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#1 |
Registered User
Join Date: Feb 2008
Location: bay area, CA
Posts: 68
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350 Chevy running rough, lots of time and effort spent
I have a 69 GMC with a 350 (85 Blazer block?)/3898993 heads/Holley 600 carb, fuel pump and intake.
It has been running great for years. The truck seems to start and idle fine. As soon as I take it down the street, it starts running really rough. Idle drops and it almost dies. If I shut it off for a few minutes, it's fine again until I drive it down the street. No choke, manual or electric, never need it before. Choke is wide open. This seems to have happened when I ran the tank low on gas. So I've replaced the fuel filter and found alot of rust and crud in the old one. I took out the FSU and blew it out with compressed air. I have new plugs r43ts ACDelco, .035 gap. New wires, cap and rotor. Fresh coolant and oil. Timing is set at 8 BTDC. I can't find any exhaust or intake leaks. I was thinking maybe the wires were overheating, but I don't think so. I checked each wire with a timing light and they are all sparking. I'm running out of ideas and I'm about to do a leakdown test. Seems like a fuel problem to me though. Any suggestions?
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#2 |
Registered User
Join Date: Aug 2009
Location: Alden NY
Posts: 2,705
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Re: 350 Chevy running rough, lots of time and effort spent
Did you pull the carb apart to see how much gunk and rust made it into it? Could be a bunch of crap moving around in there.
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1961 C1 Corvette 1959 El Camino 350 TPI, 9" 4 w disc 69 Blazer K5 - sold July '20 2021 Durango RT 5.7 |
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#3 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: 350 Chevy running rough, lots of time and effort spent
have you check cleaned and gapped the points?
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71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY |
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#4 |
Registered User
Join Date: Jul 2009
Location: La Crosse, WI
Posts: 218
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Re: 350 Chevy running rough, lots of time and effort spent
What are the odds that your fuel line has a pinhole in it?
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Currently truckless, previous trucks: 67 K20, 87 K10 aka V10 & 72 C10 |
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#5 |
Registered User
Join Date: Feb 2008
Location: bay area, CA
Posts: 68
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Re: 350 Chevy running rough, lots of time and effort spent
Thanks for the replies.
I have not taken the carb apart. I guess that should be my next step. Any suggestions as to what to take apart and clean? It's a 4160 Holley. The cap and rotor is new. There are no holes or leaks in the fuel lines.
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#6 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: 350 Chevy running rough, lots of time and effort spent
cap and rotor dont mean much if you have points and havent maintained them
on the other hand if you have an HEI dizzy, your plugs are gapped wrong they should b at >045 another most common problem with hei conversions is failure to have it wired properly with a 12v supply. if you use the original wiring it get lo voltage and causes the module to overheat and cause a problem like your describing i'd check all that stuff b4 touching the carb
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71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY |
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#7 |
Junior Member
Join Date: Dec 2006
Location: Southeast Missouri
Posts: 2,436
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Re: 350 Chevy running rough, lots of time and effort spent
Another thing to check, the in tank filter may be clogging.
Danny
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'67 Chevy C-20 short stepper - build complete, 454/SM-465. '75 C-30 Single Cab DRW-350 small block/NP-435. '77 GMC-6500 Dump Truck, 427 Tall Deck. '92 GMC K-3500 Duallie, 454/4L80E. Last edited by Shyguy; 06-05-2010 at 05:54 PM. Reason: Mis-spelled word |
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#8 |
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![]() Join Date: Aug 2001
Location: SOMERSET KY.
Posts: 6,427
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Re: 350 Chevy running rough, lots of time and effort spent
IF YOUR FUEL FILTER WAS FULL OF RUST & CRUD... & THERES NO FILTER BETWEEN YOUR TANK & FUEL PUMP... I WOULD BE SUSPECT OF THE FUEL PUMP DIAFRAM.
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junkyardjohn 69 1 TON TOW TRUCK // 84 4WD CUCV BLAZER// 85 1 TON 4WD STAKE TRUCK// 86 M1031 5/4 TON 4WD CUCV// ALOT OF OLD TRUCKS FOR ONE OLD MAN TO DRIVE. ![]() LIFE MEMBER OF P.E.T.A (PEOPLE EATING TASTY ANIMALS) DON'T RENT U-HAUL ALWAYS TELL THE TRUTH IT WILL AMAZE PART OF THE PEOPLE & ASTONISH THE REST Last edited by junkyardjohn; 06-05-2010 at 06:34 PM. |
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#9 |
Registered User
Join Date: Feb 2008
Location: bay area, CA
Posts: 68
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Re: 350 Chevy running rough, lots of time and effort spent
Old points distributor. No filter in the tank or before the pump.
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#10 |
Registered User
Join Date: Feb 2008
Location: bay area, CA
Posts: 68
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Re: 350 Chevy running rough, lots of time and effort spent
Took it out this morning. Got about 2 miles without any issues. Engine runs strong. On the way back to my house, it started shaking and running rough just as I got home.
I'm at a loss here. If it were fuel delivery, then it wouldn't run fine when it's cold, would it? I'm starting to think something is heating up and causing this, but what? No smoke from the engine and the head gaskets were just done about a month back. I might just post a video here in a few.
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#11 |
Senior Member
Join Date: Jan 2005
Location: SUNNY WARM BIKE RIDING COTTONWOOD ARIZONA
Posts: 2,097
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Re: 350 Chevy running rough, lots of time and effort spent
kinda sounds like a vacumn leak at the base gasket on the carb..... have ya checked it once hot ? maybe the modual in the HEI getting warm ? def. worth your time to pull the bowls and check the carb for crap....
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#12 |
Registered User
Join Date: Oct 2008
Location: Meridian, Idaho
Posts: 321
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Re: 350 Chevy running rough, lots of time and effort spent
anyone cosidered vapor lock? maybe weak fuel pump
Matt
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72 chevy k-10, swb, auto, 35's, rally's, posi, 4" lift, 2.5" old style 40 series flows with headers and crossover pipe and some other stuff!! |
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#13 |
Registered User
Join Date: Nov 2009
Location: Mesa, AZ
Posts: 226
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Re: 350 Chevy running rough, lots of time and effort spent
Were the #7 and 8 plugs fouled at all? I had this and replaced the vacuum modulator on the back of the transmission because I was getting trans fluid up the vacuum line. Seems to have helped.
Also ensure your wires are separated, particularly #5 and #7. |
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#14 |
Registered User
Join Date: Jul 2002
Location: Winnipeg, MB
Posts: 9
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Re: 350 Chevy running rough, lots of time and effort spent
Try checking the fuel filter right after it dies, mine would suck up rust and crap then after it sat it (the crap) would go back down the fuel line. When i started it again it would slowly accumulate again and die. Got so P*ss&d off I cut some windshield washer hose out and siphoned some gas into a jerry can and ran fuel line into the jerry can on the seat beside me and drove home like that.
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#15 |
Registered User
Join Date: May 2010
Location: ft smith arkansas
Posts: 131
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Re: 350 Chevy running rough, lots of time and effort spent
sounds like the coil maybe. my timing light has a long lead so i can drive it and have the light in the cab to troubleshoot.
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1972 super cheyenne 1970 Suburb Last edited by trusty72; 06-06-2010 at 11:40 PM. |
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#16 | ||
Registered User
Join Date: Feb 2008
Location: bay area, CA
Posts: 68
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Re: 350 Chevy running rough, lots of time and effort spent
Quote:
The coil and alternator are ancient. The volt gauge seems to read the same as it always has and no issues with the headlights or battery, so the alternator at least works. Coils are cheap, might go pick one up tomorrow. Quote:
The tank is full now. I need to run the gas down a bit before I can clean out the tank. I will probably take the air compressor to the entire fuel line and clean out the carb tomorrow. Also might borrow a friends HEI, to swap out and see. I did untwist and reroute a couple of the new plug wires I put on, didn't seem to make a difference, but I will check that 5 and 7 are not touching. These are brand new plugs, they might have 5 miles on them. I pulled a couple and they just looked brand new, might as well check them all. I was looking up vapor lock, as Matt suggested. I wonder if I have an exhaust leak in the collector that is heating up the fuel pump. I put my hand down there and didn't feel any exhaust leak though. Just a thought.
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#17 |
Registered User
Join Date: Feb 2008
Location: bay area, CA
Posts: 68
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Re: 350 Chevy running rough, lots of time and effort spent
Alright, I think I fixed the problem. Unfortunately, 3 things changed at once and I'm not sure which one did it, but I have a good idea:
#3, Had to pay a bill downtown, so I drove it on the freeway for about 5 miles. Possibly losensing up some gunk and clearing out the carb, but it ran like crap the whole way until I stopped and idled for a minute, then shut it off. I had already cleaned out the lines and replaced the fuel filter, so this is unlikely the fix. #2, I reseated the spark plug wires on the cap, after shutting it off. They were all on there pretty well. #1 probability, I had a manual choke cable that rusted and siezed. I rolled it up and stuck it behind the dash one day, not realizing that the terminals on the back of the instrument cluster are live. My temp gauge started flipping out after the freeway run and I reached my hand under there and felt the choke cable rubbing on the terminals. Started it back up. Now my temp sensor doesn't work, but the truck drives great. Back to normal/full power. My guess is the really old (possibly original) alternator couldn't produce enough spark with the temp sensor grounded out to do anything but idle. Still, the headlights were working bright, so it's hard to say for certain. Thanks again to everyone who helped me out with this! Much appreciated! Time to get back to sanding the new cab ![]() ![]() ![]() ![]() ![]() ![]()
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