I just installed a wieand intake manifold and holly street avenger carb on my 78f100 with swapped in 86 351w. the engine starts up pretty decent,and idles very smooth. the problem I am having is that it is backfiring through the carb on acceleration when the engine is cold,and it takes a few seconds to get back to normal idle after I rev it up. I backed the idle mixture screws out a half turn each,and that didn't seem to make a difference in the backfiring or slow return to idle speed. I really didn't want to back them out much more than that and get very far off the factory settings. what else would cause these problems? I am pretty sure I got the distributor in the same way it came out. would timing being off a little cause the backfiring only until the engine is warmed up? I tried the best i could to check for vacuum leaks,but couldn't find any. thanks for the ideas,Ben

 

i had a similar problem. for me it was the timing. it was off just enough. it worth a shot to check.( for future reference, i normally try to put a visible mark on the dist and the intake manifold. it may sound funny but i've found that neon or glo in the dark nail polish(my girlfreinds idea) works the best)

 

ok,i just checked timing and have a question. I am supposed to check it with the dist advance plugged,right? that is where I am supposed to get the factory recommended 10 degrees of advance,correct? I highlighted 3 marks on the harmonic balancer before I checked the timing. ATC and BTC,whatever those mean,and the 10 degrees of advance mark. when i checked the timing (dist advance plugged) the timing marks lined up on the ATC mark. shouldn't it be reading on the 10 degree mark with the timing light? thanks for the help,Ben

 

you are on the right track. when you check timing you need your engine idle set properly aprox 700 to 800 in park or n for manual trans. next you need to set the idle screws to the recomended settings which is usually about 1to1 1/2 turns out this should put you fairly close. now some people disconnect the vaccum advance and plug the line from the carb so you dont get any vaccum leaks. this is not necessary because you need engine rpm to increase to create vaccum to move the advance rod inside the distributor. now all you need to do is set the timming to 10deg btdc as indacated on the dampner.

to explain atdc and btdc. atdc is short for after top dead center which means the spark happens however many degrees after top dead center. btdc means before top dead center which means spark happens before the piston gets to top dead center. in general most fords like advanced timming usually 10 to 12 deg advanced. all of this is at a loss if any of the timming components are at all worn. ie timming chain, distributor, camshaft.

hope this helps and i did not confuse you any.

 

Have you made sure the carb floats are adjusted correctly? Did you get the timing set to 10 btc? You can go up to 14 btc if you use good gas and want a little more power. Let us know if you still have a problem.

 

thanks for the help guys, I didn't have time to work on it tonight,will try again tomorrow night and post my results back on here.....Ben

 

I just had enough time this evening to start it up,let it warm up and adjust the timing to 10 btc. no more backfire!!!! so i think the timing was the backfire problem. next time I have a few minutes,i need to turn the idle speed down some,then we should be all set thanks again for the help