Stampie SuperDork
July 15, 2017 10:04 a.m.
Pete Gossett wrote: In reply to GTXVette: Oh it spins the tires quite easily. They're 10-year old Hoosiers though, so I'm not sure it's much of an accomplishment.

You tease us with this yet you still haven't given us a burnout video.

Pete Gossett MegaDork
July 15, 2017 11:05 a.m.

In reply to Stampie:

I've not done any all-out burnouts, but the first vid did show me getting a bit sideways.

Pete Gossett MegaDork
July 15, 2017 8:17 p.m.

I took the Vette out for a bit longer drive tonight, probably about 12-miles round-trip. Unlike previous evenings where I'd been running/tuning/test-driving, I'd not touched it tonight. I let it idle about a minute, drove to the end of the street & pulled out onto the highway somewhat slowly. I was met with it damn near stalling out for an instant - way worse than it had bogged when hot and I was accelerating more briskly. I also noticed that when I pulled away from a stop at a more normal/legal pace it would always bog about the same RPM, regardless of throttle position.

Given that it seems to be RPM-dependent I'm thinking it's more than likely ignition not fuel, correct? Especially considering I've made drastic changes to the timing and advance curve, but it's only made moderate changes to the bog.

So I ordered a new set of plugs tonight. I know the ones in it didn't look great when I'd been fooling with getting it running, so it seemed like something cheap & easy to try. I can also check/confirm TDC vs. the timing mark while the plugs are out.

AngryCorvair UltimaDork
July 15, 2017 9:31 p.m.

Time to throw away the timing light, disconnect and plug the vacuum advance, and keep advancing the base timing until:

1 the starter won't crank it when its hot;
2 it runs worse than the last run; or
3 it pings

Pete Gossett MegaDork
July 16, 2017 10:36 a.m.

I just swapped the plugs out, anyone have any insight on reading them? The left side is 1/3/5/7 top to bottom, and right is 2/4/6/8. 1 & 3 were very wet. They look oily, but smell more like gas. The electrodes & grounds on all plugs were whitish in color.

Here's #1 up close.


After it finally finished storming today I took the Vette for a spin. The new plugs made no difference. I was able to hook up the multimeter/tach so I could run it into the cabin, and on a subsequent drive I confirmed the miss is occurring from 1800-2100rpm consistently - it first comes on at 1800rpm and is completely goon by 2000rpm. Is there anything specific that would be occurring in that RPM range that could be related?

Lastly, I attempted to find TDC using the zip-tie technique while the plugs were out. I found the stopping point going forward easily, but I turned the crank backwards 4-times/2-cycles and never could find it while going counter-clockwise.

Pete Gossett MegaDork
July 17, 2017 5:11 a.m.

Bump for the weekday crew, any input appreciated!

GTXVette Dork
July 17, 2017 5:50 a.m.

they are pretty wet looking maybe just a little oily find a compression gauge do the cyls. for a comparison if you are not going to drive it for a couple days let it sit with the plugs out then Do NOT give it gas Spin it over while you Hold some paper against the sides over the plug holes.... see what Spits out then do the compression test. I know the Guide seals are new,but the oil is coming from somewhere very low comp. COULD mean rings high but even comp. COULD mean Seals. don't worry though do the check first May just need a hotter plug.

Pete Gossett MegaDork
July 17, 2017 8:11 a.m.

In reply to GTXVette:

Any suggestions on why the miss is occurring consistently between 1800-2100rpm and whether that sounds ignition or fuel related?

TED_fiestaHP Reader
July 17, 2017 8:20 a.m.

Is it really a "miss" or does the power seem to go flat.... If the power drops off, could be fuel tuning. The carb should have a true idle circuit, with adjustment screws, then a idle circuit of some type, then the main jets. I don't know anything about the type carb you have, but the idle circuit could be a tad lean. You could have some oil fouling and maybe the mains are to rich, causing the plugs to also turn black. But that could also be related to the timing experimenting. Now that it has run some, put in a fresh set of plugs, run it a little more and pull a few out and see how they look. After only a little running they should be fairly clean to light tan.

Pete Gossett MegaDork
July 17, 2017 10:38 a.m.

In reply to TED_fiestaHP:

If I'm in a steady cruise below 1800rpm, and very gradually accelerate until I'm between 1800-2000, there's a very noticeable sputter/miss/bog the entire time I'm within that RPM range. When I accelerate more quickly it feels more like a brief hesitation, especially if I accelerate hard enough to downshift.

TED_fiestaHP Reader
July 17, 2017 10:45 a.m.

Sounds like once you get into the main jets it might be OK, there is a idle or mid range fuel circuit that needs tuning.... I mostly deal with webers or similar stuff, but all carbs are somewhat similar. Or the timing at that range could use some adjustment.... If you play with the timing and it does the same thing, then its fuel. But it's fairly simple, only a couple things that could be off.

Gunchsta Reader
July 17, 2017 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 MegaDork
July 17, 2017 12:33 p.m.

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

GTXVette Dork
July 17, 2017 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 MegaDork
July 17, 2017 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 MegaDork
July 17, 2017 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 Reader
July 17, 2017 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 Reader
July 17, 2017 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 Reader
July 17, 2017 2:16 p.m.

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

GTXVette Dork
July 17, 2017 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 MegaDork
July 17, 2017 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 MegaDork
July 17, 2017 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 MegaDork
July 17, 2017 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 MegaDork
July 17, 2017 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 MegaDork
July 17, 2017 5:24 p.m.

In reply to Ian F:

You can park it here.

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