IAT-4405 question

[BillT]

My 1952 CJ3A has the original engine but not the original distributor. It has the AutoLite IAT-4405, the last three symbols are difficult to read, possibly - 01?. It is the vacuum advance model.

The distributor was changed out by the PO.

Doing a tune up today I checked the timing. Using a vacuum gauge the reading was 19”. Adjusting for the deepest vacuum the reading came up to 20” but I could go further because I ran out of room on the adjustment slot. Does my description make sense to you? Hope so. Has this occurred to any of you? Is this because this distributor is not designed for this engine or is there an installation issue? Jeep runs well. I have a rebuilt IAD-4008-11y 2 ready to install but this one does a great job. Thanks for any thoughts.

[Mark W.]

I have a brand new Prestolite (same as the Autolite) IAT-4405 And have no trouble getting the adjustment needed. For one thing if you are running E-10 87 octane your going to want 12°-14° BTDC initial timing.. Here is a photo of how my distributor is oriented



You can see where the Vac can is pointed,

I run 12° and ported vacuum at a 650rpm idle I am seeing 21inHg of vacuum.

[Ron D]

How much vacuum you pull has something to do with your location (elevation).
Not going to pull the same vacuum at 5000 feet up as at sea level.
I seem to recall seeing a conversion chart of some sorts.
I think temperature figures in there somewhere as well.

[BillT]

Mark my distributor is oriented same as yours. The available non ethanol here is 92 octane. I set the timing solely by vacuum. Rpm is 650 and timing is retarded to 19.5”. I’m just wondering if I had the adjustment I might get a bit more vacuum.

Ron the elevation here is 950’ and temp today was 51°.

As I mentioned the Jeep runs very well, starts easy and pulls well.
 

[Mark W.]

Not to debate nonethanol vs E-10 but running a 92 Octane fuel in an engine with a compression ratio designed for 68-70 octane is problematic. The fuel ignites so much slower then what the engine was designed for. I am using e-10 at 87 Octane and having to run 7° more BTDC to help make up for it. I have absolutely no ping and could go a couple more degrees.

I know a lot of people have this thing about E-10 but I have run it in everything from lawn mowers to 450HP SBC's and never had any trouble YMMV

[BillT]

Mark I respect your opinion. If we all had the same thoughts and opinions who in the hell would we argue with. LOL
For me the E10 can be problematic as well.
Back to my original question about running out of adjustment on the advance end of the plate. I was trying to determine if there was something wrong with the installation. But as it is I’m going to leave well enough alone.
Thanks