Hesitating Holley

[YENKO DEUCE REGISTRY]

If my Holley stumbles just off idle, how do you tell if it requires a pump cam change or a different shooter? I have already checked/adjusted the following:

-secondary throttle plates fully closed at idle,
-vacuum checked, 18-20" at 1,000 rpm,
-set primary mixture screws to achieve the 20",
-set idle rpm to 1,000,
-acc. pump arm gap set at .0010",
-rejetted the primary side from 70's to 68's,
-something I've forgotten in my frustration /ubbthreads/images/icons/mad.gif

[69L89396]

From my experance, you have to make sure there is NO play in the acc. pump arm. Just make sure that the pump arm moves as soon as the throttle arm moves. I have tried the acc. pump arm gap set at .0010" and have not had any luck. If you get it too tight, you won't get a full pump but that usally doesn't effect anything. Most of the time it is just a little too much slack.
If you don't find any slack, check the plunger under the nozzle. It might be letting the fuel drain back to the pump a little. If this is the case, when the pump starts to move, it just pumps air.
What is happening is the vaccum is dropping when you first open the throttle and the pump shot covers up the dwell time until the vaccum picks back up. I hope I explained this right.
Good luck

[YENKO DEUCE REGISTRY]

Your explanation is correct, the acc. pump is a mechanical delivery of fuel until the vacuum signaled fuel shows up. I'll reset the gap at 0 and see what I have. My hunch is that the duration of the fuel from the shooter is too short, thereby requiring a smaller diameter shooter to 'lengthen' the jet stream.

In the book I have on Holley's, it says: 'This function - mechanical injection - is most important when the carburetor is somewhat higher in capacity than ideal for the application, or with a double-pumper type carburetor using mechanical secondaries.' I know that my stock 780cfm Holley is much too large for the LT1, but I don't understand why that makes the acc. pump circuit more critical. Any ideas?

The most frustrating part is that the carb ran excellent before I sent it out over the winter to get 'concoursed' /ubbthreads/images/icons/confused.gif /ubbthreads/images/icons/mad.gif /ubbthreads/images/icons/confused.gif /ubbthreads/images/icons/frown.gif

[69L89396]

One other thing I have done before to help with this sort of problem. I had to up the idle a tad and it helped. You might need a cam that will give more shot when the throttle first opens. I don't think the problem is with the carb size. LOL

[COPO PETE]

Hey Marlin.....I'll try and take a look what squirter and what colour cam is in my Nova carb! Stay "tuned"!
Peter

[restorer]

69L89396,your right about upping the idle a tad, your starting to uncover the transfer slot sooner. If nothing else works it's an easy fix. Wes

[NOCOPO]

Marlin, Just my 2 cents on hesitating holleys.(1) Power valve, make sure its not blown out. even the smallest backfire can ruin one. (2) The old fuel gyser out of the vent tube. If the float level is just the slightest bit high, when you jump on it, the fuel sloshes up and out down into the primaries giving you a hesitation. just my $.02 /ubbthreads/images/icons/grin.gif

[YENKO DEUCE REGISTRY]

Thanks for the tips!! I purchased a pump cam kit and found a graph for their parameters, putting the orange one in Friday night. I found that the Pink one that was currently in there didn't activate the acc. pump until the throttle linkage moved almost a 1/4 in" /ubbthreads/images/icons/shocked.gif It runs much better now, but still needs some more tweaking. I will have to try some of the others to find the one that works best.

I believe that this 780 Holley is too big for the LT1, especially with stock manifolds and smog system. We know for a fact that they run quicker in the 1/4 mile with the secondaries disconnected, (as do the '66 L79 Novas). GM put 780's on the solid lifter big blocks, and our theory goes that they just tossed one on the LT1 knowing that most would have headers installed anyway.

Pete, what did your dyno guy use on your 427/425 test from MCR? I thought he started with a 750 shop carb, and then went to ??

[COPO PETE]

Marlin. I am running the clear (no colour) cam with a 31 squirter. 72 primary and 82 back jets. And sorry, don't agree with you on the 780 being to big. You need it to run 106 mph through the traps! My car revs like a motor bike with the 780 on. On the 427, we stated with a 650. Way to small. Then we tried two different 780's on it. Oh ya, are you running a vent baffle on the metering block...that can help stop the stumble.
Peter

[YENKO DEUCE REGISTRY]

Thanks for the info Pete, will try the clear one next.
As for the 780, Neal and I accidentally disconnected his secondaries and he ran 102mph!! I plan on keeping my secondaries connected, putting a plugged power valve in there and bumping the jets up - - after I get the stumble ironed out.

When will we see the silver bullet again??

[YENKO DEUCE REGISTRY]

Hey Pete;
Tried the clear pump cam, good call!! This woke the car up a bit, still a little stumble left so I'm going to put in the jets that you suggested. Thanks for the advice /ubbthreads/images/icons/smile.gif

[YENKO DEUCE REGISTRY]

Pete;
What's a vent baffle?
/ubbthreads/images/icons/confused.gif

[Chevy454]

Not to "interrupt" here, but what Pete is talking about is a brass(?) piece hangs on the 2 studs near the top of the metering block, and keeps fuel from exiting out the vent. I have one in my pocket (don't ask!/ubbthreads/images/icons/grin.gif), and I will try and nab a picture here in a second.

[COPO PETE]

The vent baffle is better than the little piece of brass Rob is talking about. Jegs or any speed place sells them. They are a plastic tube about 2 inches long that snaps in place of the brass wannabe. To see if you really need it, take of the air cleaner lid and put about a 5 or six inch piece of rubber gas hose in a "u" shape connecting the two vent tubes on your holley. Cut a little hole in the top of the hose so it can breath. Take the car out and run the [censored] out of it.....well, for about 60 feet. If your stumble goes away, you need 'em. What squirter are you running Marlin???
Hey Rob, great buddy of yours on the Buick site, he knows all!!!!
Peter /ubbthreads/images/icons/smirk.gif
"Censored".........WTF is that!!!!!....oops

[Chevy454]

Ok, I will snap a picture of an OEM vent baffle! What advantage does the aftermarket have over the OEM Pete? I would have assumed the factory piece worked.

As for 99Z1LE...let's just say "he's not well"/ubbthreads/images/icons/smirk.gif!

[YENKO DEUCE REGISTRY]

Thanks for the tip, I will give that a try as well. I don't know which squirter Dotterer put into it. I was hoping to get rid of the stumble without taking it out, since I didn't have another one to try yet, and I was concerned about dropping something down the carb. I will have to stuff some rags, and take it out to see the number.

The first step is to richen up the primaries since I put 68's in there trying to keep the plugs from fowling. I think I fixed the plug problem by adjusting the mixture screws based on the vacuum reading.

Exactly how do you set the accelerator pump adjustment?

I have no problem taking it out and running the 'feces' out of it for 60+ feet! The only thing better than that is kicking some Rice Derier'.
/ubbthreads/images/icons/grin.gif

[COPO PETE]

Marlin....You better have a look at squirter size right away. Very important part of your stumble. Use some needle nose vise grips to grab that little devil!
Peter /ubbthreads/images/icons/smirk.gif

[bbdon]

I know that there is somtimes some confusion about the pump clearance setting. You need to set the accelerator pump lever to .015 clearance at wide open throttle. To do that you need to use something to push the accelerator pump lever down all the way while also opening the throttle all of the way. Then you use a feeler gauge to check the clearance with your third hand. The idea is that you don't want the the accelerator pump to bottom out at full throttle, which will harm it. Some people read the spec and set some clearance between the cam and lever at idle. You don't want to do that because the accelerator pump will not work soon enough, there should be no clearance at idle. This has probably already been set up for you, but I thought that I'd mention it.

[YENKO DEUCE REGISTRY]

Hey bbdon;
Thanks for the info, if it was set up for me - I have changed it several times already!! None of the other adjustments seemed to set up, so I just figured the acc. pump wasn't either. I will find my third hand and check it out, after I change the jets, examine the squirter, and ....
/ubbthreads/images/icons/confused.gif

[YENKO DEUCE REGISTRY]

Had a little bit of time now that the NNN show is over to tinker with the Holley. Schoneye and COPO PETE were both helpful. I put the white pump cam in, made sure I had the '31' squirter, changed the secondary spring, rejet the primary's, and most importantly, rerouted the vacuum lines from the carb/dist. advance. That stupid TCS stuff was messing up the advance.

The hesitation is practically gone, but it still lacks the super strong midrange power it had before. So, the only thing I had before that I didn't re-install is the blocked power valve on the secondary side with '82' jets. They are on order, so I will install and retest, will let you know /ubbthreads/images/icons/grin.gif

Thanks for the tips!

[YENKO DEUCE REGISTRY]

It's taken me a while to get things changed around on my carb! But, it's off the car and I'm changing the jets etc... Pete, or others, do you use a blocked power valve in the secondary side? What is the advantage, if any, of doing so?

[John Brown]

Marlin, if you block the rear power valve you must increase the rear jet size 6 to 8 jet sizes to compensate. The power valves job is to keep mixture lean while crusing and richen when accelerating. However since the rear barrels are either fully closed or fully open on the dragstrip, there is no need for a variable air/fuel mixture. The advantages to blocking the power valve are that the power valve now can't stick closed and cause a lean condition, and won't blow out and leak if you should have an intake manifold backfire.
You gonna go to Norwalk? /ubbthreads/images/graemlins/3gears.gif

[Chevy454]

John's right on all counts. But, I'm running both my power valves...is that best? Probably not, but it's worked ok so far. As for blowing it out, I did the backfire protection piece that Holley sells, so that isn't a threat. I'd like to block the power valve and try it before Norwalk, but I'm running out of time. So, should I keep a lookout for a Gobi Deuce when I'm there?

[JoeG]

The only reason I am mentioning this is because you said everything was O.K. before you stored the car for the winter. I would also lay my car up for long periods of time and when started would not respond crisply. I found that I would have to take the metering blocks off the carb and gunk all passageways to get rid of any varnish build-up.Put a gas stabilizer in your tank or a good fuel additive. You should also read your plugs after each carb adjustment. JUST A THOUGHT. /ubbthreads/images/graemlins/wink.gif

[YENKO DEUCE REGISTRY]

Many thanks for the info! I plan to install a blocked power valve and use all of Pete's COPO Nova setup suggestions from earlier in this thread. I'll let you know how I make out.

I would like to make it to the drag strip this month - but it won't be Norwalk /ubbthreads/images/graemlins/frown.gif I have not installed the driveshaft safety loop yet, not sure I like that extra spacer between the trans and the mount. I'm going to try to make the bend modification to mine like Casey did on his. I don't expect to break into the 13's my first time out, but would still like to have the loop installed for safety reasons. I've been re-reading all the stock racing topics in this category in preparation for my jaunt to the drag strip one of these Grudge Nights /ubbthreads/images/graemlins/smile.gif

[YENKO DEUCE REGISTRY]

This may sound stupid, but I have a funny feeling that the metering block gaskets might be reversed on my carb after getting it rebuilt last winter. How can you tell which gasket goes where? If they are switched, what would that do to driveability?

[MotownMadman]

Marlin, I read this whole thread, one thing comes to mind as for an initial stumble, you said it worked fine until you removed, rebuilt and reinstalled. One thing I would check is for a vaccum leak on the base gasket, even the smallest leak coming off idle can cause enough of a unmetered air draw to make the car stumble. Several ways to check for a leak, I am sure you know the protocol on that. Just a thought.
Motown /ubbthreads/images/graemlins/beers.gif

[YENKO DEUCE REGISTRY]

Matt;
Good call! When I reinstall it this time I will put my hand over the carb to see if the idle speed picks up, and also spray a little carb cleaner around the gasket areas. A small vac leak would indeed create a hesitation.

One thing I noticed yesterday was that if I moved the clear acc. pump cam to the number 1 hole instead of the number 2 hole, I could see a 'more' immediate shot of fuel from the squirter. I did not drain the fuel from the bowls right away, this way I could recreate the scenario on the bench. So, I'm anxious to reinstall the carb to see if that helped as well.

So little time to work on these things, especially with 21 month old Benjamin trying to climb under the car every time I turn around /ubbthreads/images/graemlins/smile.gif Kids are a joy, he can't really talk yet but makes the engine rev / burnout sounds! I have no idea where he learned that from /ubbthreads/images/graemlins/naughty.gif

[JoeG]

The metering block has pins so you can't reverse gasket, make sure everthing is tight. /ubbthreads/images/graemlins/wink.gif

[YENKO DEUCE REGISTRY]

JoeG;
Ok, thanks - I was starting to go crazy yesterday thinking how that scenario may have happened. I saw on the secondary side that the gasket covers several of the holes in the main body, and was running away with the possibilities that the gaskets were swapped!

[Salvatore]

Hey Marlin. Call Pete (610)326-8322 He will help you out!

[YENKO DEUCE REGISTRY]

Sam; That's where I plan to go after I get the carb back on! I figure I will be able to bring it over to him on a Saturday morning to have him check it out, and go over the setup - if we could get a rain-free weekend around here!

[John Brown]

Marlin, just one more thing. If your accelerator pump spring (the one that has a bolt thru it that pushes on the acc. pump lever) is a late style Holley red spring with the bolt head on the pump arm and a chrome looking ny-lock nut on the top instead of the 1970 style spring and bolt set-up, then the spring is usually too soft, and you won't get an immediate pump shot. On most every Holley I do, I use the early style spring and bolt and tighten up the thru bolt a bit to make it firmer, then re-bend (in a slight curve) the arm that runs on the accelerator pump cam to get rid of slop in the linkage. /ubbthreads/images/graemlins/burnout.gif

[Zman]

Hey Marlin,
Sorry to butt in....
There's been a lot of discussion regarding Holleys on the "other" site lately. THE largest contributer to an off idle stumble is the Power valve. There are a couple different recomendations, but I have found that if you start with a power valve rated about 1/2 of the manifold vacuum, you'll be pretty close. In your case, you have around 20" of manifold vacuum, so I'd try a 10.5 primary power valve. You may have to experiment a bit to find out which one works best, but they're cheap, and simple to change. I would NOT recomend blocking off the power valve for a street driven car.
Ignition man on Steve's site is an X Holley employee, and 64pronova seems to know his stuff, and has helped several guys get their holleys dialed in.
I just went through this same thing when I changed engines in my 69 nova. I have a pretty radical solid cam (548 lift adv. 304* 264*@.50 duration with 108* seperation) and I have only 7-8" of manifold vacuum. The new Holley double pump I just installed (on a Victor jr intake) comes stock with a 6.5 power valve. In my case, the power valve was pretty much open all the time, creating a rich condition at idle, and poor throttle response. I changed to a 3.5 power valve, and the idle cleaned up, and the throttle response improved dramaticly. I may experiment with shooter size, and acc. pump cams, but just the power valve alone made a big difference.
In your case, I'd guess the power valve is too low, and not opening soon enough. I think you're just masking the real problem by changing shooters, and acc. cams. The main jets will have little or nothing to do with the off idle condition. I would suggest that you put everything back to stock, and start with the correct power valve. THEN experiment with shooters, and pump cams until you're happy with the performance. I'd be willing to bet that with the correct power valve, you won't have to tweek it much to get the desired performance.
Hope this helps,
Dennis

[YENKO DEUCE REGISTRY]

Dennis;
Thanks a bunch, I will do exactly that - check the power valve to see what is in there. I didn't put the carb back together yet, so I will check it tonight. I have to get the carb back on the car soon, there is a show this weekend!

[Chevy454]

Upon reading this thread, and after having Pete and JJ tell me (for YEARS) how I need to set up my carb, I finally listened. I was planning on heading to Memphis Thursday night with a buddy of mine, and figured I'd try and "fiddle" with the carb a little since I was going anyway. So, I put a 6.5 power valve in the front, blocked the rear, and took a stab at the jetting.

The primaries were pretty close, but it took me a few trys to get the secondaries where they needed to be. But, I think it worked out ok...
http://www.yenko.net/attachments/42284-NEW-2.jpg

I was rather impressed with the majority of my lights last night, as I had several 0's...

[COPO PETE]

Congrats Rob! 12.60's are just around the corner! Just think how fast these magazine cars of the late 60's would have gone if they actually had time to really dick with them! /ubbthreads/images/graemlins/3gears.gif
Peter

[YENKO DEUCE REGISTRY]

Wow! Well done Rob!

I need to thank Pete as well! I put Pete's carb setup into my Holley this week, and brought it to work today. What a world of difference! Zero, none, Zilch hesitating, so very good throttle response, with very good power through the whole range - better than ever before. I didn't try any 'blast' runs on my way to work this morning in it, but will test it a little bit more on my way home at lunch. I noticed that it revved quicker than I was used to, I was shifting at 5k where I normally shift at 3-4k = fun!!

Looks like I need to get to a track! I'm waiting for your advice to Frank's post as well /ubbthreads/images/graemlins/smile.gif

[sYc]

Marlin, Glad to see you have the carb problem sorted out. Its amazing what a little "massaging" will do to these cars. /ubbthreads/images/graemlins/haha.gif Right Pete/Rob?

[hvychev]

Wow. Cool Rob! /ubbthreads/images/graemlins/biggthumpup.gif

[Chevy454]

Yeah, after I "massaged" my jetting to what it actually needed to be, I picked up a solid TENTH from my first 2 passes of the evening.

Many thanks again to the "LaBatt" brothers (Pete and JJ) for the help again! /ubbthreads/images/graemlins/biggthumpup.gif

[COPO PETE]

Hey.... glad to hear it all came together. You too Marlin. Only too glad to help out, and I'm sure there is more to come! When you get back from Norwalk next week, you will be able to post your 12.6 time.
Peter /ubbthreads/images/graemlins/beers.gif