I am ordering a new distributor for the 400 in my 78 F250. Will I have to recurve the new one? Also is there a preferred year for distributor that I should order for my truck.

 

Yep, you want to for sure check that your all-in advance is set at least in the ballpark at some figure like 2500 or 3000 RPM. Some dizzys use springs and vacuum, etc. if you are racing it's one thing to remove vacuum advance for best performance but for most uses some kind of nod towards fuel economy is a good thing.

Lots of aftermarket vacuum units are adjustable with an Allen wrench through the canister port. Replaced distributor on the 292, while it runs far better overall, it probably needs lighter springs and some adjustment. The trick way is with a vacuum pump and a timing light, tho still ... involves driving around after the adjustment and checking for ping at full throttle and part throttle. Full throttle ping supposedly means back off on initial timing advance, and. part throttle ping means back off on vacuum advance.

Dug through a few allen wrenches and finally found one (sez 2.5 mm) last night that seemed to fit on my engine. All of the new remans seem to have this type of canister adjustment. Set full CCW, about two and a half turns but haven't fired it up yet. Sent from my iPhone using IB AutoGroup

 

Ok. I adjusted the vacuum advance pretty much all-in as per the instructions, at least it seemed like it started to bottom out counter-clockwise. Don't want to snap anything inside the canister? Initial distributor advance isn't too radical but Y blocks like a lot of initial. No idea what springs are installed, prolly stock.

This put a little zing back!!! ... not quite there yet. Definitely the right direction though!!! No pinging, and it cruises along real nice just tooling around with what they used to call driveability. It seems to idle a lot nicer too, tho vacuum advance shouldn't be involved at idle. This is definitely worth spending the time on to get right!

Sent from my iPhone using IB AutoGroup

 

. WOT pinging can be from too much initial(idle) advance and/or from mechanical/computer advance coming in too early/too low RPMs...

. Hooking the vacuum advance to a ported carb. port prevents vacuum advance coming in at idle... hooking it to 'all the time' manifold vacuum will bring the vacuum advance in at idle and add it to the initial/idle advance, making it impossible to tune the distributor/engine properly...

 

OK, that makes sense.

Now I'm thinking about sending an extry distributor off to somebody who can set it up right. The vacuum and mechanical advance have nothing to do with each other in one sense.

The total advance is important, but when it advances is more important for my purposes because I can't really adjust that without swapping springs. The vacuum advance comes into play for part throttle, cruising speeds with very little load. Seat of the pants dyno works pretty good here. I should look at the spring setup in the old dizzy and swap them over to the new one. It was wore plumb out but was setup a bit hotter. Do distributor springs or weights take a few dozen miles to loosen up or are they pretty much solid from the git go?

This stuff can be tedious tho it really pays off in performance and economy.

Sent from my iPhone using IB AutoGroup

 

. Both the spring strength and the weight of the advance weights affect what happens and when...

. Kits with various weights and springs available at a reasonable price...

. The old springs might help...

. A timing light and tach is needed so that you can set the initial/idle timing and watch the ignition timing advance as the engine is revved up (vacuum advance disconnected and vac line plugged) to see what you have and guesstimate where you prolly want to go with it...

 

Right. So now I have a new career for a week? Dang it, can't a dizzy be setup right prior to install? If I buy a dizzy for a specific motor shouldn't it be setup pretty much curved already?

Sent from my iPhone using IB AutoGroup

 

. Is your 400 stock for a '78? Or modified? Every engine likes a different advance/tune... even stock engines can vary a little...