Help with tuning my 750 doublepumper.

[team39763]

I decided to try tuning my carb once again.  I know I should just send it away for someone else to tune it, but I can't...I HAVE to learn myself.  Right now what I'm having a problem with is running too rich at idle.  I dropped in some new plugs yesterday and let it idle to get up to temp.  After a while, I pulled the plugs to look at them and they atleast had some color aswell as the usual carbon.  The center electrode was pretty clean and the side electrode was clean in only the spot above the center electrode.  After that I decided to mess with the idle mixture to get a smooth idle and max vacuum reading.  I did that and came out with 17inches and it was pretty smooth, the only problem was that the idle speed was too high.  Anyways, I pulled the plugs to check them, and they were completely fouled.  I lost count how many times I've fouled the plugs with this motor, but I know it's over 20 now.  They are completely black except for maybe 1mm of white/gray on the tip of the center electrode.  What does that mean?  I've read several holley tuning books, but nothing seems to work for me.  I've tried 7 carbs at this point and fouled my plugs atleast 20 times.  I'd appreciate any help ya'll could give me.

My setup is a Holley 750 doublepumper, victor jr intake w/ 1" 4hole spacer.  No vacuum advance.  timing is set at 12 initial and ramps up to 32 at 2800rpm.  I have longtube headers and no mufflers.  I have e-fans and my timing is controlled by a MSD box(no distributor).  Cam is a 226 on 114LSA. 

[HAULIN IT]

Team, A few thoughts that come to mind. Do you have an air/fuel ratio meter in the exhaust, or are you going by the Black plugs thinking it's rich at idle? Do your idle screws have sensitivity (do they quickly change the vacuum & idle speed)?  My first guess is that the front throttle blades are too far open, uncovering the transition slot. Now the extra air is pulling extra fuel. Do you have a hesitation just off of idle also? If this seems like a possability, try opening the rear blades slightly (to get more idle air) & closing the front ones (to cover the transition slot). To open the rears, you may have to remove the carb, however with the spacer you may not. The screw comes up from the bottom & looks like the one for the front, but is on the rear throttle shaft. Keep us posted, Lorne     

[team39763]

I did just what you said with rears and closed the fronts a bit.  Now the idle screws are very responsive.  I actually killed it 4 times with just the screws.  It never did that before.  Another thing I noticed is that it'll die when open up a major vacuum leak, before, it would just rev higher.  So I'm guessing it doesn't have the extra fuel to rev like it did before.  Does it sound like I'm heading in the right direction?  I don't have a air/fuel meter.  Everytime I get some money, I find other stuff to spend it on - like pump cams, squirters, jets, PV's, jet extensions, etc.  Could I use a narrowband rather than a wideband?  I know wideband is better, but I can't afford one right now.  I haven't driven the truck just yet, but there seems to be a little hesitation when the secondaries open.  I have 35 squirter back there with the green cam in #1hole.

What should my plugs look like?  Every plug I've seen from the local guys is carbon fouled and some are wet, but they insist that's how carbureted engines run.

[Blue 82]

Since you drag race your truck
this may help
the second half explains about unleaded fuel

http://www.angelfire.com/fl4/pontiacdude428/Readplugs.html

Get your WOT jetting/timing right,
then you can play with your idle issues

Posting pics of your plugs will help

[team39763]

Thanks Blue 82.  I'll post pictures in a bit, my camera phone has been taking fuzzy pics lately so I'm gonna have to find a real camera.
I took the truck out and played with it a bit.  First run(on the street), I waited until 15mph then I smashed it.  My brother told me it blew a cloud of black smoke.  I assumed I had too much all at once on the secondaries.  I installed the pink cam on the secondary side and it seemed pretty nice.  There's just a small bit of a hiccup at WOT now.  My slicks were under-inflated, so the runs pretty much sucked.  I layed 2 strips of rubber for about 2 blocks, but I didn't even feel it get loose.  Can I use a narrowband Air/Fuel meter to tell if I need to jet up or down?  I don't have a speedo to check my speed.  The local crappy track doesn't open until November.

[HAULIN IT]

Team, Sounds like your headed on the right track. I have no experience with a "narrowband" air/fuel meter. I have an Innovate unit & have had pretty good results with it on several vehicles. The "hiccup" your referring to: Is it just as you nail it or does the engine start to go & then hiccup? Have someone watch & listen  to find out if the Black smoke is at the same time as the hiccup or a moment later. Keep us posted, Lorne 

[team39763]

We're gonna take it out to the back roads soon and do some test'n'tune.  On my last run, my brother said there wasn't any more black smoke.  When I stalled it up, there didn't seem to be any hesitation.  Only when I was going from just off idle(which could probably be cured with the mixture screws).

[HAULIN IT]

Team, If the hesitation is just off of idle & there is no Black smoke, I would try two numbers higher on the squirters & try again. The accelerator cam profile with a bigger lump &/or sooner may also work if you have them. Lorne

[Blue 82]

Team, If the hesitation is just off of idle & there is no Black smoke, I would try two numbers higher on the squirters & try again. The accelerator cam profile with a bigger lump &/or sooner may also work if you have them. Lorne

the squirters on the left side of the pic will help that off idle hesitation,
look down the carb while it's running and crack the throttle.
use a timing light to "freeze" the pump shot (point the timing light inside the carb at night or in a darkened garage)

We're gonna take it out to the back roads soon and do some test'n'tune.  On my last run, my brother said there wasn't any more black smoke.  When I stalled it up, there didn't seem to be any hesitation.  Only when I was going from just off idle(which could probably be cured with the mixture screws).

make sure that as soon as the throttle blades move there is fuel coming out of the squirters, any delay will cause hesitation.

using an air fuel meter to set your mixture will work fine at WOT
using it to set part throttle/cruise will drive you nuts,
simply because you have limited control of your spark
running 32* at part throttle cruise will make it seem like it's always running rich (you have no vac advance to get you in the 45*+ range for efficiant cruise)

32 degrees seems a little on the low side at WOT unless you have some very efficiant heads.

[team39763]

I thought I had it sorted out a few weeks ago, but just last week it died on me.  I was planning to take it to a dyno tuner who quoted me a reasonable price.  But just today I decided to check the directions to my regulator and fuel pump.  It turns out that when these two particular models are used together, it has specific instructions for the combo.  Previously I could only get a max of around 6psi and that wasn't consistant.  After following the special intructions I actually maxed out the FP gauge(over 15psi).  Now I have a rock solid 6.5 PSI and I can hear my pump working strong.  I haven't turned the truck on yet, but I will next week when it stops raining.  I still plan to go to the dyno to atleast see what my powerband is.

EDIT: I installed a 31 squirter in front and a tube type 31 in rear of the carb.

[team39763]

I think I'm finally headed in the right direction for real this time.  The fuel pressure is strong and constant.  I corrected the float levels since they were way off(don't know how that happened).  I accidentally disabled my tach, so when I went out to test it, I had to be careful.  I was too scared to do a WOT test from a stop since usually I have to shift before the pedal hits the floor, but I didn't have my tach/shiftlight and I can't shift by ear.  I almost got busted by the cops twice...they came by right at the end of each run(seconds after I shut down).We are trying to get a camera to take some more video.  We'll be headed to San Antonio Raceway next month when I get my new axles and spool.  Thanks for the help ya'll.

[Captkaos]

Glad you figured it out, or at least on the path of....

[team39763]

Yep, I'm definately headed in the right direction.  I got it pretty close to perfect(as far as launching without a bog/hiccup) with just playing with the different pump cams.  Then last week my wife bought me a 50cc pump kit and it works perfectly now.  I tested it in front of my house real quick and it smoked the tires right off the line.  That's what I wanted.  It still doesn't have that BBC feel, but it seems like it's going somewhere now.  Thanks for all the help and advice guys.

EDIT: Nevermind, I took it out today and it nearly died while trying to go WOT from 5mph.  I'm looking into some other problems I might have overlooked. 

[SFord]

Ever figure it out?

[team39763]

Sorry I didn't see this thread come back up.  I thought I figured it out, but I ended up flooding the motor and just let it sit since then.  I'm gonna try one more time to get it running before I take it to an actual dyno tuner.  I've found out that I had a bunch of little issues that might have been collectively making it run like crap.  But we'll see when/if I get it running again.