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Gunchsta
Gunchsta Reader
7/17/17 10:54 a.m.

In reply to Pete Gossett:

Does it seem like at that RPM you're at a similar throttle position? I've had lots of Holley carbs be finnicky in part throttle transition. They'll get angry at 1/8 to 1/4 throttle then clear up if you get past that. I've usually cleaned it up with accelerator pump changes- either cleaning the needle under the discharge nozzle, changing the nozzle size (which it sounds like you've tried) or swapping around the accelerator pump cams (position & color).

I've also had some luck raising the float level just a tiny bit on the primary side to add a little fuel weight, sometimes it seems to help things function more effectively.

Same two cents as before basically.

BrokenYugo
BrokenYugo MegaDork
7/17/17 12:33 p.m.

I'd be inclined to agree that its a fuel problem, too lean in the midrange.

GTXVette
GTXVette Dork
7/17/17 12:33 p.m.

Sorry pete been at work, boss just got a New Car, 1970 GTO JUDGE 400 Ram air III. But they have kinda covered it 1800 is a little high to be coming out of Idle circuit and Don't remember what jets were in front but again let me think a bit and I will check in later, I will reread that part of my book, may do a combo of the last 3 suggustions but let me dwell on it. did you ever get the rear Butterflys Closed down to a sliver of light? Being a 750 the fronts are about all it will ever need to run anyway

Pete Gossett
Pete Gossett MegaDork
7/17/17 12:58 p.m.

In reply to TED_fiestaHP:

I've been doing more research this morning and found a couple things, though I'm a bit hesitant to take them at face value given a lot of the "knowledge" presented on hotrod forums seems to be passed-down misconceptions, but two different suggestions were given to other people with similar problems, on two different forums:

1-The main jets on Holley carbs are undersized because people typically buy way too big of a carb for their application.

2-Delaying the opening of the secondaries has cured this problem for at least one person.

I checked the actuation between the primaries and secondaries, and discovered the secondaries open just after the primaries, barely off-idle. This carb was used on a dirt-track car previously, so I'm not sure if it's supposed to be this way, or if it's a racing-only mod. There's not really any adjustment to it, as the slot in the secondary throttle shaft is only about 1/8" bigger than the diameter of the linkage rod.

In reply to Gunchsta:

Good question on the throttle position, and I'm not really sure. When I accelerate quickly it's hard to tell what the position is when it bogs.

It sounds like cleaning the discharge needle & seat would be worth a try. I soaked the main body in carb cleaner, but I didn't run a brush down the discharge path. I only have red(or formerly red, now whitish-pink) cams, but from what I read they typically only need changed if the base idle is fairly high?

Pete Gossett
Pete Gossett MegaDork
7/17/17 1:06 p.m.

In reply to GTXVette:

I've been running the 650 double-pumper from Ovid_and_Flem - thanks again for letting me borrow yours! - and if I'm remembering it had 65 main/73 secondary jets. One difference between this 4150 and your 4160 is the minimal adjustment on the secondaries.

Gunchsta
Gunchsta Reader
7/17/17 1:55 p.m.

In reply to Pete Gossett:

I've had that little needle and seat get clogged up on multiple occasions- just little specs of dirt most of the time but it usually causes some pretty erratic behavior. It's a pain to deal with (unless you take the carb off) on something with a choke horn but it's worth cleaning again and making sure that those discharge nozzles are blasting fuel at the boosters when you press on the accelerator pump, not just dribbling out. They should have a fair amount of velocity and basically hit that booster tube in the center with a tap of the accelerator pump diaphragm.

As for the colored cams they control the volume and duration of the discharge- so WHEN in the throttle position and HOW LONG the accelerator pump nozzle squirts out fuel. I have generally had good luck with the red/pink one but obviously as with anything there isn't a one size fits all solution. Worst part about those is the pack of em is like $30 bucks. Not exactly cheap for some stupid plastic.

Good luck- I know you'll get it dialed in sooner than later!

TED_fiestaHP
TED_fiestaHP Reader
7/17/17 2:13 p.m.

If the secondary is opening to soon, that could be a issue. That could create a flat spot as the air velocity suddenly drops, a sudden decrease in air velocity will basically shut off the fuel supply. Increasing the accelerator pump output will sort of fix that, or getting the secondary to open a little later. Just needs a little tuning....

TED_fiestaHP
TED_fiestaHP Reader
7/17/17 2:16 p.m.

Does the secondary have a accelerator pump? and is that working.....

GTXVette
GTXVette Dork
7/17/17 3:04 p.m.

is there a bend in the arm from the front to rear butterfly's ? Either straighten OR Bend it to shorten the legnth to the rears and get the arm so the fronts open farther before the seconds open, Comprenda. I'll still take the carb back if the O&F carb suits you better.

Pete Gossett
Pete Gossett MegaDork
7/17/17 3:28 p.m.

In reply to TED_fiestaHP:

Yes, visually confirmed both accelerator pumps are working.

In reply to GTXVette:

I'll get pics of your carb & this one to compare. There may be a tiny bit of wiggle/bend room, but not much.

Pete Gossett
Pete Gossett MegaDork
7/17/17 3:36 p.m.

In reply to GTXVette:

Ok, here's the linkage on your carb(though I think the rod may have come from my 3rd carb I got off Craigslist). This one is vacuum secondary though.

Here's the one off the 650, which is mechanical secondary.

The rod doesn't protrude as far from the bracket, so there's not much room for adjustment.

BrokenYugo
BrokenYugo MegaDork
7/17/17 4:16 p.m.

This might be another one of those hotoddder passed down misconceptions, but aren't mechanical secondary carbs generally not recommenced for mild auto trans cars?

Ian F
Ian F MegaDork
7/17/17 5:09 p.m.

I read this thread... and watch a Spitfire buddy work on an '84 Vette he go for free from his FIL... and then I see an '84 Vette on the local FB trading group... gold with brown lower panels... also an automatic... asking price a few weeks ago: $3000. Recently dropped to $2700. I sit here wondering if I wave $2000 in his face if he'd take it. Supposedly "runs and drives great!"

(I really, REALLY don't have room for another car...)

Pete Gossett
Pete Gossett MegaDork
7/17/17 5:24 p.m.

In reply to Ian F:

You can park it here.

GTXVette
GTXVette Dork
7/18/17 6:31 a.m.

Ian, wave 1500.00 and walk away if he dosn't want it but show the C4 Post in here that is in 2017 Classifieds for the cheapC4's, I recently bought one not running for 800.00 and drove home one for 1000.00. Z51's and LT4's are the only ones worth anything Because WE are Going to Bugger them up Any way.

Ian F
Ian F MegaDork
7/18/17 6:33 a.m.

In reply to GTXVette:

I would, but it's on Facebook and listed on a local trading group you need approval to view.

GTXVette
GTXVette Dork
7/18/17 6:41 a.m.

Pete Get what adj. you can , Ian I'm not real fimilar with that, FB Market place? but My wife's daughter has some Stuff posted there for me and people ask for pics but no one calls.

Ian F
Ian F MegaDork
7/18/17 7:44 a.m.

In reply to GTXVette:

Sort of. This car is posted on an area trading group in the marketplace, but there is so much traffic things gets buried quickly. I've bought a few things, but so far only guitar and biking stuff. I sold a bunch of old bicycle parts on a trading group.

As far as offering $1500... I don't know... I doubt he is quite ready to accept half of his original asking price just yet. But that would leave more in the Challenge budget for things like half-decent tires.

Pete Gossett
Pete Gossett MegaDork
7/18/17 11:26 a.m.

I watched the actuation of the primary and secondary accelerator pumps/discharge, and I think they're working correctly. The way the primary/secondary linkage is setup does actually cause a delay between primary and secondary enrichment. Also, the discharge from all-4 nozzles is a nice solid stream.

I'm guessing the primaries should continue to discharge after the secondaries have opened, which they do, correct?

TED_fiestaHP
TED_fiestaHP Reader
7/18/17 11:37 a.m.

Well the theory is... As you open the throttle, the air velocity will drop, which will reduce the fuel flow, at least until the air velocity picks up to account for the larger opening. The accelerator pump helps to correct for the sudden change. You could have to large a carb, if so opening the throttle slowly until there is more RPM could help.

Pete Gossett
Pete Gossett MegaDork
7/18/17 12:33 p.m.

In reply to TED_fiestaHP:

It's a 650, which shouldn't be too large from what I've read, though throttle speed doesn't affect the bog/miss. It will occur indefinitely between 1800-2100rpm if hold the speed steady.

GTXVette
GTXVette Dork
7/18/17 3:43 p.m.

I don't doubt they are working correctly just that they (rears) come in to soon. it looks from the pic that the rod is in the middle of the hole/slot, so bend it so that the fronts Open farther before the rears begin to open. the rears also need to be closed down to the Sliver of light I spoke of, Look at the new plugs and see if they are looking wet.

Ovid_and_Flem
Ovid_and_Flem HalfDork
7/18/17 3:57 p.m.

Just a crazy thought but have you put the timing light on it and bring up RPMs until it stumbles to see if timing is jumping around erratically at 1800-2200?

Also...has it backfired through the double pumper since you installed that carb?

Pete Gossett
Pete Gossett MegaDork
7/18/17 5:50 p.m.

In reply to Ovid_and_Flem:

Unfortunately it only misbehaves under load. It's not backfired, though there was a very slight pop once after I shut it off. The miss/bog occurred before and after though.

EvanR
EvanR SuperDork
7/18/17 7:04 p.m.

Just brainstorming... don't know if this would apply to your particular engine...

I once had a Chevrolet upon which the harmonic balancer had slipped. The ignition timing marks were dead on, but the car exhibited similar symptoms to yours, because the ignition timing was, in reality, waaaaaaay off.

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