Holley Ultra XP Issues

Discussion in 'Technical' started by 1974Comet, Feb 20, 2017.

  1. 1974Comet

    1974Comet Enthusiast

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    Hi everybody, I've been away from the forums for some time now just due to every day life and have tried to keep up through facebook, but I think it's time I ask for tuning advice here. I have a 347 in my Comet with a fairly wild camshaft. In fact, I'll post my entire build here.

    347 Forged rotating Assembly
    Twisted Wedge 170's
    10.5:1 Static Compression w/ Flat Top Pistons
    Victor Jr. Intake
    MSD 6AL ignition with pro-billet distributor
    Cam Specs:
    Solid Flat Tappet Cam:
    Adv: 274 Int. 281 exh.
    @ .050: 244 int. 252 exh.
    Lift: .596 int. .592 exh.
    Rocker: 1.72
    LSA: 108 (with 4* adv ground in)
    (Yes, it is a very large cam. Not exactly what I asked for, but I'm trying to make it work)
    Shorty Headers with 3" exhaust all the way back
    T5WC Transmission
    Holley Ultra XP 750

    Now for the issue. My biggest issue is that this carb is hardly ever consistent. I can dial in the idle mixture to a perfect 14:1 once it warms in the morning, and the second I drive away my tune is thrown out the window. Generally speaking my off-idle and part-throttle response is absolutely terrible with cruise AFR sitting around 12.5 and off idle dropping down to the 9.5 range. I've tried messing with the accelerator pump circuit, I've tried putting in slightly larger air bleeds, and I've tried making the IFR smaller. My current jetting has me sitting at 73's in the primary, and 79's in the secondary with the power valves sitting at 3.5. The idle RPM is usually around 1000 as anything below that tends to get a little shifty, and my idle vacuum sits around 8" in neutral. I guess my question is.. What do I do to fix this tuning nightmare? It's pig rich down low and lean up top. Is there any advice anybody can give me to help me dial this car in? Another thing it does is when I set the idle at say... 1000 rpm. And i go out and drive for a little while, it won't always return to 1000 rpm. Sometimes it gets stuck at 1500 shaking and bucking, and after about 15-20 seconds will return to 1000rpm. It's really weird and I swear to god that this car hates me. She runs different every time I start her up.

    My timing sits at about 18* initial, with 12 extra degrees to be in by 2800. The distributor advance seems to work fine and as far as I know, my MSD box works just fine too. Am I chasing a gremlin or something? :banghead:

    Is there anybody out there than can help me solve this issue? If any more information is required, let me know!
     
  2. Maverick Dude

    Maverick Dude Member

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    Very cool. This is basically a full out race engine. High compression, low vacuum, advanced timing, mechanical secondaries. It's made for one thing; going 1/4 mile at full throttle. Long tube headers would help with scavenging. What octane gasoline are you running?

    :chirp:

    MD
     
    Last edited: Feb 20, 2017
  3. groberts101

    groberts101 Member

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    Highly doubt those are gremlins.. looks to be much more a parts combo/tuning/calibration issue. I can help you get it sorted but probably best if just call me if you want to make faster progress. Busy grinding/prepping parts but it should take 15 minutes or less to give an overview of what's likely going on here. This back and forth "tech support chat" stuff is for the birds and takes forever and a day. Some things I immediately noticed and hopefully get you started. 2 BIG areas I see that are killing the motors peak manifold vacuum and mixture consistency.

    Do you have a vac advance pot on the distributor? If so?.. what source feeds it.. full manifold or ported/timed spark? If not?.. then initial advance is far too low for that bigger cam in this particular combo.

    Won't go into great detail here but that supplemental vac advance assist won't solve your problems once you drop it into gear and blip the throttle it goes away and the engine still struggles against the carbs t-slot/booster.. metering becomes erratic all over again. Basically, the vacuum advance pots added assist only acts as a tuning tool to show you what the engine really prefers during idle/light throttle cruise from an ignition timing standpoint. A REALLY SIMPLE TEST to see what you're missing out on here is to lock the distributors mechanical advance/timing out and test drive it(after you've readjusted the throttle stop and mixture screws). 34-36° is perfectly safe base tune to work off of.. works throughout the whole rev range idle to redline. If you're starter protests against all the extra cylinder pressure created then you may need to pull the initial setting back 10° to get it started then set preferred total timing with the light and lock it down. You will literally be stunned how manifold vacuum levels rise and the amount of extra torque and throttle response the engine will suddenly have. I'd lay some cash that we can get you to 12" of manifold vacuum and it won't go away nearly as quickly during lighter throttle transitions.

    Tighter LSA increases overlap and the mixture speed/combustion event is lazier than usual. Single plane manifolds just exaggerate the cams rowdy character. Shorter primary headers with too big collector and too big intermediate pipe makes for lazier and more easily reversed exhaust flow/increased intake reversion. Having partially marginal static compression ratio for this engine size/cam timing combo adds more insult to injury by reducing cylinder pulse strength on both sides of the cylinder head. All this stuff is cumulative and this obviously severely affects manifold vacuum and hurts a big race carbs ability to stay metered correctly. Engines always hunting for the perfect mixture but the carb just can't keep up with the manifold vacuum fluctuations.

    Front and rear throttle shaft adjustments and how they relate to the T-slot is extremely important to get right with bigger cams. Quick-n-dirty test is to close the rear throttle stops just short of the secondary plate sticking in its bore(not good on the parts) and then readjust the front throttle stop and mixture screws to lowest/smoothest(relatively speaking) idle speed. Should be able to make around 875-900 rpm idle speeds when the timing and t-slot exposure becomes closer to ideal. The gains created from each one compliments the other for even greater gains than typically expected. Motor will generate more cylinder pressure at idle/light cruise and tip in/throttle response will be much improved even coming up from that now slightly lower idle speed.

    PM me and I will give greater overview over the phone on a few other details and quicker ways to troubleshoot/dial in the tune.
     
    1974Comet, rotorr22 and RMiller like this.
  4. RMiller

    RMiller My name is Rick

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    I wish I knew half the stuff you have forgot when it comes to tuning! Sounds like the OP is in good hands here, I always appreciate when guys like you are willing to help those in need.
     
  5. groberts101

    groberts101 Member

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    It would be cool to make a video of how to properly recurve a distributor and the major affect it can have. but I barely find time to even take and post a dang picture. lol

    Seriously though, Rick.. if more people knew how much manifold vacuum they were leaving on the table with all this "that's too much timing" mentality they'd be disgusted by all the wasted power and efficiency they have p'd away over the years. I don't care if you or I have 400 horsepower under the hood of one of these cars, they're light and proper tuning should be netting you closer to 20 mpg at around 2,500 rpm highway speeds. Light throttle torque production(cylinder pressure) is key. Well, that.. and staying out of the carb's secondaries. :D
     
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  6. groberts101

    groberts101 Member

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    PM returned
     
  7. groberts101

    groberts101 Member

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    Last we talked, you were starting to close in on the tune.

    Did you figure out how to adjust that idle bypass valve to get the front t-slot exposure back up around .040-.050"?

    What about the shorter/fatter pump shot on the primaries?
     
  8. greasemonkey

    greasemonkey Burnin corn

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    Lock the timing out. Jet down in the front. See how it acts. You can jet up some in the rear. But if the spread seems way off I'd change the high speed air bleeds. But, above all. Be sure all the air bleeds are clean and inside the carb is clean. With the low vacuum driveability isn't going to be great no matter what you do. Mine doesn't make much vacuum either and is sensitive to the weather. Also the amount of transfer slot exposed can make a huge difference. So, if you had to open it up quite a bit in the primaries the transfer slot may be to exposed.
     
  9. dan gregory

    dan gregory Member

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    One other thing to think about is how much vacumm do you have at idle,if it is 6,then you need a 6.5 power valve.I don`t understand power valves completely but I know they have a huge effect on your carb,so matching your vacumm to the power valve may help you if you have not done it.Gregg can probably shine some light on this.
     
  10. 1974Comet

    1974Comet Enthusiast

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    My apologies to everyone replying in this thread. The first chance I got to play with the car in the past week was yesterday, and I was able to take it for a short jaunt through town for about half an hour. I locked out the timing at 33* but plan to increase that a few more degrees next time I get the chance.

    I increased the squirter size to a 37 and changed the pump cam to a blue cam in position 1. Seems to have made a dramatic difference in throttle response and overall low end torque all together, but I'm still pulling no more than 9-10* of vacuum regardless of any of these changes. Though, it does indeed seem to run better, but I havent exactly gotten to the point of dialing in the transition slot exposure perfectly. Right now, I actually don't believe any of the transition slot is showing at all, and the idle is still in the 900 range... With throttle blades nearly closed shut.. But I can't find a vacuum leak anywhere either, so maybe this engine just seems to really enjoy it's timing?

    Overall, the car performs great, but the cruise afr is still a smidge rich around 12.5-13, and part throttle cruising (especially right off idle) is a very rich 10-11:1 afr, which sometimes even dwindles down into the 9's if I really kinda get into it. Any way to lean out the lower end of the spectrum? I'll try to add 3 more degrees of timing and see if that continues to help my situation. I will also unplug the vacuum advance to see if that helps me in the long run as well.

    Anything else I should keep in mind?
     
  11. greasemonkey

    greasemonkey Burnin corn

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    Jet it down. The transition slots are what you are jetting. And where you cruise. The main metering circuit is booster and high speed air bleeds. Most people don't understand that. Jetting will affect wot simply because they pull each circuit in one after the other. Idle,transition, main metering.
     
  12. groberts101

    groberts101 Member

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    John. You have a decent combustion chamber on that head with smaller "fast ports" and moderately sufficient compression ratio. But none of that will save you from the huge.. approximately 2" sq/in sized hole created during the overlap window created by that cam. In fact, you'd probably crap yourself with all the extra manifold vacuum bottom end power throttle response a big dual plane would add to the equation. Would tame that big cam right the heck down.

    About your idle speed. Didn't you read the instructions to adjust the bypass on that carb? It's located under the air cleaner stud. Set your t-slot exposure as mentioned earlier and then never touch it again for fear of screwing it up. From there you can use the secondary side and bypass valve adjustments to control idle speed. Nothing but bandaids for this fuel curve until you get that front t-slot setting dialed in.

    I'd also be shooting towards 36* of initial/locked timing too. But.. to sucessfully run a vac advance pot(ported or full) will require fully tightening it's adjustment to limit its contribution to around 8-10* max assist. Adding vac assisted timing will likely leave you shorted on the initial/locked setting though. That limitation and severe fluctuations of available assist are the Achilles of the vac pot setup and where the programable box mentioned via PM would help fill in the gap.
     
    Last edited: Mar 2, 2017
  13. groberts101

    groberts101 Member

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    Typical cookie cutter recomendation for PV choice is.. in gear idle vaccum ÷ 2. To be much more accurate requires a visible vac gauge to be studied at the various cruise rpm's and typical heavier throttle transitions(not to be confused with WOT) that are most commonly used in real world driving scenarios. You know.. you're in high gear and decide to push the throttle hard enough to drop vacuum into the enrichment circuit.. but not quite enough throttle to actually cause a downshift.

    Some of the best tuners I've seen will lean out the main jet for clean crisp cruise and then fatten up the enrichment circuit to keep the fuel flow where it should be under power. In that scenario they may also allow the power valve to come in a tad earlier throttle openong too.

    Big trick with all this carb tuning stuff is to seperate the various circuits to how they actually relate to specific throttle positions at varying engine loads. No use in screwing around trying to find the perfect power valve if the fueling is off for the initial portion of the fuel curve. Otherwise you will get false positives and positive falses while chasing your tail around in circles.
     
  14. dan gregory

    dan gregory Member

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    Hey Gregg,that is why I know several people who have gone to the Fi-Tech fuel injection set up.BIG BUCKS but they love it & not all the tuning headaches of a carb,too rich for my blood.What do you think about the old Hilborn fuel injection,there is a guy in PRO Stick using it in a little yellow 63 Falcon,& another guy{same class}64 Falcon,both cars extremely fast at 8s in the qtr.I read an article somewhere a while back & they tested the Hilborn against most of the newer carbs,Hilborn out did them by 25HP.Just a thought,on a drag car how hard is it to tune the Hilborn.
     
  15. groberts101

    groberts101 Member

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    I've only ever watched others lay hands on them over the years but Hillborn are awesome designs. The biggest advantage of any stack type system is the added flexibility to modify torque curves(to adjust the tire hit or match a gear to ET better) by adjusting stack lengths and taper percentages. You're essentially changing the inductions overall tuned lengths(bellmouth to back of valve) via the stack lengths, taper angles, and bell radii/sizing.

    That aspect along with mechanical adjustments makes them highly refinable from a tuning standpoint. The better version for more limited hood clearance would look something like this. The shorter runner castings allow more stack length adjustments.

    MD-JAN16-Kaase-web-11-1080x675.jpg
    302_gold_fuel_railsex_gif.gif

    Look at those prices and you can see why I seriously want to make one out of carbon fiber with some kevlar and possibly even nomex reinforcement. Lighter with less heat soak. Basically a dual-plenum EFI style like some of the high-tech euro elite stuff. As of now I have some partial mockups and roughly drafted pieces but ideally I need to invest in a vacuum bagger/infusion based system to do show quality work. I will have to save that for next phase engine buildup of my all-aluminum stroker bullet.

    As of now my Kasse P38's are going to be fed by a hacked up(valley removed) ultra-high rise(at least that's the way a 9.2" deck manifold looks sitting on an 8.2" deck block!) Edelbrock Air-gap 351 Cleveland dual-plane manifold. I would prefer CHI's supremely designed air-gap version but hacking away on a $350 Edelbrock manifold is the highest level of crazy I can afford right now. If the theory holds true in actual testing?.. then that manifold/head combo should have decently stout torque characteristics even on this littler 310" mule shortblock while still revving higher than is typical of these style dual planes for some decent "single plane like" topend power numbers. Camshaft design will become especially important because of the P38's huge valves and bowls on this little motor.
     

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