Ok, I've about had it with the Mopar Performance distributor/ignition

[bigmanjbmopar]

He would only get a total of 34° on a mech advance distributor only, if he is running a vac and mech combo his total should be just over 50 total.

moparedtn follow this guide to help you get your timing correct, this is by far the most accurate explanation I have ever seen and has helped me out a lot.good luck it's not as hard as you think.


http://www.mopar1.us/engine2.html

 

[SlinktRR]

After having driven it several times recently, everything is fine when I get on it up until it gets over 4500rpm.
Then the stumbling gremlins come out. This is more pronounced when I have the vacuum advance hooked up.
I gotta think it's something to do with the advance setup in the MP distributor.

Could also be the orange ecu pulling timing out, especially with the 4500 rpm comment. Go to napa and try their ecu it's around 20 dollars or so depending on the store you go to. It was my backup when my orange box died, been in the car ever since. Cheaper than buying a distributor.

 

[mopar 3 B]

He would only get a total of 34° on a mech advance distributor only, if he is running a vac and mech combo his total should be just over 50 total.

moparedtn follow this guide to help you get your timing correct, this is by far the most accurate explanation I have ever seen and has helped me out a lot.good luck it's not as hard as you think.


http://www.mopar1.us/engine2.html[/QUOTE


I think you had better read and study this artical again. He is not setting up his distributor using a distributor machine it is in the engine and 34-38° at the crank is going to be max..

- - - Updated - - -

Could also be the orange ecu pulling timing out, especially with the 4500 rpm comment. Go to napa and try their ecu it's around 20 dollars or so depending on the store you go to. It was my backup when my orange box died, been in the car ever since. Cheaper than buying a distributor.

To the best of my knowledge of this system from stock to the chrome box the ECU has no effect nor the ability to change timing. The grade of box is to insure spark to a certain rpm level and that is all.

- - - Updated - - -

From all the testing and replacements done and the current symptoms replacing the distributor coil pickup is what the FSM recommends.

 

[69Runner]

Lots to read in this thread, so my apologies if this has already been covered. At the start you talk about timing successfully by ear at 3500 rpm, but above 4500 it stumbles. Drawing on my experience with a rebuilt 383, Comp cams 280H and Holley double pumper, what if you try the following:

Set the timing again so it is smooth at 3500. Then take some timing out, maybe 5 degrees. At idle it should be around 0 BTDC, right? THEN connect the vacuum advance on the distributor to full manifold on the carb. This way you can regain some timing at idle. Now take for a test drive.

My train of thought is this- the engine seems to want less advance at the higher rpm, ie 4500+. If your test drive shows no change, then the problem lies elsewhere. What if it's too lean at that rpm, could that cause the stumble?

My Holley was a 750 with mechanical secondaries so it was a lot of carb and a big cam for the street. But it had a mean idle and really came alive above 3500 rpm. The idle was easier to deal with also being a 4 speed car.

 

[moparedtn]

At what rpm is the distributor go full advance and what is the total timing when it gets there? It should have total advance at 3800 with timing at about 34°. Do you know what the vacuum readings are before collapse? What happens to the rpm readings while every thing have gone south?

1. I'm figuring around 4000, so 3800 is real close. I don't have the ability to figure out total advance, so I'm thinking it's whatever mechanical advance these kits come with - distributor has not been fooled with at all, that much I do know.
2. Don't have a vacuum meter rigged up for driving.
3. The Super Tach II doesn't do anything weird when the stumbling occurs. Car acts like modern rev limiters in ECU's, where they just cut fuel/spark momentarily to a couple cylinders, then all 8 hits again.
No backfires or anything like that sound-wise - just intermittent stumbles, boppity boppity.
I've stayed in it, lifted then hammered again just to see what it does. It will continue to climb in RPMs, sloooowly, all the while doing the stumbling dance.

 

[bigmanjbmopar]

I have read the article closely and he is describing it in the car as we would all be doing. I said nothing of a curve machine which is ancient tech by the way lol

here is a quote -

"Total timing requirements are dependent upon many variables. A typical street engine with a compression ratio of 9.0:1 runs very well with around 36 degrees of timing (initial plus mechanical) for a rough total of 15-55 degrees of timing at light throttle when vacuum advance is employed. If the engine detonates or pings under WOT reduce the timing. If it surges or pings at part throttle, reduce the amount of vacuum advance. Experimentation with timing can help performance, driveability, and mileage by customizing the ignition curve to your particular application. Don't be afraid to make changes."

Sounds like it's a minor issue moparedtn and you probably will have it fixed in no time with some simple adjustments. All I can offer is what i have found with mine at higher rpm blips its been electrical, spark jump from a bad insulator or bad plug. Good luck man hope you get it fixed soon.

He would only get a total of 34° on a mech advance distributor only, if he is running a vac and mech combo his total should be just over 50 total.

moparedtn follow this guide to help you get your timing correct, this is by far the most accurate explanation I have ever seen and has helped me out a lot.good luck it's not as hard as you think.


http://www.mopar1.us/engine2.html[/QUOTE


I think you had better read and study this artical again. He is not setting up his distributor using a distributor machine it is in the engine and 34-38° at the crank is going to be max..

- - - Updated - - -


To the best of my knowledge of this system from stock to the chrome box the ECU has no effect nor the ability to change timing. The grade of box is to insure spark to a certain rpm level and that is all.



- - - Updated - - -

From all the testing and replacements done and the current symptoms replacing the distributor coil pickup is what the FSM recommends.

 

[SlinktRR]

He would only get a total of 34° on a mech advance distributor only, if he is running a vac and mech combo his total should be just over 50 total.

moparedtn follow this guide to help you get your timing correct, this is by far the most accurate explanation I have ever seen and has helped me out a lot.good luck it's not as hard as you think.


http://www.mopar1.us/engine2.html[/QUOTE


I think you had better read and study this artical again. He is not setting up his distributor using a distributor machine it is in the engine and 34-38° at the crank is going to be max..

- - - Updated - - -


To the best of my knowledge of this system from stock to the chrome box the ECU has no effect nor the ability to change timing. The grade of box is to insure spark to a certain rpm level and that is all.

- - - Updated - - -

From all the testing and replacements done and the current symptoms replacing the distributor coil pickup is what the FSM recommends.

Hot rod did a test of various ecu boxes, the orange box had real problems above 4000 rpm and pulled 5 degrees timing at 4500.

http://www.hotrod.com/how-to/engine/mopp-1211-3-2-1-ignition-box/

Also one of the selling points of the rev-n-nator along with its rev limiter. The Napa box is much cheaper though.

 

[moparedtn]

Real quick, I put a "store bought" ECM on it a few weeks ago just to eliminate that possibility.
Didn't make much of a difference.
I'll get back to all your fine answers here in a little bit when I get back from the latest test drive; I've backed off initial a few more degrees, will see what that does. Far as I can tell, that puts initial around 2* BTDC.

 

[moparedtn]

Ok, results of latest test drive - and this was by far the longest test drive (over 50 miles - a milestone of sorts for this thing!).
After running around for a while on our beautiful backroads, last part of the drive was on a 4 lane in order to beat on her some on the way home:
(3.55 gears)
1st gear - pulled real good up to around shifting time, say just shy of 5000rpm. A little bobble at the top end.
2nd gear - pulled real good up to about 4500 - then stumbled pretty hard, wouldn't stop stumbling til I let off a little.
3rd gear - pulled again real well up to around 4400-4500 - then RAPITA RAPITA RAPITA, like I was hitting a rev limiter.
Stumbling so hard it acted like it stalled before I let out of it and let it catch its' breath.
4th - back down to 2800rpm cruise speed and things settled right down like nothing happened.

The initial timing is too low now, too - she's stumbling a little off idle, gotta "clear her throat" when pulling out.
No biggie, easily corrected.

Guys, after today, I'm ready to think it may actually be starving, which is mind-boggling to me given the new Holley 3310 750cfm vacsec carb, new lines, new tank w/new pickup, etc.
Only thing not new (that I didn't do myself, anyways) is the fuel pump and now that I think about it, I think the previous owner told me that it was a "fuel return" type pump and that he had disconnected the return line and plugged it off.
Would that explain the possibility of starvation caused by the pump?

 

[mopar 3 B]

Vapor lock? Hook the line backup and see what happens.

 

[moparedtn]

Vapor lock? Hook the line backup and see what happens.

I'm thinking now that the fuel return line hooked up to a fuel filter with a 3rd nipple on it.
It's got a normal pass-thru filter on it now, between pump and carb.
I also had put a vented gas tank filler cap on the thing in the past; it also has the usual tank vents that pass up into the trunk.

Anyone else thinking fuel pump like I am? If so, what pump do I put on it?
Remember, this is a stock 440 with a near-stock cam and a Holley 750 vacsec.
I'd also strongly want to stay away from electric ones.

 

[bigmanjbmopar]

Just get a holley or edelbrock pump unless you gotta have that stock look. What plugs do you run? I run race NGK's but champions have been **** lately along with autolites.

 

[SlinktRR]

I'm thinking now that the fuel return line hooked up to a fuel filter with a 3rd nipple on it.
It's got a normal pass-thru filter on it now, between pump and carb.
I also had put a vented gas tank filler cap on the thing in the past; it also has the usual tank vents that pass up into the trunk.

Anyone else thinking fuel pump like I am? If so, what pump do I put on it?
Remember, this is a stock 440 with a near-stock cam and a Holley 750 vacsec.
I'd also strongly want to stay away from electric ones.

Fuel starvation would definitely cause those symptoms, you are right. Slide out and measure the fuel pump pushrod. Put a gauge on the pump outlet and see how it handles WOT, if it drops to like 1-2 there is a problem. Could be filters, tank filter, pushrod, or pump just can't put out the pressure you need to fill the bowls at full throttle. I use an electric pusher with a carter mechanical but I have considered getting a clay smith as it does like 16psi peak, which you can then regulate down but the volume is there.

http://www.claysmithcams.com/fuel-pumps/

 

[moparedtn]

Just get a holley or edelbrock pump unless you gotta have that stock look. What plugs do you run? I run race NGK's but champions have been **** lately along with autolites.

It's got new Autolites in it now.
What was the factory pump on these 440 magnums? The Carter rebuildable type?

- - - Updated - - -

Fuel starvation would definitely cause those symptoms, you are right. Slide out and measure the fuel pump pushrod. Put a gauge on the pump outlet and see how it handles WOT, if it drops to like 1-2 there is a problem. Could be filters, tank filter, pushrod, or pump just can't put out the pressure you need to fill the bowls at full throttle. I use an electric pusher with a carter mechanical but I have considered getting a clay smith as it does like 16psi peak, which you can then regulate down but the volume is there.

http://www.claysmithcams.com/fuel-pumps/

Oops. According to that site, the Mopar big block pumps aren't available.

The pickup, fuel filter, tank, etc. are all new. 3/8" stuff all the way, as factory. The pump "looks" new, but I can't personally verify that.

Come to think of it, though, one thing I haven't tried is bigger jets on the primary side of the Holley. When I changed out the cam from the big purpleshaft cam that wiped lobes and went with the Comp that's pretty close to stock specs, I put the original 72 jets back in the Holley, having had success with them in similar conditions in the past.
I still have a set of 75's I could toss in there. Would primary jets contribute to this particular problem?

 

[69Runner]

The primaries would play a minor role at WOT compared to the power valve and secondaries, which should be dumping more fuel. It sounds like the primaries are doing a pretty darn good job all the way to 4500! But if you have some richer jets then it might tell you something. While you are in there take a quick look at the power valve rating, it's probably a 65. Below it is a restrictor. Also with your carb the secondary jets might or might not be adjustable, but if its lean at WOT then the power valve restrictor and secondary jetting are places to look.

And just be careful about too many high rpm lean blasts which can melt pistons. It sounds like you are really getting close to figuring this out. If ignition/timing is ruled out as the cause then fuel delivery, as mentioned by several of us, is the likely culprit.

And sorry if I sound like Captain obvious but have you checked the floats? I'm just wondering why your first gear run mentioned above was good up to 5000 while 2nd and 3rd only to 4500. What if you started off in second gear, would it make it to 5000 the first time? Again it's a simple thing to try, raise the floats a bit to see if you are on the edge of fuel delivery at high rpm.

 

[moparedtn]

The primaries would play a minor role at WOT compared to the power valve and secondaries, which should be dumping more fuel. It sounds like the primaries are doing a pretty darn good job all the way to 4500! But if you have some richer jets then it might tell you something. While you are in there take a quick look at the power valve rating, it's probably a 65. Below it is a restrictor. Also with your carb the secondary jets might or might not be adjustable, but if its lean at WOT then the power valve restrictor and secondary jetting are places to look.

And just be careful about too many high rpm lean blasts which can melt pistons. It sounds like you are really getting close. If timing is ruled out as the cause then fuel delivery, as mentioned by several of us, is the likely culprit.

Totally digging what you're saying here.
I mentioned the 75's because they helped with the old cam a bunch in a similar condition - yep, same motor with a purpleshaft (509) did the same thing at about the same RPM's and the 75's helped some with that. Of course, I had a different power valve in it then, since the vacuum was so much lower with the purpleshaft.

This is all ticking me off because in a couple of former Mopars ('68 Super Bees, both with stock 440's in them) the Holley 3310 right out of the box worked GREAT, along with the Mopar electronic ignition conversion kits.
Figured I was in the same ballpark with this car, so I ordered the exact same carb.

When I put the Comp Cam 270 in it, vacuum was really good again as expected, so I returned the stock 65 power valve and 72 primary jets back in the carb.
It won't hurt a thing to pop the 75's back in there, but the car definitely didn't like the 35 power valve when I swapped cams.
The secondaries aren't adjustable, of course, but I suppose I could swap the secondary metering block out for one with more flow?

Tell me more about the power valve restrictor too. Easy mod? Any harm in trying it?
Thanks!

PS - Guess it shouldn't matter, but in neutral sitting still, the engine happily revs over 5000RPMs, so I'm assuming there's nothing internally in the engine holding this rascal back?

 

[69Runner]

At the rated vacuum value on the power valve it opens, dumping fuel via the restrictor orifice which is under the power valve. Simply unscrew the PV and you should see one or 2 orifices. Like your secondaries they might or might not be adjustable, but there are ways of modifying if you are feeling dangerous.

- - - Updated - - -

The secondaries aren't adjustable, of course, but I suppose I could swap the secondary metering block out for one with more flow?

Tell me more about the power valve restrictor too. Easy mod? Any harm in trying it?
Thanks!

PS - Guess it shouldn't matter, but in neutral sitting still, the engine happily revs over 5000RPMs, so I'm assuming there's nothing internally in the engine holding this rascal back?

Yes I would think the secondary block could be swapped out. About the restrictor, I never had to go so far as to modify it, but doing a google search you will easily find where others have drilled+tapped them out to 6-32 or 8-32 thread then used drilled plugs to tailor orifices to their liking. Metal shavings would be my biggest concern, keep everything clean.

And that last part about 5000 rpm in neutral, very interesting. Fuel bowls are full and pump is keeping up but on the street something changes. It's telling us something. Good luck!

 

[moparedtn]

Oh no, I won't be drilling out any orifices.
I keep going back to "same motor, same ignition, same carb as before - what the heck?"
Whatever is wrong, it can't be that much. Just got to figure it out is all.

This does get me thinking of beyond the jets on the carb, though. That Holley, fresh out of the box, is supposed to have 72 primaries in it. When I tore into it, it had 70's for some reason...so now I'm wondering if it has the right secondary metering plate in it, too.

Does anyone out there have the same carb sitting on a relatively stock 440? If so, what jets and plate are in it?
What power valve?

 

[moparedtn]

Well shoot, seems all the 3310 Holleys have the same secondary metering plate, so that's not it.
I've sent off a tech request to Holley. Maybe they can come up with something, since it's gotten real quiet here...

 

[bigmanjbmopar]

I had an edelbrock 800 AFB carb once had a weird stumble at a certain RPM, no matter how many combinations of rods and springs / jets I tried which was every possibility it just wouldn't fix the issue, a new QFT 850 was good, I use a QFT 780 vac sec now for just cruising but have the 850 for fun time point is maybe it's just a bad carb out of the box? I still think its electrical though