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Hi There, I finally got my 69 427 convertible running a little better after cleaning out old fuel and replacing the fuel pump. The car starts and runs now but next on my list is to determine if the outside carbs are actually working. (they may actually be working but I don't know how to tell unless I am driving which I can't at this stage until is is licensed. How can I check this, when I hit the accelerator hard as I look into the carbs, neither the front now the back carb valves are opening up.
Some of my inexperienced ideas,,,,
1. manifold vacuum no good? 2. engine needs to be driving? 3. carbs plugged up?
In very basic terms, does anyone have some basic troubleshooting ideas for a novice. Most of the threads are way beyond me as I am new to all this. (they get into jetting diameter etc etc) I was thinking of starting with the vacuum and making sure I have enough to actually open the valves. (I realize vacuum opens them and they are mechanically closed) I did take the float bowls out and know they both actually do have fuel as I can see it though the side screws on the sides of each bowl. A few basic troubleshooting ideas would be much appreciated.
Thanks, Pete
The 1st and 3rd carbs can be tested buy manually advancing each ones carb linkage while engine is running in neutral gear to see if they are working.
Simply remove the hold down clip that connects the linkage rods from each of them to the center carb. the engine speed will increase.
These carbs do also have a small fixed idle circuit so that fresh fuel is always being sent to their bowls. There are no adjustments to these carbs. The middle carb has all of the adjustments. Think of the tri-power setup as a "6 barrel carb".
They usually won't even start to open until like 4k RPMs as they are operated by the Venturi vacuum at high RPM's.
You can check each vacuum assembly with a mighty vac vacuum pump to see if the diaphragms in each of the 2 carbs are still good.
The only way to confirm if they are working at all is to accelerate (actually driving the car) and get above 4500Rpm and you will feel the pull of they are working.
Be careful, when mine pull in its almost scary!
Check out one of my old threads regarding the 3x2 setup; https://www.corvetteforum.com/forums...errerid=184680
Thanks Babbah,
I will do that tomorrow to at least see it the RPMs increase by manually advancing the throttle linkage on each one. I do have a mighty vac so will also test and then hold on to my hat when I get it out for a test run. I hadn't realized it was nearly 4000RPM when they cut in so you have probably answered my question.
Much appreciated, Pete
Hi Pete
The mighty vac is to Bench Test the vacuum diagram units.
disconnect the rods to each end carb and apply vacuum to rah one where the hose connects.
they should each hold and pull the carb linkage open on each one.
From: Graceland in a Not Correctly Restored Stingray
Assuming the primary is properly tuned, the diaphragms are good and linkage is correctly adjusted, get yourself two vacuum secondary spring kits (Holley # 20-13), and install the next weakest set until it bogs at WOT under load, then reinstall the last set that didn't bog. Done.
Hi Pete
The mighty vac is to Bench Test the vacuum diagram units.
disconnect the rods to each end carb and apply vacuum to rah one where the hose connects.
they should each hold and pull the carb linkage open on each one.
Hey Babbah,
Thanks for the tips, good news this AM, as you mentioned, I pulled off each rod clip and at idle moved accelerator linkage of the front then the rear carb by hand and the car instantly increased idle speed considerably.
I then with the engine off, kept the throttle linkage wide open and sucked on each vacuum hose of front and rear carb and butterfly valves opened.
I think these are good signs!?!
So I will try the mighty vac as you say to see if I get the same result and see if they open and stay open???
Assuming the primary is properly tuned, the diaphragms are good and linkage is correctly adjusted, get yourself two vacuum secondary spring kits (Holley # 20-13), and install the next weakest set until it bogs at WOT under load, then reinstall the last set that didn't bog. Done.
Are these the spring kits inside the vacuum secondary diaphragms?
Also, when I take it out for a spin what is WOT
From: Graceland in a Not Correctly Restored Stingray
Originally Posted by VancouverL71
Are these the spring kits inside the vacuum secondary diaphragms?
Also, when I take it out for a spin what is WOT
Sorry, relative newbie
Pete
No apologies necessary.
Yes, the ones in the secondary carb diaphragm pots.
And, as already answered, Wide Open Throttle. Very important it is to determine the bog point during WOT under load as opposed to while sitting static in the garage.
Happy motoring!
Tripower Tuning
