carb to big?
hey fellas, ive got a 253 without taking it a part im pretty sure its all standerd, it bogs down when i try floor it then will miss for a while and take off like a rocket, its got a 600 holley vac sec on it, IS THIS THE PROBLEM? TOO BIG?, got pacemakers with flowmaster, big cap electric dizzy, have done new plugs new 9mm leads new filters
all i can think of now is the carbs too big? timing?
thanks
Banned
If your 253 is taking off like a rocket I would absolutely recommend not touching it at all....
rejet the carb and check timing
captain halfajob
problem with 600 vac is you cant really adjust the secondarys. does it have a pump cam on the primary? if so turn it down so it doesnt activate fully. less fuel in that initial may work.
but yeah if there is a way to keep the secondaries closed for a bit longer, then do that.
edit* is it one of these?
if so you can try fitting a heavier spring in the vacuum module which will keep the secondaries closed for a bit longer. it also looks like there IS a cam, so dial that down as well.
A 600 is way to big for a stock 253. I had good results from a 465 holley, but was running a TQ20 cam as well. Aside from bragging rights, using the 600 will wash the bores (fuel washes the oil off the cyclinder walls, which isnt good) and will just make your fuel consumption go up. Try a 350 or the 465.
check the timing that you are getting max vacuum and see if there are any problems with the carb, I doubt a vac sec 600 will be capable of over carbing a 253 as if it does not need it then the secondaries will not open up, just like the 750 Rochester that come standard on blue 253
thanks guys, im running about 10 advance on the timing, im trying to get my hands on another carb, i dont no bugger all about re jetting carbs, might try have a look at the timing today
captain halfajob
600 is fine for that engine because its vac secondaries. the quaddy is a 730 which if you look at it like that is WAY too big for a 308, but works incredibly well. you dont need a new carb, just set your carb up to work properley.
its not a jet issue, its quite simply an issue of keeping those secondarys closed until the intake velocity is such that it can pull them open.
the secondary diaphram looks a little somethin' like this:
inside it is a rubber diaphram and shaft that look like this:
and there is a spring resting on top of it that looks like one of these:
the way it works is: the diaphram and shaft is connected to the secondarys butteflys (carby base) intake air rushes through the primary venturies creating a vacuum which is passed to the top of the diaphram and it forces the diaphram to suck closed, compressing the spring and opening the secondarys.
by changing the spring to a heavier unit, it means it requires more intake velocity/vacuum to suck open the secondaries, which means they stay closed for longer. what is happening at the moment is you are getting them open too soon, its taking a HUGE gulp of air, but cant do anything with it until it gets to a slightly higher RPM. once it does it uses all the extra mixture efficiently, but before then you have a horrible flat spot.
if you buy another carby, more than likely you will just hit other issues. better to figure out what you have now and how to get it working, than move onto newer problems.
the spring kit is 12 bucks BTW. new carby is probably around 500. i know which one i would try first
Tells it like it is.
Make sure the accelerator pump doesn't dump too much fuel when you boot it at low RPM. Had that problem with my VK many years ago - it essentially flooded the motor but once that cleared it went off like a cut cat.Originally Posted by EFFDUP
Reaper
the OP did say that it's a stock 253, right?
yea mate its a 253, no internal mods that i know of
If you don't know how to sort the carby then take it to someone who can or change it, either for one that YOU KNOW is good or a new one as the old one you have maybe incorrectly adjusted or have an internal problem such as blockage or leak.
ive found a holley 450 so hopefully that should be a better starting point
That sounds better. Just make sure you dont over jet the secondaries, overwise there wont be any real gain. Hope it all goes well.
brought the carb got it home and checked its a 600 damit, number is 1850-5 thats a 600 isnt it? also has 1539 under it
the carb i already have on the car is 1850-5 3368
are they both 600 vac secs?
Last edited by EFFDUP; 16-08-2011 at 03:20 PM.
captain halfajob
well a 450 will be 2 barrel and a 600 will be 4 barrel. pretty obvious difference really. if you cant tell the two apart, best get a mechanic to set it up.
450s are 4 barrel? 350 is the biggest 2 barrel isnt it
well both carb numbers equal to a 600 vac secs so will try get my money back
captain halfajob
well ill be damned: Holley Performance Products 450 CFM Four Barrel Carburetor#0-80364 they do make 450 in 4 bbl. LOL. there are 500 2bbl, in all honesty i didnt realise 4bbls came that small.
if i had a hat, i would eat it.
Most small 4 barrel holleys are 390 or 465cfm.Holley use to make a 450 centre float,they can be ok on a 253.
will try the new 600 and see if it still bogs down,
have just put my old carb back on, advanced the timing a bit took it for a drive and it went harder than my 308 ever did,BUT after taking it for a good hard drive i pulled back in my drive and it started idling at 1500rpm, i turned the idle screw right out still did it then checked for leaks couldnt find any
why would it do this?
Torana Addict
Cause you changed the timing?
but it was running fine for the whole time i was driving just changed when i got home? will put timing back tomorrow and try that
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