here is my problem I have a 377 motor 750 demon bc carb and an ati procharger just crusing down the road the car runs fine but when I give it gas it starts to break up the harder I hit the gas the worse it breaks up can anybody give me some ideas were to look for this problem to fix

 

descripe your fuel system and how you get the extra fuel under boost.

 

it is a holley blue pump 5/8 braided feed line off a sump in the tank regulated to 7 1/2 psi there is no boost refrence for the fuel YET .BUT!!! the motor is breaking up before I even see any boost almost at 1/4 throttle

 

you have a boost gauge?

 

yes i have a boost/vac guage and a fuel pressure guage. all of my guages are liquid filles AUTOMETER 2 5/8 so i am pretty sure that they are correct

 

try it without the blower and see if it happens?

 

Well, my first guess is an ignition issue. I’d start with looking for too big a plug gap, weak coil, hei module or possibly wires.

My second guess is that it might be running lean which would cause it to pop through the intake.

When does it do it… I know that you said ¼ throttle, but is it if you punch it, if you roll into it gradually? What happens if you let is slowly climb up to the same rpm?

 

well i am useing an MSD 6AL PIGGY BACKED BY A MSD BTM AND AN MSD COIL the wires are TAYLOR 409 PRO RACE WIRES the spark plugs are new. the carb is also new it is a 750 MIGHTY DEMON BC(blower carb) I did notice that when i jetted it down alittle it got worse . What size jets do u recomend i think I am at 75 front 78 back as for the breaking up mostly under hard throttle if I drive with a light foot it is fine BUT that doesn't get me down the 1/4 mile

 

I forgot the plugs are gapped at 32 i changed the jetting when i changed the plugs and the msd parts have less then 10000 miles and two years

 

ok I tried bumping up the jet size on the carb that helped with the stumble but it still is breaking up at WOT for alittle then it takes off or fries the tires i went 4 sizes front and rear

 

I think that you partially answered your own question… went richer, runs better…

FWIW, if it was working fine at light throttle I’d venture that you only really need to richen the secondarys. If it’s stumbling on tip in I’d guess that you’ve got too much or too little accelerator pump (probably too little since again, going richer made things better).

You may find that gap to be a bit too big when you’re running a bit of boost… I’ve had to cut down as low as .022-.024 in some applications. BTW, just because you’ve got new/newish performance parts for ignition parts doesn’t mean they’re good…