Carb Problem?

[Steve R]

David,
My pleasure. Now go enjoy that car.
Steven

[John A. Simpson]

HI David,

Make sure your accelerator linkage (pump) is set to spec, it should compensate for the extra air as you tip in the throttle.

Thanks for the T-shirt that will be so cool!

John

[Jamo]

Why do they get t-shirts?

Every time they posted, you had to take time away from my car to read their guesses. Lousy gasket--which none of them figured out--and they all get rewarded for delaying my car!

Ask your Dad if I can use his car--that old dusty Cobra out back--while you play on the internet with your buddies.

[concobra]

Good Day David.

I'm glad you located your problem.

Regarding the stumble at 2000 RPM. From what I understand this is the general point when Holley's transition from the idle circuit to the main. And a common place for the stumble you wrote of. This is usually caused by the secondary circuit not picking up the signal fast enough to compensate to the primary circuit stopping. Most try to adjust around this by over feeding the accelerator pump charge. This helps but is not the true cure. You will need to decrease the amount of air feeding through your secondary cicuit air bleeds. This will pick up the fuel signal faster and create better response with a more precise fuel metered amount. Probably down 4 sizes to start.

It's just a suggestion and I hope this helps.

[Hal Copple]

I have studied my several Holley's and made any number of modifications, some not so successful, to them. Here are my opinions. On my Edlebrock RPM intake manifold, the right and left sides are separated by a plenum divider. I tried an open half inch spacer, to reduce winter gas fuel/carb percolation. It did not run quite so well, as when i kept the separation with a four hole spacer. (The four hole spacer gives a more accurate "signal" to the boosters). On my first vac sec 750, i put on a 50cc "squirter", it did nothing, good or bad. I cut off the choke horn, to make the air flow under the aircleaner top less abrupt. I noted that the "booster" venturies were straight, and not downleg, and wondered then if they metered less accurately, allowing perhaps some unmetered air to flow around and down the venturies, since i changed the air flow path by cutting off the choke tower.

But it seemed to run fine, and actually seemed to get better mpg, although my ET's in the quarter mile were a bit slower after this.

Took out the sintered bronze fuel inlet filters, and ran a large Holley canister filter, found it necessary by watching my fuel pressure on long WOT, to change it about every 10K miles, due to debris in the fuel. Even with the huge holley filtter.

Put on AN 8 lines, .10 needle and seat, plenty of gas, had enought before this. Put on all radiused hard fuel connections, no abrupt right angle fittings anywhere in my fuel system. Run the Carter mechanical pump, running always 7.4 psi.

Learned that it was necessary to have a little bit of slack in the squirter to avoid too much fuel with abrupt throttle "tip in."

Drove around with a vacuum gage hooked up, watching my vacuum under light load, to determine that a 6.5 power valve was best, and safest, and worked the best. Dilegently studied power valve theory to determine this.

Had the first carb on a chassis dyno, put in the white or lightest spring in the vacuum actuation, picked up 40 hp in the mid ranges.

Put on a 750 Pro HP, vac secondary. put in the white spring, put on a slightly smaller squirter nozzle, so i have a less abrupt but longer "squirt", this carb had down leg boosters, run 70 front and 72 rears, with brass floats which have a longer arm to ensure the fuel supply is cut off even with my higher fuel pressure, as the shorter arm on the stock Nitrophil floats may not have enough leverage to do this reliably.

In the end, using Bob Olhtoff's suggestions , my stroked windsor has a vac sec Holley 750 Pro, 30cc squirter, sitting over a half inch four hole spacer, on a divided plenum RPM intake, feeding Twisted Wedge heads. the linkage cam is the stock one, set with the standard screw setting. Three inch 14 inch round K&N air filter, chrome top, the pleated K&N top upset the air flow into the engine.

My driveability is perfect. I can run my car down to 900 rpm in fifth, and and accelerate without protest to 6000 rpm, with absolutely no hesitation or stumble anywhere, with a torque curve on the dyno that is perfectly smooth, without any jags or other indications of improper fuel delivery. I have excellent MPG, about 15-18 mpg at cruise.

assuming no fuel leaks, and proper floats and float levels, i sometimes think that when people have a problem with stumble or hesitation, they assume the engine needs more gas, while actually, in my case every time, the engine needed less gas on "tip in", to avoid momentary richness and "bog". Larger jets made for worse drivabilty, so went back to Bob's suggestions, and it ran better.

In other words, sometimes less is best.

Planning on a littel 500 mile trip to Ohio friday, back sunday, should be a fine trip.

[Whaler]

Hal
Getting to this momentary richness, did you ever notice your exhaust puff out black when this happened?

Reading thru one of my Holley books tonight I see a paragraph saying that most HP carbs come a little too rich for the street engines and that they can easily go down a "few jet sizes"

My 850 has 78 and 80 out of the box. I smell rich on idle and have the 4 idle air mixture screws turned to only 3/4 of a turn out.

I am happy to see that the mixture screws can be brought in with an effect on idle. If the idle screws have no effect, when seated or close to seating, then one has other problems to chase after.

I wonder if I should just simply go down a couple jet sizes right off the bat? They say to do it 2 sizes at a time. I am practically at seal level.

I have not down roadtests as it not roadworthy or legal right now.

Last thing that bugs me is that I have a pop sometimes at the carb when cold starting the car. It has the manual choke wired open and I wonder if this pop is purely a function of a cold start or me not knowing( learning) how to throttle the carb. If it's timing, am I too advanced at 16 or should I go back toward 12ish.
Many suggest 2 good pumps before starting to get some gas into the carb as the signal is weaker with the choke plate open. BTW, Poor atomization and all. It's not even 60 degrees up here ....My car takes at least 5 minutes at 1500- 2000 rpm before I am at 80C on the gage.
Then I might be lucky and can take my foot off the gas for an idle of about 900rpm.....lol

Tim

[Turk]

I already have a Kirkham shirt. Do you guys have any 38 waist Kirkham dnderwear? Briefs, please!

TURK

[Steve R]

Turk,
I believe they are out of stock on that item. Maybe you could get one of those Kirkham bras for the Mrs. My wife loves hers and thinks the aluminum underwires are the best.
Steven

[blown]

david it sounds like you need to put the advance spacer in your dist that will give you 18-20 deg. in the dist. set your timming at 12 deg. initial and put the lighter spings in it make shur no one has messed with your pump squerters they shold be fully extended that should do it then you can slowly advance your timming until it slows your car good luck.

[David Kirkham]

Thank you all for the great advice.

Working on the dreaded 2000 part throttle hesitation right now. I will let you know about the progress.

David

[Hal Copple]

Tim, it is my opinion that a 428 might be a bit rich with that much jetting, i know when the car magazines put engines on the dyno, they run them incredibly rich, but then they aren't concerned with things like "tip in" and drivability, just peak HP numbers.

If i had a nice 428, i think i would put in 72 fronts and rear, or perhaps a 74 rear just for "insurance".

No, never noted any black smoke from the sidepipes, i think you have to be way way too rich to note that.

all the best,

[Jamo]

Warning to you t-shirt groopies.

Kirkhams are the only ones to ever give me a t-shirt that was too BIG! Actually had to shrink it. Funny thing--I didn't know Abdul had a tent making shop in Utah.

[CSX 4027]

Jamo,
Some areas of the country seem to breed bigger people. I think it's in their jeans. I checked my Wranglers and they seem to be fine but are expanding a bit.
I believe the t-shirt guys make 3 new sizes.
Very Large
Very Very Large &
Oh My God, It's moving!

[Jamo]

Steve

Obviously, my problem is that I have trouble stayin in my jeans.

[CSX 4027]

I bet you tell that to all the girls.....
Seriously, Too much weight potentially causes lots of problems. In my business, I have saved peoples lives by helping them get on a program to trim down. I had a guy a few weeks ago that took a stress ekg and had a heart attack on the treadmill. He is now fine after bypass surgery but, he might have never known about the problem until he applied for life insurance. Being an agent you practically become a doctor from a knowledge standpoint. And no i don't operate. I can't stand the sight of oil leaking down a crankcase no less blood! Stay healthy my friend. We are only here for a short visit. Lets not make it shorter.

[Jamo]

Geez Stevie--give me a break! I just quit a four pack a day cigarette habit a week and a half ago. Now ya got my ass on a diet?

[CSX 4027]

At 4 packs the only time you didn't smoke was when you slept
Lets see at NY prices
4 packs at $7.00 = $28.00 per day = $196.00 Per week
= $784 per month
WOW....Sound like a nice car lease to me
-I am glad you stopped