First Ride with Wideband 02 gauge

[Canadian1968]

question ..... when I am running rich at wot I am running on the power valve circuit correct ?  A higher power valve 6.5 opposed to 4.5. Would allow more gas sooner ? 4.5 would open later and possibly lean out my wot ?

[cdr]

yes, BUT at WOT , a 4.5 or 6.5 are both open, if rich at WOT you need to change the main jet.

[stuubi]

From steady cruise,does the lean spot come:
-immediatly after throtlle(hit pedal and instant lean)
-slightly after throtlle(hit pedal,engine starts to climb but falls lean right after)

[XH29N0G]

My inclination would be to get the main circuit sorted with the main jets first. 

(I also missed the 10-11 A/F reading). 

I anticipate that when you drop the main jet size(s) to bring the A/F at WOT into the 12/13 range that you will make your lean condition at tip in worse, but I think that is something to fix after the jesting is correct.

The lean tip in is a combination of power valve, secondary opening rate (spring), and gas supply from the accelerator pump circuit.  Larger squirters and different pump cams as well as how the cams are adjusted can make a difference.  Generally you want a strong shot right when the throttle is moved and then adjust from there.
 

[Canadian1968]

So the shop I go to did not have any 70 jets so I grabbed 71. I also asked about bigger pump nozzels.  The carb has 31, I guess holley next size is 35 according the person behind the counter regardless they didn't have any in srock.  So I went home threw in the 71 jets . I couldn't help myself, I grabbed my drill and drilled the nozzels.   

Cruise is now 13.3 -13.5 . I see in posted 13.0 in my original post that was my mistake it was lower 12.6 - 13.0 with the orginal 72 jets
Slight accel gives 14.6 - 15  so I would say my drill job actually worked !
wot is still rich 11.0.

I need to do some more drives with some longer wot to see what it does. But still rich.  I could drop to 70 jet probably put my cruise bang on around 13.8 or so but don't know if it will be eought for my wot.

[XH29N0G]

A quick clarification.  

The Jets some into play at RPM above 3000-3500 - in other words at WOT.

The cruise A/F is usually at lower RPM and often controlled by how much gas is fed through the transition slot.  There are other parts of this. The Cruise A/F can respond to the Jets.  Moving to jets that give you a higher A/F (I would think you need to move about 4 jet sizes to get from 11, but I would move in steps of 2 sizes to be careful) at WOT could raise your A/F at cruise.  I wouldn't be worried about a cruise A/F of 15 or so as long as the engine is not bucking.

Drilling the nozzle will have a big effect.  Flow through an orifice usually goes as something like the square of the radius, and you could have changed a lot depending on how much you changed the radius.  This would change how fast the shot of gas comes in because the cam is what mostly controls the amount of gas.  But if it works, then go with it.  I have used needle to see the different sizes and those changes are very small.  

I would still work on the Jets first, then see where you stand and tune from there.  I also would recommend finding some books on this - but I didn't follow this advice and instead searched the internet where I found I could still learn a lot.  

Do you have a way to log the A/F?  Or are you reading it off the gauge as you test?  If you don't have a way to log it, I would suggest looking into that.  It could be as simple as connecting some wires to computer plug with USB adapter and downloading some software from your A/F gauge manufacturer.  

PS  there are people on here who know much more than I do.  If they pipe in with advice, I will let them take the discussion until I see something I think I can help with.

[Canadian1968]

I am just peaking at the gauge as I drive. I know it has the capability of data logging I will have to see if I can just FL a program onto my tablet .

went for another drive and did a few off idle 3/4 stomps . Getting a lean stumble / backfire threw carb. I think my problem is in the pump cam. I may have masked it by drilling the nozzles bigger, which helped me with my off cruise accel , but from a stop stumbling. Both situation use the cam in same position or close to. A more aggressive ramp should help.

i am pretty happy with the main  jets. I could go one smaller but would rather have a bit safety room. maybe if get the rest dialed right in but right  now it gives me some play room as I am leaning oUT at certain points

[BSB67]

Fatten up the idle to see if it helps the stumble
Sound like it might want a larger IFR
Decrease your secondary main feed restriction/jet.  You are not going to fix the WOT by leaning the primary.

This is assuming everything else is right with the carb. 

[Canadian1968]

I can riches up the idea for sure.  But pretty sure the 4160 series carb (3310-5). doesn't have replace able idle or secondary jet. I read about closing up the air bleed with a thin wire.

[cdr]

I can riches up the idea for sure.  But pretty sure the 4160 series carb (3310-5). doesn't have replace able idle or secondary jet. I read about closing up the air bleed with a thin wire.

closing up the air bleed will make it richer

[Canadian1968]

well that's what I need for my transitions. I have lean tip in and then rich wot ( higher rpm )  I can see why people get frustrated with these things lol .

[cdr]

well that's what I need for my transitions. I have lean tip in and then rich wot ( higher rpm )  I can see why people get frustrated with these things lol .

can you feel the lean tip in ? if not,don't worry about it.

[Canadian1968]

The lean tip in off cruise is fine . It the off idle fall on its face lean that's the problem and then the rich at wot

[cdr]

what accel pump cam do you have, I had to put the brown one on mine.

[Canadian1968]

I have the factory orange one. I think i could benifit from a different one. But I got a book and read about the secondary idle adjustment screw i didn't even know about. It points out that if the transfer slot is exposed to much to get the car to idle correctly that it will mess up your transitions . I am going to try reserring this and double check my float levels . And see where I am !

[Canadian1968]

so pulled the carb and set the secondary idle 1/2 turn in and dame with primary . Threw it on, had to turn the primary another 1/4 to get it to idle around 800. checked my float level they were acruelly a bit low. brough them up to even with bottom of the sight plug hole, adjusted the accel pump again. Stabbing the throttle in park, there was a noticeable crispness to the throttle response. A drive showed me an even smaller tip in off cruise, only dropping to 15.2 ish. A stab from idle lights up the tires with ease. But where as before it would spin an hook fairly quick, now it just keep spinning threw out the rpm haha. So taking it back and double checking the basics seems to have helped a lot.  Next is to check out WOT .

[BSB67]

.......................This is assuming everything else is right with the carb. 

[Canadian1968]

So I finally got a set of 70 jets and a .35 tube style pump nozzel. Idel is now set around 700 rpm no bog off the line
, cruise is 13.6 ish ,
tip in off cruise is minimal down to 15.0 .
gradual acceleration is 14.0
my last problem is wot. I am still hitting 10.8 - 11.3.

I also did a run with vaccum gauge hooked up  and a buddy reading it for me. Cruise barely any throttle is around 18" . 1/2 throttle gets me around 8". A WOT pull showed me with 3.5 at 5000 rpm in second .

The reading I did said to aim for 1" of vaccum or 0 for an all out race application . The 3.5 is
telling me I could use a bit more cfm from the carb ? 

What do people think. The rich at WOT from not enough air or to much fuel ?  If it is to much fuel I am stuck because the 4160 holley does not come with tunable pvrc or air bleeds . I would need to get an aftermarket metering block.  I forgot to do thr paper clip trick to see if thr secondaries are opening but the way it pulls I would think they are....

[cdr]

the rear jet plate can be changed, they make them in sizes. if it were me I would get a different carb.

[Canadian1968]

I think that's the plan for next year. Save up over winter ! The 3310 is a great carb but just doesn't offer the adjustability I am looking for.

Any suggestions on carb ?

[firefighter3931]

I think that's the plan for next year. Save up over winter ! The 3310 is a great carb but just doesn't offer the adjustability I am looking for.

Any suggestions on carb ?

Proform 750 DP "street series" carb is what I would run  Quit messing with the silly vac secondary stuff and put a real carb on that engine ! 

https://www.summitracing.com/int/parts/pro-67213/overview/


Ron

[Canadian1968]

I think that's the plan for next year. Save up over winter ! The 3310 is a great carb but just doesn't offer the adjustability I am looking for.

Any suggestions on carb ?

LOL. What does the 3.5 of vaccum at wot tell me. Does it not mean the motor is trying to pull more air then the carb will allow ?


Proform 750 DP "street series" carb is what I would run  Quit messing with the silly vac secondary stuff and put a real carb on that engine ! 

https://www.summitracing.com/int/parts/pro-67213/overview/


Ron

[firefighter3931]

LOL. What does the 3.5 of vaccum at wot tell me. Does it not mean the motor is trying to pull more air then the carb will allow ?

The current carb is a restriction at WOT based on the vacuum reading. The Proform carbs flow more than their advertised rating....my old PF750 main body flowed ~830 cfm. The trick when sizing a carb for street use is to pick something  that has strong throttle response yet still has good top end charge. The venturi sizing is critical....go too big on the venturies and the low speed manners will suffer. It's all about balance ; smaller radiused venturies will deliver on all counts.  

The PF carbs have lots of nice features and are very adjustable. I like the adjustable idle/high speed air bleed tunability that you won't get with a 3310. Four corner idle adjustment is a huge bonus. The glass sight bowls make float adjustment a breeze. The street series DP'er also comes with an electric choke as well. With a combo like yours the fuel curve should be darn near perfect. You might have to adjust jetting but that would be about it.  

If you had ported aluminum heads and more cam you could upsize to a bigger 850DP'er but for the current combo with 906 heads and smallish cam the PF750 street carb would be my choice. It'll do everything well.  


Ron

[Canadian1968]

Yes I read over the details of proform . Looks like it has all the bells and whistles !  Well I will start saving my pennies . Until then the 3310 is still suiting me well for a car that is 80% street driven..... I just don't like leaving power on the table 

[68pplcharger]

Got mine installed last weekend, now I can finally tune the motor the rest of the way.