02_CETA_ws6

iTrader: (6)

I cant seem to get this lean spot figured out it does it on initial take of like it hesitates and then goes, have a innovate motorsports air fuel gauge on it and you can watch it go lean then richen back up also does it when your cruising and start to accelerate. Have upgraded to a 50cc pump with red cam and its got a 48 squirter i believe in it may be a 42 but i dont think the squirter size is helping. Its a street avenger 6xx have it at around 13.5-14.3 idle air fuel. Not sure ive been fighting this issue any advice is appreciated.

speedtigger

iTrader: (16)

These low speed lean spots are common in carbureted LS engines. What has to be determined is if this lean condition is transitional or constant. Here are two examples that will determine this:

If you lightly and slowly open the throttle to just above idle and the car hesitates momentarily then goes and the fuel mixture returns to normal, that is transitional and can be solved with the accelerator pump system.

If you lightly and slowly open the throttle to just above idle and the car hesitates and continues to run rough and the mixture stays lean as long as you hold that same throttle opening just above idle, then it is an idle circuit problem. The most common cure for this is to increase the size of the IFR (idle fuel restrictor orifice/jet).

jerr6

iTrader: (1)

you should hook up a vacuum gauge and drive around. see what your vacuum drops to when you start to accelerate. could have to low of power valve. i did the divide idle vacuum in half to pick a power valve and it was totally wrong.

02_CETA_ws6

iTrader: (6)

I've been sick today I'll mess with it some when I start feeling better, It won't hesitate with no load in neutral but when I put it in gear and lightly throttle it it seem to stay hesitant and lean until I push the throttle more I'm thinking its in the IFR, also seems worse when cold. Thanks for all the advice I need to check the power valve because I don't know what came in it.

speedtigger

iTrader: (16)

I have heard many people suggest this method and I have never seen any evidence that it proves true. The best way to do this is with a wideband. If you do not have a wideband, my favorite method is to select the lowest number powervalve you can run without getting a lean condition at aggressive part throttle.

stinkybutt

I usually use a power valve that has a # just below the vacuum @ idle in gear.
If you have 12"@ idle in gear then a 10.5 will work. If you have a rear power valve that is the rule for 1/2 the value of the front. This can go out the door if the carb is too small because I've seen engines pull vacuum at wot and close the rear. Usually no power valve in the rear and 8-10 jet #'s bigger than front to start.
I.ve also found that AED and ProForm carbs have too large of a hole in the PV restriction and had to reduce them to keep part throttle from being overly rich on tip in.
Timing comes into play here as well.
All about load on the engine and vacuum signal. A heavy car with a tight converter and no gear needs more fuel to move than a light car with a loose converter and gear.
Also the idle air bleeds come into play at 1,500-2,000rpm. A/F at idle can be 14.2-14.7ish then getting up to just below the point of the main jet supplying fuel thru the boosters is where you need to make sure the A/F does not go lean.
Once you learn about transition and how to control the A/F you will be a hero at tuning driveability. AND you need to learn that #'s are a guide and some combinations need you to look outside the box. Give the engine what it wants. The O2 sensor and a vacuum gauge are the key.
I never believe the # on a shooter either. I always measure with drill bits. Demon's seem the worst.

A few ramblings from me and my tuning ideas .
Aleck

jerr6

iTrader: (1)

Having the wideband and vacuum gauge really helped me understand how to dial in my carb better. Before I was just guessing and wasting time and money.

handyandy496

iTrader: (9)

I would go with bigger squirters first. No luck, power valve. No luck, pick up a new circuit section or clean the one you have. Those little holes can plug up easily. My 496 bb with a 850 double pumper needed a lot more squirt than it came with. I had to pick up faster cams too. The red ones might not be big enough. Especially if you only have one squirter and a high lift camshaft. You can use drills to open the squirters instead of buying a handful. Oh watch for the clearance between the cam and the arm. There should be almost no clearance there. As I remember I always had a very hard time with vacuum secondary type carbs and 60 ft times.
Had to give up on them but they are good on gas.

stinkybutt

Pump shot is all about plenum volume. A single plane manifold needs more than a single plane. The bigger the plenum the weaker the signal to the booster. Most engines start to pull fuel from the boosters/jets somewhere around 2,000 rpm.
When I have a car that has a stumble I drive along at 2,500 rpm and tip the throttle to get the car to go to say 2,700-2,800 . Not an abrupt movement but a smooth one. Remember we are not trying to get a pump shot to hide the problem. If the car has 15 or so inches of vacuum at this cruise and only drops to lets say 10"and the power valve has a # less than 10 like an 8.5 it will not open thus causing a lean transition. By increasing the pump shot you are not fixing it correctly. This is where picking a power valve becomes very important. We need it closed at idle, but also need it to open when moving the throttle just enough to cover the part that the pump shot will not.
I see you trying to fix this by using a BIG squirter and BIG pump. Also you need a hollow screw on the squirter with anything over 0.031". Your idea can work kinda. But if you were to see how the fuel just dribbles out of a big squirter with a big pump at small movements you should understand how this is not efficient as liquid fuel will not burn.
Learning how to tune with air bleeds and power valve restrictions is where it's at for drive ability.
As you get into bigger cams it becomes harder to get a power valve with a big enough # it will open soon enough to help this transition and stay closed with the low idle vacuum.
Looking like a "Dog chasing his tail" now I bet.

Aleck

The deeper we look the more confusing it can get.

02_CETA_ws6

iTrader: (6)

Im going to try and mess with it some today, thanks for all the input, this carburetor has been a learning curve for me, i was thinking there has to be another way then upsizing the squirters and pump. When i get a chance ill post up some more info about whats exactly going on.

speedtigger

iTrader: (16)

Just to clarify, the power valve has a very specific job. Its job is to add extra fuel for aggressive part throttle and WOT operation. Holley created this valve so that the engine could run leaner during part throttle operation where the engine did not need as rich of a mixture. This allows the engine to save fuel and keep the spark plugs and the oil cleaner.

The power valve does NOT operate at idle. The power valve circuit only operates once the throttle is open, so it does not affect idle and idle vacuum does not determine the ideal power valve.

The power valve operates off of the pressure differential under the carburetor vs the atmosphere when the throttle is open. The power valve is not a simple open or closed thing that happens at a certain pressure differential. Opens a little, then more, then more, then full open as the pressure differential equalizes or as the throttle transitions toward WOT.

When driving at LIGHT part throttle, fuel mixtures of 14:1 to nearly 16:1 are fine as long as the engine does not experience misfire or bog. As the throttle is opened aggressively, the AFR should progressively richen until full throttle where AFRs might be better at 12:1 to 13:1. Power valve selection is all about achieving these air fuel ratios.

The best and easiest method I know to tune for the best power valve if you do not have a wideband air fuel ratio meter is to simply run the lowest number power valve you can without experiencing a lean misfire or lean bog at aggressive part throttle. If you can successfully run a power valve of 3.5 or less, there is a good chance that your main jetting is too rich. If you need more than a 10.5 power valve to get rid of a lean bog or misfire, there is a good chance that your main jetting is too lean.

stinkybutt

I,m in your corner Tigger. I totally agree. I was just trying to make sure he was not thinking the pump shot was the only/right fix.
Most in this forum would get lost trying to tune with emulsion tubes and metering blocks with screw in air bleeds in the main well.
Using the main jet air bleeds to trim A/F at full throttle etc.
Aleck

stinkybutt

I had an AED 750 that would go from 14.5 at cruise 2,000rpm to 11.8 as soon as you tried to get to 2,200. I had to take the PV restriction down from 0.065" to 0.028". Now it goes from 14.5 to 13.8 on the same tip. The car no longer lays down due to crazy rich. The combination of 347 Ford with Twisted Wedge heads and Lentec AOD with lock-up converter and 224* @ 0.050" caused a load on the motor that vacuum dropped so far that the pv opened . If I used a smaller # like 3.5 the car would lean out unless you applied so much pedal that it would backshift. I tried a 10.5 and it opened just right except it was way rich.
So I started going down on PV restriction. Only problem was the wrong converter caused a vacuum of 8" @ idle in gear. A looser converter would be best choice BUT customer was committed to combo. Using a 7.5 PV got me back to lean tip. SO band aid fix was two #'s up on main jet making cruise A/F of 14.1 and I went .004" smaller on idle air bleed.
New combo got rid of all the stumble in the gentle 2,000 to 2,200 tip in traffic driving.
Again the better way would be either no lock-up until 2,500 and/or a higher stall from the 1,800 to a 2,600.

Aleck

02_CETA_ws6

iTrader: (6)

I think it's something other than squirter I can hold it in gear at say 12-1400rpm and it wants to go lean 16.1-16.5 if it was a squirter it should just be lean for a second right? Then richen back up? Also if I'm driving and I'm around 1600rpm and lightly accelerate it will go as far as 17.1-17.5 then as you accelerate it will richen back up.

speedtigger

iTrader: (16)

As long as your main jets are optimal, I would drill out the IFRs .002 at a time until it gets into the 15s on the AFR in those light throttle conditions. Then it should be a happy camper.

02_CETA_ws6

iTrader: (6)

Should I drop my pump shot down also this is a daily driver so I figure that may help my mpg?

stinkybutt

Fix one thing at a time. Try this.Take a wire the size of the one in a twist tie for a loaf of bread. Get a piece about 6"-8" long. Make a loop in the middle, slide it over the carb stud. Now stick each end into the the idle air bleed on the front of the carb. The loop will prevent the wire from falling into the intake. The air bleeds are the small outboard holes inside the choke horn. Now go for a drive and see how the A/F goes richer. This will give you an idea how this works. The A/F should change around 1,400 to 2,000 rpm. If your carb has screw in air bleeds you can change them. Press in I buy blanks and drill them as needed. Get the wire at a hobby store or craft shop.
Or try in the laneway. Just bring the rpm just below 2,000rpm and watch the A/F reading. You only need a very fine wire. I've used fine drill bits to show customers in the laneway. Don't rev the engine without securing them with your fingers. Don't want the engine to swallow them.
Aleck

speedtigger

iTrader: (16)

Once you get the lean spot out, you can start stepping down the pump shot to see how much you actually need.

Pop N Wood

iTrader: (1)

I fixed that problem by adjusting the idle air bleeds and IFR. You will be able to get rid of the 50 cc pump and massively downsize the squirters if you adjust the slow throttle movement mixture right. These engines don't need the bigger pump, it is a dead give away that the low speed circuits aren't adjusted right.

Pretty easy to drill out pressed in air bleeds and restrictors and replace them with brass set screws you drill yourself. Information on how to do that has been posted multiple times.

02_CETA_ws6

iTrader: (6)

Idle feed restrictions were at .028 drilled multiple times ended at .033 re-adjusted mixture screws, stumble is gone on light throttle, seems to idle better air fuel is more stable. It seems to want to go rich on real light throttle like on flat road keeping speed steady wants to run about 12.1 as soon as any load comes on goes strait to 14.1-15.1 not sure if that's normal. Also took the 50cc pump tonigh and put the smaller one on with 45 squirter going to try it tomorrow.