A few more Issues

[Guest tony78_280z]

My car is running MUCH better. Each day it gets better and better and is quite exiting. I’ve gone out to get my plates already and am eager to drive it on the roads. But I’ve got a few issues I need to address still.

 

1 Slow to warm up. I know a Carbed motor is gonna take awhile to warm up. Are there any tricks or upgrades (other than EFI) to get it to warm up quicker?

 

2. Throttle Lag. I push on the gas it stumbles and sputters for a second than it tears on down the road. It seems to have the power just not the take off. I can’t do a good burn out. Why? What is causing this? (BTW Swapped the Quadra back in to work on the Holley. But has the problem with either.)

 

3. Starting the car is weird. I hit the key and the starter spins and the motor turns, but the motor doesn’t start until I let up off of the key. I’m I insane or is there some reason for this?

 

4. Too much exhaust smoke. Not overly white, not black, just a lot of exhaust smoke. It doesn’t smell of fuel anymore (since I put in the pressure regulator) and it’s not burning oil. My exhaust setup isn’t complete in that I have headers a pipe bend and then the mufflers. No Cat, No EGR. Is that the reason or should I look to other areas?

 

5. Speedo Gauges. Has anyone had any success with removing the Speedo cable and gauge from their donor vehicle and put it in the dash of their Z? Sounds like the easiest and cheapest way to have the Speedo setup. If the gauges are roughly the same size, that is.

 

Thanks

 

-T

[Tim240z]

1 Slow to warm up. I know a Carbed motor is gonna take awhile to warm up. Are there any tricks or upgrades (other than EFI) to get it to warm up quicker?

Electric choke. You won't get the engine to warm up any quicker, unless you rev the crap out of it (not a good idea), but you can make it a bit more driveable by choking it a bit

 

2. Throttle Lag. I push on the gas it stumbles and sputters for a second than it tears on down the road. It seems to have the power just not the take off. I can’t do a good burn out. Why? What is causing this? (BTW Swapped the Quadra back in to work on the Holley. But has the problem with either.)

Sounds like the accelerator pump cam needs some tuning. Try adjusting it so that it tips in earlier and harder when opening the butterflies

 

3. Starting the car is weird. I hit the key and the starter spins and the motor turns, but the motor doesn’t start until I let up off of the key. I’m I insane or is there some reason for this?

Make sure that the power to the coil is constant, and not getting cut when the key is at the start position. Sounds like the coil isn't getting juice when the key is at "start", but the engine has enough momentum that once you release the key to the "run" position, it fires

 

4. Too much exhaust smoke. Not overly white, not black, just a lot of exhaust smoke. It doesn’t smell of fuel anymore (since I put in the pressure regulator) and it’s not burning oil. My exhaust setup isn’t complete in that I have headers a pipe bend and then the mufflers. No Cat, No EGR. Is that the reason or should I look to other areas?

Sounds like water vapor...normal. Can you see water droplets falling from the exhaust tip?

 

Tim

[Pyro]

Also, check the ignition timing curve. It should advance when you hit the throttle. If you have the vacuum advance on the wrong port it will retard when the throttle is opend and the engine will fall flat.

 

Your carb has two types of vacuum ports. One is manifold vacuum and the other is called "ported".

 

It is a very common mistake to put the distributor vacuum advance on the wrong carb port. GM vacuum advance distributors use a "ported" vacuum source which means it will NOT have any vacuum on it at idle. Vacuum from the ported source is produced when a lot of air passes the throttle blades (like when you give it the gas). Therefore, vacuum is caused by a ventri effect. So when you hit the gas the timing advances.

 

FYI, old fords use the vacuum port on there distributors. I think they did it that way just to be different. Distributors up front, vacuum advance, firing order, ect. LOL

[80LS1T]

5. Speedo Gauges. Has anyone had any success with removing the Speedo cable and gauge from their donor vehicle and put it in the dash of their Z? Sounds like the easiest and cheapest way to have the Speedo setup. If the gauges are roughly the same size' date=' that is.

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You could do that but it wont be very accurate. The speedo that you get out of that other car will be calibrated to the rear axle ratio and tire size. You could probably get it close though with the correct speedometer cable gear.

 

 

Guy

[HICKL]

Pyro wrote "GM vacuum advance distributors use a "ported" vacuum source which means it will NOT have any vacuum on it at idle. "

 

Is this true? I have mine set up with vacuum at Idle and motor runs great? Mechanical advance kicks in as RPM's go up.

[Pyro]

It is easy to check. Get a timing light and watch the timing mark on the crank when the engine revs off of idle. If the timing mark retards at first then it is not on the right port.

[HICKL]

I thought that was how it was supposed to work. See this excerpt

 

"The basic reason for the change in optimum timing at light loads is that when operating at light loads, the mixture is leaner for fuel economy and less dense because of light load. These conditions cause the charge to burn slower, and thus, to reach peak pressure at optimum point in the cycle, the spark must be initiated earlier. Failure to do this will result in "retarded" spark timing and all the aforementioned losses."

 

Not trying to be argumentative, just trying to learn.

[Pyro]

Advancing the timing is starting the spark sooner.

 

When the throttle is opened, the vacuum advance quickly advances the timing to increase cylinder pressure. The mechanical advance is totally rpm dependent. Therefore, the vacuum advance gives low rpm timing advance that is not possible with the mechanical advance.

 

The timing curve is just as important as the fuel curve. Old vacuum and mechanical advance systems are not very good. Modern day ignition curves produce better power, gas mileage, and is ONE of the reasons engines can use higher compression ratios now. The new curves look much different than the old timing curves and are made possible because of computers. New systems normally give a bunch of timing right off of idle and during light loads as you have already mentioned.

[Brad-ManQ45]

Actually Pyro, when you first open the throttle, the vacuum is lowered until the engine reaches steady state again, during this time, there is not as much advance. The air/fuel ratio is higher because of the shot from the accelerator pump as the throttle is opened requires less advance because the mixture is richer.

 

Basically, at light load (high vacuum conditions) there is more advance dialed in to work on the flamefront, which moves slower under high Air/Fuel ratios. Under load, when Air/Fuel ratios are lower, there isn't as much vacuum and therefore not as much advance, which isn't needed because the A/F ratio is more conducive to propagating the flamefront.

 

The mechanical advance it there to provide for the proper amount of advance at a certain engine speed when there is no vacuum advance - under full throttle conditions.

 

Think of vacuum advance as a way of tuning the timing when not operating under full throttle conditions.

 

It is the combination of fuel injection and timing maps that work to make modern cars more driveable at low speeds/cold start conditions and get good fuel mileage. It is only an aproximation because it doesn't take into consideration temperature like FI systems do.

 

The accelerator pump/cam is basically an approximate way of covering up the lack of airflow/vacuum signal to draw in fuel when the throttle is initially opened. Sure, there are ways to tune this behavior, but it still will not come close to matching FI done right as regards fuel economy.

[Pyro]

That is right. There isn't much vacuum in the manifold when the throttle first opens or at WOT. That is why chevy is using "ported" vacuum. So, under zero vacuum or dropping vacuum conditions in the manifold, the distribitor will still advance.

 

Don't mix up manifold vacuum and the vacumm signal produced by air flow thru the carb. If fact, the lower the intake pressure the higher the ported vacuum goes.

 

So when the throttle is openned, a vacuum is created above the throttle blades which creates a big pull on the distributor no matter how much vacuum is in the manifold.

 

Most cars have maximum vacuum at idle (cars with stock cams). So if the vacuum line is on the manifold vacuum port, the distributor will retard when you step on the gas and make it stumble.

[Brad-ManQ45]

Being an old FORD man, I never did mess with Chevy's much, and never used the ported vacuum provision on some of the Holley's I used. Ford DID use ported vacuum on some of their engines - the 351C for instance had a vacuum canister that you attached both maiifold AND ported vacuum to. As a hot rodder, I simply used only the middle port on this distributor when turboing and hooked it to the manifold port. Normally the middle/inner port was for ported vacuum and the outer port for manifold...or was it the other way around?????

 

We're talking over 25 years ago....

[Pyro]

Yes, ford did it different in most cases. I have very little experience with fords but I did work on a few 69 mustangs. I noticed the vacuum advance difference at that time. Being a chevy man it is hard for me to say, but I think the ford system works better. However, in any case, the timing should advance when the throttle is depressed.

[Guest 305240]

In answer to your starting issues. Run a wire from the solinoid to the coil. It gives the coil juice while you are starting. It cuts off when the start key is released, then the regular ingnition system takes over.