'68 Fi conversion Dual Weber questions

[tbb]

'68 SB converted to Dual Weber IDF. Not my choice, but here we are.

I'm trying to sync the carbs using a "snail" carb airflow tool, cylinders 1,2,4 all reading at 5 but cylinder 3 reading at 3. even if I change the position of the idle screw cylinder 3 pulls less air than the rest of the cylinders.

it also seems like cylinders 1 and 2 are doing more work than 3/4. When i pull individual spark plug wires there's very little difference in rpm from cylinder 4 wire but especially cylinder 3. with cylinders 1/2 the engine practically dies when wires are disconnected.

At first i thought it could be low compression, but both cylinders 3/4 are reading 140psi. haven't checked cylinders 1/2 yet. I was thinking it could be a tight intake valve, but wouldn't the compression reading suffer if it was valve related? ill adjust valves tomorrow morning anyways.

now I'm thinking it could be an intake leak. Could an intake leak cause the snail sync tool to read low?

also, with an fi to carbs conversion, what should be done with the exhaust recirculation hose that typically feeds back into the stock air cleaner?

Thanks, Tyler

[Multi69s]

[tbb]

ok, valves have all been checked/adjusted and are 6 thousandths. they were all pretty good before the adjustment. all cylinders were tested and read 135 psi give or take 5psi. i sprayed carb cleaner near the intake gaskets and noticed no difference in rpms near cylinder 3 (low vacuum problem cylinder).

i sprayed a bit of fuel into each cylinder and could only hear a difference in rpms on cylinders 1,2,4. no change with cylinder 3. also when changing the air fuel mixture screw for cylinder 3 there is no difference in rpms.

i replaced plugs, checked for spark and spark is good.

so how is it possible to have compression, spark, and fuel, but have a cylinder that isn't performing as well as the others? is there a way to test the output of individual cylinders? is it possible I'm leaking through a valve?

air bypass screws are fully seated

oh and its a 1600 with weber 40 idf

thank you for the help

[Multi69s]

Four other steps:

First, make sure that both carbs have the same size jets.

Second, make sure that the carb's butterflies are open the same amount (1&2 compared to 3&4), some people use a feeler gauge. Right now trying to get the carb to react to the mixture screw, instead of the snail number.

Third, take the carb apart the from the number 3 & 4 side, and clean it very well with carb cleaner and compressed air. Concentrate on the idle circuit. Hold the idle jets up to the sun, or bright light. You should be able to look through them.

Fourth, swap the carbs from side to side and see if you have the same results.

Get back to us.

Is there any popping or farting at the carbs?
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[W1K1]

Were the carbs jetted for a 1600cc when you bought them?
do you know what the jetting is on them?
those 40's could be run on anything from 1600cc to a 2332cc with vastly different jetting and venturies.
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1965 squareback 1500E
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