Distributor work

[2059]

Over the past couple weeks been following a thread about ported vs. manifold vacuum as it relates to emissions, performance, application, etc. one of the posts talked about engine cooling at idle and another about tuning carb(s) and setting idle; both of which I was having issues. So, after reading everything that Hemirunner, Meep-Meep and 383man along with others; i finally had some time and a spare Distributor to give it a go.

I talked to the engine builder and he said he "never uses the Vac. Adv.. Disconnect it." which is what Hemirunner said. Here is what I started with;

MoPar electronic ignition dist.
10* BTDC Initial
Full mechanical adv. ~20*

Couldn't get the engine to idle below 1200 rpm and was running on the warm side. One notch below "HOT" on the guage.

Started with the stock dist. drilled and "pinned" the vac. adv. plate. (the screw was a little close to the mechanical advance so I cut it and reinstalled)
Removed the vac. adv. can.
Made a cover plate and fashioned the Dist cap. tyne. (yes, I said Fashioned).
Adjusted the mechanical adv. to give 1/2 travel.
set the initial timing at ~28*. Which gave me ~38* @ 3K rpm.

Result... Idles much cooler and was able to get some adjusting on the carbs done. No test drive; Raining... Again...

yes; there are pictures. here ya go...

 

[Hemirunner]

Let us know how the test drive goes!

 

[Gpuller]

Amazing what happens when you get the motor timed correctly. Ran into the same thing with my 440. Never idled right, stumbled and so on, always thought it was fuel related. Had an old MP dist with no adjust ability. Replaced it with a Firecore, that has adjustments for the mechanical advance. No vac hooked up.
My initial is set at 25 deg and limited the mechanical to 36. Car runs like a total different animal, starts, idles, no stumbles. Win, win.
Moral of the story...Always dial in ignition first.

 

[Hemirunner]

Every recommended timing chart I've ever seen has been like this....

All of my real world experience tells me that what works best is an inverted version of this. Especially with performance engines and big cube nitrous engines in particular. More timing at a higher rpm is never a good thing. At increasing rpm and load, the timing requirement will be less rather than more and the increased timing will actually be working against you. Also what is key to note when tuning these is that more spark lead produces a leaner burn and less spark lead equates to a richer burn.

 

[383man]

Very nice work. Actually there is nothing wrong with using the vacum advance if you set it up right but I myself dont use one since my dist dont have one. I have a setup almost the same as you as I idle with around 24 degrees and a total about 37 to 38 and it runs great like that. The extra timing from a vacum advance can help fuel milage and help to run a bit cooler but you have to build the eng to take about 50 degrees timing at part throttle. Course when racing vacum drops to zero and the vacum advance dont work anyway. Lets us know how your road test goes as if it drives like mine you will love it. Ron

 

[2059]

Well, was able to get out for a bit last night. It bucked the starter a little more than before but not a show stopper. it always fires on the second compression stroke when hot. I did get a little pinging at WOT which will be fixed by pulling down the mech adv. by a couple degrees. Which is what you said would probably happen Hemirunner.

Next point of detail will be Idle, throttle linkage is a bit loose and I notice I can smooth out the "surging" when I apply very light pressure on the gas peddle. which telsl me I don't have the carbs synced and my linkage may not be balanced. I post the problem/results in another section and a new thread.

Thanks again for all you guys that helped. This site and community is the best!!

 

[Hemirunner]

If it's bucking the starter, You can put a start retard on it depending upon what igntion you have or you can just put a togle switch on the ignition. Spin it with the starter and flip on the ignition.

- - - Updated - - -

If you lock it out at 34 or so, i'd recommend a minimum 10 degree start retard. Don't wanna bend a rod!