed by lifting out the seat. If the car is the 4 passenger Sport tourer which has a lower profile, the front seat sits flat on the floor with no storage space underneath.
Incidentally the bodies for all First and Second Series 6 & 8 cylinder cars are the same from the scuttle or firewall back. The extra length of the eights is all in the hood.

Tom,
Your 833 looks great. I would definitely have the wheels balanced. I had the disc wheels on my 633 balanced on the car at a regular tire centre. They used adhesive lead strips on the inside of the rims.