69 L71 just dies after a warm idle

[Lawrence S.]

Re: 69 L71 just dies after a warm idle

Guys,

Below are my results using a digital timing light with an integral tach:

RPM Timing
830 . 6.2 . vacuum advance plugged (Initial)
1180 . 27 . vacuum advance plugged in to full manifold vacuum
2060 . 35
2600 . 35.5
2960 . 37.6

I stopped here.

I am assuming that my springs are too light because of the high timing at such a low RPM. The centrifugal is coming in when I plug in the vacuum advance. Tomorrow I will change out the springs for tighter springs to see what happens. The car runs much better up high with a hard pull at full acceleration but does seem to have lost a little punch down low? Maybe I am expecting too much from an L71 with an M21 and 3.70 gears? Pretty wimpy as compared to my 67 L36 with an M20.
I will let you know what happens when I change to tighter springs. Or if anyone has any advice I am all ears.

Thanks and Happy Memorial Day

Lawrence

[Timothy B.]

Re: 69 L71 just dies after a warm idle

My car starts well cold, drives great does not miss or act up while warming up. Bring it home after a 5 or 10 mile drive and let it idle in the driveway. It idles nice between 750 to 800 rpms and then suddenly just stops running. To get it to start back I push the accelerator pedal to the floor turn the the key fires right back up runs for a while then dies. Sounds like I am losing fuel after the car get up to temp? I have 110 octane no lead fuel in the car now after running 93 10% ethanol with same results. Naturally the car runs better with the 110 octane fuel, but I am not going to be putting that in the car all the time. I checked float levels in the carbs, they check out well. The air fuel ratio is set correctly. Is the fuel pump going bad? Vapor lock? Any suggestions are welcome.

Thanks
Lawrence

Did you recheck the emulsion screws after the engine is good and hot. If the car restarts immediately I'm not sure it's a fuel problem, there could be a carburetor problem, what's the history on the carburetors. Does the car restart like it's a little flooded.

There could be many causes but at idle the high engine vacuum can pull fuel around the power valve gasket and cause a over rich idle then possibly stall. This fuel will not be noticeable because it's pulled from under the throttle blade.

[Chris H.]

Re: 69 L71 just dies after a warm idle

Lawrence, happy to see you're making progress. It's important to follow the tune up process as exactly stated in the CSM regarding the carburetors and ignition timing.

For my L71 ignition curve, the short story is I set my initial by advancing it until it pinged. If memory serves I'm at 10 degrees initial. I then went with progressively lighter springs until it pinged. I'm at 40 degrees total, all in by 2500 rpm. I'm using 100 LL avgas at sea level so it's pretty aggressive.

The car runs fantastic.

[Lawrence S.]

Re: 69 L71 just dies after a warm idle

Did you recheck the emulsion screws after the engine is good and hot. If the car restarts immediately I'm not sure it's a fuel problem, there could be a carburetor problem, what's the history on the carburetors. Does the car restart like it's a little flooded.

There could be many causes but at idle the high engine vacuum can pull fuel around the power valve gasket and cause a over rich idle then possibly stall. This fuel will not be noticeable because it's pulled from under the throttle blade.

Air fuel mixture screws?

[Lawrence S.]

Re: 69 L71 just dies after a warm idle

Chris I would not be surprised if I don't have a little runway left before my car pings. I was doing this by myself and it seemed every centimeter of turning the distributor was worth 10 degrees. I am exaggerating but a lot of trial and errors! And a lot of no starts!! I may advance it another two degrees but want to get the right springs in the distributor and start again. I agree about the CSM. I have my 67 L79 dialed straight in per the CSM. Car runs best it has run in the 25 years I have owned it.

[Duke W.]

Re: 69 L71 just dies after a warm idle

Guys,

Below are my results using a digital timing light with an integral tach:

RPM Timing
830 . 6.2 . vacuum advance plugged (Initial)
1180 . 27 . vacuum advance plugged in to full manifold vacuum
2060 . 35
2600 . 35.5
2960 . 37.6

I stopped here.

I am assuming that my springs are too light because of the high timing at such a low RPM. The centrifugal is coming in when I plug in the vacuum advance. Tomorrow I will change out the springs for tighter springs to see what happens. The car runs much better up high with a hard pull at full acceleration but does seem to have lost a little punch down low? Maybe I am expecting too much from an L71 with an M21 and 3.70 gears? Pretty wimpy as compared to my 67 L36 with an M20.
I will let you know what happens when I change to tighter springs. Or if anyone has any advice I am all ears.

Thanks and Happy Memorial Day

Lawrence

Yeah, that centrifugal curve is too aggressive. The OE curve is start @ 900, 30 at 3800, which is not that bad. Best would be the same start point, right about at idle speed and 30 @ 2500 with 10 initial, same as what Chris reported.

With a full time B26 VAC total idle advance should be about 26 with about 14" @900 idle behavior. If the CR is near OE this aggressive map probably probably will ping on the highest available pump gas.

Duke

[Lawrence S.]

Re: 69 L71 just dies after a warm idle

Today I went to change out the distributor springs, and the ones that were in there were completely worn out and stretched. I believe that my initial timing yesterday was flawed with a little centrifugal as part of the timing. I put in stiff springs today, and my initial was 2.4*. So I need to start all over with 8* of initial and then map the centrifugal. On a test drive today I could not get any detonation in high gear going up a hill. So I have a lot of timing left. Will start all over and let you guys know what I find out.
On another note. I have the diverter valve in the A.I.R plugged into full manifold vacuum via a "T" that is inline with the VAC tube. Is this ok?

Thanks

[Duke W.]

Re: 69 L71 just dies after a warm idle

The best way to set timing is to set total WOT timing assuming you have light springs and don't need to rev it much over 3500 for all the centrifugal to be in, and with 100LL avgas set it at 40. Of course, the VAC signal line must be disconnected and plugged for this procedure.

The diverter valve vacuum source is full time and fine for the VAC. The diverter valve closes at about 19-20" vacuum. Without it afterfire would be common whenever you lift off the throttle.

The most common way to convert to full time vacuum advance with a Holley is to tee into the choke vacuum break line - my advice is to get a couple of feet of 1/8" tubing and a tee to make a new harness, especially if your choke vacuum break hose is original.

In the long run if you are happy with full time vacuum advance you can modify the base of the center carb by plugging one hole and drilling another to place the vacuum signal pickup below the throttle plate, and the mod is invisible.

Duke

[Timothy B.]

Re: 69 L71 just dies after a warm idle

Today I went to change out the distributor springs, and the ones that were in there were completely worn out and stretched. I believe that my initial timing yesterday was flawed with a little centrifugal as part of the timing. I put in stiff springs today, and my initial was 2.4*. So I need to start all over with 8* of initial and then map the centrifugal. On a test drive today I could not get any detonation in high gear going up a hill. So I have a lot of timing left. Will start all over and let you guys know what I find out.
On another note. I have the diverter valve in the A.I.R plugged into full manifold vacuum via a "T" that is inline with the VAC tube. Is this ok?

Thanks

Are any of these changes correcting the idle stalling problem you have?

[Lawrence S.]

Re: 69 L71 just dies after a warm idle

Are any of these changes correcting the idle stalling problem you have?

Yes that problem has gone away. Car runs much better in traffic at idle.

[Lawrence S.]

Re: 69 L71 just dies after a warm idle

The best way to set timing is to set total WOT timing assuming you have light springs and don't need to rev it much over 3500 for all the centrifugal to be in, and with 100LL avgas set it at 40. Of course, the VAC signal line must be disconnected and plugged for this procedure.

The diverter valve vacuum source is full time and fine for the VAC. The diverter valve closes at about 19-20" vacuum. Without it afterfire would be common whenever you lift off the throttle.

The most common way to convert to full time vacuum advance with a Holley is to tee into the choke vacuum break line - my advice is to get a couple of feet of 1/8" tubing and a tee to make a new harness, especially if your choke vacuum break hose is original.

In the long run if you are happy with full time vacuum advance you can modify the base of the center carb by plugging one hole and drilling another to place the vacuum signal pickup below the throttle plate, and the mod is invisible.

Duke

I have the tubing harness per your suggestions above. I did buy a few T's and new tubing. I think I am set there. I just need to start at 8* initial and go from there I believe. I will see what I come up with. Thanks for all the help from everyone.

[Chris H.]

Re: 69 L71 just dies after a warm idle

Lawrence, nice find on the springs. Bumping initial from 2 to 8 degrees will make a huge difference.

[Lawrence S.]

Re: 69 L71 just dies after a warm idle

Here is the latest

10.3* initial at 915 RPM. I can't get the car to idle any lower. Is there an issue with the linkage being out of adjustment. When I plug in the vacuum advance I can't get the car to idle lower than 1200 rpm. Very annoying. Or is this engine just making more vacuum than a normal L71? I have no idea the history of the engine? I can hear the mechanical lifters!! But barely.
The centrifugal is as follows:
900 rpm . 0*
1100 rpm . 12.9*
1720 rpm . 25.2*
2510 rpm . 30.3*
3270 rpm . 32.4*
It appears I need to install lighter springs. I know I have stiff ones in there.

Still can't get the car to detonate.

Car runs best it has run since I have owned it. Tempted to leave it be, but would like to get to 36* TT at 2500 RPM. The idle issue is bugging me. Not sure how to fix that??

Ideas??

[Chris H.]

[Lawrence S.]

Re: 69 L71 just dies after a warm idle

Ohhhhhh..... I had no idea. First tri-power I have worked on. Is that process in the CSM? Once I hook up the secondary wouldn't that just boost the idle back up to where it is now? I did not even think of a vacuum leak. Probably the situation. That is going to be a pita to find I am sure.

I switched in weaker springs and got a few more degrees of total timing. Car runs great no issues but want the idle lower for sure.

Latest results of centrifugal advance

900 RPM . 0*
1100 . 16.8*
1720 . 28.7*
2510 . 32*
3210 . 33.4*

Would like to get to 36* at 2500, right?