Cascade Crew

[aaron_sK]

The wideband O2 on the Mercury has revealed a pretty big idle tip-in lean problem. When you're rolling along in gear and romp it even a little it will flash way high (like 15-17 AFR, sometimes even maxing the gauge) for just a second, then come back into the 12-13 range.

Carb is a Holley 600cfm 4160 VS on a 390 F*rd. I'm running the pink cam on the #3 cam hole (#2 throttle lever hole). I'm not sure what spring is in it, or what size the nozzles are.

I don't know much at all about carbs, but after reading up on TGO and TeamChevelle I adjusted the primary stop so that the idle transition slot was squared. I then adjusted the set-screw on the pump cam so that it had instant movement when I touched the throttle. After that I did not move the primary stop screw at all, using only the secondary stop screw to adjust the idle, so I'm certain that I didn't mess up the cam by tuning the idle.

Should I be looking at a heavier spring, bigger nozzles, different cam, or what?

Thanks guys.

[Twilightoptics]

Lots of ways to skin this cat.

When you set your idle circuit stops, you set front plates and back equally?

Brandon will chime in more here.

If you have a long pump shot you get the same amount of fuel as a short one, but it's dragged out over a longer period.

I'd try putting the cam slot where it actuates the plunger at a more rapid rate.

See how it changes. Does it get better does it get worse etc.

Can you feel this quick lean spike? Alot of times you will get a small lean spike on the WB that you cannot feel. In those cases I roll with it. When I've tried to tune the number out, it makes other pump shot conditions worse.

[aaron_sK]

I didn't set the plates equally. I set the primary to square up the transition slot, and then adjusted the secondaries to give me 600rpm in gear. Could that be causing some of this?

There is a noticeable bog, and sometimes a lean pop from the exhaust as well, so it's not just the sensor.

[chevymad]

You actually want all 4 plates open equally. But you cant set the rear plates to square, because the slots are in a different location. You have to look at the crescent of light coming around the plate and try to make it the same as the front. Then adjust both front and rear plates til you get desired idle.

As paul said, the pump shot will always be the same amount of fuel. The cam will set when and how fast it comes in, and the squirters will determine how long the shot lasts. Large squirter, short fast pump shot. Small one, long slow pump shot. There are 2 different size accelerator pumps you can use too though, a 50cc and the normal 35cc. You sound like you could use either a faster acting cam, or possibly a larger squirter.

Another way to sort of tune around the issue is to richen the idle mixture a bit, so that it covers more of the transition. You could possibly also have the wrong power valve. I forget how to actually choose one, i'm sure you can find that on the net though.

After all this there's always air bleed tuning. But i've never gotten into that myself.. its a bit hardcore.

[Twilightoptics]

Pop out the exhaust is going to be a rich condition. Lean backfires are typically through the intake/carb. Kind of sounds like a pop/thunk sound.

[Quasi-Traction]

[aaron_sK]

@ Brandon. I'll yank the squirter tomorrow and see what size it is.

I'm pretty sure the idle isn't too lean. Off the choke idle AFR is around 13.6. I am running a 10.5 power valve. The carb had a 6.5 in it, which was a joke trying to get a 2 ton car up a hill. Dunno if I should go higher though.

@ Chris curb idle is around 1000-1100, in gear is 700-800 (dunno why I typed 600 earlier ). Cam is a Delta 270, 235@050. Not lopey, but far from the stock 205@050 FE cam.

[Twilightoptics]

Change things to give it what the engine wants.


Throttle plates need to be equal front back.

[chevymad]

Wasnt really talking about whether the idle was actually lean or not. By putting it to the rich side you'll change the entire curve and maybe cover the bog area. It's just a cheap/easy compromise.

[blue89]

I wish I had a way to monitor that. No way my narrow band will catch tip-in.

http://www.stockcarracing.com/techarticles/scrp_0601_holley_accelerator_pump_adjustment/index.html

Cheezx and I tuned my V6 to get rid of this problem. Seemed like the cure is just more fuel! How long does it take for the pump shot to be depleted? Seems like a larger nozzle size would be the quickest way to fix it.

[Twilightoptics]

Pump shot is over when the throttle stops moving.

[blue89]

How long will a 50cc pump take to push through an 0.xxx tipped nozzle? Just thinking if there is a way to look at the wideband reading and map sensor curves to figure out where the pump shot needs to go.

[Dewey316]

There seems to be some sort of black voodo magic to tuning pump shot. I know that if I tune mine "by the numbers" I end up blowing black smoke, and boggng. Tuning by the numbers is great, but I honestly believe, that even a WB, is too slow reacting,to get good numbers for something like pump shot.

[aaron_sK]

Brandon and Paul hit another one out of the park.

Pulled the squirter today; 31. Next size up in the Holley book is a 35, so that went in. I also richened the idle up about 1/8 of a turn on either side, and unscrewed the stop nut on the cam arm to tighten up a little slop.

When the car is stopped and you gun it (off a light or whatever) it's bat-out-of-hell responsive. When you're cruising out of the throttle and goose it, there is sometimes (but not always) a tiny bit of bog. Way less than before though, so I'm thinking a 12.5 power valve might be in order. I'll have to take more vacuum readings while driving.

Paul also called it on the wideband going lean very quickly without any noticeable bog, although it's a lot less lean than before (14-16, no 18 or off-chart high anymore).

Thanks for the help guys.

[Twilightoptics]

I think any O2 is a valuable tool in tuning AE. It will show you trends. It may not react quick enough to give you exact numbers. But if it reads above or below 14.7 you know which way to start going. Then adjust until it FEELS right.

I just took a whole bunch of pump shot out of the Camaro because it was sluggesh off idle until the load hit. Told me I had too much pumpshot and it needed more MAP (powervalve) based fueling.

Much nicer to drive now!

[BigDaddyVu]

does your car hestitate off idle while accelerating? a dead spot? and have good idle and WOT AFR's before changing the squirter and pump. I recommend taking a vacum gauge and measure you manifold vac. You may have too replace the Power Valve which it uses the vacum drop off point to tell the metering block to open up the fuel to the primary jets. The higher the number on the power valve means a longer delay for the fuel to reach the boosters.

for example.

This is how I tune my holley. if your vacum gauge reads 10 Hg at idle you need to divide it by 2 which give you 5 since holley power valves only sell them in .5 values swap out your power valve to a 4.5 and then test it you'll notice a huge improvement ( the New power valve is allowing the fuel to flow through the primary jets early narrowing the gap between acc. pump shot and boosters making the transition smoother) but if you still notice a slight dead spot (lean) swap it out to a 2.5 which i did then you can fine tune the acc. cam.

[aaron_sK]

I'm not an expert in this by any means, but from all of the reading I've done the idea of your power valve being half of your idle vacuum has been much been shot down.

The recommendations that I've seen have been more like 2 inches below the lowest cruise vacuum. On my particular car I can watch the power valve kick in on my O2. When driving at high speeds (70-ish) it comes in fairly quickly, but cruising at lower speeds (40-50) I can't help but think a 12.5 might do me a little better than the current 10.5.

I need to run a vacuum gauge next to the O2 and watch exactly what's happening though.

[BigDaddyVu]

take the filter off romp on it and watch the primary barrels and look for no fuel between the pump shot and venturies