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Old 05-13-2017, 12:47 PM   #1
bigB98
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Loss of power and engine runs rough... Help???

So I have a new built sbc 350 engine with maybe 700 miles. I was driven by one day when I noticed something wasn't right. Pulled over and my truck was running really rough and the idle was loping more than it usually does. Along with that there is a massive loss of power. Pulled it in the garage and thought it may have been a timing issue. Nope. Timed it and it was good. So maybe a fuel delivery issue. Just rebuilt the carb and put it on and replaced the vacuum cap on the carb because it was torn (thinking oh it coulda been a vacuum issue). Test drive it and still a loss of power but it does now lope as bad but still runs rough. Any troubleshooting y'all can help me with?
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Old 05-13-2017, 01:16 PM   #2
truckdude239
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Re: Loss of power and engine runs rough... Help???

flat cam lope
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Old 05-13-2017, 02:30 PM   #3
bigB98
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Quote:
Originally Posted by truckdude239 View Post
flat cam lope
I was hoping it wasn't that but I had a feeling. Wonder if the guy who built it didn't do a proper can break in..
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Old 05-14-2017, 12:03 PM   #4
Coley
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Re: Loss of power and engine runs rough... Help???

Start with a compression test before you assume too much.
Then physically check your timing to make sure you haven't skipped or broken a tooth on the timing chain.
Pull the valve cover and the spark plug and physically find tdc on the number one cylinder and then accurately relate that to your distributor #1 rotor position.
Again....to early to assume anything just yet.

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Old 05-14-2017, 12:25 PM   #5
68gmsee
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Re: Loss of power and engine runs rough... Help???

When something like this happens and I'm not sure I always do the easy stuff first before any engine disassembly or dismantling of parts.

Timing, fuel delivery and vacuum are some of the first things to check and you've check that but on top of this, check for flooding by visually checking if there's excessive dark gray to black smoke coming out of the exhaust.

I always block off all vacuum ports on the carb and intake manifold: vacuum advance, power brake booster, transmission modulator vacuum source, etc. to see if the idling improves.

If all that checks out, fuel contamination could also cause this. When I suspect this, I use a one gallon container with fresh gas placed under the fuel pump and run a short section of fuel hose to the pump intake from the container.
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Old 05-14-2017, 01:58 PM   #6
gvw5400
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Re: Loss of power and engine runs rough... Help???

Of course checking timing and fuel delivery makes good sense.
But go with your gut feeling, pull your valve covers, disable the ignition power and have
someone crank the engine over while you observe the rocker arms in motion. Hopefully everything will look normal! But in my case I had 3 "dying twitches" rockers and 3 bad lobes when my engine signed off in a similar fashion, I hope you don't!!
All the best, Dirk
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