Holley 600 Carb Question about the Secondaries

[Stoopalini]

Hey guys and gals,

I used a Holley Trick Kit to replace all the seals in my carb last night because, well, it needed it. Before the rebuild, the secondaries were not opening and there were some other issues too (leaks, accel pump, etc ....)

Well, now that I've finished, all the problems are solved except the secondaries are still not opening. Do they open up from crank case pressure? I noticed a vac line
(tube) from the top of one of the valve covers goes to the secondaries. If this is what opens them up, I don't know why it wont open. I blew through the tube and it is clear.

Any help is, as always, greatly appreciated!

Thanks,

Thomas.

-- '84 K5 Blazer --

 

[rocko]

Damn Thomas.. no one know's about carb's.. hmmm...
Time for fuel injection...

..
Back to the top for you.

I haven't failed, I've found 10,000 ways that don't work. www.rocko.rockcrawler.com

 

[dyeager535]

Ok, knowing nothing about Holleys, but some about q-jets, vacuum secondaries are held SHUT by vacuum. With no load on the engine (rev it to the moon in park if you like, they won't open much) there isn't enough engine "demand" that the secondaries open up. Engine demand (airflow) keeps vac. secondaries open, vacuum keeps them shut.



Dorian
My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
No anti-theft measures on your truck? No pity when its stolen

 

[Jason73K5]

there is a spring in a housing with a diaphram on the right hand side which controls when the secondaries open. you can change these springs to adjust it.

73K-5: TBI350/TH-400/NP-203/14FF/D44
Topless, doorless and no tailgate!
Fresno, CA

 

[mike reeh]

your holley carb is undoubtedly vacuum secondaries (as opposed to a double pumper) .. these carbs use something called venturi vacuum to open the secondaries.. when you floor it, high velocity air through the primary barrels draws a vacuum thru a tube right in the middle of the primaries, that leads to the vacuum diaphragm, in turn opening the secondaries.. its a demand-driven system, they will only open if really needed. many people get confused by the whole vacuum secondary thing but its quite simple.. its the same principle as an airbrush, or paint sprayer (i think, i dont use those very often) .. people always say, at full throttle, the engine has little vacuum, so how does it open the vacuum secondaries?? it doesnt work on manifold vacuum.

venturi vacuum is the same thing that sucks fuel from the floatbowl, on demand..

you wont be able to see the secondaries open in your driveway, unless you REALLY rev the crap out of the motor, in which case they will sometimes start to open for just a second before you have to let off. (I dont recommend this)

make sure all the linkage is free from binding, etc, and that the secondaries operate freely, along with the vacuum diaphragm rod.. if all is well, they should be working fine.. sometimes you can hear them open while driving, especially if you have an open element air cleaner and semi-sane mufflers. with a Q-jet you can REALLY hear them open..

hope this clears some things up

mike

 

[Neil]

what is the other end of your vacuum lines hooked to? make sure they are all sucking well like the EGR and distributor vacuum advance which can fail to work sometimes. Also the spring the fella mentioned before can get rusty and stop working because the engine will take moisture in over a long period of time into the diaphram housing on the carb. I have seen Holleys do this before. I have rebuilt many Holleys and seen this spring rusty and diaphram collapsed and worn out. If you want to, different rated springs are available to make the secondaries kick in quicker or slower. they are color coded depending on how you want to run 'em. Hope this helps some. Later....

Neil H.. Alabama.. '78 K5 400ci 4x4 AT,AC,PW Cheyenne. '74 C10 3spd/floor 250ci 4x2

 

[Stoopalini]

Thanks guys!

So the air velocity going through the primaries creates a suction on a channel that leads to the diaphram which opens the secondaries ........ right?

If that's true, and I'm not confused, I can troubleshoot this.

The reason I say their not opening is because I do have an open air element, and I cannot hear them opening with max throttle. I have had many a 4BBL carb with open air, and I could always hear the secondaries opening up.

On a side note, I found out last night that the secondary float is filling with gas! I don't see how this would stop them from opening, but I'm going to get new floats and see if it makes a difference; for now, I adjusted that fuel stop thing all the way down so fuel doesn't come up through the vent at the top of the bowl.

Thanks again guys,

Thomas.

-- '84 K5 Blazer --

 

[mike reeh]

the floats are fine, did you set the float level after the rebuild?? you have to remove the sight plug and adjust the nut &amp; screw on top of the bowl until the level is right at the bottom of the sight hole.. it should JUST trickle out, on both bowls.

mike

 

[Stoopalini]

Yea, During the rebuild, when I had the bowl off, I set the float level so it's even with the bowl when held upsidown.

I replaced the float after work today and also tightened down that plate (whatever it is) that is behind the secondary bowl. (It was a little loose).

I then installed it and adjusted the bowls by looking through the site holes you spoke of, and it's running great

Thanks man, I appreciate the info

Thomas.

-- '84 K5 Blazer --

 

[ymatt]

Interesting. I've just rebuilt my Holley 1850-3 600cfm carb. It was covered in hard carbon deposits because the previous owner had neglected to change the air filter. The secondaries were particularly filthy, so it seems they were not opening.

I have not been able to test it out yet, because I'm still waiting to get my transmission back. What's the best way to be sure the secondaries are opening?

 

[Stoopalini]

Well, the only may I've ever been able to tell is by sound. Sorry .....

One thing I had to do was install a 1/2" carb spacer because the throttle blades were hanging on the intake and causing problems. You might want to look into that??

Good Luck,

Thomas.

-- '84 K5 Blazer --