tuning vacuum secondaries

[Jonstantine]

sorry, i didnt reply sooner. right now i just have internet at work for the most part

i ordered the demon tuning book and i hope that will help me some

i was going to try a bigger accel pump or smaller squirter but neither oreilly's nor auto zone have any
so i figured i would just wait

i called 4secondsflat.com and he just told me to buy a 525 from him and sell the 625
he said something about the airspeed my engine was pulling was only about half what i needed... bla bla bla

when my book gets here on monday im going to take the carb apart and look for anything that might be setup wrong or any restrictions that arent supposed to be there

if that doesnt work, ill probably get the smaller squirter and a 50cc pump

also, i have a performer intake sitting in the garage... would the problem possibly be eliminated with a dual plane? (of course id put a big open spacer and probably do some porting)

thanks again

 

[BlueMonster65]

what is your base timing and total advance timing set at? these play a critical role in the rpm range you are experienceing trouble in. i have a road demon 625 on my 302. no problems. i changed to a red pump cam 1st step. found that the silver secondary spring works best. have 14 deg intial with 36 total by 3000rpm. i have cast iron PAW heads and 9.67:1 compression.

 

[ashford]

took mine completely apart-again remove every little bit of flashing followed every port used a small piece of wire off a brush to check every emulsion hole, bleeds etc nothing wrong anywhere. reassembled it put it on drove it same problem, took it off again and put on the 7 year old holley i have, runs perfect.

and again i tried it on other motors a 302 fox that runs a 13.1 1/4, a 350 that makes torque to 6500 rpm no change excep the rpm range. its the engineering, the primaries and the secondaries use the same metering block the same high speed bleeds but use different boosters.

 

[one2gamble]

id return it, mine works fine once I figured out how totune it.

 

[Jonstantine]

im back again

it seems to be transfer slot dependent
yesterday i reset the secondary transfer slot for square (like its supposed to be)
i also put in the small yellow spring
idled like crap puffing smoke, but no bog

well, lastnight i did some more reading of my demon book and it said if you idled below 1k rpms that the secondary butterfly should be closed below transfer slot - well, the butterfly wont even close that much, but i did close it as much as possible
i also set the primary butterfly back square with the transfer slot (just to make sure) and before i started it up i put the idle set screws at 1/2 open
started real quick with a nice idle - i closed the idle set screws about 1/8th more with no problems (although once the engine got real warm, it idled a little worse)
now it bogs
so today, i check the deman manuals online, and it says the butterfly slots (primary and secondary) should be opened equal amounts
so, im going to open the secondary butterflies a bit and probably open the idle mixture screws, depending on what the engine seems to want when its warm.
hopefully this will fix the problem

ashford, all i can say is, try a lighter spring (short yellow) and recheck your butterfly positions on the transfer slots underneath the carb

i let you guys know what happened around 7pm central tomorrow

i feel like part of this is my own stupidity, and it kinda is - but hopefully anyone who has similar problems down the road can come here and maybe get some ideas

also, after i try these changes, im going to go with a smaller squirter

 

[BlueMonster65]

the yellow spring opens the secondaries way too soon for a 289 or 302. try the brown spring and work your way to a larger spring. but you are on the right track by reseting the idle transfer slot and idle conditions. make sure the acc. pump is not be activated too soon, i found it works best with a tiny bit of slop in the linkage, it just touches teh acc.pump. once again demon carbs like lots of timing advance so take a look at your timing. and advance it if possible.

 

[Jonstantine]

ok, i opened the secondaries about a 3/8ths turn
idle is better... but i still have a definite tip in problem (since i closed the idle screws below 3/4)
next step - open the idle screws back to 3/4ths and test

if im still having the problems... im going to change the pump cam hole
here is a good chart i found about when the gas comes in with different cams and stuff
http://www.gofastforless.com/fuel/cams.gif
the 330 cam is purple, and im going to switch to hole 2 or 3 (i think its in hole 1 now, something ill have to check)

next step will be to work on the secondary spring again
that is the plan for now...

*one thing ive learned is, only make one adjustment at a time
but, ive learned alot about how to adjust and what to adjust - its really been a trial and error type thing

 

[Jonstantine]

well, i determined it was a lean bog because turning the idle screws out to 3/4 would result in smoke at idle but less/no bog

so, i go yesterday to buy some new slightly bigger jets
stock is 70 primary 78 secondary
so, im pulling out teh old jets and what do i find - 66 primary 70 secondary

put in my new 72 and 80's
check the butterflies
loosen the accelerator pump linkage (it was coming in too quick [smoke] - probably should change the squirter)

runs great

im going to try the idle screws at 1/2 later
right now im just enjoy it... for probably a day or so and then the bug will bite for me to try and perfect it
but this is the happiest ive been at work

the guy that sold me the car is a doushebag - sorry had to get that out

 

[Jonstantine]

new questions...

why would a lighter spring affect how the car starts cold?
with the short yellow spring, the car starts right up and runs good when its cold

second, can someone explain to me what exactly happens when you overtighten the accelorator pump spring
(it seems to get looser, why?)

but again, the hole problem i have been having is a lean bog that can be fixed by opening the idle screws wider than the engine would theoretically appreciate

my setup:
short yellow secondary spring
31 size squirter (stock)
.5 open idle screws
secondary transfer slot closed as much as possible (wont close all the way with carb off engine)
primary transfer slot showing very little

right now, its still got a off idle bog (when floored immediately) that goes away when i open the idle screws 1/4th more
i think that by either getting a bigger squirter or by properly adjusting the accelorator pump spring

sorry to bring this up, but i had these questions and i wanted to give a bit of a follow up with anyone who's been paying attention

oh, and the secondary spring was not the problem in the bog - in case i havent made that clear

*thanks

 

[BlueMonster65]

idle

right now, its still got a off idle bog (when floored immediately) that goes away when i open the idle screws 1/4th more

i had a similar problem, with the four corner idle its difficult to get it set right. heres what i did: first i set the transfer slot and curb idle screw. then i turned all the screws all the way in. i found that only one of the screws was actually doing anything becasue it was almost 3 turns out. don't know how i messed that up but oh well. then i marked the position with a sharpie on both the carb body and idle screw. then i turned them out 1 1/2 turns like the demon book says. this made the car run like total poopie. so i hooked up my vacume guage and turned each screw in an even 1/8th turn until it arrived at max vacume and idled correctly. i'm at 3/4 turn out on each screw. i also have the added benifit of an A/F guage which enabled me to make sure i was not idling lean or too rich. now there is no more lean stumble when i punch it.

i think you need to readjust your idle circuit. if that doesn't do it try changing the accel pump cam to a more agressive profile. the stock pink cam i found doesn't give enough initial fuel. i switched to the orange on the number 2 profile overall it is less fuel 24.5cc vs. 30cc on the pink#1 but the orange#2 squirts more fuel initially and the trails off faster. it seems to work much better because the powervalve picks up after the intial squirt and with the pink it was just dumping too much fuel later in the acceleration process where i didn't need it.

i hope this helps

 

[pabear89]

Your Off idle bog is eather too much or too little squirter shot from the accel pump.
The spring on a Holley will make the settings looser when you tighten it,
Try it with about .008 - .10 gap on the pump lever and adjust it in small settings till bog is gone.

PB