Hard Starting carb'd car, Very hard to start need some guidance Options

[North Coast Jim]

My 3 year old, 3600 mile on the rebuild, 914 has a starting problem. Everything was new when rebuilt. It has had the annoying issue of being very hard to start. Just had engine out to fix an oil leak - fixed. Took the opportunity to adjust valves and ensure preliminary timing was correct. Hard start condition was present before engine pull. As I have a lift the carbs did not have to be removed. With engine back in we then set timing to 29BTDC at 3000 RPM. Car runs great once started actually runs very strong. Issue is very hard to start. On successive days tried one gas pedal push, then tried no peddle push, then tried 2 peddle push. In all cases it was still very hard to start. Car seems flooded and holding the peddle to the floor may provide the start accompanied with a loud backfire through the muffler. Not good nor dependable way to start the thing. Sometimes I can go out and a cold start may occur with no gas peddle push and no backfire but usually not. Need some help to understand the needed fix. Appreciate any all input.

Engine particulars - Totally rebuilt with stock flat top pistons and cylinders, HAM heads, WEB cam for carbs, 009 disti with a blue coil, Pertronix ignition. 3600 miles on the rebuild

Carbs - New 40IDF's from Redline. Jetting is 50 idle, 120 main, 180 Air Correction, with an F11 Emulsion tube, 28mm choke/venturi. Run 3PSI regulated fuel. Floats levels were checked prior to assembly to the engine. Air corrections were open upon delivery and they are now closed. We are at 600 ft elevation. There is no drivability issue with this set up. Car runs strong once started. OK a seldom occurring "pfft" thru the carb.

A Weber knowledgeable racer at the PIB Vintage Races took a look at the set up and mentioned that the accelerator pump linkage had too long a throw. I was flooding the engine before start or overfueling when running. Mileage is not the best but who cares. Took a pick, attached. He stated that only 2-3 threads should show. I've found no reference anywhere on the accelerator pump adjustments needs. This pic is as the carbs were delivered.

Thanks all

[michael7810]

I'm just thinking out loud here:
Probably carb related but did you check the spark plug gap?? What size if you engine? If it's overfilling the bowls you should be able to see fuel dripping into the venturi. You can back off the accel pump adjustments and try that but I don't think that's it. What is your idle timing at? Too much advance at idle can make it hard to start. I realize you set it at 3K rpm but if the advance isn't working correctly the timing won't back off enough at idle. Backfire in the muffler is usually a rich condition. You could disconnect the fuel pump power (assuming the bowls are full) and see if it gets easier to start once the fuel level goes down a bit. Mine was not easy to start unless you did it just right. Cold push the. pedal about 1/3 and hold until started. Hot/warm push the pedal to the floor until running. Pumping it was not necessary unless it hadn't run for several weeks. I might help to pull the plugs after a start attempt to see if they're wet. Good luck....sorry for the rambling