69 L68 tri power linkage adjustment

[Douglas C.]

In fine tuning my 69 L68 I refer to a 1969 Chevrolet Motor manual, and there it states to place the front carb rod in the throttle lever hole "dead on", and the rear rod one turn in on that throttle lever.

So, is that correct, maybe correct for factory settings, or is there another method that contributes to better idle quality, etc.?

Thanks,

Doug

[Wayne M.]

Re: 69 L68 tri power linkage adjustment

Doug -- sounds like you've got the basics. But there's a little more detail in the 1967 issue of Chevrolet Service News . Apparently this procedure "does not appear in either the 1967 or 1968 Service Manual". I assume this will apply to the 1969 MY as well.

(begin quote)
1. Start engine and allow to warm up (choke in fully open position).
2. Disconnect closing rod ends from each secondary carb. Set idle to spec. Turn off engine
3. With clevis pin bottomed in primary carburetor throttle slot, adjust rear secondary carb closing rod so that it falls short of entering the rear secondary throttle lever hole by half a rod diameter. Install rod and secure with special clip.
4. Next, adjust forward secondary carb closing rod so that it just enters the forward secondary throttle lever hole. Install rod and secure with special clip.

When the adjustment is completed, the clevis pin will be at a point just above the bottom of the primary throttle slot, thus insuring that there is freedom in the linkage and a positive secondary throttle closure. (end quote)

[Douglas C.]

Re: 69 L68 tri power linkage adjustment

Doug -- sounds like you've got the basics. But there's a little more detail in the 1967 issue of Chevrolet Service News . Apparently this procedure "does not appear in either the 1967 or 1968 Service Manual". I assume this will apply to the 1969 MY as well.

(begin quote)
1. Start engine and allow to warm up (choke in fully open position).
2. Disconnect closing rod ends from each secondary carb. Set idle to spec. Turn off engine
3. With clevis pin bottomed in primary carburetor throttle slot, adjust rear secondary carb closing rod so that it falls short of entering the rear secondary throttle lever hole by half a rod diameter. Install rod and secure with special clip.
4. Next, adjust forward secondary carb closing rod so that it just enters the forward secondary throttle lever hole. Install rod and secure with special clip.

When the adjustment is completed, the clevis pin will be at a point just above the bottom of the primary throttle slot, thus insuring that there is freedom in the linkage and a positive secondary throttle closure. (end quote)

Thanks Wayne. I also found the above in my 69 AIM. My thought / question is on the rear secondary carb, as adjusting the rod one half diameter short of the lever and once hooked up would I think crack the throttle plate slightly open. So, was this something that related to the stock emissions function, and maybe in the real world where we make small changes to improve idle, etc., like manifold vacuum instead of ported, has someone found having the secondary throttle plate completly closed to be a better?

Tks. Doug

[Wayne M.]

Re: 69 L68 tri power linkage adjustment

Doug -- if the clevis is held at the bottom of the slot, when you go to insert the rear [half dia. short] rod into the lever, (if you're still holding the clevis at the bottom slot) this will crack open the rear throttle, but when you release, the throttle plates will close (under diaphragm spring force) and the clevis will rise in the center carb slot to the amount required (to assure linkage freedom).

[Douglas C.]

Re: 69 L68 tri power linkage adjustment

Doug -- if the clevis is held at the bottom of the slot, when you go to insert the rear [half dia. short] rod into the lever, (if you're still holding the clevis at the bottom slot) this will crack open the rear throttle, but when you release, the throttle plates will close (under diaphragm spring force) and the clevis will rise in the center carb slot to the amount required (to assure linkage freedom).

O/k, did the above. Rear carb I think may still be slightly open, at idle if I push lightly on the rear carb throttle lever I can speed up or slow down the rpm's. So, I will check the adjustment again. Right now it will idle around 950 rpm's for a good amount of time, then stumble up and down, 800 rpm's to 1200 rpm's, then settle back down. Engine runs cool, no pinging, but stumbles off idle. I did just install a B26 vac. advance cannister, and that seems fine.

But, tri power gurus tell me this. While at idle if I place my hand over the fromt carb not much of any effect on idle, and I feel a slight amount of vacuum, very little. Now, when I put my hand over the rear carb it sucked my palm flat, got a blast of fuel on my palm and the engine just about stalled.

Thanks. Doug

[Clem Z.]

Re: 69 L68 tri power linkage adjustment

the linkage on 3X2 carb set up is to make sure the end carbs close when the center carb throttle closes. they are opened by vacuum. it acts the same as the little link between the primary and secondary used on 4 barrel carbs