I need some help on this one it is driving me crazy to the point of removing this ignition and installing an updated points distributor, coil and resistor.

Here is what I have:

1. 1967, L71

2. TI ignition

3. TI unit purchased from another member on here, said it was good. Can’t remember but I think that he stated it is an updated unit from a couple of years ago, around 2015.

4. Low inductance coil for the TI ignition

5. TI distributor, purchased from a member on here, for the L71, total of 16 deg advance @ 4000 rpms

6. Fresh rebuilt motor, less than 1 hour of run time, frame off restoration

7. 190 psi avg in each cylinder

8. 26 deg of timing at 1000 rpm’s, total of 38 deg.

9. 12 inches of vacuum @ idle

10. #66 jets in my center carb with a 5.5 power valve, 0.030” of transfer slot exposed at idle, car idles at 950 – 1000 rpms really nice and steady

11. Secondary metering plate, #73

12. New spark plugs, R45

I have adjusted the timing up and down, same issue exists. The car starts and idles good, throttle response good. Car runs down the road good as long as you do not floor the car or punch the car hard. You can drive the car up to 4000 RPM’s as long as you gradually apply acceleration, as soon as you load the car up it misses really bad, I mean really bad and gains no speed and no power. You can do this at low RPM’s or high, as soon as you apply a load, it breaks down. I thought that it was carbs at first but have been into them so many times and have no ruled them out. It must be something in this TI ignition breaking down under load. I do not know anything about these TI ignitions, but this is a documented car with tank sticker so I put it back that way but I am thinking that this is my issue. Does this sound familiar to anyone out there that has had a TI ignition go bad?

 

My 66 had a similar problem and it turned out to be the pick up inside the distributor.
Here's a link that may help.
http://www.tispecialty.com/articles/article1.htm

 

I agree. The gap is critical and the pick up is the first suspect. The second suspect is the coil.

 

bingo

 

I don't know much about the tripower setup, but it sounds like you are getting a massive miss when your secondaries get involved. Flooding or too lean situation.

 

I can't make any sense out of your spark advance map data. The L-71 OE centrifugal is start @ 900, 30 (crank deg.) @ 3800. You said 16 @ 4000. Were you quoting distributor rather than crank degrees?

The OE VAC is stamped 201 16, and it is ported, so there is no vacuum advance at idle. Maybe it was converted to full time, which I recommend, but the OE VAC must be replaced with a 12" B26 to pass the Two-Inch Rule. What's the ID of the installed VAC?

Initial timing should be set in the range of 6-10 to achieve 36-40 total WOT advance. With the OE ported vacuum advance there is no vacuum advance at idle, so total idle advance is the same as initial. With full time vacuum advance total idle advance should be 22-26 at 900 or less. The engine doesn't make enough idle vacuum to pull the OE VAC to the limit, which will likely cause idle instability since the VAC with be dithering.

Do the end carbs still have the vacuum controlled opening? Some were converted to straight mechanical linkage, which will definitely cause the symptoms you report.

You said the engine pulls 12" at idle. I've lost count of how many times I've said this, but stating idle vacuum without stating the actual idle speed is MEANINGLESS because idle vacuum is highly effected by idle speed. The higher the idle speed the higher the manifold vacuum. Typical L-71 idle behavior is 14" @ 900.

You said the plugs are AC R45. Are you sure? These are 3/8" reach plugs that are commonly installed in small blocks. Early big blocks use a much longer reach plug (3/4" as I recall), and the R45XLS is a popular choice. If the installed plug are really R45 then the spark is halfway up the plug bore, which will likely cause some significant operational issues.

Why didn't any of you other guys who responded point this out?

Duke

 

He stated 12 inch vac at idle, then in the next bullet he stated car idles very stable at 950 to 1000 rpm.
He also stated that the car would go to 4000 rpm under light throttle. I believe he isn't going to higher rpm's because of a breaking period.
Sparkplug and TI ignition are not affected by throttle.
Vacuum advance seems to be functioning since the car runs fine under light throttle.
Mechanical advance seemed screwy so I hoped someone would address that, but his mechanical is all in at 4000rpm under light throttle.
Now under heavy throttle regardless of rpm he loses power and developes a miss. This could only be from lack of advance with the lack of vacuum advance or a carboration issue caused by the secondaries. IMHO.

 

This is why chevy made hei.

 

Why didn't we point this out? Maybe because its dang hard to get a 3/8 length plug to seat in a BB head, where the plug openings aren't threaded all the way out.

Maybe we see the OP let a few typos and contradictory items get loose, like 26 degrees advance at 1000 and 38 total, but 16 at 4000, and maybe those aren't a big deal when trying to help the OP with his question. The TI guys probably got it right about the pole piece/pickup coil gap.

We could ask the OP more about the actual symptoms, which I will, and that is, does it sputter and spit, or just plain shut down, like turning the key off? The key off symptom is more likely a pickup coil gap issue. Spitting is often too much timing at full advance. Let us know, Lyle, and we will dig a little deeper.

....and this is for you, Duke, the centrifugal and vacuum advance responses are curves, not maps. The advance functions are one dimensional and have no relationship to each other. Map became a common term only when ignition timing started being controlled electronically.. The term "map" doesnt apply to mechanical, independent controls.. Why is this an issue? Because you don't seem able to post a reply without busting chops over words you don't like and giving other posters grief over it. People don't post on here to learn how to write SAE papers. They want help with problems. You have a ton of knowledge. People tend to tune it out when they get a hard time over a word issue that doesn't change the answer. A loss all around.

 

If you load the engine (open the throttle blades) and it sputters then back off the throttle and it runs normal again my feeling is it's going lean. Go after the accelerator pump adjustment, accelerator pump cam, accelerator pump squirter nozzel size. The engine will not recover from a lean condition caused by this when going WOT.

 

Most carb issues are ignition issues. Good rule of thumb.

 

At any given engine operating condition spark advance is controlled by the combination of centrifugal and vacuum advance. If you plot it out on a XYZ axis you get a surface, which is a "map". There is an example in my tuning seminar. Modern engines also control spark advance primarily by engine revs and manifold vacuum, except they do it via transducers that convert a mechanical signal into an electric signal rather than by purely mechanical means. Same end, just different means.

Duke

 

The TI is functioning correctly. It's function is unaffected by throttle. 4000rpm is 4000rpm regardless of air fuel mixture or vacuum. Could it be mechanical advance, yes. Could it be vacuum advance, yes. Could it be sparkplug, no. Could it be an air fuel mixture with heavy throttle, most likely.

Why does everyone assume it's TI before looking at the common problems? If this was a points distributor what would your diagnosis be?