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03-31-2018, 09:45 PM | #1 |
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Help with rough running engine
1970 C-10 w/ a 350 small block that has been sitting for 10+ years. Fires up just fine but idle and acceleration are very rough, like it’s not firing on all eight.
When I brought it home last fall: Changed oil and filter Squirted Mystery oil into cylinders and over valvetrain New plugs/wires Dumped old fuel, new inline filter. At that point it started and ran briefly, just wanted to make sure it wasn’t seized or dead on arrival. Fast forward to now, I’ve come full circle ready to revisit the engine. This issue was first noticed when I added a new intake (Edelbrock) and carb (Demon). It sounded like a dead cylinder so I checked compression (135-140 psi all around). I installed a new HEI distributor too (set at 8 degrees) but that didn’t solve the problem. There’s some white smoke out the tailpipe but I suspect that’s the Marvels oil burning out of the cylinders. At this point I’m not sure where to go next. It certainly seems like an ignition issue but the plugs, wires and distributor are all new. Maybe the carb, but it’s new too. I’d appreciate any troubleshooting suggestions or maybe a second set of eyes to see if I’m missing something.
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1970 C-10 "Old Yeller" |
03-31-2018, 09:51 PM | #2 |
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Re: Help with rough running engine
They did not come from the factory with model year 2018 Marvel Mystery Oil. Burn that crap out of there. Clean the plugs, check your vacuum advance make sure its working and plugged into the correct port. Focus on ignition and timing first, then carb.
Check out hotrodders forum links to Crankshaft Coalition. A ton of info there. |
04-01-2018, 07:37 AM | #3 |
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Re: Help with rough running engine
HUGE hint right there. If I read this right and it was running good before, then it was not. Start with what you changed, odds are great you did something that is causing the issue.
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04-01-2018, 08:45 AM | #4 |
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Re: Help with rough running engine
New intake + one cylinder missing likely = intake gasket vacuum leak. Carb gasket leak usually causes several lean cylinders or the entire motor depending on manifold type.
Might pull and check the plugs. One might have been fouled by too much oil. Also could have got a dead out of the box plug. |
04-01-2018, 09:12 AM | #5 |
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Re: Help with rough running engine
Seems to me it's never really run very good -right?
A rough running engine can be a bunch of thing -even a combination. You've done some of the preliminaries so next is to do the simplest, easiest things first. Make sure you don't have any vacuum leaks by plugging all even the vacuum advance. When unsure if the gas in the tank is contaminated I disconnect the fuel hose from the tank to the fuel pump and then place a fuel hose into a one gallon can under the truck and run it from there. From there it's a matter of elimination; ignition components and/or internal engine components like worn out cam lobes. Just do the simplest, cheapest first.
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68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... Last edited by 68gmsee; 04-01-2018 at 09:20 AM. |
04-01-2018, 09:15 AM | #6 |
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Re: Help with rough running engine
Last edited by YoungPup1977; 04-01-2018 at 09:55 AM. |
04-01-2018, 10:42 AM | #7 | |||
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Re: Help with rough running engine
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Thanks for the tips everybody, I’ll keep you posted of my progress.
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1970 C-10 "Old Yeller" |
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04-01-2018, 11:34 AM | #8 | |
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Re: Help with rough running engine
Quote:
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68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
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04-01-2018, 12:35 PM | #9 |
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Re: Help with rough running engine
Pretty slick website, bookmarked. Imagine if every automotive forum member contributed a bit of their expertise...that would be quite a database of information.
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04-01-2018, 02:43 PM | #10 | |
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Re: Help with rough running engine
Quote:
Running like a champ now, even smoothed out considerably, with more felt power. |
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04-11-2018, 10:48 PM | #11 |
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Location: Poway, CA
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Re: Help with rough running engine
Welp, the solution to this problem looked something like this:
Long story short, the electric choke wasn't working, closing off the air intake. I opened it up and the engine fired to life, on all eight! It turns out that lack or air sounds strikingly similar to lack of spark; a fine lesson learned. But the true lesson here boys and girls is when you're troubleshooting air, fuel and spark...don't discredit the air part. Thanks again for the help everyone. I hope info this helps another poor soul in the future.
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