I was fiddling with the tune on the 70 GS today and finally addressed a problem I was having. It was one of those, "I gotta look at that one of these days" problems that I was reminded about every time I drove the car. And usually forgot about. The issue was that the secondaries on the Q-Jet were opening but not as fast as I liked even with the air flaps adjusted on the loose side. The pull off was not unloading fast enough. I took it off and examioned the restrictor hole. It was approx .015. I drilled it out to .025. What a difference. It was so much faster I actually had to tighten up on the air flaps as they were now opening too fast. I really have that car tuned to the razors edge now. I should take a look at the secondary rods and hangar now:idea2: Amazing what a .010 change made, Naturally, its an aftermarket pull off. I you wonder what the factory restrictor size was?
Glad it worked. I have my Q-Jet running pretty smoothly now, maybe I'll tinker with the restrictor opening on the pull-off, too. Though I don't race the thing, it'd be nice to have the pull-off unloading faster. My secondary air valves are also on loose tension, but don't seem to open unless I really nail the throttle hard.
Glad you got it worked out. That was the latest issue I solved on mine, however my aftermarket pulloff was to large and I had to restrict it.
If it turns out that the restriction in the pull-off is too large, one solution is to install one of these valves in line between the pull-off and the carb vacuum nipple. It has a large 3/32" opening, so would never be used in the full open position, but will allow adjustments at the track without the need to modify pull-off restrictions. Cliff Ruggles stocks these, they may also be available from Greg Gessler and others. Jim J.
We have adjustable pull-offs for those models. Something I came up with a while back so the tuner would have full control over the opening rate of the secondaries. They are easy to adjust and do not need to be removed.....Cliff http://www.cliffshighperformance.com/parts.html
Factory settings were really small from what Ive seen. Like .008-.010 small. anywhere from 2.5-4s release time yours must be releasing in like .5s with that big a hole?
We started making the adjustable pull-offs for the Pure Stock and FAST Class racers. They need the ability to control the power applied to the tires on the launch due to limited traction with bias ply tires. The problem with drilling the pull-offs is that they are very sensitive to the slightest change in the hole diameter. Going past about .018" and the pull-off releases almost instantly. This produces a stumble/hesitation/bog for most set-ups. The other problem associated with this topic, is that folks street test the opening rate "by the seat of their pants". This has them thinking that a huge "lunge" or noticable "kick" when the secondaries open improves performance, which in most cases it does not. When dialed in correctly, the transition should be "seamless" and smooth. This will produce the best 60' times and ET at the track. Here is an example, not how smooth the car leaves and how smooth the power comes on. 60' time for that run was around 1.61, on DOT tires with 8" tread. http://www.youtube.com/watch?v=6zVdoLR-VzM&context=C3e4a3f3ADOEgsToPDskLN6xs9w6YNF-3XYco3MFqf ....Cliff
If I went too large in drilling it out to .025, wouldnt making the tension on the secondary air flaps compensate for that somewhat? I did notice a slight hesitation or stumbler after the change prior to adjusting the air flaps. As I kept adjusting the air flaps, the hesitation seemed to go away.o No: The car definitely had more power as I had trouble controlling the wheel spin in first gear after the adjustments. This could be the holeshot edge I need to gain that 1/2 car I lost by against my friends worked 454 Camino
If you have to wind the spring past apprx 1 full turn, slow the pull-off down some. Also keep in mind that EVERYTHING changes when you find good traction. If the tires spin, the engine revs right through "transition" and into the good power. The entire tune will change if you install good tires and get to the track, vs spinning the tires HARD on the street. What I find most interesting as it relates to this topic, is that "seat of the pants" tuning can really lie to you. The smoothest launch and no noticable transition at the track produces the best timeslips. Any time I speed things up so I "feel" the secondaries "kick-in", I'm rewarded with worse 60' times and slower ET's. What happens with "seat of the pants" tuning, is that we interpret a noticable change in power as an improvement. This is basically going from not making good power to a nice "rush" in power. That "rush" fools us into thinking we are going the right direction more times than not. To this day it simply amazes me how the runs I consider the most "boring", just pulls hard from the instant I load the engine till I shift it, makes for better runs than when I loosen things up and dump all the carb on the motor almost all at once......Cliff
I have this adjustable pulloff on my 350. I'm trying to get it right. I finally put on new spark plugs because I thought my Bosch platinum plugs were giving my engine fits. I have that adjuster now to where I really don't know where it is at. Where should I start? Screw turned all the way clockwise? All the way counter clockwise? Also when checking the 2 seconds it should take for it to release when pushed by hand, is that engine idling or off? Thanks
Jason. I would recommend that you start with the valve just slightly open. Turn clockwise until it is closed, then slightly counter-clockwise. The engine should be off when checking the pulloff release time. The pulloffs are designed to release as vacuum drops off. At idle the pulloff will be under full vacuum.
Just an FYI guys ...I have been "experimenting with small orifice restrictions and nylon plugs in the vacuum line for these plastic primary pulloffs. I have found that an ~.008" orifice gets about a 4 sec release time. ~.011" gets about 2 sec release ~.013 gets about 1 sec the restrictors are a pain to make. The holes clog easily - make sure the drill job is clean. The tiny drill bits are like needles - will stick right in you. ask how i know Also they break really easily - WEAR EYE PROTECTION FWIW
Cliff Ruggles markets an adjustable valve that goes in the vacuum line of the primary pull off. It comes with a fully drilled out primary pull off. You can adjust release time with it very effectively.
The adjustable units are much more effective than any sort of drilling on the plastic orifice. It's actually better to make a very small tapered reamer from an old drill bit, than to try to drill them to larger sizes to adjust the opening rate. I made a tapered reamer years ago to do this, then came up with our adjustable units, which are light years ahead of any sort of drilling the hole larger set-ups. At least you can go back and make them slower if you drill too large a hole in one!......Cliff
Cliff, Couldn't find the adjustable pulloff on your website. What years quadrajets are they good for?
I was also searching for that adjustable pull-off on Cliff's site and no resulto No:... Cliff could You add it to your catalogs?
