HEI distributor tuning problem

[WadmalawJoe]

Well, I adjusted timing down to 8 degrees but nope.....still doing it. It is reading 47 degrees at all in at 3,000 rpm, its actually all in well before that.
Here is some more info,
I rigged up my multi-meter/tachometer to reach inside the cab.
The detonation issue happens at 2,500-2,600 rpm (50-55 mph)
I came back, reconnected timing light and noticed its all in (47 degrees) around 2,100-2,200 rpm.

Should I go with a heavier spring so it goes all in later or just back the timing down more?

[JOJABOY]

People say 3000 because it's definitely all in by then. Most curves kick in total advance around 2200 like you mentioned. So that part is good. You just have to figure out why your motor is so finicky. I would check my plug gaps. But I would venture to say change to heavier spring is going to be your next move. Try to get that all in down from 47. It shouldn't take much. Some people put stops in their HEI to keep the weights from fully advancing or a stop in their Vac advance to keep it from fully advancing. You can google "vacuum advance can stop" and see what I am talking about.

I am running two blue springs with my cam set up. My vac advance can was advancing around 18* like yours (which is quite a bit) and I got an adjustable one and dialed it back to 12* of advance.

So my initial timing is 10* plus 16* of mechanical advance (centrifugal) and my vac can advances it another 12* so my all in is at 48*

Yours is 8, 20 and 19 it sounds like to get 47* all in. Will your vacuum advance dial it down any???? 19* vacuum advance is ALOT

[WadmalawJoe]

I went back out and backed timing down to 5°, it got a little better, then I went to tdc and it was almost gone. It would only make the noise around 2,510-2,530. Trying to find the noise and hold the rpms is easier said then done.
So I'm thinking either my tape is incorrect, as in the parts guy gave me the wrong one or the tdc mark is off. I measured my balancer and told him the size, if the tape is supposed to go all the way around, mine doesn't because I cut it shorter to make it easier to put on. Wish I would've thought to check the length.
It ran ok at tdc, just had to tweak the idle up a touch while the advance was disconnected. Soon as you plug in the advance it jumps to 19-20° .
My spark plugs are all gaped at 40 or 45? Whatever your supposed to gap them to with going to hei.
With limiting adjustable advance, you mean that little cam piece? I've seen it in pictures, it must be up under the rotor or something? if I have one I can't see it.
The adjustment screw inside the can controls how fast the vacuum advance kicks in right ?
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[LONGHAIR]

The vacuum advance seems to be the issue here. But, you never have stated (or I missed it) what you actual vacuum reading is at idle? Also, what amount of vacuum it takes to make the canister advance?
You see, the thing that screws up most people is the term "vacuum advance". It's really backward. The thing is actually releasing the advance that it holds as you accelerate.
This is why you must remove and plug the line when setting the base timing with the light. Because as soon as you plug it back in, you get all of the advance it has to give...at idle, when the vacuum is highest.
So, as you accelerate, the vacuum advance starts to "go away", while the mechanical (centrifugal) advance is "coming in". The only time they are both all-in would be if you suddenly took you foot off of the throttle at highway speed...not much pinging there.

So my thinking at this point is that your engine makes pretty good vacuum and the canister that you have will not release early enough. You really need a vacuum reading at your 2500 rpm pinging point. That, and the vacuum rating of you canister will tell us a lot.

[LONGHAIR]

Dupe.

[WadmalawJoe]

I was reading up on the vacuum advance stops or limiters and came across this explanation its pretty good and with good pictures imho
http://temp.corvetteforum.net/c3/joe..._Recurve.shtml

I think I need to pick up a kit that comes with the stop and install it. Instead of backing my timing down until it the highway tapping goes away, I just need to limit the advance to maybe 10 instead of the full 20 degree jump.
Which is basically what JoJaboy and others have been saying all along and what I have been reading. I guess I just have been trying to make what I have work, but my motor is just real finicky.

Longhair to answer your question on the current advance can, it starts to work with very little vacuum at all, maybe 3-4 inches of vacuum, its at full advance by 10 inches for sure.

[LONGHAIR]

Originally Posted by WadmalawJoe

Longhair to answer your question on the current advance can, it starts to work with very little vacuum at all, maybe 3-4 inches of vacuum, its at full advance by 10 inches for sure.

How much vacuum does your engine make? At idle? At the pinging point?
It seems like there is still too much vacuum advance at that rpm.


This is the screwy thing about a distributor set-up for "ported vacuum". Since there is no vacuum to the distributor at idle, it has more initial advance and less vacuum advance to keep the total similar.
Which is why you can't just change which place where the hose is plugged, bad things can happen.....
Many older trucks are converted to HEI, with "unknown" distributors. They really should be calibrated to match the points-type distributor that came out. The conversion is not done because the timing curve itself is wrong.

The carburetor companies have no idea what is going on, how could they?
Maybe for a few "specific applications" where is was that way in the first place, but how many of those are there? That is certainly not the case with the more universal-fit models.

[formikaus]

Sorry to hear all the problems you are having. When i put my Accel billiet HEI with a supercoil cap in, I did not use the vacuum advance. I just left it capped off out of the box. I did still have some pinging at the same speed range ONCE THEY STARTED ADDING ETHANOL!!!!! I started putting in 93 and it quit. With it capped off I did still get around 18 mpg's, but I am running a stock cam, 700R4, and 308 gears. Like I have said before, I feel for you. A engine noise is as bad as door glass without weatherstripping....it will drive you crazy! Lol.

[WadmalawJoe]

[quote=LONGHAIR;5950317]How much vacuum does your engine make? At idle? At the pinging point?
It seems like there is still too much vacuum advance at that rpm.

I have a vacuum pump, but not a vacuum gauge.... its on the list...
I might could use the gauge on the vacuum pump somehow, I will look into that.

Originally Posted by formikaus

Sorry to hear all the problems you are having. When i put my Accel billiet HEI with a supercoil cap in, I did not use the vacuum advance. I just left it capped off out of the box. I did still have some pinging at the same speed range ONCE THEY STARTED ADDING ETHANOL!!!!! I started putting in 93 and it quit. With it capped off I did still get around 18 mpg's, but I am running a stock cam, 700R4, and 308 gears. Like I have said before, I feel for you. A engine noise is as bad as door glass without weatherstripping....it will drive you crazy! Lol.

18 mpg!!!! nice, this isn't downhill is it? ...lol


Nobody in town has a adjustable vacuum can with a limiter plate, so I would either have to order one or take it out of the mechanical advance.
I read some about making one, I have three vacuum cans to use, so I might try that.

Thank you everyone and I will update with more info asap.

[WadmalawJoe]

I ordered a limiter plate from Summit. They actually sell the little piece by itself for $3. Cost more to ship it...lol They also carry it in their stores.
I think it will get here in the next couple of days.

[WadmalawJoe]

Alright, I got the limiter plate and installed it. I immediately went to the half way notch hoping to cut the advance in half after all the hassle its been giving me. Well, it didn't, I still had a full 20 degree advance and for some reason it was all in as soon as I plugged in the advance! I ended up switching to the heaviest springs and all the way to the last notch. That cut the advance by 6 degrees.
Right now I have the initial timing at +8 , then centrifugal/mechanical is +20, the advance at +14 totaling 43. The tapping/predetonation is gone and she runs fairly smooth. I want to do some more fine tuning because I think it can tweak it up a little. I'm waiting on some nicer weather, its been ugly lately.
I will post again when I get it fine tuned some more.

[Longhorn 70]

Originally Posted by WadmalawJoe

...
Right now I have the initial timing at +8 , then centrifugal/mechanical is +20, the advance at +14 totaling 43. The tapping/predetonation is gone and she runs fairly smooth. I want to do some more fine tuning because I think it can tweak it up a little. I'm waiting on some nicer weather, its been ugly lately.
I will post again when I get it fine tuned some more.

Good going Joe. We are proud of you for getting this far. Let us know how the tuning goes.

[magwakeenercew2jh]

62 posts and a "Job well done".

What a great Forum.
Made up of a great group of folks.

[WadmalawJoe]

Well, the job is not done.....
The noise came back after a couple days. It was warmer last weekend when I set everything. Then it turned colder for the week. I drove the truck everyday last week. So I'm thinking maybe the carb (edelbrock a pos imho) has something to do with it. It has a manual choke so I'm controlling the choke, but the thing never consistently idles the same. So I'm thinking the vacuum probably changes to. I don't know.... I will be adding a vacuum gauge soon though.
Another tidbit of info; I noticed the limiter plate would only limit the advance by 6 degrees at the maximum setting. The advance can was a Mr. Gasket brand that I picked up a couple weeks ago. Yesterday, I took that off and put the other one back on (the one that came with the distributor) I had swapped them around thinking it was a can issue. Right away I noticed the arm coming from the can is slightly different in length. If I wanted to max the limiting plate I would have to jam the arm all the way, which would probably mean zero advance. I set it at the halfway notch and closed the distributor up and checked it out. Timing was at +10 initially, plugged the dist. in and it went to +20, so apparently the halfway notch cuts the advance by 10.
I adjusted the initial timing to +15 and took it for a drive. Well the tapping started at 2,300 rpms and was present through 2,600 rpms. My wife rode with me and says I'm overly paranoid as the tapping isn't very loud. That statement worries me some, because at some point I might hear, the car was only making a little noise before it died....lol
Anyway, I feel like I'm back to square one. At least, I have gained some knowledge about distributors and such, thanks to everyone on here. I will keep picking at it and see what I come up with.
Maybe I should have titled this Joe's HEI and tapping blog....