hangar18 mods
750 pro form
holley dp

jets : 72's & 82's

Im trying to adjust the air mixture screws or thats what i call it (the one on the side of the metering block). If i run it all the way in or all the way out it doesnt change anything. is this normal....? what does that screw effect, the air or the fuel?

 

they reg fuel at an idle-a lot can affect it, cam size, vacume, intake design-they all can make it so you have to crack the throttle plates open more to get it to idle-when you do that, it gets you out of the idle cir. and more into the trans slot
sometimes you can open the sec a little, allow the pri to close and get back into the idle cir
pull the carb and flip it over, look at the slot, see how much of the slot is exposed, should be around .020
also, should know your idle vacume, and p/v size-if the vacume is low, the p/v # is high and close to the idle vac., could be trying to open it, let in more fuel
of course, the carb has to be right, no leaks, etc

 

vacuum at idle is around 10-11" and the pv is a 6.5 in the front and the back is blocked.

cam size is a .570/.570 234/242 114 lsa
victor jr intake


what do you mean by the trans slot?

If you run those screws all the way in I thought it would make the engine cut off. (it dont change anything)

i would just like to get it to idle around 8-900 but it wants to cut off. if you idle it up to 1000-1100 its fine (vacuum is up to about 15")

thanks for your help
-corey

 

If you have them screwed all the way in with no effect, that means you are getting idle fuel from some other source. . .most likely the transfer slots as ratkiller advised. If you look at the throttle bores with the throttle open, you will see them just off center of each bore on the front side of the primaries and the bck side of the secondaries. This slot provides fuel when the throttle position is in between the idle circuit and mail system startup. If too much of the slot is exposed on either side, vacuum will pull fuel through them and leave you no adjustment on the idle mixture screws.

Pull the carb as ratkiller suggested and see how much is exposed under the throttle blade.

 

Depending upon your setup, boost, and power, you're going to want to jet that thing up before you hurt something. 72/82 is damn near stock jetting for a downleg/straight leg 750 DP. Start with a lot of fuel and conservative timing until you can verify AFR at WOT.

 

i will pull the carb and check the trans slots. if there is too much exposed, what next?

thanks for the advise on the jets. i wasnt sure where to start.


hopefully 10-12psi to start with. wg has a 8psi spring and a mbc.
306 ci
8.75:1
Mexican Block
DSS main girdle
home made valley girdle
flat top with valve relief
Victor jr intake (ported)
Victor jr heads (ported and polished)
eagle I-beam rods
Balanced
Lunati Cam .570/.570 on 114*
blow thru proform 750
MPt 76 .96
EV carb hat with 1" spacer
Front mount intercooler A/A


any ideas for the jet size to start with?

thanks for everything!

-corey

 

What is your timing at idle? What HSAB's? I would add at least 5 to front and back if you did not drill the PVCR's. Here ias a good post on transfer slots and idle.

 

good pic Brian
curious what you are running for timing, are you running a vacume advance? kind of strange that it cuts off at 800-900 idle speed, but just set the mixture screws around 1 1/2 turn out for now(4 corner idling?)-if its a proform body prob has rem a/b's (for later tuning)
you prob want to go at least 92-95 jets in the rear, not sure if you did anything to the PVCR's in the pri side with the mods
make sure if you pull the carb, that the butterflys are set where it idles now, so you can see whats going underneath
maybe post a pic of the underside, pri & sec

 

i have the timing at 3000 @26. not sure at idle. msd pro billet with digital 6 and msd btm. no 4 corner idle. pvcr's are .094". I starts acting funny when you get it around the 800 rpm mark....acts kinda lean but idles up to about 1300, sometimes, by itself and then comes back down. (stupid afr gauge isnt working right now) i will try and get a pic of it when i take it off. what about he jets on the front side? the carb hat being on a 45 shouldnt affect this.

the hsba are what are sent factory in the proform main body......

what is rem a/b's?

 

what is rem a/b's? Removable air bleeds? The pic is from 393bird in a different thread. Timing at idle is critical. That sounds like a pretty big cam in a 306. If it is set at 110+ icl it will like a lot of initial timing, 20* or more at idle. That will allow you to close the primaries quite a bit. With only 26* total you may be close to 0 at idle, assuming 20-26 degrees of mechanical advance.

I found that running a proform main body on a N/A motor the HSAB's are a little big. When I got my turbo on I tried taking them down to .020 and later plugged them to get a flat curve under boost. With my new turbo it seems to be getting leaner as RPM goes up. I am up to 87 and 98 jets with . 078 PVCR and need more fuel. I am thinking of going back to my 650 Holley MB. What metering blocks do you have?

Edit: I agree with the above post on upping the rears to 92 or more. Also a novice tuner w/o a wideband can cause problem real fast. If you continue w/o a WB be very careful.

 

it has standard 650dp metering blocks.

 

This was a help to me, maybe it will help you also.

http://www.candsspecialties.com/tuning.html

-Eldon

 

thanks that some good info...

i bump the timing up to about 20 at idle.

vacuum at 900 is about 14-15"

8psi fuel pressure

i will post a pic in a little while but i got the carb off and found the t-slot was way more that .020". I adjusted it down with the idle screw? (that the only way i saw to adjust it)? anyways put it back on. it done the same thing! I adjusted the sec. open just a little and it made it worse. (to the ear it sounds like its flooding.) I jetted it up to 81's and 85's (biggest i had). put a new 6.5 pv in and I closed the sec. and got it to idle finally, FOR ABOUT 30 SECONDS @800 and then it would cut off. Started it up again with the same results.

Im sending the wideband off tomorrow to get worked on.

i have another baseplate to try and i think im going to check the depth of those pvcr just to insure the guy i got the carb from didnt drill them too far.

 

why do you have the timming so low?? didnt you say it has a btm?? I would put alot more timming in it and then have the btm pull it out..

we have a pumpgas car with a Vortech J trim it makes 15psi and we have it locked out at 34degrees and have the BTM pull out 1.5 degrees per pound of boost.. The car used to have real low timming and didnt want to start or idle much at all..

 

im still new to all this. i dont have my dist. locked. (i was trying to get around that...?)

maybe im starting to understand this a little better. under boost the most total timing i should have is around is around 25deg. if i plan on running 10psi and i pull 1.5 with the btm i need to set the total timing to around 40deg?

have the msd 5462 and it says it will pull a maximum of 15° retard.

 

Or you could set the max to 35º and pull 1º per pound to get your 25º . That way if you over boost it will continue to pull timing back to 20º .

That box has a setting so you can tell it when to start pulling timing also . That will help if your running a t-brake to keep timing in it longer for building boost .

Example : If you have it set to start pulling timing at 5psi and your total timing is 35º , you will need to set it at 2º per pound to get your timing to 25º at 10psi .

Hope this helps .

 

ok thanks man...i think i got it now!

 

yea the motor will run and idle like shit with 20degres total, then having the BTM pulling from there it isnt going to want to do anything..

what gas are you going to run in this thing???

 

but first you need to lock the dist...

 

Are you doing all this when the car is warmed up?

First, turn your fuel pressure down to no more than 7 psi. Get that idle at 900 or as close to 800 as you can get it by adjusting the secondary stop when it is warmed up since you have the primary side close at .020". Before doing anything else, check the float levels and set them if necessary. Adjust the idle mixture screws for highest idle, then try getting the idle speed down and start playing with the mixture screws again. I highly doubt that there is anything wrong with the baseplate, unless the guy that did the carb modified it, put the butterflies in backwards, or it is a mismached baseplate. If you do happen to have it off, make sure the idle fuel crossover passage is not blocked, as this would mean you have a 4-corner idle baseplate with a 2-corner idle carb.

Remember, timing is going to affect the idle, so you'll want to get your desired setting locked in, otherwise you'll just be going in circles.