NB141FD

Car starts, idles and runs great until I 'get on it' then it seems to bog and stumble. Timing is good, fuel filters (carb and fuel line) all checked and good, floats adjusted right, power valve (6.5) good. Suspected secondaries so I tied a twisty wire to top of secondary rod and went out and drove it hard (several times). Wire did not move verifying that secondaries never opened. Performed the following:

1-took diaphragm housing apart and verified that diaphragm is in good condition by pulling rod up and putting finger over opening; rod didn't move until finger removed. Cork gasket is in good condition.

2-Bought Holley secondary spring kit and tried every single spring including the lightest (white) with no change in secondary twisty test.

3-With engine off opened throttle to WOT and was able to operate secondaries with lever (driver's side). Secondaries move freely and seem to go through entire range of motion with no sticking or problems.

4-blew air throughout the carb and it appears that the passage to the secondary housing is clear. Unfortunately, I couldn't find the opening in the primary bowl that triggers the secondaries to open.

Would love to find the opening (hole) in the primary bowl that triggers secondaries to open so I could blow air across it to see if I can get secondaries to move. I know that on a lot of carbs (http://www.chevyhiperformance.com/te...ion/index.html) this opening is located on the bottom of bowl, but not on my Street Avenger. Anybody know where this opening is located on a 570SA?

If anyone has any advice on additional troubleshooting ideas I'm more than happy to give them a shot. TIA

Tony

2+2GT

I like to stick a paper clip on the secondary rod. If it gets pushed down, they opened.

Stumbling and bogging are NOT symptoms of shut secondaries. The engine might exhibit poor high rpm power, but would run smoothly. You have another problem. Once the engine is not bogging, the secondaries will open.

Have you ever had the advance curves of the distributor set? I'll bet you $1 that it's off. Statistically, it's probably way off.

boogerschnot

Have you checked the accelerator pump? Does the car pick up after its initial stumble and start running right? Makes me think that the pump shot is off.. and how old is your fuel pump? Could be starving the engine at higher rpms.

Hwyman

Most of the time when you "get on it" and it stumbles, it's from lack of fuel. When you floor it and open the butterflies, your vacuum drops to almost zero. With no vacuum, no fuel is sucked out of the tubes in to the verturi. The accelerator pump is supposed to give a shot of fuel at this point to compensate until air starts flowing again, and drawing fuel. Obviously, there would also be no vacuum for vacuum secondaries.

Try accelerating without flooring it until you are at a decent rpm and then ease over into the secondaries. If they now open, your problem is with the accelerator pump portion of the carb. There are several fixes for that, depending on what the problem is.

NB141FD

2+2GT- I used a wire tied around the vacuum plunger rod to verify that the secondaries were not opening, pretty much the same as using a paperclip. I also am beginning to suspect the ignition system. I'm running a Duraspark distributor with a MSD 6AL. After losing 2 coils including a brand new Blaster 2 I'm dumping this system and getting a Pertronix Ignitor III this week. I'll let you know if a new ignition system solves my problem.

Boogerschnot- I've had the accelerator pump apart and checked it's diaphragm and found no problem. I've also adjusted it according to Holley specs. The car starts and runs great, its only when I step on it that I have any hesitation. New Holley mechanical fuel pump has only 500 miles on it.

Hwyman- I'll try your recommendation when I get the carburetor back together.

I've taken the carb off and gone completely through it including cleaning all passages, installing a new power valve and thoroughly cleaning it. I will be replacing the secondary diaphragm since it is cheap insurance. Can any of you gentlemen tell me where and how my secondary butterflies should be set using the secondary idle screw at the bottom of the baseplate?

Thank you very much for your help.

Tony

jlg2002

Unless you have fuel level problems in the primary bowl, I'm curious why it would bog when you step on it if the secondaries are not opening. Anyway, This should help you:

http://www.holley.com/data/Products/...0219-3rev3.pdf