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#1377 06/12/2004 11:23 AM | Joined: Nov 2002 Posts: 18 Junior Member | | Junior Member Joined: Nov 2002 Posts: 18 | I just put a new crate engine in my 70 chevy truck. It's a Gm 350 HO with a Holley 770 carb. I'm getting gas in my oil. Both GM and Holley say the carb is not too big. So it isn't the carb pushing too much gas into the engine. The guy from Holley asked if I had a vented gas cap. I did put a new locking gas cap on and I'm pretty sure it's not vented. He said all 70's had vented gas caps to prevent too much pressure building up in the tank. he also said that the pressure builds up and when the engine is shut off it continues to push fuel into the engine which ends up bleeding over? the rings and into the oil. Does this make sense? | | | | | Joined: Jan 2003 Posts: 687 Shop Shark | | Shop Shark Joined: Jan 2003 Posts: 687 | Scott: yes!! popcorn The Truth is Out There (770 Whoa!! oh I forgot I got a 750 sitting on mine) | | | | | Joined: Dec 2001 Posts: 1,745 Member | | Member Joined: Dec 2001 Posts: 1,745 | I guess I am dumb but if the fuel pump removes fuel from the tank wouldn't that cause a vacuum situation and not a pressure situation? How could a vacuum push fuel into the engine? Enlighten me please.
I could see how expanding fuel on a hot day might push, but he mentions pressure building up with the engine running.
54 3100 with 235
62 flatbed dump C60 with 261
| | | | | Joined: Jun 2001 Posts: 379 Shop Shark | | Shop Shark Joined: Jun 2001 Posts: 379 | Time for a compression test!  | | | | | Joined: May 2001 Posts: 1,904 'Bolter | | 'Bolter Joined: May 2001 Posts: 1,904 | I had a '75 Hornet which got gasoline into the oil through a bad fuel pump. I went to check the oil one day. It was a quart over full and really smelled of gasoline.
1948 3/4-Ton 5-Window Flatbed Chevrolet 34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
| | | | | Joined: Dec 2003 Posts: 299 Wrench Fetcher | | Wrench Fetcher Joined: Dec 2003 Posts: 299 | I once had a defective stock fuel pump. It was leaking gas directly into the bottom of the engine, where it sat at the side of the block.Do you have an electric pump or a stock one? | | | | | Joined: Feb 2004 Posts: 29,821 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,821 | The non-vented caps are used with a charcoal vapor canister on the newer-model vehicles. The canister stores the vapors while the engine is stopped, then vents then through the intake system on startup. Older fuel systems either have a tank vent, or a vented cap, or both. I'd check for a leaky fuel pump, putting raw gas into the crankcase.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Nov 2002 Posts: 18 Junior Member | | Junior Member Joined: Nov 2002 Posts: 18 | The consensus seems to be that the fuel pump is the problem, so I'm putting a new holley fuel pump on in the morning.
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