Guest tony78_280z Posted July 14, 2004 Share Posted July 14, 2004 got the holley back on. And I'm zoomin around. It accelerates like a dream in mid and high speeds. Don't got the speedo workin yet, but I can feel it. But from a stop at the initial flooring of the peddle the car bogs and stalls. it dies sometimes, others it picks up after a second and goes tearing on down the road. I'm thinking my spark advance is off. How do I check such a thing if it only advances when the car is under load? Second theory is that the power valve on the carb is dumping too much gas and flooding it for a second. What can I do about that? And how can I check it? My Third theory is possible a vacuum leak somewhere, but I sure as hell can't find it. DO I hear a frouth theory? Any help is appreciated -Tony Quote Link to comment Share on other sites More sharing options...
DaleMX Posted July 14, 2004 Share Posted July 14, 2004 Sounds like the carb to me. The secondaries may be opening too quick and you loose air velocity and go lean. My old 396 was bad at that. Or your power valve is broken and not dumping any fuel. I guess that's theory 4. Dale Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted July 14, 2004 Share Posted July 14, 2004 Sounds like a lean condition to me too, needs more fuel. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted July 14, 2004 Share Posted July 14, 2004 Yup...likely too lean. Adjust the squirters on the accel. pump to come in earlier, or change the little cam so that it gives more quicker. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted July 14, 2004 Share Posted July 14, 2004 The accelerator pump/nozzle size sounds like the problem to me. Some remedies if so: 1) 50cc pump and diaphram (but this is usually an overkill); 2) larger nozzle (#25 I belive is OEM, and I've at times had to go as high as a #40 to fix off-line stumble; or 3) Swapping the cam that operates the accelerator pump to one more aggressive (Personally, I've not had a lot of success with this method as it needs to be well coordinated with both of the above) ramp or profile. All 3 of the above will have an affect on each of the others, but changing the nozzle (IMHO) will give you a quick and easy idea if the lack of fuel at this transition from idle to WOT is the problem. Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted July 14, 2004 Share Posted July 14, 2004 The guys have it right... lack of fuel off the line. There is a bit of time as the throttles are dumped open when there is very little airflow through the carbs venturis; getting rpms up and thus past that point quickly minimizes bog. There are several factors involved- cam, gears, stall speed and mechanical vs. vacuum secondaries among them. If the fixes suggested in earlier posts aren't enough to cure the problem, deeper gears (higher numerical), looser converter/higher stall speed and a vacuum secondary carb all help The accelerator pump covers for the lack of fuel through the main system after the transfer slots have been uncovered. If your cam needs more RPM to idle, tweaking the set screw/ throttle stop on the secondaries open a bit more will allow the primary's transfer slots to remain in play. Believe it or not, there once was a time when it was ultra cool to have a mechanical sec. carb so big that the engine could be killed by flooring the throttle. Note that I said cool, not logical. Quote Link to comment Share on other sites More sharing options...
Guest tony78_280z Posted July 15, 2004 Share Posted July 15, 2004 My motor is completely stock excepting the carb and the exhaust. So Cam and ratios really don't apply to this problem. The carb is a Holley 600cfm vacuum secondaries. When (in park) I manually throw back the throttle I can see a large volume of fuel squirt into the front boosters and then the motor bogs and sputters. Thus I'm assuming the engine is getting flooded. Note in park a vacuum secondary will not open (or so they say) unless the motor is under load. "Swapping the cam that operates the accelerator pump to one more aggressive" -- Can I get one that is LESS aggressive? Quote Link to comment Share on other sites More sharing options...
A. G. Olphart Posted July 15, 2004 Share Posted July 15, 2004 Sorry about the earlier dissertation; I generally read posts to the signature & ignore the rest... Got bit this time. Should have left Terry's answer alone. If your secondaries were opening you would see the diaphragm rod go up, and the throttle shaft turn. Unless you are seeing great gobs of black smoke (like a stuck choke) at the same time that the engine stumbles, I'd still guess lean. Snapping the throttle wide open from idle pretty much kills any vacuum, so the pump is all that feeds the engine for a while. If it eats the pump shot before RPM and vacuum come up... Holley sells an assortment of cams for us tinkerers to play with; hope you find the right one. (You might want to try the other hole in the one you have just to see what happens). Quote Link to comment Share on other sites More sharing options...
Pyro Posted July 16, 2004 Share Posted July 16, 2004 It could also be an ignition timing problem. Use a timing light to verify the timing is advancing when you hit the throttle. A common mistake on GM engines is to plug the vacuum advance in the wrong port on the carb. The correct vacuum port WILL NOT have any vacuum at idle (called ported vacuum). Vacuum to the vacuum advance is only produced when the throttle blades are opened. Vacuum on this port is taken from above the throttle blades (not manifold vacuum). You can feel the difference between the two vacuum ports with your finger as the engine is running. If you have the vacuum advance on the wrong vacuum port then the timing will retard when the throttle is opened which will cause a bog. Quote Link to comment Share on other sites More sharing options...
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