Street Demon tuning experience

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I found out the engine doesn't like 35 degrees advance, at least not all the time. When hitting the gas in 4th gear around 35 miles per hour I got spark knock that I have never had before. At least I know what that sounds like now. The starter also kicked back when I tried to start it hot, so I backed it down to 30 degrees. As far as I could tell, both symptoms went away, but I'll have to drive it some more this week/end to see if the starter kick back is really gone or not. I left the distributor advance locked out because I'm too lazy to take it off and try to set it again. If I have to back the timing down again I'll reset the mechanical advance.

The other thing I did was put in the 62/54 rod. When I had the 64/56 rod in there was a little bit of hesitation that I figured I would take out with a nozzle, but I went down one rod size instead. The carb runs great in this configuration even though it shows really rich (Cruise is around 13, but acceleration is 11-12 and WOT gets richer). I'll run it like this for a while and see what kind of mileage I get.
 
This is where ign tuning comes in. In particular vac adv connected to manifold vacuum. Ideally an adj VA unit.

As an example: init timing is 12*; then there is the centri curve in the dist. Vac adv adds 23* at idle to give you 35*. You can have any combination that gets you where you want to be. Under the load, the VA drops away.
 
Why are you running so much advance? Do you have the timing locked out?
 
Based on one of the previous suggestions I increased my initial timing to get the idle mixture screws to have more affect. RPM increased until 35 degrees so that's where I put it and then adjusted it back to 30. I did lock out the distributor.
 
13:1 cruise *seems* rich but based on my experience and what the Street Demon instructions say that's close to ideal (instructions say 13.5:1).

I still think the outer ring on the harmonic balancer slipped which is why your ignition timing advance is reading so high for how it runs. I think next order of business is to verify TDC with a piston stop tool.

Also adjusting the advance by 5 degrees is quite a bit, it can be tricky but changing it in increments of 1-2 will get you closer to ideal and can make a noticeable difference in response, power and fuel efficiency. The more advance you can run without pinging the less hesitation you'll experience when opening the throttle and will be able to run a leaner mixture without stumbling or hesitation. I just finished doing this on my D200 pickup (360 with Edelbrock 1406 carb and Summit Billet distributor); it took quite a while to get it fully dialed in with lots of back-and-forth adjusting timing then carb then timing then carb then timing (lol) but it runs awesome now. It is true you should get the timing dialed in first, only reason I was changing it after carb adjustments is that I don't have a WBO2 sensor on my truck and am tuning it based solely on feel; it ran good but my gas mileage was lower than normal so I leaned out the primaries which caused it to be stumble-y off idle. I then modified the the distributor to allow more initial advance and slightly quicker mechanical advance curve with the same total advance while also adjusting the vacuum advance pot a bit (less advance relative to vacuum) and now it's smooth as silk.

Tuning can be a pain and tests your patience but it's SO satisfying. I barely have to touch the gas pedal now to get the truck to accelerate and maintain speed up hills which there are a lot of where I live. When I step on it the torque is instantaneous, the truck really moves from a standstill in an impressive way considering it weighs 4400 lbs and has a 727 trans with stock 1800-RPM stall converter, 3.54:1 axle gears and 33" tires.
 
I did test tdc before starting this using one of those spring tools that moves up and down with the piston. I can go back and double check with a stop tool. I was just a little worried about damaging the piston by cranking too hard on it since I've never used a piston stop before.

I'll do some more testing over the next week as time permits.
 
What is this "spring tool" you used, care to share a pic?

Don't worry about damaging the piston, by the time you put enough force on the piston to cause a dimple (which isn't a big deal to begin with) you'd likely bend or break the stop tool itself. And you'd have to crank it pretty hard after you felt the resistance on your breaker bar of the piston hitting the stop tool.
 
I don't care what "experts" say. Locking out a distributor for a street car is nonsense. I wouldn't even do it on a race only car. When I busted off the slant 6 in Vixen for the first time, she had about 45 degrees initial timing, but it didn't touch it until the cam and lifters were broken it. It ran just dreadful. Once broken in, I backed it down to about 19 initial and worked from there. There's just no reason for initial timing that high.
 
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NukeBass said:
Yeah, but I got paranoid with metal on metal contact and a breaker bar:)
Click to expand...
Here are a few tips.

Remove all the spark plugs so you don't have to turn against the compression of other cylinders with your breaker bar.
This is not true for all motors/cylinder heads but with a stock headed small block mopar you should not have to remove the rockers to prevent the valve from hitting the piston stop. Somebody chime in if they think this is not correct.
It's not a bad idea to unhook the battery cable to prevent accidentally cranking the starter with the piston stop in.
Remove the piston stop as soon as you have your marks so you don't forget it's still in there.
Watch the tdc mark on the balancer so you know when you are approaching your stop.
Use a light touch with the breaker bar.
Get a small narrow flexable tape measure Like a what is known as a "stagger tape" in the circle track world to measure your marks.
 
It's hard to see in the photo but this is a harmonic balancer I just pulled off a motor I was dynoing day before yesterday and it was slipping.
If you look closely you can see where it it delaminated. It was so bad you could see it move 10 degrees each direction while Idling.
This was the first time the motor had been run since the race car that it was in was wrecked. I suspect the wreck may have contributed to it slipping but I don't know that.
I have seen slipped balancers on the dyno several times over the years along with incorrect marked tdc. Enough that I check each motor before I start to tune. I learned the hard way.

IMG_20230912_160316_01.jpg
 
I just checked with a piston stop and if it isn't dead on it's one or two degrees off. That's similar to what I found using this tool a couple of months ago, so i feel pretty confident in the timing marks.

20230912_193552.jpg
 
Posts # 28 & 30 are 100000% correct & are the starting point for awesome performance....from any carb.
 
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