Big NA intake port will not start
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Big NA intake port will not start
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.
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.
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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.
anyways.
i think step 1 is to check compression. step 2 you get to work on the carb.
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immanuel__7
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09-05-15 10:23 AM