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I've never been happy with my tri-power's throttle response even after re-curving the distributor and setting the timing as described in Lars' article (which, BTW, made a huge improvement in overall performance). The carbs are brand new units purchased in the 1980s by the car's PO so I don't think they're necessarily set up for a 427. I'd like to know if there's any improvement to be had by messing around with accelerator pump cams and nozzles. Currently installed are a red cam and a #21 nozzle.
Before changing anything have you checked if the pump arm spring is correctly adjusted?
With the engine off, hold the throttle wide open, push down on the accelerator pump arm and you should be able to insert a .015 feeler gauge between the arm and the head of the screw attached to the pump linkage.
If you feel it is too tight or too loose turn the nut located on the top of the screw on the arm to adjust the clearance.
Before changing anything have you checked if the pump arm spring is correctly adjusted?
With the engine off, hold the throttle wide open, push down on the accelerator pump arm and you should be able to insert a .015 feeler gauge between the arm and the head of the screw attached to the pump linkage.
If you feel it is too tight or too loose turn the nut located on the top of the screw on the arm to adjust the clearance.
....and ZERO clearance in the linkage at idle is critical. You need .015" additional travel available at wide open throttle but no slack at rest. Slack results in a backfire, bog or hicup as you push down on the gas.
MelWff - I set the pump lever adjustment just before the carbs were installed. That was 2-1/2 years and ~600 miles ago so I'll check that again. JBrooke825 - In looking online at a few of throttle position vs. cam lift graphs, this one (attached) shows the red and pink cams (in hole 1, the broad pink line) profiles are very similar until around 70% of WOT.
Have you ever tested the front and rear carbs to see if they fully open by placing a paper clip on the vacuum diaphragm rod and seeing if it moves after a WOT drive?
Can you describe the Throttle Response? I can say that my 560ish HP 460ci (Tri-power, 4spd, 4:11's, 295/50-15's) is not super impressive from a dead stop (the center Carb is 3xx CFM) but the driving Throttle Response is very snappy. The Secondaries are ported to the center Carb and it takes a fair amount of time to reach enough engine load for them to open (I used a Borescope to video mine opening under driving conditions and also filmed during Engine and Chassis Dyno testing). There are a lot of folks on the forum with tri-powers, I'm sure they'll chime in. I've had several 1/4 mile runs on this setup, it ain't ideal for Drag Strip but I still trap around 119mph so they work.
Also, the size of the Squirter can sometimes be too big (I don't know a specific for your application) for a 30cc Pump. You want the stream to cover the length of time the Bog exists and sometimes a smaller Squirter will provide enough volume for a longer time. There are plenty of good tips on the WEB for Pump Shot tuning, if you can't find any let me know, I can send you some PDF's if needed.
It doesn't bog down or kick back when you "mash" the throttle it's just initially slow to respond before it comes on strong to ~4k RPM, goes flat for just a second, and then surges a second time to ~6k+ RPM. It feels like the secondaries are opening (1st surge) then gets up on the cam (or maybe vice versa). I should mention that it's not a stock L71. It's a .030 over 427 (512 block) with open chamber, 118cc (990) heads that lower the CR to ~10:1 and it's running this Engle flat tappet solid lift cam:
Have you checked to see if the accelerator pump 'squirters' are providing streams of fuel to the carb[s]? Remove air cleaner, hold upper choke flap open and look down into the carb venturi, then exercise throttle. There should be a solid stream of fuel being dispensed into each bore of the center carb. If you get no fuel being dispensed, or if you get a weak/spotty stream of fuel, the accelerator pump seal is likely worn out or has fallen off the pump rod. Not unusual for a carb with significant miles on it.
You need to remove the carb to repair it. If you decide to do that, just give the carb a good cleaning and a new rebuild kit. It MUST have an accelerator pump seal that can tolerate ethanol laced fuels.
Get an AFR guage installed, I use innovative motorsports LM-1. I was running a lunati 402A3 cam almost identical to what you are running. Hit hard 1.64 60ft. launching from a 1300 rpm idle on the brakes. You need to know what is going on , and not guessing. Good luck.
Tri-power Accelerator Pump Set Up Question
