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#1 |
Registered User
Join Date: Feb 2002
Location: Cadiz, OH
Posts: 628
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Running rough...Help please
Took my POS for a 56 mi. each way jaunt today. Had about 400lb of gravel in the bed. Engine is 350, HEI with 1 yr. old module, new plugs, Edelbrock 600 Model 1406 (electric choke) and Edelbrock performer EPS. First 5-10 mi. no problem. After that anytime it was under load ie. going uphill or passing it seemed like it was fighting itself to spin faster. Back off the accelerator and it runs smooth. A couple of times it backfired. Timing is set at 12 before initial, has stock vacuum advance and weights. Average speed was about 65-70 mph. Did very little adjusting on the carb. out of the box. Seemed to run great on local trips.....Uh no I didn't put a fuel pressure regulator on it. Any ideas?
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68 1 ton dually 292, 2001 Sebring, 2004 Trailblazer, 11 Camaro Convertible. |
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#2 |
Senior Member
Join Date: Apr 2000
Location: Delta,Pa
Posts: 14,950
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are you running headers if so make sure there is enough clearance between the fuel line and the headers the fuel will actually get hot enough to boil if there isnt enough clearance and it will run out of fuel under load
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Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member. |
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#3 |
Registered User
Join Date: Feb 2002
Location: Cadiz, OH
Posts: 628
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No headers, center dump ramhorns. Gas line follows the framerail to the front of the motor then rubber line over to the fuel pump. Probably stock location except for the line that runs over top the intake to the inlet at the back of the carb.
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68 1 ton dually 292, 2001 Sebring, 2004 Trailblazer, 11 Camaro Convertible. |
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#4 |
Thats the Hillbilly way
Join Date: Jul 2001
Location: Torrance,Ca
Posts: 5,980
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I always like to check the simple stuff first.
How old is the Fuel Filter ![]() ![]()
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BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen , |
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#5 |
Registered User
Join Date: Feb 2002
Location: Cadiz, OH
Posts: 628
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Fuel filter, fuel pump, Carb., intake and all rubber fuel lines all about 1 month old, no leaks that I could find. Rotor, dist. cap. and module about 1 yr. Wires???
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68 1 ton dually 292, 2001 Sebring, 2004 Trailblazer, 11 Camaro Convertible. |
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#6 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,647
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Is the vacuum advance working? Had my weights stuck one time....
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#7 |
Weapons Of Construction
Join Date: Apr 2000
Location: Colorado, USA
Posts: 1,095
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If you're still running a cab tank, pull the sending unit and check the "sock" on the end of the pickup line. Chances are it's full of rust like mine was.
I had so much crap in my tank & lines I had to change out the filter every couple of weeks until it finally cleared out most of it. I had the tank boiled out, but didn't want to mess with cleaning out the fuel lines - filters were a lot easier to change!
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1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO |
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#8 |
Registered Cruiser
Join Date: May 2002
Location: Las Vegas NV
Posts: 2,230
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Was it popping through the carburator, or backfiring through the exhaust? How many miles are on this engine?
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I intend to live forever. So far, so good. |
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#9 |
Registered User
Join Date: Feb 2002
Location: Cadiz, OH
Posts: 628
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Backfired through the exhaust by the sound of it, no burn on the air filter either. Runs great not under load. Goin 70 down the highway just cruisin no problem, but going up a grade or trying to pass it stumbles, backfired a few times. Weights on the dizzy are fairly easy to move (just spring tension). Back it off to about 55mph and smooths out. Mileage on engine is negotiable lol Could be anywhere but definetly not new. Clock says 86,000 so I'd say by the looks of things at least 186,000 assuming its even the original engine. Took gas line off and runs free and clear but the sock is still a possibility I suppose.
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68 1 ton dually 292, 2001 Sebring, 2004 Trailblazer, 11 Camaro Convertible. |
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#10 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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I don't know timeing numbers, I'm one to go by ear, but is 12 degrees a pit buch for when you are loaded down?
I think I'd try backing it off a bit, maybe 10 or so. (if it is still loaded down) and try it again. |
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#11 |
Weapons Of Construction
Join Date: Apr 2000
Location: Colorado, USA
Posts: 1,095
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This is an interesting problem. What happens under load that isn't there normally?
Vacuum Advance? (retards the ignition) I've seen a condenser in an ignition system that had a wire that had broken from flexing w/ the vac advance. The insulation was still intact, but when I pulled on the wire, it stretched. Try throwing in a new condenser. They sometimes sell the whole harness assy with the condenser. On the truck I was working on, it would run fine until he tried to speed up, then it would buck and snort until he let off, where it ran fine. It was about a '76 to '78 Chevy pickup, which might be the same era as your HEI. Pull the distributor, the rotor, and then actuate the vac advance manually by moving the part that the vac advance diaphragm would move (or apply vacuum if you have the right equipment). Watch to see which wires flex. If one of them is the condenser, look closer and pull on the wire like mentioned above. Let us know what you find, and good luck troubleshooting! Heck, it could still be from lack of fuel!
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1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO |
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#12 |
Seasonal Poster
Join Date: Apr 2002
Location: Kelowna BC Canada
Posts: 896
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I just a story about putting a newer style carb on an older manifold. A friend of mine bought a new edelbrock carb and popped it on his old manifold and apparently the older manifolds dont have some sort of cooling holes that are supposed to connect to ones on the carb, so it was always boiling the gasoline and he had the same problems as you...he would have to pull over and wait for it to cool down before the truck would run smoothly again. Sorry I don't really know the technical terms, but until a couple days ago I didn't even know such things existed. Hopes this helps a little...just another possible option
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67 GMC Short Step 350/4-Speed/3.08 Posi Front/Rear Sway Bars Kelowna BC, Canada Member of DTPW |
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#13 |
Registered User
Join Date: Feb 2002
Location: Cadiz, OH
Posts: 628
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Well problem solved. It was the plug wires, the only thing I didn't change when I had the manifold off. The problem got progressively worse, even at no load. One plug wire fell? out of the boot on the cap and another was burnt on the pass. side exhaust but was not arcing that I could see. Put a new set on and when I started the motor the accelerator cable broke
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68 1 ton dually 292, 2001 Sebring, 2004 Trailblazer, 11 Camaro Convertible. |
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#14 |
Thats the Hillbilly way
Join Date: Jul 2001
Location: Torrance,Ca
Posts: 5,980
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Glad you found it .
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BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen , |
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#15 |
Weapons Of Construction
Join Date: Apr 2000
Location: Colorado, USA
Posts: 1,095
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Yeah, Thanks for letting us know! Sure is nice when people actually post what fixed their problem!
Now I have yet another thing to add to my mental checklist for when the ol' beast isn't running up to par.
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1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO |
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