Distributor curve

[CamaroAdam73]

Alright i tried to check exactly when my vacuum advance was coming in at by removing it and hooking it up to my hand operated vacuum pump.

At 10" of vacuum according to my pump the advance had deployed fullly. So that means that at 10" manifold vacuum this vacuum advance is supplying the maximum advance it is set to apply?

 

[Fox80]

Did you change the canister? That sounds correct if you did, now you should have stable vacuum advance at idle because the motor makes enough vacuum to supply a constant 10". If you get a good retard of the mechanical advance at idle, a good mechanical advance up through the rpm's and stable timing when the vacuum line is attached you should be ready to drive it and see how it acts. When you drive it try some hard launches from idle when the car is at a stop, that is the most load you can put on a motor, let the car part throttle cruise, then kick it down into passing gear, find a hill let the car coast down the hill with no throttle input. In all of these conditions you are looking for a stumble,pinging, or surging. If it drives nice and runs good I would say you are done

 

[CamaroAdam73]

No i checked the canister i have, it's fully advanced at 10" vacuum. I read over the manual it came with again to see if it mentioned when it should come in and it doesn't but i miss-read it the first time and set the advance up wrong, your supposed to use a 3/32 allen wrench and turn it counter clockwise to retard the amount of advance it supplys, i did the opposite and started off with the advance supplying MAX adjusted advance, i'll reset that tomorrow.

Tomorrow i'm going to mark some extra degrees on the balancer and try to run through some checks.


I've already road tested the car a few times and after the most recent adjustments it's running pretty strong, no stumbles or hesitations. The only notable thing is an occasional pop in the exhaust when letting off from hard acceleration.


I'm trying to keep a close eye out for PINGING but i don't have the exhaust hooked up so its really loud and hard to tell, will the engine stumble if it starts pinging?

 

[pontiacgp]

The only notable thing is an occasional pop in the exhaust when letting off from hard acceleration.

that is a caused by the lean condition at idle...I had the same problem so I turned the gas up at idle and no more popping.

 

[Fox80]

Sounds like your got it figured out, see if you take your time and understand how the system works its actually easy to set up, it just takes time. I would agree with the pop on rapid throttle plate closing more than likely its a little lean on the idle circuits. The motor may be lean over-all as well check your plugs after some driving. A motor may not stumble if the advance is to much for it, the ping is just a noise that indicates to early ignition of the fuel, more than likely you would need the exhaust hooked up to hear it. What dist. did you end up buying, its interesting that they put a low signal canister on it to start, that's a good thing for a performance dist., with guys wanting that lopey idle in a motor they kill the idle and low end power as well as the vacuum signal

 

[CamaroAdam73]

I'll try giving the idle mix screws an extra 1/8 turn out and go from there until the popping stops, if it doesn't i'll know i'm lean overall. When i set them the final time i couldn't depend on my vacuum gauge because the cam supplys a choppy vacuum signal so i used only engine RPM as a factor. I have a digital gauge i use for tuning that at least lets me watch the RPM drop/raise in 100's.

Because i don't have a stop screw in the advance, or know my total timing i still feel like i'm miles away from completion but i definitely have a better understanding now.

Checking the plugs, that's where it gets interesting. They're burning so clean that a handfull of the plugs look literally like they are new out of the box which struck me as strange. I checked to make sure they where actually firing that's how clean they looked. I've checked them 3 times now, once right after break in, once after each test drive and timing adjustment. All clear.

The pinging noise should sound like a very very light knock right? My friend told me i was just paranoid but i swear i almost hear that at idle, i'll find out today when i dial back the vacuum advance. I'm just being on the safe side here, if a engine is pinging how long will it run like that before internal damage occurs?

With this build i decided to build my own dist. I started with a re manufactured unit from Autozone for a base, i bought an advance kit from Moroso along with the adjustable vacuum advance and a new pickup.I went with a DAVIS UNIFIED IGNITION coil/ module. I like MSD but i just trust Moroso, price wasn't a concern with this i just wanted to be IN on every aspect of this build so i built my own dizzy.

Sorry for the novel reply lol.

 

[pontiacgp]

by the description of your plugs it sounds like it's running lean. The popping is caused by the idle mixture been lean and not a lean condition off idle. Moroso make great parts and they are all made in the US as far as I know and DUI is known for their great products.

 

[Fox80]

Haha that's ok, your dist. doesn't HAVE to have a advance stop screw in it, that is a bandaid for a dist that wasn't made correctly. A high quality HEI will have the plate made very precise, and will include bushings to dial down the mech. advance. You wont hear a ping at idle, or ever for that fact in your driveway you need a load on the motor. The plugs you say look "new" may very well not have enough time under load on them yet to give a good reading, a car with vacuum advance done correctly will idle so much cleaner that it takes a while longer to get a carbon pattern on the plug. The fact that you have some miles on it tho might not be a bad idea to richen it up some, I would even go up a jet or two on the primary side of the carb

 

[CamaroAdam73]

I've still got something going on with the secondaries opening, wouldn't that cause a lean condition?

 

[pontiacgp]

not unless you are running on 4 barrels full time and the secondaries were not supplying any fuel