Holley Street Avenger 570 Idling Problems

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bluefish1967

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I've been running this carb on my Cuda for a while with no problems.
Recently installed a fresh rebuilt 68 model 318 engine with this carb, a new Weind aluminum intake to replace the stock , cast iron 340 intake and a Mild Comp Cam and lifter set ( 455 lift, 268 duration). Also installed an electronic distributor.
Vacuum is 14-15 at idle warmed up, timing is at 14 initial, 35 total. Will idle good in gear only after fully warmed up ( stock converter ). Otherwise, I have feather the throttle while putting it in gear, then if it doesn't stall it's OK.
Talked to Holley, they suggested cracking open the secondaries to help close the primaries at idle, to better allow the idle mix screws to work. This helped, but the problem is still there.
Started off running the factory recommended 54 jets in the primaries. Tried jumping up to 56 primaries, helped a little but the plugs are showing some black.
Have been checking for vacuuum leaks, but have found no evidence.
Any suggestions would be appreciated. Larry
 
check your fuel pressure , I have been fighting a problem with my Holley for a year now , finally got a pressure gauge on it and found the Holley pump had started putting out 12 lbs , the Holley seats are good for up to 8 lbs , I put a regulator in yesterday and set it to 7.5 lbs , the car still is going to be cold blooded because it's an HP carb so it has no choke but it smoothed out quite a bit and doesn't idle rough at the lights in gear . I am no Holley expert but in the past year I have read everything out there about rebuilding and tuning these carbs and every article starts with making sure you are running the correct fuel pressure . The next suggestion I have would be to blow out the air bleeds and idle circuits with carb cleaner to remove any varnish or debris .
 
- Its true that excess fuel pressure can overpower the float valves. the engine will idle for several minutes on the fuel thats in the bowls. If you have an electric pump you can shut it off and see if the idle speed and vacuum come up and if the pump is mechanical you could clamp the rubber line. I clamp the inlet side.
-Have you set your accelerator pump?
-It may just be a leaky powervalve
-I think that cam should be pulling a bit more idle vacuum, at your initial timing.Probably close to 2 more inches.Depends on things like; the cam centerline, and,what idle speed youre targeting.I suggest at least 700rpm target.
- You could crank in some more initial timing.If the engine responds well, dont forget to limit the other end.I kinda think that cam should not need the secondaries cracked, and that may also contribute to the hesitation. Myself, I would try hard to not use that.How far out are the mixture screws?
-With a stable float level, correctly lashed valves,and a properly working power valve,I would be working with; idle speed,idle mix, and initial timing.But before that I would make real sure that there is not a vacuum leak, that the vacuum advance unit is correctly hooked up and not engaging too soon, and that the valves are correctly lashed.Are you running a PCV system? The mains shouldnt be flowing/dribbling at idle.Its also possible to plug the power valve and go for a spin.Mine starts flowing when vacuum falls to about 10 inchs
-If you absolutely cant get it, I would suggest to do a quick check on the position of the split overlap.It should fall within a few degrees of TDC.If it doesnt I would check the cam install.But these are last resort go-tos, since your vacuum is reasonable.
OK, so, good luck.
 
bluefish1967 said:
Will idle good in gear only after fully warmed up ( stock converter ). Otherwise, I have feather the throttle while putting it in gear, then if it doesn't stall it's OK.
Click to expand...
This sounds like a little more choke and fast idle would be at least part of the answer.
You should have to enrich the carb when the engine is not up to temperature.

Try this test, open the idle mix screws 1/2 or 3/4 turn each. Does the rpm go up? Does it go into gear with a significant drop in rpm?

Agree maybe up to 16 degrees base timing might appropriate with that cam. 14 should be OK though. This is assuming vac advance is not hooked to manifold vacuum. With that much manifold vac on top of your base timing, that would put the idle timing way high, which would run lean and OK in neutral, but die when put in gear. Either plug or use ported vac for now. Or if you're going to use manifold vac, set idle timing with it hooked up. IMO it's trickier to do it that way with a performance cam, but there's more than one way to skin this cat.
 
Thanks for the input guys!! Didn't think about checking fuel pump pressure...and I did install a new fuel pump during the rebuild.
This problem didn't happen during the summer, when I first installed the new engine. It's become a problem now with the cold, and my efforts so far with the choke and jetting changes have not cured it.
I originally did not have the vacuum advance hooked up. When I tried to install it last week to a ported source, it had vacuum all the time. That's when I discovered that the idle speed had to be set higher, causing the front blades to be open too far. That's when Holley told me to crack open the secondaries slightly. That made the stalling problem worse. It you can get it to idle in gar by feathering the throttle, it's OK. Thanks. Larry
 
Opening the secondaries can be helpful on radical cams, but in your case I think they just went to the jar of likely answers. It got worse when you put it in gear because the engine was making even less power - way too lean.

As far as getting full vac on your ported source, Holley tech was logically guessing. The port is located just above the throttle blade's idle position. At idle the nearly closed throttle creates the pressure drop which is the manifold vacuum. As the throttle opens past the port, the port becomes exposed to the manifold vacuum.

At this point, my suggestion is start over because too many things have been changed.
Always good idea to checking the fuel pressure and (if the avenger has sight hole) correct fuel level in bowls. (Higher fuel level will make slightly richer).

Adjust the throttle stop position (aka speed adjustment) so the transition slot looks square below the throttle. If you don't want to take the carb off to look, then back the screw off until it doesn't touch, then turn in whatever number of turns the instruction sheet for that carb recommends. Probably 1 to 1 1/2 turns in. Keep track of that.

Bring the initial timing up to 15 degrees and plug the ported source for now. Now after warming it up, see if you can get the engine to go into gear without dying and not needed the assistance of a little pump shot. Once its fully warmed, adjust the idle mix screws. You should be able to be able to find a sweet spot (max vacuum, max rpm) between 1/4 and 2 turns out. Set it a on the rich side of that sweet spot to help keep the power when you go into Drive.

While the engine is warming up, you try to figure out the fast idle and choke positions. it may not need much of either, but it will need a little when cold if the carb is set correct for flly warmed up engine.

If you can get all that squared away, then you can figure out the other things such as
where the ported vac source is an try hooking that up and also the distributor advance total, and the vacum can adjustment. You can also experiment with a little more and a little less initial timing. Just remember that in neutral, the engine will be happy with more timing and leaner mix, but the real test is whethrer it has power when put in gear.
 
Jar of likely answers.I like that, and agree.
Still havent heard what youve been targeting for idle rpm.
-Post #5 spilled the beans, and Post#7 is a great plan.
-#5 says there is continuous vacuum at the spark-port.If you are sure you correctly identified the spark-port for the vacuum advance, and in fact there is continuous vacuum there, then the primary butterflies are definitely open too far.And ,yes, if you try to idle it with the v-can pulling timing in,adding some to the 14* initial, the engine might not like that.
-Post#7 should get results
-And Id like to add;
-We need to figure out why the primaries are open so far, and fix that.Cracking the secondaries can help, esp if they have their own adjustable idle circuits.But, like previous posters have said, its a small cam and we shouldnt have to resort to that.Is your PCV system hooked up?If no, Id start there. If yes, Id put a different timing lite on it and verify the 14* initial. If the 2nd lite says the same, then I would be proving the balancer mark.If all that checks out, Id go back and prove the float level isnt too low, which could make idle fuel pull-over difficult,necessitating the extra butterfly opening for the engine to get the fuel it so desperately wants.
-Post#8 below, triggered something in my sleepy brain cells.You might want to check at what rpm the mechanical advance starts coming in. It should not begin until a couple to a few hundred rpm above idle. In your case,say 1000 to 1200 rpm
 
That cam, installed correctly, should idle easily at 700-750 in P/N and 650-700 in gear. It's only 218 at .050. Barely larger than a stock camshaft.

Timing dropping out when in gear. Would seem odd with such a mellow cam as idle rpm should be well below any mechanical advance coming in. If it won't idle at those level, look at vacuum leaks and fuel dripping in the carb boosters. Exhaust should not smell like a fuel truck dumping gasoline!

Carb could have some bad surfaces allowing cross over issues on main body and metering blocks, etc.
 
Yes, the cam is very mild. When the temperatures were warm, I could idle it down around 600 rpm and drop it into gear without any issues.Only issues at that time were the ported vacuum port for the vacuum advance had full vacuum, so I was just running it with mechanical advance.
I'm trying to idle it around 700-750 or so in gear, something the engine would be happy with without having problems holding it with the brakes.It does have power drum brakes.
I had returned the carb to original specs, since this engine is slightly different. The cam was degreed in when installed. I have not run a fuel pressure test, or a compression test or leakdown test yet. The engine has 0 miles on the road since being installed. Thought everything was good to go until the weather changed.
 
I'm running the Shell Rotella 15w-40 .
Been doing a lot of reading and research in the last week or so to refresh my memory on carb tuning.
My next step is to remove the carb this Saturday, disassemble it and give it a thorough cleaning and inspection. At that point I'll put the 54 primary jets back in, and close the secondaries, basically putting it back to factory specs. Then I'll start fresh again.
My only experience with having to crack the secondaries slightly was with a stroker motor with a radical cam. Really shouldn't have to do that with this engine/cam combo, in my opinion.
Through my research, I rediscovered a lot of info on the idle circuit and transfer slot, and the way mine is adjusted right now is not correct....with the secondaries cracked open, the main idle screw is completely backed off to get the idle slow enough. As a result, the transfer slot opening is not correct.
I'll keep trying...thanks for all of the ideas. Larry
 
UPDATE : Well, things have gone from bad to worse...
Removed the carb yesterday, and returned it back to factory settings with the 54 primary jets, and by closing the secondaries. The engine started easily, and sounded better but still stalled when putting it in gear when cold. After warming up it was better, like before.
I decided to focus on the timing, and try setting it old-school with a vacuum gauge. Was surprised that I could not get any more than 16 inches of vacuum, settled on 15 inches at nearly 20 degrees initial timing. Adjusted the idle mix and idle speed, vacuum dropped to 12 inches at 750 rpm in gear but sounded very good.
Finally made it's maiden drive around the block. First trip was good, second trip noticed some valvetrain noise, along with some squeaking. One or more lifters were tapping loudly, and the oil pressure at idle was lower than before. I removed the alternator and power steering belts, but the noise remained. I jacked the car up and checked the flex plate for cracks, but it was OK.At this point I said the hell with it.
My guess without going any further is that I broke another rocker arm.I broke 2 different rocker arms on the old engine after installing the new Comp Cam and lifters. Great care was taken to check/measure lifter preload with a pushrod length checking tool. That engine had the heavy duty non adjustable stamped rocker arms from Mancini.
This engine has the adjustable 273 rocker arms, with custom pushrods. Comp replaced the old cam and lifters under warranty, so that was installed in the new engine.
The only parts carried over to the new engine were the oil pan, timing chain cover and water pump, the 570 carb, and the Comp Cam and lifters.
Hopefully by next weekend I'll have calmed down. If what I suspect is true, I'm going to pull the Comp cam and lifters and install the old 340 cam and lifters back it in.....Larry
 
Mattax said:
As far as getting full vac on your ported source, Holley tech was logically guessing. The port is located just above the throttle blade's idle position. At idle the nearly closed throttle creates the pressure drop which is the manifold vacuum. As the throttle opens past the port, the port becomes exposed to the manifold vacuum..
Click to expand...


When any port above the throttle blades (ported) start to pull, Is it the vacuum from the intake that is now being "seen" or is it the fact that high velocity air traveling over a tube end pulls the column from the tube? Thought it was the latter, like the vacuum secondary of a Holley 3310, only opens when secondary air passes over the vacuum put inlet. Either way, I would get the front idle transition slots perfectly square and then adjiust the secondary throttle stops to get desired idle, not the throttle stop.
 
Yes, I ran the break-in additive that came with the new cam both times.
First cam was very noisy. Comp said that was normal because of the fast ramps of the cam. When the second rocker arm broke, they inspected the cam and lifters.and replaced them under warranty.
This time everything was normal sounding until I took it for a drive.
I'll just have to see what I find when I tear it down.
 
pishta said:
When any port above the throttle blades (ported) start to pull, Is it the vacuum from the intake that is now being "seen" or is it the fact that high velocity air traveling over a tube end pulls the column from the tube? Thought it was the latter, like the vacuum secondary of a Holley 3310, only opens when secondary air passes over the vacuum put inlet. Either way, I would get the front idle transition slots perfectly square and then adjiust the secondary throttle stops to get desired idle, not the throttle stop.
Click to expand...

Pishta, As best I can tell, the answer can be both! Normally, the idle port and transfer slot primarily see the pressure difference from above the throttle to below the throttle. Basicly in plain language, manifold vacuum. Then when running at wide open throttle, the pressure drop created in the venturis is usually so much higher than created down in the throttle bore that the the idle system actually reverses.

However, some of the folks who have done lots of testing (and sometimes even filming) have seen cases where the idle port flows fuel at WOT. This is the latter situation you describe. My guess is that a restricted carb (like many circle track classes) might do this, and other cases it would depend on the details of the carb as well as the engine.

Here's a post by one of these gentlemen describing the typical situation
http://racingfuelsystems.myfunforum.org/viewtopic.php?f=25&t=219

If you want, I can try to dig up posts on when it goes the other way. I'm pretty sure Shrinker wrote about it on the old Innovate forum and maybe even provide a photo. Ryan Brown may also have video of it - in the video of the 4412 2bbl it looks to me like the idle circuit shuts off, but then fuel gets pulled thorugh accelerator pump! - http://www.ryanbrownracing.com/Video.html
 
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