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#1 |
Registered User
![]() Join Date: Feb 2000
Location: Maquoketa, Ia/ Orr, Mn
Posts: 3,009
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engine backfiring
This began Tuesday night when the fuel pump died on the way home and ended up changing it in a parking lot, but now the motor will backfire when going up hill or accelerating when down shifted. The timing is right on, carb is set, new fuel filter, complete tune up two weeks ago. Also feels sluggish when under load but only backfires when it is kicked down into second gear. Any ideas? Thanks
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#2 |
Registered User
Join Date: Mar 2002
Location: Bondurant, IA but in Worcester, MA for school
Posts: 767
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What kind of setup you running as far as carb./engine? It could be that the new pump is putting out too high pressure for your carb I dont know. Cut the Edelbrock carbs can only take like 6psi I think. Double check you timing as well because the exact same thing happened to me and it was because my distributer clamp broke so the distributor would torque itself around when I accelerated hard and under load.
HotRod
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1970 Chevy C-20 350 V-8 Turbo 350 w/ shift kit Dana 60 w/ 4.10 gears AND Powr-Loc POSI New Additions: Summit Headers 135amp alternator Proform HEI Edelbrock 1406 600cfm carb Sunpro Tach Powr-Loc POSI Edelbrock Performer RPM Intake MSD 6A Ignition Box AIM: HotRod929 Visit My Site: http://1970chevy.netfirms.com/ |
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#3 |
newly minted old timer
Join Date: Dec 1999
Location: Hudson WI
Posts: 3,511
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are you sure you dont have a miss? or a miswired sparkplug wire?
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____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban |
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#4 |
Registered User
![]() Join Date: Feb 2000
Location: Maquoketa, Ia/ Orr, Mn
Posts: 3,009
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It is a 350 with a mild cam and a rebuilt Quadrajet. I had it running beautifully before the fuel pump went out and now it just isn't the same. I've been through everything in the ignition and it all is new. Thanks
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#5 |
Registered User
![]() Join Date: Feb 2000
Location: Maquoketa, Ia/ Orr, Mn
Posts: 3,009
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heres an update, now the backfire went away, but it still feels sluggish and underpowered when giving it moderate to heavy throttle. Will try carb adjustment again but could there be something connected to the fuel pump that I'm missing?
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#6 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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try cleaning the fuel filter in the carb or take of the fuel supply line to the pump and blow about 10lbs of pressure back thru the tank [with the gas cap off]
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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 |
My other Love
Join Date: Aug 2001
Location: Castlegar B.C. Canada
Posts: 4,085
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could you be having a problem with the vacum advance?, did you change brands or octane's of gasoline?
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#8 |
Registered User
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Location: Maquoketa, Ia/ Orr, Mn
Posts: 3,009
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as far as I know the advance is working fine, I haven't had a chance to get gas yet, but I'll get some today and see what happens. What would blowing pressure back into the tank do? I've done that on diesels but not on gas stuff before.
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#9 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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theres a screen on the fuel pick up tube that some times gets gooked up
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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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#10 |
Recovering Truck Driver
Join Date: Mar 2002
Location: Orleans, NE USA
Posts: 1,883
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try changing fuel pumps again, with another new one. The last time I bought a new fuel pump for my truck I had the same problem.......not the backfire, but the miss and power loss were there. I was not happy with my new purchase. I pulled a used on off a junk car so I could use the truck and that used fuel pump is still running my truck.
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67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska |
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#11 |
Black 72 Chevy
Join Date: May 2002
Location: Los Angeles, California
Posts: 662
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Your problem started after you replaced the fuel pump. Replace it again. Some times new parts don't work.
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#12 |
Registered User
![]() Join Date: Feb 2000
Location: Maquoketa, Ia/ Orr, Mn
Posts: 3,009
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The fuel pump is actually a used one off my pickup that I threw on my Blazer but since the pump only has about 1000 miles on it and the truck ran fine I thought it should work. Depending on how it runs during the week I might change the pump again. Thanks
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#13 |
Registered User
![]() Join Date: Feb 2000
Location: Maquoketa, Ia/ Orr, Mn
Posts: 3,009
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well on the way to school this morning, I was accelrating after turning onto the road and it backfired, then lost all power. Then after that I floored it and it sounded like it flooded out, started popping, coughing and stumbling until I let off to about idle. I might try another carb but if it was running fine last week, what else could it be?
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#14 |
Registered User
Join Date: Apr 2000
Location: Frisco, Tx, USA
Posts: 606
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I'd try a new fuel pump. Since it's the only thing you changed. Also, do the Quadrajets have a sintered bronze filter or are you running a filter after the pump before the carb? May be your pumpu puked into your fuel line. You may want to test your pump out by killing your ignition system (remove the coile wire) and turning the engine over to pump some gas into a jar to see if you are getting a good squirt.
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#15 |
Registered User
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Location: Hampton, Ga, USA
Posts: 217
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If you are running an HEI, sometimes the wire to the pickup inside the dist. will have a cracked/worn spot on insulation and it will short to dist. body and will cause backfire and loss of power when vacuum advance mechanism moves .
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#16 |
Registered User
![]() Join Date: Feb 2000
Location: Maquoketa, Ia/ Orr, Mn
Posts: 3,009
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My dad says it sounds like it isn't advancing, which could be possible since I was messing with the module and had to take off the rotor, I might have popped a spring off under that and that might be the whole problem. I'll have to check it out closer when I have some daylight to mess with that thing. Thanks
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#17 |
Registered User
![]() Join Date: Feb 2000
Location: Maquoketa, Ia/ Orr, Mn
Posts: 3,009
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Yep, wasn't advancing the spark. The weights under the rotor got messed up from the night I put the rotor back on in the dark. Glad that was all. Runs great now. Thanks
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#18 |
Designated A-hole!
Join Date: Mar 2003
Location: South Mississippi
Posts: 36,450
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Glad to hear it was something simple (and cheap) to fix.
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