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Chevy 305 timing degrees


Jim S
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On the 87 Avanti, what should the timing mark be set at?  On most of the GM forums people say between 6-8 degrees BTDC.  What is recommended for the Avanti 305?

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Get engine to operating temperature. Disconnect single wire connector in engine harness between distributor and ECM.


Setting should be on Emission sticker, or set to 6*.

Reconnect wire connector.

Good luck,

Jim Wood

 

 

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Most of the smog stuff has been disconnected.  Still proceed as you said?

 

 

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Yes. The ECM will not hold base time unless you disconnect the distributor to ECM wire.

I'll check tomorrow on the wire colors, but it will be a single wire with a connector.

Good luck,

Jim Wood

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There are two connectors on the distributer.  One has two wires and the other has several.

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This is a single wire NEAR the distributor, should be tan on one side of the connector and tan\black on other side.

You can also go to www.montecarloSS.com and search their site for info.

Their site is full of good info for your Avanti.

Good luck,

Jim Wood

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11 hours ago, IndyJimW said:

This is a single wire NEAR the distributor, should be tan on one side of the connector and tan\black on other side.

You can also go to www.montecarloSS.com and search their site for info.

Their site is full of good info for your Avanti.

Good luck,

Jim Wood

I looked everywhere, and cannot find any wires as you described on my car.

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May be located under the passenger dash near the ECM. Not sure where Avanti hid it, but its there.

Should be 1 of the wires coming off of the distributor, follow the tan wire.

Good luck,

Jim Wood

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Posted (edited)

What's going on with my engine is hard starts sometimes.  And when you shut it down, sometimes it will diesel and knock for a few seconds before it stops running.  I was told that the timing was off and setting it properly should correct it.

 

Edited by Jim S
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1 hour ago, 64studeavanti said:

Sometimes dieseling can be caused by the throttle plates not closing all the way. Could be cause of hard starting as well.

There was a new carburetor installed by the previous owner just before I got the car.  I'll look at that.  Thanks. 

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15 hours ago, Jim S said:

What's going on with my engine is hard starts sometimes.  And when you shut it down, sometimes it will diesel and knock for a few seconds before it stops running.  I was told that the timing was off and setting it properly should correct it.

 

 

13 hours ago, Jim S said:

There was a new carburetor installed by the previous owner just before I got the car.  I'll look at that.  Thanks. 

Set the timing.

Is the carburetor a Quadrajet E4M or an aftermarket.

There should be a solenoid that controls plate closing during shutdown. This helps prevent dieseling.

Dieseling and knock can also be caused in the Chevy small block by heated deposits. Go to a GM dealers part counter and get a bottle of ACDelco 10-3015 Top Engine Cleaner and follow the directions. You SLOWLY pour it into the carburetor with the engine running, before this came out we would use water at the dealers I worked.

Good luck,

Jim Wood

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Posted (edited)

Yes it is a Quadrajet.  Thanks for the info.  I looked at the carb and besides the choke coil heater there is only a fast idle solenoid on the opposite side.  I took the connector off because it was idling very high when in gear and I could barely stop the car when driving!  This car is a real mess!

Edited by Jim S
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On 4/29/2021 at 8:36 PM, IndyJimW said:

May be located under the passenger dash near the ECM. Not sure where Avanti hid it, but its there.

Should be 1 of the wires coming off of the distributor, follow the tan wire.

Good luck,

Jim Wood

I can not find any single wires with a connector in this car.  (At least that's accessible)  Here are photos of the distributer connector and the ECM connectors.  The ECM connectors each have a tan wire with a black tracer.  I don't know which one to disconnect.  I'll have to cut the right one and reconnect.

IMG-0658.jpg

IMG-0659.jpg

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I would unplug the distributor connector and remove the wiring from the harness back about two feet, the OEM connector should be there. Or cut the tan wire a couple inches from the distributor, set the timing and reconnect the wire.

From what I have been told you can also hook up a scanner and with the engine running it will make the ECM go into base mode. I have never done this and don't know if it works.

Good luck,

Jim Wood

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