Phantom fluttering

[custom10nut]

I took the truck out for a ride to my favorite vintage car lot today. While driving at cruising speed, I'm getting a "fluttering" feel. It's not really a hesitation, as the tach is staying at a steady rpm. When Iaccelerate the flutter goes away until a few seconds after I level off the speed.
These are what I think are the possible causes:
Ignition: I am using a Mallory electronic conversion in place of points.
Carburetor: I'm running a new Edelbrock 1406 that has been tuned
Transmission: about 5000 miles ago, I had it "rebuilt", but the guy only put a new clutch pack in, without replcing the front pump, he told me the pump and torque converter were "fine". Now I'm beginning to wonder
This phantom is really starting to frustrate me.
Anyone out there have any suggestions?

[garyd1961]

Vacuum leak?

[custom10nut]

It could be. I dug my Vacuume gauge out tonight to test for that tomorrow. Would that cause my issue at cruise and not acceleration?

[jocko]

By the title, I was thinking of something my old dog does sometimes and then wags his tail and moves from where he's been lying to somewhere else in the room.

Gotta ask for a bit more description please. Did this start after the trans rebuild?
Does it always happen at the same speed? Or at the same RPM?
Could it be:
U-joint?
D/S balance (perhaps messed up someone how when trans rebuilt)?
Could the seal between the fender and door be flapping loose at speed?
Trans modulator?
Vac leak also a good diagnosis by gary.

[1969c10joe]

ok more fun need more info but my gut feeling is you have a lean surge. when was carb tuned? why? can you tell me your jet size, metering rod, and color of step upsprings?

[1969c10joe]

your vacuum at idle and the altitude please 1406 runs lean usually out of the box. Its easilytuned though.

[1969c10joe]

I have an edelbrock manual their tech line is pretty good too

[casper71]

I'm having the same issue. I have a 402 with the points and a Rochester 4bl. Thinking it may be vacuum advance in distributor as it diesels some times and is hard to start at times. Post up what you find. Thanks

[1969c10joe]

the 1406 is calibrated for fuel economy at sea level where i live they all run lean from the box I feel you have a different problem

[geezer#99]

Originally Posted by casper71

I'm having the same issue. I have a 402 with the points and a Rochester 4bl. Thinking it may be vacuum advance in distributor as it diesels some times and is hard to start at times. Post up what you find. Thanks

Likely yours and the op's problem is lack of a good timing curve for your set up.

[custom10nut]

I just came in from the garage, to look up which vacuum port is correct for the vacuum advance. As you look at the carb, should it be on the constant (right side), or the timed (left side) port? I used to run it on the right, but I had an old mechanic tell me it should be on the left. Tomorrow I'm going to switch it back, and see if that fixes the issue.
According to the manual the right side is for non-emissions engines and the left is for emissions controlled.
I run an original 1970 SB 350 (non-emission?)

[1969c10joe]

oh boy Ive used both i prefer more timing at idle it runs better for my engine man this is like tasted great more filling debate

[1969c10joe]

but that only changes timing until the other port sees vacuum then there is no difference

[1969c10joe]

so they are the same except at idle hope im not offending you

[1969c10joe]

almost every time i took my truck to a shop the mechanic would switch it over the next guy would switch it back

[custom10nut]

Originally Posted by 1969c10joe

ok more fun need more info but my gut feeling is you have a lean surge. when was carb tuned? why? can you tell me your jet size, metering rod, and color of step upsprings?

I'm running the jets that the carb came with, a smaller metering rod, and the silver springs (8Hg). Since I put this setup in, the "off the line" hesitation is almost gone but the flutter at speed is still there. I turn up the pressure on my regulator, which was kinda low, so maybe that will help.
The reason for the regulator is that through research, I sumized that the pressure off my fuel pump may be a little too high (above 6psi).

[1969c10joe]

your smart to add regulator but i dont feel you need more pressure the carb came with yellow springs so im assuming youare pulling a lot of vacuum true?

[1969c10joe]

when cruising if your vacuum is at the point where your rods aregoing between power and cruise mode change springs so rod stages at lower vacuum

[1969c10joe]

check your vacuum advance use timing light vacuum pump and and vacuum gauge

[1969c10joe]

if everything checks out ok and this fluttering is not a new development try a .100 jet Ihumbly suggest installing vacuum gauge incab

[1969c10joe]

yes check for vacuum leaks and if you change jet you will have to change rod bet you already knew that good luck

[1969c10joe]

before youchange jet you could try rod 1449 70x37 but im guessing you already have

[custom10nut]

Lower vacuum? So should I try the pink or yellow? I'm thinking that the stronger the spring the quicker the rod comes out of the jet. Am I mistaken? I have a lot of vacuum on the engine, as it has very few miles since I did the complete rebuild.
I'm all ears. If changing to the 4 or 6 Hg spring will fix it, awesome.

[1969c10joe]

what is your vacuum at idle? what is your vacuum at the speed it flutters? never heard flutters before jk

[1969c10joe]

you choose your springs according to vacuum and driving habits