B26 vacuum can

[Rich G.]

A couple of weeks ago, you all and especially Duke helped me solve an idle cooling problem in my 66 327/350.

Everything has been good, but today the idle dropped to barely running, so I stopped and cranked it up to get home. I checked the vacuum at 750 and it was the same, right around 15 inches and I touched up the idle mix. I can hear the advance can chatter even at 750 to 800 rpm. Does this mean it has died or is dying? Something obviously changed today to make the idle fall off. I don't have a working timing light, so I can't do a definitive check until tomorrow.

The vacuum can is only a few weeks old.

Rich

[John D.]

Re: B26 vacuum can

Rich, Might be a fuel problem. Our ethanol boils at a very low temperature.

Here is a fix for perculation I read in "Model A News". Author was Roger Kaufman who passed away on May 21st. Roger said to add kerosene or diesel oil to wonderful ethanol and that will increase the boiling point anywhere from 15 to 25 degrees. Now a typical Model A Ford only holds 10 or 11 gals. He said to add two gallons of kerosene to a tank full.
I am used to adding Marvel Mystery Oil. I have heard of people adding kerosene even in the old days. But I never knew you were supposed to add 20%.
Now this may not be your problem but I thought I would mention it. John

[Rich G.]

Re: B26 vacuum can

Thanks John

I am running a mix of 100 LL Avgas and pump 93. I'm actually a little heavy on the 100 rigt now. You are correct, I did notice the percolation before but not since I added the 100. I can't imagine the thing should run worse on 100, so I guess it's a coincidence. It's also stumbling on hard acceleration, so something changed.

Just gives me something else do tomorrow.

Rich

[Duke W.]

Re: B26 vacuum can

A couple of weeks ago, you all and especially Duke helped me solve an idle cooling problem in my 66 327/350.

Everything has been good, but today the idle dropped to barely running, so I stopped and cranked it up to get home. I checked the vacuum at 750 and it was the same, right around 15 inches and I touched up the idle mix. I can hear the advance can chatter even at 750 to 800 rpm. Does this mean it has died or is dying? Something obviously changed today to make the idle fall off. I don't have a working timing light, so I can't do a definitive check until tomorrow.

The vacuum can is only a few weeks old.

Rich

The B26 is fully deployed at 12", so 15" of manifold vacuum at idle should keep it locked at full advance, and it should not chatter.

There have been reports of mismarked and out-of-spec VACs in the box, or it could be in some other way, defective. I always recommend bringing a Mity-Vac to the store to test for leakage and the start and stop points before you walk out with it. Then check the advance on the engine with a dial back timing light.

Duke

[Duke W.]

Re: B26 vacuum can

Rich, Might be a fuel problem. Our ethanol boils at a very low temperature.

Here is a fix for perculation I read in "Model A News". Author was Roger Kaufman who passed away on May 21st. Roger said to add kerosene or diesel oil to wonderful ethanol and that will increase the boiling point anywhere from 15 to 25 degrees. Now a typical Model A Ford only holds 10 or 11 gals. He said to add two gallons of kerosene to a tank full.
I am used to adding Marvel Mystery Oil. I have heard of people adding kerosene even in the old days. But I never knew you were supposed to add 20%.
Now this may not be your problem but I thought I would mention it. John

Adding kerosene or any distillate like diesel - to gasoline will substantially lower the octane rating. The model A only needs about 80 RON.

Duke

[Timothy B.]

Re: B26 vacuum can

Rich,

If the car has a Holley there may be something going on inside like a gasket leak between the main body and metering block on the primary side and vacuum finding gas at this union, this will make idle unstable and rich.

The distributor may be fine and the V/A may be fine. Double check that the chatter/rattle is not the PCV valve at this low idle speed.