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Old 05-13-2002, 12:56 PM
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powerdodge powerdodge is offline
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Default backfire trough the carb

hello! question from norway

I have a dodge ram with a 318 who i changed a lot of parts in last summer...
the cam, gear, intake , carb, and ported the heads a bit.

when i starts up, it runs grate, and idle grate, but when i snap the pedal, it boom... backfire throug the carburettor.. i have the timing set to 10 BTDC, as it should be , but a few days ago, I set the timing to 4 BTDC, and then the engine runs perfect..

why doesnt it work with the timing set at 10 BTDC as i should be??
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Old 05-13-2002, 04:59 PM
Jims451 Jims451 is offline
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First, make sure you do not have any vacuum leaks, and the car is not running too lean.
Also, make sure you have the correct spark plug routing, expecially the #5 and #7 wires.
Second, remove the vacuum advance line to the distribitor and plug it, then see if that helps.
Third, have you checked the timming mark on the dampner to make sure it is correct?
A simple way to check is with a Top Dead Center tool that screws in through the spark plug hole. Just screw the tool in so the engine stops at 10 before TDC (when turning engine over by hand / with a socket on the crank dampner bolt), then turn the engine backward and it should stop at 10 ATDC on the timming mark. If it does that then the TDC mark on the dampner and timming tab are OK. If not, the dampner timming mark is off and you need to make a new mark so that when the piston stops on the TDC tool, the mark is at the same degrees before and after TDC.

If the timming marks are OK, and you have no vacuum leaks, you need to check the disrtibitor advance curve and the distribitor total timming in the plate (mechanical advance, not vacuum advance.) The easiest way is with a dial-back timming light, or you can use the degreeing tape that tapes to the dampner (sold by Mopar, but it usually falls off after a few miles.)
Usually you will only want about 36 degrees (plus or minus 2 degrees) of Total advance (the amount of advance when the engine is at high RPM, usually by 3,000 RPM all the advance is "in".)
When you return the engine to idle, the initial timming will be the difference of the total timming minus the mechanical advance in the distribitor. By "re-curving" the distribitor you can change how much advance is in the distribitor "plate". This way you can set the initial timming at idle for best idle quality and starting, while maintaing the correct total timming.
Once this is set, re-connect the vacuum advance. If you get pinging with the vacuum advance, you can make some adjustments to how much advace it gives by adjusting the spring tension inside the vacuum cannister (through the vacuum line nipple, using an allen wrench.)
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Old 05-14-2002, 12:24 PM
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powerdodge powerdodge is offline
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tnx! a lot of stuff! i'm on my way to the car soon

oh...about the vacuum line to the distributor...
I have a carter afb carb, with a timed, and a full vacuum tube... I could not find out who I had to use? right now i have it conected to the timed port...
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