Mr.Fixit - Carb Question.

WBofTN · #1 (**permalink**) 11-21-2003, 08:27 AM

Mr.Fixit:
I need help trouble shooting a carb problem.
I have a Holley 750dp Manual atop a 351w stroker.
Had the thing running great, and out of the blue
it has started back firing thru the carb. This happens
when engine is at operating temp after sitting at
a red light (idle) .When I give her the gas - POP.
Then she goes dead for a second and comes alive again,
or goes dead totally (hard to refire then). I have check for
vacuum leaks / made shure everything is snug. The back fire
happens when the carb makes the transission from the idle
circuit to the mains. Your expertise has been a big help to me in the past.
Thanks
WB

Mr.Fixit · #2 (**permalink**) 11-21-2003, 08:39 AM

A pop when you jaz the throttle sounds to me like your accellerator pump is not covering up the lean spot as it waits for fuel to get pulled out of the boosters. Check the accell pump components, make sure gas is getting squirted out the discharge nozzle as soon as the throttle blades move. It could be as simple as a bad check valve or bad diaphram in the accel pump. (Could also be an intake valve not closing all the way, or sticking.)

WBofTN · #3 (**permalink**) 11-21-2003, 08:50 AM

Thanks: I will check the squirt . Could it be that I just need to adjust accell pump "lag"?? How much Play sould there be?

Mr.Fixit · #4 (**permalink**) 11-21-2003, 09:20 AM

I prefer no lag, but you have to be carefull that the pump arm is not bottoming out the diaphram, that can bend the arm and such.

Chaplin · #5 (**permalink**) 11-21-2003, 09:35 AM

Fixit is right. No lag. Adjust it so that as soon as the throttle begins to move it immediately begins to activate the accelerator pump. According to Holley there should be .015 clearnace between the pump arm and the pump lever when the throttle is in the wide open position, but the pump should be activated as soon as the throtte begins to move.

Jack21 · #6 (**permalink**) 11-21-2003, 03:54 PM

Another thing to check for off-idle flat spot is primary butterflys open too far and exposing too much of the transfer slot. Bring the idle air up with secondary butterflys.

What cam, lifter type, and intake are you using? What is your idle vacuum? What kind of distributor are you using? Initial advance? Vacuum advance? Centrifugal advance, @ what RPM?

V-8 · #7 (**permalink**) 12-01-2003, 08:16 PM

hi everybody,
ý have got 67 mustang with 3.60 rear gear.A-1 made 2500 stall converter, gm th-350 auto trans.car weight 3222pound +200pound driver=3422pound.
the engine spects:ford 351w bored 0.040,victor jr intake #edl-2981,tfs heads #tfs-51400002,10.5:1 comp ratio flat top ross custom made forged aluminum pistons for use with 250hp nos,headman headers,x-pipe,flow masters,compcams mechanic roller camshaft kit #35-771-8,dui hýgh voltage electronic ignition,speed pro rings,federal mogul bearings,roller rockers,200hp nos cheater,standart block,crank & rods with arp bolt,holley street mechanic fuel pump...
note:ý cant take & find more than 92 octan fuel

first ý drove my car with my old 750cfm holley #hly-0-4779c.it gone 12.7sec 114mph with 245/45/17 kumho's and 100-150 meters slip

.after 1-2 weeks later ý have got some problems with my carb.it start to made back fires,idle stop and lastly it burned because of back fires.then we put my friends 800cfm carb #hly-0-4780c#,it didnt work properly in idle and some times made back fires because he made some things in it by himself.then we took it off.
lastly we put a #hly-0-80509-1# hp series 830cfm carb today and we solve all the problems with this carb. but ý think 830cfm is get too much for engine.note: redline 6600-6800rpm
Q:which type of holley carb would you prefer to me.hp series or ?
Q:vacuum or mechanical secondaries?
Q:how much cfm get enough?
" ý m thinking 750cfm hp series mechanical secondaries carb #hly-0-80528-1"
please help me!!!!!!! ý m going to get crazy

))
special thanks.
atay/turkey-istanbul

Turk · #8 (**permalink**) 12-01-2003, 11:44 PM

Atay from Istanbul Turkey?

Small world.
I am Aytac from Vacaville California, originally from Izmir Turkey.
Welcome to the forum, and even though this is not a Mustang forum, many in here are very familiar with all things Ford and Mustangs especially, that you will probably get a satisfactory reponse to your questions.

Enjoy your stay.

Aytac "TURK" Ercen
Club Cobra Moderator.

Mr.Fixit · #9 (**permalink**) 12-02-2003, 08:05 AM

An 830 CFM carb is going to have less low RPM throttle response on the street, but may actually run a mile per hour faster in the quarter mile on your 351. I would go with a 750 vac secondary if it sees the street.

V-8 · #10 (**permalink**) 12-02-2003, 01:44 PM

Quote:

Originally posted by Turk

Atay from Istanbul Turkey?

Small world.
I am Aytac from Vacaville California, originally from Izmir Turkey.
Welcome to the forum, and even though this is not a Mustang forum, many in here are very familiar with all things Ford and Mustangs especially, that you will probably get a satisfactory reponse to your questions.

Enjoy your stay.

Aytac "TURK" Ercen
Club Cobra Moderator.

selam Aytaç,
i also have a cobra snake emblems on my front fenders of my car.they seems well.i love them...
because i put eleanor body kit.and in the movie there were cobra emblems on the front fenders.