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New engine, timing/high idle issues

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Currently have a 2001 Wakesetter with the indmar 350 vortec, just replaced the shortblock. I can get the engine started fine, it fires right up. at TDC it will idle at 800, (thats with the shunt in the ALDC) If I advance the timing, it jumps the RPMs big time. At 6 BTDC, Im at 1500rpm, with shunt in. Taking it out takes it to 2100rpm (well out of operational range). 10 BTDC would be nuts. The computer doesnt seem to be compensating for the advance. I suspected the IAC and TPS (lots of posts about TPS sensors doing that) replaced the TPS, cleaned the IAC with carb cleaner. The top of the motor was installed by our local machine shop. Its done well, ive checked every possible area for a vacuum leak, and there certainly isnt anything leaking that much air past the throttle body. Ive triple checked the shunt is in A & B. I get the drop in RPM when the shunt goes in and the timing goes into base. Im stumped.

Anyone have any thoughts?

:) Thank you

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I assume you replaced the long block, although it shouldn't be relevant.

Base timing should stop the adavance and increase rpm to 1000, to allow setting it to 10 BTDC as you mentioned.

Idle should be set at 650 rpm.

I'm guessing based on your description that you have a MPI/EFI engine, such as Monsoon or HH, and is placed into base timing with the computer (or jumper). If you have a Vortec 310 carb then you add the shunt and add 12vdc power.


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