Loss of power and engine runs rough... Help??? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bigB98 · 05-13-2017, 12:47 PM

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?
Posted via Mobile Device

**truckdude239** · 05-13-2017, 01:16 PM

flat cam lope

bigB98 · 05-13-2017, 02:30 PM

Quote:

Originally Posted by truckdude239

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..
Posted via Mobile Device

Coley · 05-14-2017, 12:03 PM

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.

My two bit
Coley

68gmsee · 05-14-2017, 12:25 PM

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.

gvw5400 · 05-14-2017, 01:58 PM

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

05-13-2017, 01:16 PM	#2
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,217	Re: Loss of power and engine runs rough... Help??? flat cam lope __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

05-14-2017, 12:03 PM	#4
Coley Registered User Join Date: Oct 2011 Location: Victoria, B.C Posts: 3,794	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. My two bit Coley __________________ ....for some men, there is experience, skill and effort....for the others...there is visa and UPS LOL 1966 Chevy 1/2 ton (Florida- Red/white) 1972 Chevy 1/2 ton (California- Blue/white) 2005 Chevy Silverado HD2500/Duramax 2000 Dodge Ram 1500

05-14-2017, 12:25 PM	#5
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	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. __________________ 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...

05-14-2017, 01:58 PM	#6
gvw5400 Registered User Join Date: May 2013 Location: Colorado Rocky Mountains Posts: 263	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

05-13-2017, 12:47 PM	#1
bigB98 Registered User Join Date: Apr 2015 Location: Port Orchard, Washington Posts: 27	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? Posted via Mobile Device



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.