Team Camaro Tech banner

1 - 9 of 9 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
I have just bought a 68 camaro and I cant get the timing right. The car keeps detonating when it is turned off. The camaro has a rebuilt 327 block bored out to a 350. I think the detonation has to do with the cam, does any one have any ideas how to fix this timing.
 

·
Registered
Joined
·
138 Posts
Is your car idling fast? What did you set your timing on?
 

·
Registered
Joined
·
12 Posts
Discussion Starter #3
Ive set the idle at about 800 rpm. The timing right now is set at 4 btdc. This is where I have got it to detonate the least. I thought I read somewhere that if an engine was rebuilt the crankshaft could be off so the timing is not accurate.
 

·
Premium Member
Joined
·
7,728 Posts
It's not detonating, it's "running-on" or "dieseling"; usually caused because it's still getting fuel when shut off, when the throttle plate is too far open so it's metering from the transfer slot or main metering system instead of from the idle system. Is it idling on the idle mixture system? Does it respond to changes in the idle mixture screws?

------------------
JohnZ
CRG
'69 Z28 Fathom Green
 

·
Registered
Joined
·
12 Posts
Discussion Starter #6
I alway run the highest octane pump fuel. I had someone tell me it might be the compression which is making it run on. Could that be what it is?
 

·
Retired
Joined
·
26,644 Posts
Go back and read John Z's post again... If the throttle is open more than it should be and the idle mixture screws are adjusted to set the idle then what you describe can occure even though the idle isn't excessively high...

------------------
...Dennis
"The '69, the '96 & the club"
 

·
Registered
Joined
·
122 Posts
Yea.... I would agree with the other guy who posted...JohnZ has good advice...

This problem is pertubative...meaning that it chases it's tail and gets worse..
The lower you put the base timing...the idle lowers and gets rougher...now you crank up the idle screw to try to bring up the idle and then you start getting into the primary circuit, thus leaving the curb-idle circuit useless...this makes the butterfly open further which in turns can make for a engine run-on after the ignition is shut-off....
Try doing the opposite.... Bring the timing up in the 10 to 12 range, then turn the idle screw down to bring it to normal idle...now you might see the idle getting rough or wanting to cough and spit and stall..this may be that you now need to properly adjust the idle-mixture screws to maximize the rpm and vacuum ....
As for detonation while you are driving...that is not a function of your base timing...you need to adjust the tab in the distributor so it does not advance as much mechanically....also proper spring selection.
Are you running vacuum advance????
If so...make sure to disconnect it and plug it when doing the timing..
If your not running vacuum advance a normal set-up for your 327 engine and timming would be 18 to 20 degrees of base timing at 800 RPM idle with a mechanical advance kicking in about 1000 to 1200 RPM and ending with about 12 degress advance fully in by about 3200 RPM...
This would be a total advance of about 32 degrees....adjust the total advance stop-tab to stay just below the detonation point..
Generally a cooler plug, a richer jet, and a lower thermostat all help in keeping that detonation point from creaping down a degree or two...this all depends on your situation.
Regards
Chris
 
1 - 9 of 9 Posts
Top