ANY OTHER ADVICE??

**Mr. Chevy** · #1 08-07-2015, 01:33 AM

I am working on a 1967 Impala with a factory 327/275 HP motor, 4 barrel,and powerglide trans. The motor is factory stock with 37,500 miles. It has been sitting for 5 years and I recently got it running. I have gone completely through the ignition system changing everything with new parts, checked the timing setting it between 6 and 8 degrees before TDC per factory specs, flushed and refilled the cooling system, opened the heat riser and changed the fuel filter.

I have a detonation issue while under a load. It is driving me nuts. The hotter the motor gets the worse it is. When the engine is cold it does not do it.. It sounds like it is restricted to the passenger side head area. The motor otherwise runs fantastic. I have had all kinds of thoughts from friends and mechanics about different issues that might be causing the problem. The gas in the tank that had been sitting for 5 years was siphoned out and Shell 89 octane was put in about one month ago by the prior owner. One old time mechanic told me this is the issue. He said that octane rating is too low for that motor plus there is most likely a carbon build up.

Research shows the compression rating on this motor is 10:01. The heads are the double hump heads. My thought is to drain ALL of this fuel out and put in some 110 octane racing fuel mixed with Sunoco 93 and then BLOW OUT THE CARBON. Trouble is the tank is 3/4 full...

Any ideas or thoughts from anyone???? It could simply be just this fuel issue and maybe bump the timing down a bit...

Thanks.....Rich

**John Brown** · #2 08-07-2015, 01:59 AM

Water or Seafoam through the carb to blow out the carbon, before draining the gas. If that cures it, you have a cheap fix.

**PxTx** · #3 08-07-2015, 02:05 AM

I'd be surprised carbon was an issue with the low mileage.

Any chance of a pic with the air cleaner off from the passenger side? Just want to see how the distributor is indexed and how the vac advance is run. Is the mechanical advance operating freely?

**Mr. Chevy** · #4 08-07-2015, 02:11 AM

Paul, the advance appears to be working fine...

Rich

**300deluxeL79** · #5 08-07-2015, 02:47 AM

i would try timing at 4 or 2 degrees, see if it reduces ping. don't know shell gas down there but i avoid using it here. i had the same 10:1 327/275hp in a '69 impala (transplanted) years ago, it ran like crap on shell fuel, compared to other brands.

**L89DRMR** · #6 08-07-2015, 03:52 AM

Don't overlook the distributor advance springs. They may need to be replaced with heavier springs to prevent excessive timing advance.

Schonyenko2 · #7 08-07-2015, 04:02 AM

Is the gas an ethanol blend? Ethanol blends at even 10% can cause that. And Stihl chainsaws will overheat in a heartbeat on a mix with that stuff.

novadude · #8 08-07-2015, 11:14 AM

What's the total timing? How much vacuum advance and how much vacuum to reach full advance?

The factory used rubber bushings to limit advance, and these often get brittle and fall off after 50 years.

Check basic "timing 101" stuff first.

68l30 · #9 08-07-2015, 12:12 PM

They like to run on Sunoco 93, retard it a few degrees if it continues. Not knowing what the camshaft specs are, it may not be too suitable for a factory spec tune....Get it quiet, then fine tune it from there.

BIG

**m22mike** · #10 08-07-2015, 12:49 PM

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: novadude</div><div class="ubbcode-body">What's the total timing? How much vacuum advance and how much vacuum to reach full advance?

The factory used rubber bushings to limit advance, and these often get brittle and fall off after 50 years.

Check basic "timing 101" stuff first. </div></div>

Rich
All of the above is where I think you should concentrate, JMO, gas alone may not be the fix.
Also what is the total advance at idle with the vac can hooked up ?
Spend some time reading this, very informative.
Vacuum advance and timing