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Discussion Starter · #1 ·
I've got an HP1000 that I'm trying to dial in a bit better - I can't determine where to tune it. Just had it on the dyno a few days ago and have the WOT tuned to about 12.8 or 12.9:1 with 86's up front and 94's in the back. I have a 6.5 PV in the front only, rear is blocked. Problem is that it's fouling plugs when driving around town/cruising - this is a street car (plugs are on the HOT side - exceptionally white immediately after dyno run, actually). With an LM-2 meter, I've determined the idle to be decent at 13.8-14.0 with vac in the 8-9 inch range. Light cruise is 14.0-14.5 with vac in 8-9 range, moderate acceleration is 11.5-12.0 a/f with 7-8 vac. This is with a 6.5 PV, which works well - with a 5.5 PV, there is a bog when pulling out, and bucking/hesitation during light cruise. This is a stick car, 555ci with a big solid roller cam, 1200rpm idle, and timing locked out at 37 degrees - 800 hp/700 tq, roughly. 4 corner screws are 1.25 turns out. Transfer slots are a bit more than square, but front and back are open equally.

So it seems obvious to me that I need the 6.5 PV for the bog/hesitation issues, but think I'm getting too much fuel when the PV opens (based on the the A/F ratio under moderate acceleration). So how should I try to tune this out? Do I go to larger IAB's? Do I try to restrict the IFR's? Are the PVCR's too large? I don't know enough about these parts of the carb circuitry to determine what to tune next. Seems like a fine line between an idle that's too lean and a transition that's too rich.

I have been searching/reading on here for the past two days but can't find anything exactly specific to my situation. Thanks in advance!
 

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Just try putting the 84 jets back in the front to see if it gets better. Why its somewhat ok idling and on light cruise is because its still on the idle circuit there.


Dave
 

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Discussion Starter · #3 ·
Just try putting the 84 jets back in the front to see if it gets better. Why its somewhat ok idling and on light cruise is because its still on the idle circuit there.


Dave
Well, it was fouling plugs on the 84's too - before. I took it to the dyno expecting to see that the jets were too big at 84 and 92 and being the reason for the fouled plugs...I was surprised to see that it was lean on the 84's and 92's at WOT.
 

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What plugs are you running? Your set up is very similar to mine. Actually your cruise is leaner than mine and I am not fouling plugs. My idle is around 14 also. WOT is around 12.9. Timing is loccked out at 40. My car sees mostly street use too. I am using a 4.5 power valve.
 

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I try for a somewhat rich idle and leaner transition-the moderate acceleration you describe Is kinda fat-I shoot for 12.5+ in that range.
I'm in the proccess of leaning out the same light cruise?acceleration as you describe
Neck down the ifr .002 and see what happens-I usualy cut it down .006 or so and work up from there-I also do the same with the IAB
stock on the new carb is .036ifr & 070 iab,I started at .028 ifr & .54 iab
and am now at .030 ifr & .062 iab and it's REAL close,I'll probablly up the Iab one more size up as i't will still bump 12-1 but Way less than the stock setting(10-11-1)
I would leave the main jet's alone as you have a nice safe WOT
Vacuum advance set right is also a must for light cruise/acc.
 

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it seems crazy your fouling plugs with 11.5 a/f ? i bet more than half the cars on this planet using an out of the box holley is worse than that ! hmmm , think there is someting else going on ?
 

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I think that the power valve is still closed under "moderate acceleration." You stated 7-8" vacuum and a 6.5" power valve.

When I tested actual opening points with several Holley power valves I found that they often started to open later than their advertised rating. When they do open they open slowly (not like turning on a light switch) so the power enrichment circuit is not likely to add much fuel until vacuum is a couple inches below the power valve rating.

That being said, I think it would be a good idea to try dropping the primary main jet 2-4 numbers to see if the engine leans out under the same conditions where you saw 11.5:1. If the AFR comes up to 12:0 'ish, then the next step is to open up the PVCR to ensure full enrichment at WOT when the power valve is really open. As a general rule, I open up the PVCR .003" for every 2 jet sizes I decrease the PMJ.

For now, I'd leave the bleeds alone.

Hope that helps.

PS. By the way, the problem you have is a good one to have, usually I get to fight with the opposite (going lean at mid-throttle)
 

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Discussion Starter · #8 ·
What plugs are you running? Your set up is very similar to mine. Actually your cruise is leaner than mine and I am not fouling plugs. My idle is around 14 also. WOT is around 12.9. Timing is loccked out at 40. My car sees mostly street use too. I am using a 4.5 power valve.
Plugs are NGK FR4's. I had much colder plugs in before, but have been working up to these in attempts to clean them up, after thinking the carb had been dialed in pretty close (I wasn't aware of the 11.5-12.0 at the time...but the car was running great!).

yellow heap said:
Neck down the ifr .002 and see what happens
Thanks - the IFR's are currently at .035, IAB's at .065. If I were going to 'neck down' the IFR's - can you tell me where I would find an .002-.005 diameter wire to put in there?

Jason Snyder said:
hmmm , think there is someting else going on ?
Not sure - any other places to look? Could one of the main body to metering block gaskets be bad? Timing is good - ignition is good. The only other thing I know to be wrong is that fuel pressure is dropping off at WOT under load. It's at 7-7.5 psi at idle right now, but slowly fell to 4psi on the dyno, in 4th gear. I haven't looked into this more, but the dyno operator thought it was because the return line was too big. We have an A1000 pump with 1/2 supply, 3/8 return lines...he thought the 3/8 return was returning too much fuel too quickly. He suggested a few different ways to choke that line off a bit. No chance that this is causing any problem, is there? WAIT! If fuel pressure is low, is there a chance that the carb is jetted too big, to compensate for the lack of fuel pressure, which is in turn fouling the plugs during cruise/moderate acceleration!?!?!?!?! Pressure readings were taken off a non-liquid filled gauge installed on the fuel log.

Eric68 said:
I think that the power valve is still closed under "moderate acceleration." You stated 7-8" vacuum and a 6.5" power valve.
Eric - any idea why a 6.5 pv would take the stumble/hesitation away that the 5.5 had in it if neither was opening at all? Maybe my vac gauge is bad?

Great tips on the PVCR's too - thanks. I would have never thought to open them up if I jetted down.


Thanks to all - much appreciated. I'm wondering if we're on to something here with the fuel pressure.....
 

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Seems like a fine line between an idle that's too lean and a transition that's too rich.

I have been searching/reading on here for the past two days but can't find anything exactly specific to my situation. Thanks in advance!
Interesting. I was told to use the smallest of the three pvcr on 2bbl 2300s I had for the center carb, the only one to recieve a PV. Off the top of my head the measurements were either .057 or .065.

To adjust the channel , one could use a "fine line" of wire. A stainless steel guitar high "E" string is .006-.010" . Or lead shot and an index drill. But I aint never done it :)

The front accel pump is possibly not covering the initial acceleration hence the 065 aiding it. It seems. Tell you what, if you put 84s back in, you might put a 075 PV in. It will cover some of the leanness at primary tip-in. Heck I run a 095. And idle is only 9-10"Hg.

Yet I still suspect the front acel pump is not dialed in. Shot too early, too much, or possibly too little. Is it lean or rich hesitation, plugs notwithstanding?

Dyno tuning a carb is one thing, tuning for good street manners takes a bit more experimentation w/o instruments!

And btw, same coil used for the dyno run? Again, 2 seconds to check and see if there still 10K ohms between primary and secondary. 2 more to check for 12+v.

Good luck!
 

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My experience with (2) Holley HP1000's is that they run awesome, but very rich in the cruise area...around 10.8AFR! Yeah, I could get it to idle at 14.5, but cruise was too rich. If I pulled jet out or played with the bleeds, IFRs, etc, all I did was mess up the phenomenal response of the carb. Same exact #'s with the 950HP's I've had. WOT was right on the money at ~12.5-12.8. This was factory specs.
 

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Well there ya go. And Vince seems to be a very fastidious tuner, so...... fwiw.
 
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