Over the last 25 years I have built over twenty motors but I have one new rebuild that will not start without starting fluid and oil down the carb. The exhaust port is a normal race exhaust port using a RB template plus another 1/16 on the close. The intake port is the largest I have even seen on a domestic NA motor. By that I mean the closing is very very gradual and adds another half inch to the normal intake closing template. There is no sharp lip on the close. I made the close very gradual thinking it would reduce turbulance. I realize that the late closing of this 12A motor is forcing air back up the runners at low RPM. I was willing to make that trade off for a race only motor. The intake close on this 12A is almost the same as the aux on a 13B. I have pulled this motor apart 3 times. The carbon seals are new and the correct length. The new ide seals are set on the tight side but float freely. The corner seals have new soft seals. At 2 or 3K RPM the motor idled the smoothest with 25 degrees of timing, maybe even a little more. I didn't want to leave it that far advanced though. I replaced the rotors and eccentric shaft on a prior rebuild. The only constant in each motor is the housings. The starter is turning fast enough. The distributor and coils are stock first gen. I have used a 48 IDA weber and super stock Nikki that ran great on other motors but neither would start well . Once started they would idle for 20 - 30 minutes easily. Dyno header is long primary with dyno max muffler.

Since 13B aux also have very late closing and guys run them without the sleeves I can't see how it can be the port timing but I have replaced eveything but the housings.

If you have had this problem or know the solution let me know.

 

the closing timing on a side port does seem to affect starting, all the ITS/PS1/PT cars with no sleeves take a lot of cranking to start. i'm working on a PP now, and its actually quite good, fires right up...

anyways.

i think step 1 is to check compression. step 2 you get to work on the carb.

 

my 6-port with no sleeves was never difficult to start with my 48DCO. Put in the next size up idle jet or richen the idle mixture screw, a lean idle is what always makes it difficult to start my REPU

 

^ i second that.

i've run a 6-port without sleeves and it never gave me starting problems until i lost a water seal. play it sounds like all the engine seals are fine, so i'd say start with the jetting.

 

I am running a very early opening aggresive streetport 12A with a 45DCOE and I had a similar problem. I stepped up the idle jet and turned the mixture screws out one more turn. It takes a bit of cranking but it idles clean at 1350 rpms.

Good luck.

 

Based on my motorcycling experiences, I have to agree that your mixture at idle might be a little lean. Good luck figuring it out.