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By 312YBlock - 3 Years Ago
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I’m using Autolite #46 plugs gapped to .034 in my 312, it runs great but every once in awhile I’ll get a little run on. I’m familiar with the carbon, fuel grade etc causes but I’m curious if anyone has found a plug that is good at combating it?
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By Ted - 3 Years Ago
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The spark plug heat range is not much of a player when having engine ‘run on’. The engine not stopping cleanly when killing it is more related to the gasoline octane level being too low and/or too much throttle opening on the carburetor. You can try setting the idle speed lower and see if that helps.
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By 312YBlock - 3 Years Ago
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I’m running Sunoco 91 octane, in addition to reducing idle speed is there any harm in trying the 93?
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By Ted - 3 Years Ago
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Gut feel says you’ll not see a difference between 91 and 93 octane fuels. That’s assuming those fuels are as advertised. Idle speed being too high is still at the top of my list. Have you looked at your ignition timing? Could simply be too much ignition advance.
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By 312YBlock - 3 Years Ago
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Hmm, I’m at 12ish BTDC, no pinging or hesitation, great acceleration. The idle is comfortable at 500 on the factory tech that sits at 100 with the engine off but I’ll try shaving a few RPM and see what happens. Thanks much Ted for the feedback.
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By 312YBlock - 3 Years Ago
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I add an oz of Sea Foam to every gallon, I recently replaced both exhaust manifolds and put my finger into several exhaust ports finding only a tiny trace of carbon. The cylinders used to be choking on it.
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By Ted - 3 Years Ago
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Are you using a conventional or ‘Dial Back’ timing light? If a ‘Dial Back’ light, then I’ll suggest checking the timing with a conventional light just to ensure that that the ignition timing is the same with both timing lights. ‘Dial Back’ lights are notorious for giving erroneous readings as they get older.
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By 312YBlock - 3 Years Ago
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I have a relatively new conventional conductive timing light.
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By Ted - 3 Years Ago
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This brings us full circle and now back again to the quality of the fuel. Have you tried fuel from another location?
I bring this up as I had a 454 BBC on the dyno that had a serious ‘run on’ issue after making the first dyno pull. Once it was verified that the ignition timing and idle speed were not the problem, a quick check for the ethanol content in the gasoline being used showed it had 35%. The fuel was purchased by the customer from his local station and was advertised as 93 octane Premium on the pump. This was from pumps with stickers staying ‘May contain up to 10% ethanol’. I had the customer go to the nearby local grocery store and purchase five gallons of 93 Premium and a quick check showed it had only 5% ethanol. That fuel in the same engine without any other changes solved the ‘run on’ problem.
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By 312YBlock - 3 Years Ago
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Excellent point Ted, thanks.
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By 2721955meteor - 3 Years Ago
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I have the run on issue as well, my 292 is quite stock but no blowy,good comp.i kept blaming the ign. switch. after reading these posts I followed the advice ted had given. retarded the timing a bit,got idel to 550 no run on,canadian gas which is terrible with all the additives. seems betters also had a flat spot when upshifting and engine cold. (manual 4spd with od in 4). I also hooked up the exhaust flapper to get a bit more heat to the intake. still have to go for a good run but appears to be much better intake with Holley 600cfm 4ve.
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By 2721955meteor - 3 Years Ago
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just filled up with mid grade gas. no more run after sign off
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