570 holley

[speedball]

Hi all has anyone had good luck getting rid of the off idle hesitation these carbs seem to be famous for.I have a 302 ford crate motor 345 up. The floats are adjusted right.
Thanks
Legal and on the road finnally in ny.rd6411
Tom

[Greg_M]

Yes but it was a PITA. I fought mine for months until I arrived at this recipe:

Try each and evaluate if you need to go to the next step

1. More timing helps. If you can run 14* static, it will make an improvement. 38* total all in by 2,500 rpm.
2. Change the #54 main jets out with #56 or #57.
3. Drill the idle fuel restrictors out from .023" to .027".

4. Buy a Holley 4776 600 cfm double pumper, get better performance in all modes and better fuel economy, yes I said better economy.

Greg

[RicManSr]

Went down two sizes smaller on the squirters. That fixed it.

[Lex]

Go up 2 sizes on the primary jets and squiters and install a red accelerator pump cam or fix it right by doing what Greg said and installing an out of the box 600 or 650 double pumper.

[edwardb]

Originally Posted by speedball

Hi all has anyone had good luck getting rid of the off idle hesitation these carbs seem to be famous for.I have a 302 ford crate motor 345 up. The floats are adjusted right.
Thanks
Legal and on the road finnally in ny.rd6411
Tom

Three easy steps:

1. Unbolt SA 570 and remove.
2. Bolt on 600 or 650 DP. I highly recommend Quick Fuel SS-650.
3. Hold on because you're going to think you put in a new engine.

Honestly that's the best fix. Did several hundred miles on my 306 with the SA 570, and tried a bunch of things. Replaced with the SS-650. Amazing difference. Many keep recommending them, and some don't have any problems. But in the end, you will be way happier with a DP. Vacuum secondaries just aren't a good fit for these cars.

[Greg_M]

From my adventures with 2 EDL carbs and 2 Holley carbs I will say this. Vacuum secondaries on the EDL carbs don't work well on these cars, period and that's from the mouth of the EDL tech gurus. Holley vacuum carbs work OK for the most part. The problem with the 570/670 is the lean stumble that occurs on the primary side when the top of the T-slot goes lean before the primary boosters start to flow adequately. Its a fuel flow timing issue. The wideband shows an out of the box 570/670 will go lean to the tune of 16:1 AFR at the top of the T-slot, then 13:1 when the boosters flow. That's why they all have that lean stumble when you are cruising along and make a moderate throttle input.

Greg

[CraigS]

So what is the fix? My 650 Speed Demon vac secondary has the same problem. it has always been noticeable on the LM-1 but wasn't much of a driveability until I have gotten the thing to run leaner overall. Now I can feel it. Used to go from 12-1 to maybe 14-1. Now it goes from 13-1 to 15-1 and a few 15.5 -1 readings and is noticeable. This doesn't have anything to do w/ being a vac secondary since it's a light throttle openings and still occurs even w/ the vac secondary immobilized. It's possible a bigger pump shot could help in some situations but it also occurs when driving at 45mph and just adding a little gas to go up a slight incline.The lean reading continues all the way up the incline.

[Greg_M]

Craig,
If the other modes are working well, I think the way to fix this if your carb has screw-in air bleeds is to replace the the primary hi-speed bleeds with a smaller size to get the boosters flowing earlier and compensate the lean upper T-slot.

The 570 has pressed-in bleeds that are not readily accessible to drill and tap for screw-in bleeds because the choke horn is in the way. The other alternative is what I did. Open up the idle fuel restrictors 1-3 thousands and richen the T-slot.

Greg

[speedball]

Thanks for all the info.with all the views is this a very common problem? I am definatly leaning towards a 600 double pumper rather than chase it as others like Greg and others have.
Tom

[Scott L]

I had to adjust the idle transfer slot / throttle blade on my 570. The blade expossed too much of the slot at idle. Squared this up, went up several sizes on the secondary jets, and most of the hesitation is gone. Here is a pictire that might help. This takes less than an hour.

Carburetor Idle Transfer Slot Photo 19

Good luck - I was ready to go out and buy a 650DP, but I am very happy with my 570 after the adjustment

[Greg_M]

Scott,
Even with 14* base timing which speeds up the idle, I had to open the curb idle stop to expose way too much T-slot. When I "squared it up" the car would not idle above 500 rpm. The fix was to use the recessed curb idle stop on the secondaries to open the secondary throttle plate a tiny amount to achieve 1000 rpm idle. This allowed for 100 rpm adjustment on the primary curb idle and keep the T-slots square.

I was 95% happy with the tweeked version 570 until a friend offered a slightly used 600 DP and suggested I test it on my engine. It was like I just added performance EFI! Instant throttle that tracked very well. No more lean stumbles under minor throttle inputs like CragS described (climbing a hill). The DP has a very broad lean cruise mode (17" - 6.5") where AFR stays between 13.6 and 14.7. Gone is the 15-16 AFR that caused the lean stumble. When the vacuum drops to 6.5", the PV opens and the AFR starts to drop from toward 13 and ends up at 12.3. Under high vacuum deceleration, the 570 would go rich (11 AFR) but the 600 stays between 14.4 and 13.6 AFR.

WOT is instant every time and the car will run WOT at 1500 rpm in 5th without bogging or falling on it's face! The only change I made was to lean the secondaries from #73 to #70 because they were running 11:1 AFR at WOT and now they run Low 12's to mid 12s as the RPM builds toward 6K. MPG is improved over the 570 which I always thought was impossible with a DP. I attribute this to the wider lean cruise mode which is where we drive 80% of the time. Running 70-80 mph in 5th produces a near perfect 14 range AFR. The way I tuned the 570 did nearly as well but the range was narrower, 17" to 10". Obviously your car is different but for me I will never look back.

I ran the Dragon a few days ago and it was amazing that I could run the curves in 3rd because the low end torque was always available due to the mixture staying rich enough. I climbed hills in 5th at 65 mph where before, I had to drop to 4th because the mixture would lean out and the engine would loose power. I didn't measure the MPG but I used about 5 gallons for the trip which equates to over 21 MPG on the Dragon! I did measure the MPG a few weeks ago and the DP bested the 570 by 1.5 MPG (24.5 MPG) on the 90 mile mixed driving course I test my cars.

Anyone want a tweeked 570?

Greg

[Steve1979]

I am also using a 570 SA and had a stumble problem. It seemed to be in the 2K rpm area under gradual load. I appear to have fixed it yesterday by putting in #63 primary jets (only ones I had that were a little larger than #54) and a #25 discharge nozzle I took off my old 600DP. Took out the roadster this morning for a drive and it was very nice to be able to bring up the rpm’s slowly without any problems from a stop. I’m thinking that the smaller discharge nozzle might have helped more than the larger jets.
The only issue I had was the secondary’s kicked in at one point when getting onto an expressway, which I wasn’t trying for them to kick in. I’ll have to play with different springs for that.

Steve

[Greg_M]

Steve,
63 jets (+9 jet sizes) might fix a lean stumble but I when I tested 60 jets, the cruise mode AFR was in the low 12's and the WOT was in the 10's.

Just curious how you knew the secondaries kicked in. You should not "feel" them.

Greg

[Steve1979]

Greg,
I have read that also, but I would say that a sudden increase in speed disproportionate to the amount of increase in throttle position is the secondary’s kicking in.

Steve

[Greg_M]

There should be no sudden increase in speed or power because the secondaries open in response to a vacuum signal generated inside the primary bore proportionally to air flow through the primary bore not the intake manifold vacuum signal. The result is the secondaries supplement the primaries only when needed and do it seamlessly.

If I were to offer a theory in your case with the 63 main jets, I would say the mixture is too rich on the primary to the point where power is reduced. At some point, the secondaries start to open and lean the mixture to a value more conducive to efficient combustion and you feel that difference.

Steve have you checked a plug after driving for a while with the 63 jets? What about the pipes. My plugs were very dark and my pipes were sooty with the 60 jets.

Greg

[CraigS]

GregM, thanks for your thoughts. my Speed Demon has fixed air bleeds so can only go larger. I will look into the idle restrictors which i wasn't aware of and try that. I really want a Quickfuel SS DP mech secondary carb but the $ aren't there til at least after the holidays. Thanks for the info.

[Greg_M]

Craig,
There's a tuning trick you might try before working the IFR's. If you insert a thin wire in each high speed air bleed to effectively close it a little it and reduce the size, it will alter the main booster timing to start sooner. The flip side is it will also alter the mixture toward richer when the booster flows so the LM-1 will detect a lower AFR then you have now as RPM increases. If you see an improvement in the lean stumble, you could tune with different size wires, reduce the main jets 1-2 sizes to compensate for the added fuel at RPM, and leave the wires in or tune by opening the IFR's or just buy the QF carb later.

Options

Greg

[speedball]

My new 600 double pumper arrived today.tomorrow I will install and enjoy the improvement!lets hope. Thanks for all the good information.

Tom

[speedball]

It wasn't raining today so I installed my 600dp with the electric choke from my 570 carb. Started right up and sounds great. Drove it and there is noooo hesitation at all. Thanks to all who replied for your help.

Tom

[Greg_M]

Told ya

Greg

[Silverstreak02]

Originally Posted by speedball

It wasn't raining today so I installed my 600dp with the electric choke from my 570 carb. Started right up and sounds great. Drove it and there is noooo hesitation at all. Thanks to all who replied for your help.

Tom

Tom
I'm glad to hear that solved your problem. I have a similar hesitation with my Holley 570SA on an almost stock 302. It's not horrible, but annoying all the same. What model and part number double pumper did you get and do you think the same one would work on my motor (dyno 260RWHP)? Did you need to change jets, pump cams or whatever to get the new carb running right?

Jeff

[edwardb]

Originally Posted by Greg_M

Told ya

Greg

Me too! (Post #5) Glad it worked out for you. Thanks for reporting back.

[speedball]

Jeff
I did not change anything jet wise yet.i did install the electric choke from the 570 and it starts right up and acts some what like a normal car. It is a 4776ck I believe I purchased online from advance auto.found a 20percent off sale. 319 plus tax 345 delivered to the house.with 260 hp you may have to change jets but I personally am no expert.
Tom

[SaintClairCobra]

I have fought with my holley 570 for two years now guess I'll try some of the above suggestions. If not maybe a replacements is in my future for Christmas.