|03-14-2012 06:23 AM|
this is how you limit the mech adv on a HEi to allow more initial at idle.
you can do it yourself.
do that first.
If the IAB's need fine tuning I do it by soldering up a spare IAB and drilling to 1/16th" .062" Then using a AFR gauge I file/hone the air bleed size a bit at a time by hand with the drill bit to open it up leaning the circuit. Test at idle and just off idle for smooth response and acepable AFR.
Very small change makes a big difference.
The AFR gauge will not read at idle with open exhaust.
I looked up the cam but there is some confusion on what cam you actually got there. The cam specs don;t match the cam grind number.
You may have the bigger TFS cam. Thats what your motor is acting like.
measure the lobe lift. Measure the manifold vacuum at 1000rpm idle speed.
(indicates the cam size) give it all the initial base timing it wants at idle.
|03-14-2012 05:33 AM|
|grannysbird||Oh and the 71 referring to the IAB would appear to be referring to .071", which is what I'm assuming after looking at quickfuel's website just now.|
|03-14-2012 05:26 AM|
Alright guys I'm heading out there shortly to mess with the transfer slots. Concerning messing with the power valve and what have yah, I made a few phone calls yesterday to one of the local dyno shops in the area and they put me in touch with a retired fellow who did all of their carb tuning. I gave him a call and he told me to bring the carb and/or car over, and he stocks powervalves, jets, IAB, idle restrictors etc etc. So hopefully that saves me ordering a bunch of parts and his 40 years of tuning experience should cut down on the time spent as well, hoping.
Concerning timing, I wasn't sent any extra weights with my distributor. I ordered it from Davis Unified Ignition and they asked for my cam specs, compression ratio, etc; they supposedly curved it to to match. So yeah I can bump up the base timing, but beyond that I need to make a phone call to get the proper weights, assuming they didn't install them.
Or would idling be improved by something as simple as hooking up the vacuum advance (barring the fact that I'm dumping a heinous amount of extra fuel atm)?
Anyway that's what I'll be playing with today, yesterday I ended up just having time to pick up my car hauler from my friends out of town and err hem, "modifying" the hood to close without hitting the air cleaner. It's almost like they didn't intend these cars to run with carburetors, go figure. Oh and the car has an AOD with a 9.5" 3000 stall converter, but given the last 3 valvebodies I've ordered have all not worked correctly in one way or another, and the fact that I've rebuilt the thing 2-3 times now...the automatic may not be long for this world. I should have gone with the 4r70w and retained lockup, sigh.
If I don't get on later today I'll be sure to hop on with an update later thursday, should someone with a similar combo need a ballpark for setting up their carb. So yeah off to poke around in the garage.
|03-12-2012 02:44 PM|
no panic I found it.
This cam needs 18 to 26deg at idle. You need to shorten the mechanical advance curve to around 10-14 deg.
The PCV most be hooked up to the carb and the opposing valve cover vented.
You need the idle air flow of the functional pCV.
and the extra timing at idle.
now the carbs throttles will be more closed at idle. and the idle mix screws should be responsive.
If they are not, you can fix that.
What is the actual measured size of the idle air bleeds now?
I figured the cam was a hyd or solid flat tappet with around 240-250 @.050"
Its not that big but still needs more than 14deg at idle to idle real nice.
Give it all the base timing it needs. Then fix up the curve and limit.
Automatic trans or manual transmission?
|03-12-2012 02:19 PM|
Set the both front & rear blades evenly so the transfer slot appear like a small square.
Then once you get running and you adjust idle speed always adjust both blades the same amount of turns.
You may have caused a little panic and confusion for F-bird'88 as the cam specs you posted is your advertised duration.
So kindly post you .050" duration specs?
|03-12-2012 01:03 PM|
You will never get a clean idle with 14deg of timing with that cam.
Lock out the distributormechanical adv. Use a SPST spark power interupt switch to allow easy starter cranking when hot.
goes on the spark box power on switching wire.
Crank it over 1-2-3 with no spark and throw the switch , it will fire right up.
set the locked timing at 34-36deg BTDC. It does not move with rpm.
The big cam needs this much timing at idle.
Now you can close the carb throttles down .020-.030" exposure at idle and it will idle clean. Power valve should stay closed at idle when in gear.
A 3.5 or 4.5 usually gets that done with a big cam.
just do it. You will see.
I tried to find that cam based on your specs. What cam is it ?
if you want to run 24ish idle timing with a mechanical timing curve limit the mechanical curve travel stop to 10deg.
24 +10 = 34deg at max advance.
Try the simple locked out timing, first.
|03-12-2012 11:43 AM|
Well, yeah it would appear the transfer slots are far off from square. How many thousands do I want exposed on each side?
Pictures are below.
Underside of Carb
Power valve sizing is based on engine vacuum correct? And if the valve comes on too early I'll be pumping too much fuel at the wrong time leading to an overly rich condition correct?
Concerning timing the thing won't start or run at all too far outside of 14 degrees initial. Also it's running so rich that I can't adjust the timing without the thing loading up and dying, and 22 to 26 degree's advance at idle? That seems very high for a ford, if you don't mind my asking why is 14 degrees initial not enough? If I had 22 to 26 advance at idle that would put me in the 40's with the mechanical advance...
|03-12-2012 03:26 AM|
Do not start messing with the carb untill you have corrected the timing.
14deg is not near enough.
22 tp 26deg at idle minimum . Locked out timing (34-36deg at idle) is not too much.
Then reset the carb throttles. 4.5" power valve.
|03-11-2012 04:11 PM|
Start by taking the carb back off and flip it updise down & post some pics of the throttle blade position.
Sound like the front & rear are not even and you have too much transfer slot exposed.
The transfer slot sould appear like a little square in about the right position.
Also you may need alittle more primary jet like a 72.
Start off with all four mix screw out 1 turn
|03-11-2012 02:59 PM|
Quickfuel 750 SS Super Rich at Idle
Hey Guys, I'm having trouble getting my engine to idle above 10-11 a/f. I'm new to carburetors, but it seems like I'm getting way too much fuel at idle. So far I've adjusted the float levels to 1/2 height in the sight glasses, set the fuel pressure to 6.5 psi, and set the base timing to 14 degrees advance. Beyond this I'm not sure what to try next as I'm not having much effect adjusting the 4 corner idle screws. But, I do have the next week off of school and an air fuel ratio gauge so I'd like to try and sort this out so I can get this baby on the road.
It's my understanding that if the idle cannot be leaned out with the idle screws, then I'm going to have to change either the idle air bleeds and/or add fuel restrictors to the idle circuit. Or that at idle the mains circuit is kicking in leading to rich condition. Where do I start?
Engine specs as follows:
Carburetor is a Quick Fuel ss 750 with annular boosters
Primary Main Jet #68
Secondary Jet #80
Primary Nozzle #31
Secondary Nozzle #80
Idle Air Bleed 71/71
Highspeed AirBleed 33/33
331 w/ 185 cnc trickflow heads, Edelbrock Performer RPM intake,
Cam; Duration 293/ 290, Lift .542/ .563, 112 degree lobe seperation.