I'm building a set of Holly 4000-1434 carbs for my 312 T.B. engine. The engine has been bored 60 over with a Isky 300 cam, G heads and the correct 3 speed OD trany. I'm replacing a pair of 1437's which I couldn't idle below 1000 RPM. My first question is about the throttle plates. I read that Ted said a good way to check the plate alignment was to put a light behind and check the bores. The shaft bushings seem to be tight and the plates centered and move freely, but when shinning the light through there is a minimum amount of visible light. Would this be acceptable or should there be zero light visible? Some of the screws would have to be drilled out to replace the bushings. My second question is about jet size. According to Gill a T.B. professor, the #'s for the primary main jet is # 45, secondary jet # 55 and the power jet # 32 and use the yellow secondary throttle diaphragm springs. Are these the right #'s for my engine specs? Third question is about using dashpots on this setup. Should there be one, two or no dashpots with the OD trany? After reading all the Q&A on this forum this is an excellent place to look for answers. Thanks for any input you might have. Philip   

There is should be a small bleed past the throttle plates for idle air, hence the slivers of light you're seeing. To my knowledge no dashpots were used with manual transmissions, only automatics. Can't say about the jet sizes and secondary springs but I'm sure someone will chime in soon with that info.

No dashpot on stick cars.
Jet sizes , power valve size and springs  you mention are all correct for a stock engine.

Are these correct for your modified engine requirements?  Only your hair dresser knows for sure !

If it were mine, I would say probably not. But I'm sure its in the ball park enough to run reasonably well.
Oldmics

Keep in mind that the jetting for the factory dual quad carbs will not be applicable to single four barrel Teapots being retrofitted for dual quad applications.  This is in part due to the single four carbs being larger in cfm than the original dual quad carbs and this in turn simply requires larger jets in which to compensate for the larger primary venturies.  Air bleed sizing in the fuel bowl cover plate is also a player in that the air bleeds have much to do with the overall fuel curve.  Different air bleed sizing requires different jet sizing.  The fuel bowl cover plates are numbered and those numbers can be used to track down the air bleed sizing as originally delivered.  As John brings up, any engine modifications will also affect the jetting.

Anytime two carbs are used, the vacuum signal through each is reduced in half and with this in mind, the secondary spring tension should be reduced in half.  The yellow springs available in the Holley spring kit are suitable for this.  I tend to use the short yellow spring for these conversions but the long yellow spring does a better job in closing the secondary blades more solidly when the secondary circuits are not being used.  I make it a point to use similarly numbered fuel bowl covers so that the air bleed sizing is consistent with both carbs.
 
I target for zero light through the bores when the idle screws are backed up completely.  The secondary blades should also have zero light and if there is light is showing through on those, then it becomes difficult to get the idle back down to where it needs to be.

Lorena, Texas (South of Waco)

I've received 3 good post to my carburetor problems which I am grateful. When I purchased the car in 1980 it ran well for a tired engine. Between 1957 and 1970, because of the cam change, rear stabilizers and OD modifications I believe it had a hard life as a street or drag strip car. When we rebuilt the engine in 2012 it had a stock bore but had to machined .60 over to clean it up. The Esky 300 cam ran and sounded good so I sent it to be checked out and had one of the lobes rebuilt. After putting 200 miles on the engine it runs very well with the exception of the high idle and 25# oil pressure at idle. I use 10W40 Rotella oil.

My follow up question: The car should have left the factory with 1434 carbs but had a pair of 1437s. We rebuilt the 37s and maybe didn't refine our work enough causing the high idle. I have a pair of rebuildable1434 carbs and what jetting sizes if any would be appropriate for the engine modifications?

It was important to know the throttle body light test should be close to zero, especially the secondary's to reach idle specs. The fuel bowl covers each have the same #s which I didn't realize was important. This post was very important for a positive rebuild. Thanks again, Philip

From my experience with other carbs and multi carb setups jetting should only be changed from stock when compression ratio is increased. Are you planning to use the setup as Ford did with both carbs working in unison or going possibly to a progressive set up?
If progressive it seems to me you could convert the Holley's to use a centrifugal distributor as shown to us by Ted and Idle on both but run on the primaries of the one where the primaries are most central to the engine . On this site guys guys have run them forward (non-stock) and backwards like original.
 I run my dual 4 barrel carbs on my 292 (not Holley's) with stock compression and cam; a progressive set-up and am extremely happy with idling and running.They do not use vacuum secondaries.  Both carbs are only 1/4 turn from fully closed on the Idle and the mixtures are just about the same as when I had a single 4 barrel. Both have the original size jets they were manufactured and the were sized to an engine with 9 more cubic inches and and 8-1 compression instead of the Fords 8.4-1. 
Good Luck... This is indeed the best place to get answers....................



56 Vic, B'Ville 200 MPH Club Member, So Cal.

Because this car was an original E model I'm keeping it as much original as possible. In my opinion Ford didn't have a better idea when they set the carburation up to work in unison. The progressive carb option would have been easier to tune with better gas mileage for street use. The car ran real good with the 1437s on so I'll probably use the factory size jetting in the 1434s. Thanks for your opinion on the carbs. Philip 

Ted, do you happen to know the CFM ratings for the '56 single 4 barrel carbs and the E carbs? You mention jetting issues because of the CFM difference. When I first put my E set up on my '57 Bird in '66 I used two '56 Ford single carbs and used the dual quad jetting from the '62 Hot Rod Ford Performance Manual. Put screws in the linkage to manually open the secondary's. Ran fine for many years. A little touchy off the line with the manual secondary's but it worked until I got a set of the E carbs. .

Nice looking engine. What body is it in?  Do you have the Isky RPM 300 or F 300 cam?  I have the RPM 300  advanced 4 deg. in my 312 and like it a lot. My car has 20 Lbs. oil pressure at 800 rpm hot idle. Not to worry, no problem.


"FREE SAMPLE"

I’ve used 410 cfm as the number for the single four barrel Teapot carbs.  Keep in mind that two of these would likely not be 820 cfm but some number less than this simply due to the reduced air flow in having two of these working together.  As camming, cubic inches, and/or the compression ratio changes, then jetting also changes.  The factory jetting was simply for the factory combination but is a good starting point for an unknown combination when no other information is available.

Lorena, Texas (South of Waco)