vacuum secondaries won't open

[nick71RS]

holley 3310 on perf rpm air-gap
406 10.2:1
solid roller 240/248 @ 0.050
zz430 (fastburn) heads, right springs for cam
5.7 rods, HEI/MSD module
long tube headers/H-pipe/dual exh
4spd muncie
etc.

problem is the vac secondaries NEVER open. I was suspicious so used the paperclip trick (paperclip on the little rod from the vacuum diaphragm) which would easily be pushed down the rod as they open.. it never moves.

I put the lightest spring in it, still never opened.

took the vac. secondary pot off, put vacuum on passage to carb body and the passage to both the primary and secondary side is clear and flows air.

put vacuum to the vac diaphragm assembly, it pulled the rod in just like it's supposed to and held vacuum, pull on the rod was very strong.

put the vac diaphragm assembly back onto the carb with a new cork gasket for the vacuum passage, and the vac secondaries still don't open AT ALL.

the linkage from the primary side to the secondary side is in good shape, hasn't been hacked or modified or anythying. Ssecondaries can be manually opened if the primary side is held open. carb gets full throttle from pedal, so throttle cable is ok.

check ball is in the vac secondary pod where it belongs per holley info.

test method is 2nd gear to at least 5500rpm due to inability to maintain any traction in 1st.

otherwise, motor runs great, sounds great, awesome torque, just quits pulling any harder around 3500 due to (presumed) lack of airflow. it doesn't seem to build any more horsepower once past around 3000 or so because of the carb. i'm sure the engine needs more air - the response to the throttle is VERY crisp, even the slightest amount of letting off and you feel a power loss, so it's not like the motor is lame and doesn't need anymore air. it never bogs or stumbles or acts like it has any kind of fuel delivery problem.

help?

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'71 RS 406 4spd


[This message has been edited by nick71RS (edited January 29, 2005).]

[Jim Mac]

I never heard of the paper clip trick but how about putting a small machine screw and nut in the secondary linkage to make it a mechanical secondary, I know the 3310 doesn't have an accelarator pump on the secondary but for this test just ease into the throttle till you get above where you were'nt making power and see if it changes. if you aren't finding a difference I'd check the advance on your HEI. Jim

[Mwilson]

with the canister off can you push the rod in then plug the hole with your finger let go of the rod and it stays in?

[Air_Adam]

Heres a better idea... istead of trying to convert it to mechanical linkage for a simple test, disconnect the linkage to the secondaries and see how it acts. If its the same, then your secondaries really aren't opening.

[Mwilson]

<font face="Arial,Verdana" size="2">Originally posted by Air_Adam:
Heres a better idea... istead of trying to convert it to mechanical linkage for a simple test, disconnect the linkage to the secondaries and see how it acts. If its the same, then your secondaries really aren't opening.</font>

make sure to leave the linkage rod on though take the c clip off at the canister side only because if they do open and that linkage rods off they wont close ! I lost a brand new motor and gained 10 stitches when i removewd the linkage rod in my shop and the car was idling i reved it to 2000 and bumped th secondaries on accident with my hand the motor sucked em open and went stait to 7500 until it blew! a belt flew off in peices and split my head open i was to dazed to shut it off in time

[nick71RS]

See picture for "paper clip trick". it's in one of holley's tech guides on their web site. the paper clip moves easily on the rod with the slightest bit of pressure. If the rod is pulled up into the diaphragm housing, the paperclip gets pushed down the rod. so, how far down the rod the paperclip is, is how far they opened. my paperclip doesn't move.

Timing is 20* initial (as demanded by the cam for low-rpm drivability) and 34* total (fastburn heads work best at 32-34*). mechanical doesn't start coming in to around 1300rpm and is all in @ 3300. all verified and re-verified with timing light after custom distributor work/curve work. idles at 1000. front carb blades have small hole drilled in each to acheive proper idle with transfer slots covered the right amount.

I didn't specifically check the vac diaphraghm by pushing the rod in and holding thumb over the hole, but i did check it with a vacuum pump. it held any level of vacuum and any rod postion (partial or full vacuum) for an indefinate period of time. If this isn't a valid test I can certainly pull it off and try the thumb method..

I am 100% positive the secondaries aren't opening. have played with the carb extensively and theres no way the secondaries can open without moving the paperclip, and there's no way they can close and move the clip back up against the bottom of the vac pod/canister. And the paperclip certainly isn't tight enough to prevent it from moving - it took very little vacuum to start pulling the rod in and move the paperclip with the pod off the carb. heck, with vacuum on the diaphragm i coudn't even pull the rod out by hand, it seems to have good pull under vacuum.



[This message has been edited by nick71RS (edited January 29, 2005).]

[This message has been edited by nick71RS (edited January 29, 2005).]

[nick71RS]

better picture

[Rick WI]

You used the yellow spring?

[Jim Mac]

I've never seen that paper clip trick I learned something new, thanks! Jim

[Mwilson]

man im stumped doesn't make sense!
i bought a new holley one time and the vac passage wasn't drilled but you've already verified that too?

[Jim Mac]

just throwing out ideas but could the secondary throttle stop screw backed out a bit and the secondary blades are just closed too much?

[nick71RS]

i forget the colors - but I am using the lightest (weakest) spring in my quick change kit. it's the one for the fastest opening in lightweight vehicles.

as far as I know, there are only two places where the vacuum passages are supposed to go to - one small hole in the primary side, and one small hole in the secondary side. it does indeed seem to be drilled to both, as applying vacuum to the carb body where the vac diaphraghm port is, sucks air through two tiny little holes towards the top of the two barrels closest to the vac diaphraghm.

regarding secondary stop screw.. hmm, interesting thought. will the secondaries not open if the stop screw is too low/they are shut "too far" to begin with? i'll have to check and see if they are open roughly the same amount as the primary side.

[onovakind67]

otherwise, motor runs great, sounds great, awesome torque, just quits pulling any harder around 3500 due to (presumed) lack of airflow.

Which came first - the lack of rpm or the secondaries not opening?
The primaries on a 750 Holley are identical to a 500 cfm 2-bbl, and I know that a 2-bbl will run well in excess of 5000 rpm on a 406. My 406 has a Q-jet with a removeable linkage so I can operate it on just the primaries. The primaries of a Q-jet are considerably smaller than a Holley, yet my car will run 13.20 @ 98 mph on just the primaries, with a 1.85 60'.
On a Holley it takes a certain amount of air flow to open the secondaries, and even more to keep them open. Are you sure there isn't a problem with the fuel delivery in the secondaries?

[nick71RS]

I may not have worded my post real well, i'll try to clarify if it helps.

The motor will pull to 6000+ with no problem. From about 2000-3000, you feel the increase in "pull" as the cam starts to get into it's powerband, and as it goes through the 3's it's still pulling harder, but the "increase" gets less and less and by 4000 it's gone. It's still pulling hard all the way to 6, but without the continued "increasing" you'd expect out of a cam that's meant to peak past 5000rpm (split duration solid roller, 240/248 @ 0.050, 110* LSA, 0.543"/0.561" lift).

The secondary fuel bowl has fuel in it and at the proper level. since the secondaries never open to start with (paperclip evidence), I don't really know if their is a fuel delivery problem on the secondary side, but until I can get them to open I won't know. There is definately no fuel delivery problem on the primary side.

Even at 4500+, if I lift from the gas even slightly, there is a noticable reduction in power. So it's using every bit of air the primary side is providing.

I've made dozens and dozens of passes in my 91 z28 (6spd/TPI 350 basically stock), which traps 95-96mph in the 1/4, and this 406 is easily more powerful than that. easily. So I'm pretty confident that the motor can use the airflow (the power is there, the displacement is there, and the rpm is there..it should flow the air).

The carb is a swap meet find, and was subsequently rebuilt. Is there anything that the previous owner could have done to it that I could look for?

<font face="Arial,Verdana" size="2">Originally posted by onovakind67:
Which came first - the lack of rpm or the secondaries not opening?
The primaries on a 750 Holley are identical to a 500 cfm 2-bbl, and I know that a 2-bbl will run well in excess of 5000 rpm on a 406. My 406 has a Q-jet with a removeable linkage so I can operate it on just the primaries. The primaries of a Q-jet are considerably smaller than a Holley, yet my car will run 13.20 @ 98 mph on just the primaries, with a 1.85 60'.
On a Holley it takes a certain amount of air flow to open the secondaries, and even more to keep them open. Are you sure there isn't a problem with the fuel delivery in the secondaries? [/b]</font>

[onovakind67]

Soes it have the little cork gasket between the throttle body and the VA mechanism?