89sierra

hey guys im new to the carbed ls conversions and realisticly carbs too. the motor is a lq9 with a performer rpm intake and holley 750dp that is in a 89 chevy pickup with a 700r4 and 4.88 gears. i got the motor in and adjusted the float levels so the fuel just slowly will trickle out of the sight hole. i adjusted the air mixtures as best as i could without a vacuum gauge. that is coming tomorrow as i just ordered the gauge. i am pretty sure the acellerator pumps are dead on. going to check this as well tomorrow but when i floored it she bogged off the line. i can not say if it was for a second or 2 i never counted at the time. so from my research it says to up the squirters. but that is where i get lost. should i keep both squirters the same size, should i up them equally if they are staggered or should i just up the front one and leave the rear the same?

Pop N Wood

iTrader: (1)

If you check out the stickies, both the carb data base and the one about running a distributor, there are a number of guys who posted their set ups. Squirters and accel cams rarely match primary to secondary.

I am a big proponent of tuning the accel pump last after everything else is set right. Too many guys try masking a mixture problem with a large shot.

89sierra

ya i read all that data base and thats why i was asking. some guys left the front nozzle the same and upped the back one and some upped the front and left the back one stock. then i saw some guys staggered their set ups and some just upped them both equal a huge amounts. like i said sorry for having stupid questions i am new to carbs. so if you were properly setting up a carb what order would you set things up? thanks for the help

bad67ls

iTrader: (2)

whats the timing at? running a curve or just straight? what converter is in the trans?

89sierra

i can not say what the timing is at. my guess is its the traight one since its just the pill style box. im running curve #3 which is for stock cam with high gears. as of now there is no stall factory convertor. untill i can get everything worked out then i will modify one thing at a time.

bad67ls

iTrader: (2)

double pumper with stock converter = bog thats going to be tough to tune out.

those timing pills are crap. hook a laptop up and put some real timing in it.

89sierra

ya well i wanted to try to get it running decent before i start throwing other parts at it to problem solve. so no one has any advice on where to start with tuning a 750 dp? on a lq9 with dual plane intake?

1ltcap

first thing you need to do, is to take that carb off, and put a vacuum secondary carb on. they work better with autos than double pumpers.

that said, what size jets? squirters? powervalve?

Pop N Wood

iTrader: (1)

Probably because no one feels like writing a novel this early in the morning. I have some links I can shoot you but unfortunately don’t have them at work.

I have a 750 DP on a single plane intake, which I have read is more difficult to tune. The dual planes are suppose to be easier. In my case the two keys to getting rid of the bog from a DP on a single plane was adjusting the idle air bleeds and getting the throttle opening right at idle. You shouldn’t need a 50 cc accel pump if you are doing it right.

1) Start with the carb as near stock as possible. Start with the stock jets, 30 cc accel pump and a stock power valve. Obviously make sure the carb is in good shape (good gaskets, clean, everything tight, no leaks, no blown power valves, good accel pump diaphrams, etc.)

2) With the carb off the vehicle adjust the primary and secondary idle settings so 20 thousands of the transfer slot is visible. A google search should find pictures off what I mean. You can measure this with a flat feeler gauge. Set both primary and secondaries the same. When you hold the carb up to a light you should see the same size crack of light visible around both sets of butterflies. Whenever you adjust the idle speed, adjust both primaries and secondaries the same. An aftermarket throttle plate will make this easier cause they have secondary idle screws that are accessible from the top.

3) Adjust the accel pump cam arm so there is zero play between it and the cam. The slightest movement of the throttle should cause the pump arm to move. When on the car you should see a strong shot of gas with even the slightest movement.

4) You can set the float level with the carb off the car too, or do it on the car like you did. Holley has instructions on line.

5) Set the initial timing so you have 10-12° static timing at 1000 RPM or less. Ignition timing will affect the engine idle speed. If you use too much initial timing, the engine will idle too fast forcing you to close the butterflies with the idle screws. This will cover too much of the transition circuit slots making them difficult to tune. Use a combination of the throttle idle speed screws and initial timing to set the idle speed. Don’t go too far away from 20 thou on the transition circuit slots.

6) Run a MAP sensor with the MSD box. I think I have 12° MAP advance at high vac.

7) Use some type of fuel pressure regulator set so there is 6-7 psi at the carb.

8) Put the carb on the car. Start with all 4 idle mixture screws around 1 turn out.

9) Start the car and get the engine warm.

10) Adjust the idle mixture screws to get the idle mixture right. Makes sure you set all 4 corners the same. Most DP’s seem to want to be near ½ turn. You can cheat a bit and make the primaries more rich than the secondaries, but for the most part keep them all the same. If you have a wideband O2, set the idle screws so you are at 14.7:1 at idle with the engine warm. A little richer if it helps with the off idle performance. If you don’t have a wideband, then do what Holley says and adjust them to get maximum manifold vacuum. You can hook a lap top up to the MSD box to read your MAP sensor setting.

The steps above should get you at a good starting point to tune. A wideband O2 is absolutely invaluable to get the rest of the set up right. Set the main jets based on WOT ratios. You want around 13:1 or so at full throttle. For cruise you will get the best mileage if it drops back to 14.7:1. Getting the mixture ratio to behave from idle to the point where you get into the main circuits (~ 2500-3000 RPM) is the tricky part. That is where things like air bleeds and PVCR tuning come into play. If your carb has press in air bleeds and restrictors, then you can drill those out and tap them for brass set screws that you drill yourself to whatever restriction works. Using a smaller idle air bleed on the primary side is what allowed me to ditch the 50 cc accel pump.

Just be careful, do things one step at a time and keep good notes so you can back off changes that don’t work.

Whatever you do set the accel pump last. You need to use a shot just big enough to get rid of a bog on fast throttle transitions. Get the carb to produce stable AFR’s with slow throttle transitions first before you start hosing down the air intake with the squirters.

89sierra

hey thanks alot that is some great advice. if you could post the links when ever you had a chance that would be good. i have been debating on the wideband but i could not decide on what to get since has true dauls it will only be taking a reading from one side unless i swap the sensor from side to side or sumit has a fast unit that has 2 sensors but it is nearly $500. my next thing is i have the edelbrock box. with the stupid pills so i do not think i can play with the timing. unless i switch out the pills. i do not know what the different pills run for timing. is there a chart somewhere for them? i also do have a pressure regulator and it is set to 6 psi right now i found it ran better on 6 then 7 but that could just be the way the carb was adjusted. once again thanks so much

ZONES89RS

iTrader: (25)

I take readings off the passenger side, mimic all adjustments to the driver side, all plugs look identical.

Pop N Wood

iTrader: (1)

All I have is a single channel O2 hooked to one side only. Like Zones said I don't think the AFR varies much side to side and if it did I wouldn't know what to do to fix that. There was at least on guy on here who had the dual channel fast unit but I never could get him to tell me if they vary side to side. I guess if you were building an engine for the engine master challange you would need to worry about such things. But then I guess you wouldn't be on here asking my drunk *** for advice.

Forgot to mention, the accel pump squirters need to be adjusted based upon what is happening when the primaries and secondary are being opened. It is not hard to tell which is being moved depending on how deep your foot is into it. Like I said start with a near stock set up and make single changes from there. Some guys actually go so far as to disconnect the secondaires so they can tune the primaries by themselves. I think I did go up a couple of nozzle sizes to get things right.

The timing for the different pills is in the user manual. They all seem to use around 12 degrees at idle speed. The #6 pill goes a good bit higher at idle.

http://www.jegs.com/InstallationInst...1/121-6010.pdf

The MSD box is a worthwhile investment for just the adjustable rev limiter alone. These engines rev so damn fast I have hit the limiter more times than I can count.

speedtigger

iTrader: (16)

Nothing wrong with running a DP on a dual plane, mine ran flawlessly, BUT I have a 2800 stall converter.

This is pretty much true if you want to be able to mash it to the floor at low speeds whenever you want. With a DP, you will have to ease into it at slow speeds until the RPM come up to where it can handle that much carb.

ZONES89RS

iTrader: (25)

I can mash it at low rpm in low gear, 3150 pounds, heavier vehicles not so much.

89sierra

ya i will eventualy grab a stall but i didnt want to get one till i had everything in and running good. also i didnt want to get a stall for the 700 and it not be able to hold the power and have to go to the 60 or 80 and have a stall that is no good to me. tomorrow i will be going out to set the throttle plate to the tranfer slot. and idle adjustment screws. my question with the tranfer slot should they both have a .020 square or should the rear be closed a little smaller. i dont got a wideband yet but i will try to set the idle with a vacuum gauge. what do you guys run for widebands?

The stunningman

iTrader: (47)

These guys are pointing you in the right direction, I'm just going to add. I would be doing my own curve. I would try the #6 pill.

What jets are in the carb? Is it 4 corner idle? If so did you turn all 4 idle screws out 1 and a 1/2 turns and then try adjusting them equally for best idle IN GEAR? Are you having idle problems at all? I would be running at least a 35 shooter in the front, the back I would stay 31 and see where it goes. With your gearing rpm's should rise quickly needing plenty of fuel.

What size tires are on the back? Regardless of the stall with the 700r4's 3.08 first and a 4.88 gears anything shorter than 36's should light up at will.

89sierra

does the edelbrock box have the capabilities to run a laptop or is it just the msd that does ive been getting mixed reviews here. as for the carb everything is stock that i know of. it has a 28 front squirter and 31 rear. 6.5 valve and 70 front jets and i am not sure about the secondaries right now or what colour cam arms are in there or what position they are in. it is a 4 corner idle there seems to be no problem in the idle. when i played with the 4 corners it was in park does this play a huge role compaired to being in gear? once the bog clears it just fries the tires off. i am a little bit away from my truck so tomorrow i will start with the verry basics. i will pull the carb and adjust the throttle plates so they .020 bellow the transfer slots, then adjust fuel pressure to 6 psi, then i will set the floats to just slightly trickle out of the bowls, make sure that the pumper springs are just touching the arms. i will then adjust the 4 corner idles to reach highest vacumm. i think they are at 1 turn each right now and produce around 17ines. i will give that a try. the truck goes on friday to have the exhaust from the headers to my cats redone. and i have a wideband on order but that will probably take 2 weeks to get here.