1st time poster here. Thanks for the wonderful forum. This place was a great find for me.
Anyway, hope someone can chime in with some suggestions. I have been doing some enhancements on my bird the past month due to a few years of bad neglect.
I recently: *purchased a new holley 650 double pumper with mech secondaries to replace my old crappy holley 4011 style DP I had on there which was in much need of a rebuild and lots of other things. *changed the points in the stock dist. to an electronic conversion kit.
Im having a tough time dialing in the secondaries on the new carb.
The primary circuit seems fine and the car has great pep other than a slight hesitation when blipping it from an idle (which i corrected by going from a #28 squirter to a #31 in the primaries.)
The issue is if im crusing in 3rd or 4th around 3000rmp and go WOT, you can hear the secondaries open up but it just seems kinda sluggish/boggy. It does accelerate, but just doesnt have the kind of acceleration it used to have even with that old sticky gunked up carb that was on there. Something is definatley a miss and I cant put my finger on what to try next.
So far I have: Played with timing until frustration sets in. at -9 BTDC I get backfiring through the carb. It seems to like -12 the best. Any more than that, it gets a little hard to start her when hot. I tried as much as -18 but the secondaries kinda felt flat when WOT. (no pinging under a load however) I only have a timing "light" so all timing numbers above were done at idle with the Vacumm Advace disconnected and plugged.
I should also mention reving it by hand even quickly to WOT while its sitting in the driveway seems very responsive and just like it should. Secondaries seem fine. You can feel and hear them just like you would expect.
It just seems when under a load, its either to lean or too rich. BTW there is no cloud of smoke at all in my rear view mirror when going WOT while driving.
If this turns out to be a lean condition and not timing, which part of the secondary circuit would I need to go bigger on? The squirters? The main jets? or the secondary pump CAM?
Sorry for such a long post, Just wanted to make sure I answered any questions that may arise.
Thanks
max
Last edited by maxbato; 07/18/0703:59 PM.
1968 Firebird 350|#17 Heads|Cam identical to 350 H.O. specs|Holley 650DP (mech, secondaries)|Edelbrock Performer Intake|Manual 4 Speed with 3:73 rear
First make sure you have the proper float levels in both front and rear float bowls. If they are good, start off with disconnecting the secondary linkage and test the car like that. If that tests okay, the problem is in the secondaries - sounds like it from your description but this will confirm it. Check the jet sizes in the secondary metering block and look for any signs of debris or dirt.
I will test after work today. Im just curious as to what I will be looking for when disconnecting the secondary linkage. Should it lean out at a certain point or what? Just trying to see where your going with this.
1968 Firebird 350|#17 Heads|Cam identical to 350 H.O. specs|Holley 650DP (mech, secondaries)|Edelbrock Performer Intake|Manual 4 Speed with 3:73 rear
No, if the jetting is in the right range and the power valve is working it should respond cleanly to throttle inputs and should pull fairly well at lower and mid rpm. Being on the primaries, it won't have enough airflow to pull hard above 3500-4000 rpm but should taper off gradually as the rpm builds. That's not the same as leaning out but may feel somewhat the same. A sudden application at 3000 rpm to WOT should give a smooth response without any noticable holes. You should be able to tell the difference between that and what you have now.
I've had several new carbs with garbage in them from the manufacturing process and obviously not cleaned out before assembly. I've also had defective metering blocks and such, so the best way to go about this is through the usual checklist until the problem area is found, then solve the problem!
