Carb guys in here?

[bcjjones]

I appreciate all the info. I have been tuning on carbs for a couple years now. I am by no means an expert, but I have read a couple books on them including the David Vizard version of the book above. I'll look into buying that one as well.

The secondary tube mod is used on the street avenger because it has trouble opening the secondaries. Specifically on the 770 version. The smaller version does not have this issue. It is essentially enlarging the signal hole from the primaries to the secondary vacuum pod. Holley used to make this a standard feature, but from what I assume is cost savings, they stopped doing it. It helped quite a bit along with tinkering with the secondary spring, though. The secondaries used to open way up in the RPM range, even with the lightest spring.

The guy selling the Pro Systems carb has the spec sheet. Based off of it, it would be a decent fit for my set up, but would still need some tinkering.

The street avenger does not have replaceable air bleeds but I am in the process of changing that. I ordered some blank air bleeds and I am going to drill/tap to install them. I'll at least be able to fine tune it a little more. As of now it's tuned pretty well. It doesn't have repalaceable PVCR's, though, which is unfortunate.

I have a vacuum gauge, and a wideband o2 as well. They definitely help with tuning. I'm not so much having a hard time getting it tuned right as I am deciding on whether or not a mechanical secondary is a better fit for this set up in general. I also like the additional adjustments that can be made to something like the pro systems carb.

After reading this, I believe I am going to just stick with the vacuum secondary. I can always order some quick fuel metering blocks that will allow some additional adjustments that these don't have.

Thank you for all the input!

 

[Frank Enstein]

You can drill and tap the PVCR's as well. I like to set the idle first. The test can be a bit tricky but here is the procedure.

Take the main jets out of the primary metering block. Reassemble the carb. See how fast you can go before the power falls off. Make a note of the MPH. The speed that the motor falls on it's nose is important because this tells you when the main system (jets) come on line. Everything below that point is on the idle circuit of the carb. This is tricky because the engine may stall and foul the plugs so make sure there is no traffic around when you do this test.

Pull over and put the jets back in and new plugs if needed. So if the car bogged out at 25 MPH we will set the idle feeds at 2 MPH slower. Fool around with the idle air bleeds until you can go your test speed with the highest possible vacuum. THEN we can fool around with jets! This procedure is something I came up with on my own and it isn't in the tuning book.

 

[DamHoodlum]

I appreciate all the info. I have been tuning on carbs for a couple years now. I am by no means an expert, but I have read a couple books on them including the David Vizard version of the book above. I'll look into buying that one as well.

The secondary tube mod is used on the street avenger because it has trouble opening the secondaries. Specifically on the 770 version. The smaller version does not have this issue. It is essentially enlarging the signal hole from the primaries to the secondary vacuum pod. Holley used to make this a standard feature, but from what I assume is cost savings, they stopped doing it. It helped quite a bit along with tinkering with the secondary spring, though. The secondaries used to open way up in the RPM range, even with the lightest spring.

The guy selling the Pro Systems carb has the spec sheet. Based off of it, it would be a decent fit for my set up, but would still need some tinkering.

The street avenger does not have replaceable air bleeds but I am in the process of changing that. I ordered some blank air bleeds and I am going to drill/tap to install them. I'll at least be able to fine tune it a little more. As of now it's tuned pretty well. It doesn't have repalaceable PVCR's, though, which is unfortunate.

I have a vacuum gauge, and a wideband o2 as well. They definitely help with tuning. I'm not so much having a hard time getting it tuned right as I am deciding on whether or not a mechanical secondary is a better fit for this set up in general. I also like the additional adjustments that can be made to something like the pro systems carb.

After reading this, I believe I am going to just stick with the vacuum secondary. I can always order some quick fuel metering blocks that will allow some additional adjustments that these don't have.

Thank you for all the input!

If you did all of the tuning on the vacuum secondary carb & you have all of these tools you can make a manual secondary carb work too, If you want all out performance use the manual secondary carb, I went from a 750 vacuum secondary to properly tuned 650 double pumper and the difference was night and day. Alot depends on your converter, gear, camshaft rpm range, etc........
By the time you buy everything to make a vacuum secondary carb work you can have a double pumper, manual secondary carb with more adjustments that will our perform any vacuum secondary carb