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Old 10-21-2011, 10:05 PM
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General engine questions---your opinion:

So what would cause the following:

After extended driving and/or "harder" driving the engine idles differently from "normal" commuting type driving---it has a little different lope and sounds a little different.

For example, today i had to really hammer it to make an appointment about 30 miles away; The person gets really (rhymes with itchy) if i'm even 1 min late. So i went over 70.

Normally i only commute 9 miles and this is mostly stop and go with little stretches of 55-60 thrown in.

i'm thinking there probably was a temperature difference between the two different driving patterns.

BTW this is a stock LG3 305. The 350 did pretty much the same thing.

What would cause this and should i be concerned about anything?

P.S. also when this happens, the idle speed is a little different, but not that much maybe 50-100 rpm above or below normal.

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Last edited by against all odds; 10-21-2011 at 10:07 PM. Reason: gramer and punktuashun
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Old 10-22-2011, 06:16 AM
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It's called "Cleaning out the carbon".
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Old 10-22-2011, 06:46 AM
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Quote:
Originally Posted by against all odds
So what would cause the following:

After extended driving and/or "harder" driving the engine idles differently from "normal" commuting type driving---it has a little different lope and sounds a little different.

For example, today i had to really hammer it to make an appointment about 30 miles away; The person gets really (rhymes with itchy) if i'm even 1 min late. So i went over 70.

Normally i only commute 9 miles and this is mostly stop and go with little stretches of 55-60 thrown in.

i'm thinking there probably was a temperature difference between the two different driving patterns.

BTW this is a stock LG3 305. The 350 did pretty much the same thing.

What would cause this and should i be concerned about anything?

P.S. also when this happens, the idle speed is a little different, but not that much maybe 50-100 rpm above or below normal.
As long as there's no pinging or detonation under load and the plug color looks good as in not lean/white, and the engine temp looks good, I'd not worry about it.

Be sure the vacuum advance is working and the timing curve is right and that there's no vacuum leaks and the engine is in tune, generally speaking (plugs, cap&rotor, wires, PCV valve, fuel and air filters, etc.). If you still have mostly original vacuum hoses, it would be a smart move to replace then all w/new hose. It's a tedious job, but vacuum leaks are prolly the #1 cause of driveability issues, especially on an older carbed engine.

I'm guessing the carb is a Rochester Dualjet 210 (shown below), although the @gC was used at first. The Dualjet carb is basically the primary side of a Q-jet so can deliver good mileage and throttle response, especially if tuned nice and sharp. The thing is, they are old and like anything, they will show their age by developing a loose throttle shaft, the castings can warp from overtightening the long thru-bolts and from excessive heat, the power piston spring can get weak, the pp can stick in its bore, the accelerator pump can get "lazy", the electric choke can get out of adjustment or stop working, etc. Best cure is a good 4-bbl intake and a Q-jet, but unless the carb is found to be a problem the Dualjet (or 2G) is fine for a DD, IMO.


Last edited by cobalt327; 10-22-2011 at 07:09 AM.
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Old 10-22-2011, 09:42 AM
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Close---i should have said a 78 LG3 305---so a 2GC; i think the changeover happened at 79. Curiously enough the hp went down 5. But yeah, i've used a dualjet on my 3.8 buick which, for some baffling reason, was factory installed in a 79 monte carlo?

But ok, not to worry about this symtom.
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