Hesitation

[t-waits]

I am running a 390 taken from a '65 Galaxie Police Car. The engine is equipped with a factory 4v and is much the same as a small Holley probably a 550/650. The demise is a hesitation when "gunned" and can also be felt at cruise speed. I have had the notion that is due in part to not being driven often enough and maybe the grade a fuel being used. I have recently spent alot time behind the wheel while using premium grade fuel but it's still there. Before tearing into something I would like your opinion.

TW

[Alvin in AZ]

That's an odd thing to have trouble with in a Holley IME. :)
Take it apart and clean out all the passages?
Are you running two month or older fuel? ...that can do it.

I have a "fix" for that problem in the Autolite/Motorcraft carburetors. :)
Holleys don't usually need modifying.

Alvin in AZ

[fastEdsel]

I've been down this road before and believe me this is the site where the feedback is great. I'm running bascially the same engine and you have a vacuum leak. Mine turned out to be a defective diaphram on the advance of the distributor and was sucking air. Pull off the line to the dist. from the carb and blow into it. If it blows freely, the advance is the problem. If it doesn't then the chase is on and you will have to check everything that is vacuum related to your 390. I found two more leaks using starting fluid around the vacuum sourses and the engine will speed up if there is a leak. But just make sure there are no sparks around or you and your 390 are going to end up past the sixth ring of Saturn. There probably is something safer to use but that is just what I had close by. My engine hesitation is still there but not in any great form and I blame it on the Holley. Running premium fuel will also help because these engines don't know what year it is and are not politically inclined. Keep everyone informed on your progress, as this site, as mentioned before, is a great resourse.

[mnagatani]

I'm dealing with what seems the same issue. I've got a stock 390 2V holley and just cant seem to get this flat spot out either. New coil, petronix, new plugs, wires, rebuilt carb. and just replaced the vac diaphram. I'm running 10 TDC initial. I hear a lot of talk regarding the accelerator pump needing adjustment. My biggest complaint is the hesitation or flat spot from a stop to crusing speed. It just seems to be "bogging" in the lower rmp and once I get it into a higer rpm it does fine. My question is how far in the rmps does the accelerator pump work as it transitions out to another kind of vacume or fuel deliverly. I can gun it and seems to not have any issues going hard on it, but once I back off and take it easy, its just not very smooth! Hopefully this helps with suggestions.

Mike

[Alvin in AZ]

Mike,
Sounds like the same problem Autolite/Motorcrafts have...
"too lean in the low speed circuit"

I could tell you how to fix that if it were a 2100. :/

Alvin in AZ

[mnagatani]

I forgot to mention that the plugs have been showing a very lean condition as you mentioned! I also changed the jets which started out at 61's. I switched them out for 68's and still got a lean condition. I am now currently running 64's in them now. Anything I can do to richen up the lower circuit? Am I too advanced at 10 degress initial? I know stock calls for around 6 initial. Running out of ideas to at least try. Running a mid-high octane level gas. Thanks for the input.


Mike

[Alvin in AZ]

I've never had to modify a Holley carburetor before. :)
They've always worked so good and all.

Racers do all sorts of things to all sorts of stuff but messing
with low speed circuits ain't one of them, that's a tinkerer's
job to do himself if he sees a need for it. The point is... it's
hard to find information like that on the internet, there' no
money in it, it's just something you figure out for yourself. :/

You can do it if you want to bad enough, but Holley's are
tricky to figure out with their "metering block" IME.

The Autolite/Motocraft is simple and straight forward, so it's
easy to figure out and so easy to modify too. :)

http://www.panix.com/~alvinj/file12/booster.jpg
The tips of the little tubes are squeezed down and drilled to
form a low speed circuit jet. Opening those up is all there is
to richening up an Autolite/Motorcraft's low speed circuit. :)

Alvin in AZ

[t-waits]

Since I am running the highest grade of fuel it sounds like I have a carb rebuild in the future. I am not inclined to do this myself but I do have an old time mech/racer who can get the job done.

Thanks for the info

TW

[Alvin in AZ]

I don't understand why a guy would want to own one of these old clunkers
without doing his own work on it. :(

Like buying a plastic model and having someone else build it. :(

What next? :)
You know there are guys that'd do a -better- job servicing your wife too.

Where's it end?

How about having your friend -help you- do it yourself and just ask 'im questions? :)
It's just a carburetor, not a whole lot a difference between those and a toilet. :)
It all works automatic whether it wants to or not. ;)

Alvin in AZ

[TNIceWolf]

A much safer alternative to using starter fluid to locate a vacum leak is WD-40. It gives the same result without as much risk.

[t-waits]

I don't understand why a guy would want to own one of these old clunkers
without doing his own work on it.

Like buying a plastic model and having someone else build it.

What next?
You know there are guys that'd do a -better- job servicing your wife too.

Where's it end?

How about having your friend -help you- do it yourself and just ask 'im questions?
It's just a carburetor, not a whole lot a difference between those and a toilet.
It all works automatic whether it wants to or not.

Alvin in AZ

I not sure if I understand where you are coming from and or what your saying. Unfortunately all are people not gifted enough to know everything such as you present yourself.

1. You speak of this as being a clunker...far from the truth.

2. Incidentally I do build models and have since childhood (some 30 years now) and on occasion people do ask me to build something for them that they do not have the skills for.

3. You speak of a mans spouse in a way that is not very becoming and has a tone that is unaccepatable.

4. And there is also little diference between a toilet and a post such as this. This is the last time I will look at this post due to the tone it has taken.

TW

[m-mman]

Anything you try the first time is scary and it is guaranteed that you will make a mistake.

None of us own our trucks because they are the most reliable, economical form of transporation. (A new to 5 year old model in fills that bill better. They rarely need much repair) We have them because they are supposed to be a FUN hobby.

A hobby is a place where you spend time and money for the pursuit of pleasure. A big source of pleasure (for 99%+ of us?) is working on our trucks. Reading the board you will find more discussion about FIXING and MODIFYING these things than actually driving them.

Many people around here have been lovingly WORKING on their truck for YEARS without driving it even a foot.

Working on your truck gives you a source of satisifaction that you have accomplished something in a way that you cannot get from having someone else do it for you.

Alvin was just trying to enourage you to explore and expand your skills and abilites.

For many people carburators seem to be one of these scary areas. The auto industry has not made carburatered cars for 20+(?) years. Because everything is EFI today, carbs have somehow become mysterous 'black boxes' that too many people shy away from.

Reality is that carb diagnosis and repair is the second place all mechanics over 40 y/o started fixing their vehicles. (first was the ignition - points & condensor) They really are simple mechanisms.

Survey the people on this board and I suspect their universal advice to anyone who wants to enjoy their truck to the utmost is to just experiment and play with it in ways you never thought of before.
Because it aint about the miles you actually drive it.
That 'pleasure' (untold hours just sitting behind the wheel) comes from your commuter car.

BTW - the action of a liquid passing through holes and vents for the purpose of creating a vacuum that results in a liquid flow without any type of pump makes the function of a toilet tank and a carburator virtually identical.

[mnagatani]

In my conquest to kill this hesitation, Im going to add a larger primary discharge nozzle in my holley 2V. I will let you know what finding I come up with after tonight.

[george worley]

You might try a power valve that opens at a lower manifold vacuum.There is a number on the power valve tells when it opens, the higher the number the later it opens. Might need a size or two bigger main jets. Check the float level to low a level can cause a hesation.

[Alvin in AZ]

Thanks M-M, I couldn't have said it that good ever! :)

Maybe I should get someone else to do all my posting for me? LOL ;)

---------------------------------------------------

George and MN, I believe you are both looking in the wrong place.
That's the main and/or full power circuits you are talking about.

Not saying the problem isn't there but by the sounds of it, I'm
guessing it's not. Go for it and see if it works tho? :)

The low speed circuit is just off idle before the main circuit gets
going good enough to supply the needed fuel. Sounds to me like
that's where the problem is and it's got small passages in it and
they just might be plugged up and that's all. :)

-------------------

Stupid ugly old Gringo carburetor theory:

The "main circuit" is fine after it gets going but before that it's like
a toilet trying to flush with only a half a tank of water. Not enough
water to get the siphon going so it stalls/hesitates and leaves you
staring at **** (or the rear end of Chevys;) . :/

They added the "low speed circuit" to bridge the gap between the
"main circuit" and the "idle circuit". The accelerator pump shot is
to provide more power first and help with the transition second. If
you open the throttle very slowly the accelerator pump doesn't do
much and the "low speed circuit" has to take care of the "dead zone"
between the "idle circuit" and the "main circuit". That's its job. :)

My 2100 runs fine without the accelerator rod on the pump (wimpy
sort of;) but does not stumble or hesitate. :)

Alvin in AZ