REBUILT CARB NOW ENGINE WONT IDLE AND BACKFIRES!! HELP!!

[epmustanggt]

I have a 1966 mustang gt with a 302ci motor in it. i rebuilt my holley 4150 650cfm double pumper (man secondaries no choke). when i got done i put it all back together and i noticed that the secondaries dont spray fuel at all, and the engine will not idle at all if i take my foot off the gas it will die and if i give it alot of gas it will backfire. it also sometimes backfires when trying to start it. i am trying to figure this out but i have no idea whats going on with it.

 

[FullRace]

Accelerator pump may not work. Try and manually actuate the acelerator pump and see if it sprays. If not something was assembled wrong or its got a hole in it or something. If it does spray but doesnt work with the throttle its your cam (on the carb) or the linkage setup doesnt allow the secondaries to open.

 

[D.Hearne]

How many Holley carbs have you done before? You've assembled it wrong most likely. The secondary metering block gasket must be the correct one for the accellerator pump passage to be clear. The center hole just above where the powervalve would be on the primary side block needs to be open. And unless your motor is built up a good bit above stock, that 650 DP is probably too big for your application.

 

[epmustanggt]

also an update to this problem, my engine has very little vacum when i am trying to get it to idle, like around 4 or so and i dont think there are any leaks from vacuum ports.

 

[epmustanggt]

the motor has trick flow aluminum heads with 2.02 1.60" valves, e-303 cam, tri-y headers, edelbrock rpm airgap intake manifold.

 

[epmustanggt]

this is the second time ive rebuilt a holley like this

 

[D.Hearne]

Hard to say just what the problem is, sitting miles away from it, but I sugest you take it back apart and reassemble it with a good set of instructions. Also while it's apart, blow out any and all passages with air and carb cleaner to insure you don't have a piece of trash blocking anything.

 

[epmustanggt]

ok thanks

 

[epmustanggt]

ive got the carb back apart so im going to recheck everything and try this again.

 

[D.Hearne]

Also make sure the metering block gaskets are the correct ones, I know Holley includes several different gaskets for various carb applications in their kits.

 

[epmustanggt]

all the gaskets are in the right place and nothing seems out of the ordinary... i cross checked it with the holley instructions

 

[D.Hearne]

All the metering block gaskets are very close in appearance to each other, but it only takes one blocked passage to screw things up.

 

[epmustanggt]

ok, ill look again at the old ones versus the new ones

 

[epmustanggt]

ok i know for a fact that i have the correct gaskets and they are in the correct placement and i have also found a torn check valve in the primary acclerator pump. that is the only thing i have found wrong. .... also can a needle on the secondary portion of the carb (not sure what its called) where it sprays out into the barrels, get stuck?? the secondaries were the ones not sprayin so im trying to figure that out.

 

[epmustanggt]

also anyclues to the vaccum? 4" ?? pretty out of the norm? will timing cause this vaccum problem

 

[epmustanggt]

ok well i put the carb back together, it still wont run but now the secondaries are working so i made some progress !

 

[D.Hearne]

There's a check rod down inside the passage under the squirter nozzle on both accellerator pumps, these can get stuck. The rod has a pointed bottom end. Although I've never measured vacuum on any of my engines, 4" does sound a bit low. That figure is more inline with what you'd want on the top end.

 

[epmustanggt]

well i got it running and it runs better now so thanks for the help !