Hey everyone,

I'm having a problem with my car while in cruise. Going about 30 mph, when I step on the gas lightly, for light acceleration or even to keep a constant speed. The engine bogs down a little or hesitates a second or two and then goes. However if I step a harder on the pedal the problem goes a way and I get a smoother but obviously stronger acceleration. Could this be a vacuum leak? or something else? I have noticed the problem has slowly been getting worse.

Note: I do need a new muffler (it leaks).
Also, I pulled the metal hose from the stove to the thermostatic air assemble because I was concerned the thermostatic valve wasn't opening when It was supposed to and I wasn't getting enough air to the carb.

P.S. Does anyone know what the average gas mileage is supposed to be for a new 83 Cutlass with a 3.8L V6?

Thanks in advance,
Sean

Assuming you have a carb, and going by your discription only:

Hesitation during the transition from the cruise/economy to the acceleration/power circuit is most likely a vacuum leak.


Yes.


Yes


I would not expect it to get better.


Unlikely, but possible. Since you need it anyway, replace it, and see what happens.


The problem is, too much air.

Does it idle at the correct speed? Have you adjusted it to get the speed right?

Norm

Thanks for the reply Norm,

I do have a Rochester Dualjet carb.

I am planning on replacing the gasket around the carb at the intake manifold.
Is there anywhere else I should be looking for a vacuum leak, and if so, how would you go about finding a vacuum leak?

It is idling a little high I believe, but was tuned up about 4 months ago.

OK, first we'll check the accelerator pump.

With the engine off:

Remove the coil wire.
Remove the top from the air filter housing.
Hold the choke open and "pump the gas" while looking down, into the carb. You will be looking for 2 small streams of gas, pizzing toward the intake manifold. They should be visible at the slightest movement of the throttle valve.

Check it and report back. If it checks out OK, we'll look for vacuum leaks. I'll answer your questions, in that area, as we move along, and tie any loose ends when we finish.


First, we should find out if it's needed.


Higher than it was, about 4 months ago?

A tachometer or dwell/tach and a vacuum gauge will prove invaluable to anyone who wants to do their own work.

Since he keeps up with the latest in tools, I will defer to andrewk in that area.


Was it scheduled, or was it done to address a problem?

Norm

Hi sean000, Norm, all-



My vac/pressure gauge was purchased through Kohler small engines. I am not sure who makes it, but it wasn't cheap. A tech is required to have certain tools when they take "Master service tech" tests, and this was one of them. It was cheaper than the one off the Snap-On truck, found here.

If you have an "Arnold Motor Supply" or similar store around your area, their vac gauge will be just fine. If you don't use it often, don't spend 200 dollars on a gauge. I think I paid 90 for mine, but it came with adapters for all different Kohler engines, and I made adapters for the Briggs,Tecumesh and other engines. (A side note, when you test a small engine, it can be difficult to tap into the crankcase to get a reading. I typically take a dipstick tube and epoxy a hose barb into it near the top, and install it on the engine to obtain an access point...)

For a tach, I use one designed for small engines, but I would probably stick with an inductive timing light, which will function as a tach as well, or at least enough to set idle within 100 rpm or so. The same place you acquire the vac gauge should have a decent timing light.

Hope this helps,
Andrew

I checked the Carburetor, and there is indeed two solid streams of fuel when I pump the gas.

I am not sure if the idle has changed from 4 months ago.

Andrewk: Thanks for the info. I will look into getting a inductive timing gun because that seems to be most beneficial to me as I can set idle and perform tune ups with the one tool. The Vacuun gauge however seems to be a little pricey for then amount I would use it.

Thanks,
Sean000

I would ask at the local parts store. You could probably get one for pennies on the dollar of that high end gauge. I don't have time to research it, sorry. I linked to the snap-on one so you could get an idea of what it was, what it looked like, so that you could find one cheaper somewhere else. You could even go so far as to make a manometer, out of some tubing, a 2x4 and a yard stick, but it will be more cumbersome to use than a simple gauge.

A vac gauge is the most accurate way to set up a carb. The tool is worth every penny when you can save a hefty shop bill.

Hope this helps-

Andrew

OTC Vacuum/Pressure Gauge Kit

Lifetime warranty, OTC tools, I have ordered from that dealer before.

http://www.otctools.com/products/detail.php?id=1632

TOC Admin
Brando

I am getting a shipping quote for OTC 5613 you showed me. And I'll have a look at the parts store and see what they're going for around here.

Norm: The last tune up I had was scheduled.

I should also point out that when it is cold and I switch from park into gear the car often stalls. Once it is warm the problem goes away.
(I guess this could be a sign of the idle being too low?/or vacuum leak?)

Also, sometimes when the car has warmed up, then shutdown, then started again a few minutes later, it starts with a very low idle, until I step on the pedal and then the high idle will kick in. Is this normal?

Thanks

Yes.


We will find out, as we continue.


From your description, yes.

Norm

sean000,

Remove the distributor cap, visually inspect the inside and, if OK, set it aside.
Twist the rotor by hand. it should move easily and smoothly, and return to its stop in the same manner.
Remove the rotor, and inspect it visually.
Check the mechanical advance mechanism visually, while moving the weights against the springs. It should move the same as it did earlier.

Find the "vacuum advance" pot, and the vac hose leading to it. The other end will be attached to the carb.
Remove it from the carb, and (if you don't have a vacuum pump) suck on it.
You should see the vac mechanism move to its full advance position, and remain there.
If sucking on it, you will need to contain the vacuum by plugging the hose with your tongue. If not, skip this step.

If it returns home, while still under vacuum, you have a leak in the hose, or the diaphragm. You can test each, using the same method as above.

All of the above tests are part of a standard tune up.

If everything is Okey-Dokey, we will move on.

Andrew: Can a dwell meter be used on his HEI?

Norm

Norm, are you sure that you can rotate a rotor without turning the engine over? If you did move it without turning the cam, wouldn't that throw off your ignition and cam timing?



I'm sure it could be, but the dwell angle is set permanently in the electronics of the HEI, so I don't know what good it would do. The service manual that I have says it requires no adjustment or checking, and I have read that dwell meters won't work with electronic ignition systems, but I can't verify that.

I suppose it would show us the connections being made and shut off, just like it does with points, but I think it is unnecessary.

Andrew

Ah, but then we wouldn't have learned anything.


This is the phrase that opened my eyes.

If the dwell varies, at idle, with a points dist, it indicates a bent shaft and/or worn bushings. Even though HEI has a fixed dwell normally, a bent shaft should show up on a dwell meter, right? Wrong. This would be one of my many mistakes that the clowns are unable to find. Unlike points, changing the position of a magnetic or optical trigger will not change the dwell.

Norm

Using a dwell meter to look at spark events would tell us exactly what is going on inside the distributor, and the version of HEI that I am assuming we are dealing with should work fine, although I have never personally hooked a dwell meter up to one.

If I recall correctly, electronic ignition came out in the mid 80's, like 85 or so. It was heavily advertised.

Regarding the rotor, how does the construction of the distributor allow this? It must have something to do with the advance, or at least thats all I can think of.

However unintentional, you addressed the reason for my question, and the answer is probably moot.


HEI in '74, possibly '73 in CA.


If centrifugal force moves the rotor ahead (20° - all in by 1200 RPM) of the dist shaft, while the engine is running, something under the cap must be moving independently of the shaft, for it to happen.

Here is an example of how it works. Looks like he sacrificed some accuracy to keep it simple.

Easier to understand if you have it in your hand.

Norm