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View Full Version : 350 small block carb question

cutty2fast
09-08-2008, 07:38 PM
so i got this 350, its got a demon 750 with vacume secondaries on it among other add ons, it runs fine but when i stomp the gas it bogs out but after a few seconds and you pick up speed it just opens up and runs like a bat outta hell, i adjusted the idle mixture and idle speed already i have tried all the vacume springs same thing everytime is there something else i should be adjusting???? its a older demon and in a couple weeks im gonna go buy a new carb but i dont want to if i dont have to any ideas?
J@meson
09-09-2008, 06:36 PM
1. it may need a rebuild
2. sounds like the secondarys are opening too fast, what about a hard roll does it do it?
3. 750 is also too much carb for a semi stock 350. 600 may be a lil better. i ran a 670 street avenger on a 11:1 357 with 250 shot a few years back and was deep into the 11's. so it may be too much carb
cutty2fast
09-09-2008, 06:45 PM
yeah thats what i was thinking, if tried every secondary spring i got same thing but when i go to light of a spring it bogs out horribly lol
when im haulin ass it will still do it but sometimes if i give it gass slowly and then punch it it will go i think im gonna get stuck buyin a new one WITH MECHANICAL SECONDARIES lol
MustangDave33
09-13-2008, 02:11 PM
Sound like the carb is to big. With vac sec it shouldn't fully open the secondary if the carb is to big unless you have the wrong spring in it. Does it have jets in the rear or a plate?
Mars_302
09-18-2008, 02:32 PM
that carb is way too big
Sneakin Deacon
09-19-2008, 08:22 PM
tried changing the cam? i ran a 750 on a 355 and had no problems with it...your secondary jets may be too large aswell..but check your cam 1st.
fuelie327
10-28-2008, 08:29 PM
carb is way to big.I run a 519/523 lift cam with big AFR's and a 700 is almost too big for me.
J@meson
10-28-2008, 08:59 PM
so cutty what ever happened? i see your selling the carb, did u buy a smaller one? did it make the improvement?
Sneakin Deacon
10-31-2008, 02:13 AM
carb is way to big.I run a 519/523 lift cam with big AFR's and a 700 is almost too big for me.

im not seeing the complete relevance of your cams lift, and "big" AFR's.
obituary
11-17-2008, 02:52 PM
i ran a holley 750DP/mech on a 460hp 355 ...ran rich ,but throttle was very in tune

Carburetor CFM Sizing Calculator - Shop Math (http://www.classictruckshop.com/garage/shopmathcfm1.php)

you can always rejet it to a smaller fuel curve
Tiffiny
11-17-2008, 11:29 PM
demon carb underated to begin with its more like an 850
racingrick
11-18-2008, 10:44 PM
no one mentioned it but if when you floor it the car stumbles really bad and then goes it could be either ignition relation or the (I think it's called) "accelerator pump" in the carbuertor can be bad, it's a little rubber diaphragm that can tear. (been away from carbs for many years)
obituary
11-18-2008, 11:28 PM
no one mentioned it but if when you floor it the car stumbles really bad and then goes it could be either ignition relation or the (I think it's called) "accelerator pump" in the carbuertor can be bad, it's a little rubber diaphragm that can tear. (been away from carbs for many years)

true ! the bog could be from it not working at all ,or flooding it ( blackish smoke)