350 engine pops and bacfires once or twice upon inital acceleration - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-26-2010, 05:21 PM
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350 engine pops and bacfires once or twice upon inital acceleration

Sbc 350 edelbrock 1406 600 cfm electric choke Carb pops and backfires on initial acceleration than cleared up but truck seems to surge a bit, I've played with the timing a bit and just cleaned out Carb as the truck sat for a few months was not doing this 3 months ago prior to sitting any help or advice welcomed

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Old 08-26-2010, 05:57 PM
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i would force the choke half closed and try it, if the pop goes away your most likely dealing with a lean condition. timing typically wont cuase a pop. if the plugs are soaked a pop can occur as unburnt fuel hits the exhaust....not likely your case..that would happen under no load too. valve timing/worn cam...possible but dont think about that yet. further down the list weak ignition coil... i`d scope out the lean condition first.
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Old 08-26-2010, 07:00 PM
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alright so i gave that a try and still popping on part throttle operation, with choke part closed and myself operating the throttle from under the hood. doesn't seem to have changed at all, the distributor i'm running is a MSD street fire and i did install the advance stop for vacuum adv. is that a possible factor? the engine is a new rebuild less than 150 miles on it sat for maybe 2 3 months bad gas drained it out put new in and initial problem began occuring, removed top plate on carb and cleaned carb out did not clean passages within carb just what i found internally should i go for full carb build or what. i'm stumped because truck did not have this problem prior to now, only thing thats changed is a new elec fuel pump, standard trans, and timing i initaly suspected timing to be out but i've gone from one extreme to the next and all in between and no change, also truck has not moved but a tenth of a mile and sat in the drive way for maybe 8 start ups of a few minutes and i have used the 6 gallons of fuel i put in it????
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Old 08-26-2010, 07:51 PM
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Here's a couple of tricks that I have successfully used to clear out a piece of junk out of a carb passage in an emergency . Remove the air cleaner and work the throttle by hand with a finger of the other hand on the choke plate . Bring the engine up to maybe 3000 rpm and then slam the choke plate all the way shut and at the same time open the throttle wide open , then before the engine chokes itself to death open the choke back up and bring the engine back to idle after it catches again . Repeat as neccessary . Another trick was taught to me by a guy 11 yrs my senior : cross a couple of plug wires to make a backfire in the intake . If I remember correctly it is two in order of firing . Both of these methods have worked to pop junk out of a carb port for me , it would have been better if you had blown through all the ports with compressed air when you had the cover off the carb , but give this a try Let us know if it works .
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Old 08-26-2010, 11:15 PM
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The first trick has worked for me several times. Good stuff there. Might want to pull the plugs and check them out also, or even replace them with new one's. With only 150 mi on them they could be fouled up from the initial break-in if you haven't changed them yet.
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Old 08-29-2010, 08:25 PM
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THANK YOU ALL !!!!!!! 5 and 7 were crossed and there was a little bit of build up in my carb still used the choke and WOT trick cleared it up great! found a vac leak on carb mounting gasket also and now the only problem i'm having is with part throttle accelerartion it seems to lack fuel i'm running the carb de rated for my altitude and instead of 98 and 95 for jetts i'm running 95 and 92, will be putting new plugs in tomorrow and filter oil change also trucks idling great and has great pick up i'll inspect the plugs tomorrow and see how i'm running. thanks again and invite any other advice and ideas for the part throttle solution.
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Old 08-30-2010, 07:59 PM
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Quote:
Originally Posted by 88BIGchevy
THANK YOU ALL !!!!!!! 5 and 7 were crossed and there was a little bit of build up in my carb still used the choke and WOT trick cleared it up great! found a vac leak on carb mounting gasket also and now the only problem i'm having is with part throttle accelerartion it seems to lack fuel i'm running the carb de rated for my altitude and instead of 98 and 95 for jetts i'm running 95 and 92, will be putting new plugs in tomorrow and filter oil change also trucks idling great and has great pick up i'll inspect the plugs tomorrow and see how i'm running. thanks again and invite any other advice and ideas for the part throttle solution.
It sounds to me like the primary side is NOT liking the de-rate . Try jetting up the primary side and I'll bet the part throttle hesitation goes away . Let us know .
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