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Old 02-06-2012, 11:39 AM   #1
ramey
71' Custom 10 (ole blue)
 
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Cool bad gas?

I just put a gm 350 in my truck bout 400 miles ago, its ran good until the other night i filled up with gas and ever since its ran a little rough. I put some stp gas treatment in it and ran it down to a 1/4 tank and filled up with high test and its still running rough but not quiet as bad, I'm thinking I still got some water at the bottom on the tank but ain't sure. Maybe the motors broke in and needs the timing set again or maybe the timing got thrown off somehow. Any thoughts?
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Old 02-06-2012, 12:17 PM   #2
GRX
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Re: bad gas?

If you suspect water, buy yourself a $3 bottle of 99% isopropyl alcohol from the drug store. I carry a bottle on road trips for just such occasions.
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Old 02-06-2012, 12:25 PM   #3
CC69Rat
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Re: bad gas?

Define 'running a little rough' .. Is it backfiring through the carb? just sluggish? Have you really stabbed the gas ?? (hopefully it didn't jump time)

Don't you have the 350/290 motor? Vacuum leaks or maybe a spark plug wire arcing through the headers? (new engine, and out of coincidence one of the plug boots got a little hot? ) Does it feel like it's firing on 7 cyl?
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Old 02-06-2012, 01:16 PM   #4
Stocker
20' Daredevil (Ret)
 
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Re: bad gas?

Disconnect your fuel line, crank the engine over, and collect a few ounces of fuel in a clear glass jar.
Look for water or other contaminants in the jar.

I got a tank of gas with water in it several years ago. The guy at the station refused to believe it and called me a liar. Then to prove he was right, he smeared some water-detecting compound on his stake, and staked their tank. It came up purple (water present) and his face turned red. They offered to have my tank flushed but I did it myself -- all it cost them was several gallons of water-free gas.
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Old 02-06-2012, 01:28 PM   #5
ramey
71' Custom 10 (ole blue)
 
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Cool Re: bad gas?

Quote:
Originally Posted by CC69Rat View Post
Define 'running a little rough' .. Is it backfiring through the carb? just sluggish? Have you really stabbed the gas ?? (hopefully it didn't jump time)

Don't you have the 350/290 motor? Vacuum leaks or maybe a spark plug wire arcing through the headers? (new engine, and out of coincidence one of the plug boots got a little hot? ) Does it feel like it's firing on 7 cyl?
its not backfiring it just seems like its a little sluggish while its idling, it seems to run fine going down the road. like i said it ran fine til i filled it up and i got on it a little but i wouldnt think it jumped but it couldve i guess. when i built the motor in the green 69 i had it had a similar problem and it was a vacuum line but you could hear it sucking air but i dont hear that with this truck
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Old 02-06-2012, 02:45 PM   #6
tim21391
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Re: bad gas?

i will never buy stp fuel treatment since its not petroleum based
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