Idle too high

[Sam D.]

Just to up date all of you for your responses yesterday. I went ahead and put a bottle of the Wild Bills octane boost in a full tank of gas. The idle dropped from 10.5 rpm to 8.5 rpm with out touching anything! The car ran pretty good for about 8 miles, then she started to spurt a bit. I Turned the idle up to about 9.5 / 10000 rpm. and she ran great all day! no problem on two long trips. Temp was great as well. Since I had the car it has never run better! Can these Special High performance engines run on just normal 93 octane fuel. I don't believe mine can. Should I continue to try and get the rpm down to 8500 / 9000?

Thanks,

Sam

[Duke W.]

Re: Idle too high

There is absolutely no connection between fuel octane number and idle speed.

If the engine doesn't audibly detonate, it doesn't need more octane, and if there is a little detonation, it can usually be cured by retarding the initial timing a few degrees. Most SHP engines will operate fine on unleaded premium without excessively retarding the initial timing. The initial timing range for mechanical lifter 327s with 24 deg. of centrifugal advance is 10-14 degrees, and on '64 to '65 engines it must be set with the engine running at less than 700 RPM to prevent the centrifugal advance from starting, or the centrifugal should be temporarily tied up with a stiff rubber band. If you have to go below 10 to ward off detonation, slow the centrifugal advance with stiffer springs.

Idle instability or variation is caused by various mechanical problem including vacuum leaks.

Does you engine have the correct VAC? Does it work?

Duke

[Sam D.]

Re: Idle too high

I had the Vacuum advance checked. It checked ok! But why did the idle drop with the octane boost? And the car did not die at a stop light.

[Michael W.]

Re: Idle too high

Sam,

In addition to Dukes comments of idle speed vs. octane rating, you should be aware that these octane booster products only add .1% (1/10th of 1 percent) per bottle, not 1 full percent as many believe.

1/10th percent octane rating is far less than normal variations of straight pump gas from one tank to the next.

[Duke W.]

Re: Idle too high

If you expect to get quality advice from this board, you have to start providing some real information and data. Garbage in, garbage out! You can start by posting manufacturing ID code stamped on the VAC mounting bracket. Saying you had the VAC "checked out" is meaningless, since we have no idea who checked it or their level of competence.

I say again - octane number has absolutely nothing to do with idle speed. You are chasing a ghost on this path. Most likely there is a mechanical problem - like a vacuum leak or something incorrect about the configuration - like an incorrect VAC.

If you post the VAC ID we can start there to determine if it is the correct VAC or not.

Duke

[Joe C.]

I'm Confused

"What we have here..............is a failure........to communi-cate", those are the immortal words of Strother Martin. I don't wanta be a quitter, so I'll bite! From the way you originally described the situation, you said (I think!?) that you had to increase the idle speed in order to avoid stalling once the engine heats up. If that is true, then I assume that you adjusted the idle stop screw for faster idle..............is that right? If that is so, then that is why I initially said that I suspected hot-flooding, and therefore percolation/float problems. This idle fluctuation could also be the result of a vacuum leak presenting when the engine heats up. But NOW you are saying that the idle speed changes by itself when you add elixir! Which is it??

Or, maybe, the idle speed changes erratically and randomly every time the throttle is released. In that case, Clem may have nailed it earlier when he suggested that your advance weights are sticking. If this is the case, then it could also be something as simple as a binding linkage, improper return spring, or binding throttle plates, which expand when hot and hold the throttle open.

A more serious scenario would be severely worn throttle shaft bushings, causing a vacuum leak combined with throttle plate binding.

Or, maybe Wild Bill Hickock bottles some kind of sssssnake oyl...............like Marvel Mystery Oil.

Joe

[Sam D.]

Re: Idle too high

VAC # 236 16

Sam

[Sam D.]

Re: Idle too high

Vac # is 236 16

Sam

[Duke W.]

Re: Idle too high

That's the correct number for an OE VAC or a NOS replacement. Now the next question is does it work?

One cursory check is to remove and plug the VAC signal line at idle. Assuming the hot idle is about 900, idle revs will drop to 700 or less. In fact the engine might even stall.

A better test is to pump it down to 15" Hg. vacuum with a Mighty Vac and see if it holds vacuum. If you watch the breaker plate while you do this, it should stop rotating - meaning max vacuum advance is achieved - by about 8".

If it passes the above tests it is apparently functioning propery and properly signaled by full manifold vacuum, including at idle.

The next step is to find any other potential vacuum leaks by checking all other vacuum devices, hoses, and connections. A propane torque (flame not lighted) is a good tool to search out vacuum leaks. By turning the valve on slightly and moving the head around the carb baseand manifold/head interfaces, any increase in idle speed means there is a leak in the vicinity.

Duke