holley vacume secondaries

[OUTLAW HALLETT]

i have a holley carb with vac. sec. on it and they arent opening all the way at wot ive put a lighter spring in but still not opening all the way any ideas can this be adjusted in the jets i really dont know how to adjust the carb its pretty much right out of the box as far as jets and adjustment any help would be great thanks

[Cas]

you gonna come out to the lake to meet up with some of us this weekend?
Me and mine are heading up in the morning and will be there until next Wed. If you bring it out, I can try to help you with it.

[roostwear]

As well as checking for a bind in the secondary shaft/linkage, I would check 3 things.
Pull the diaphragm housing off and put a vacuum to it. You're checking that the diaphragm doesn't have a hole or is leaking at the top of the housing. Check that the cork gasket between the housing and the main body is good and not off center/folded/missing. Last, remove the base plate and check the vacuum passage to make sure there are no obstructions and that the gasket is correct.

[OUTLAW HALLETT]

you gonna come out to the lake to meet up with some of us this weekend?
Me and mine are heading up in the morning and will be there until next Wed. If you bring it out, I can try to help you with it.
how do i find you ? call me ill make it out this weekend my name is billy 530 356 3941 thanks

[thatguy]

I am not a carb guru, but I THINK they will not open unless there is a load on the engine. Meaning I dont think they will open on the trailer. I am not sure however.
Tommy

[jetboatperformance]

Billy here is some information from a book we use regularly here in the shop. Your welcome borrow it our I can fax excerpts that may help.
The primary throttle blades work directly from the gas pedal and linkage. The secondary throttles connect to the diaphragm rod of a large vacuum servo on the right side of the carb body. A coil spring inside the servo housing pushes against the top of a diaphragm counteracting the secondary throttle opening.
As airflow volume increases, so does the venturi vacuum signal, and this applies a suction force against the diaphragm. When the signal gets high enough, the diaphragm moves, opening up the secondary throttles. In effect, the engine has indicated or "asked" for the extra air.
If the secondary opens too fast, air flow on the primary side would decrease Venturi vacuum signal will drop and the secondaries will begin to close back down, just enough to restore balance. You have all the benefits of a small carburetor for early launch, plus the air flow of a large carburetor for higher power and top end. As the engine reaches the higher rpm, it moves more air, and the secondaries will open wider depending on demand.
Hope this helps, Josh says he has lots more info as well if you need help.
Tom and Josh

[SmokinLowriderSS]

If there are no malfunctions in the carb, like linkage bind or vac leaks, they may not open fully. They will only open fully if the engine can actually use that much carb throttle opening.
Hence, if you are overcarbed, it fixes your overcarb problem.
What engine, and what size carb, and what RPM?
If you want to get max performance, run a 4150 mech seccondary. This will insure full throttle opening, wether you need it, can make use of it, or not.

[Legal Chemistry]

I believe it was posted above, are you running on the water or driveway. A quick wick to WOT in the driveway will not open the secondaries (maybe just a little bit.) Try it with load (on the water) and they should open.

[OUTLAW HALLETT]

I believe it was posted above, are you running on the water or driveway. A quick wick to WOT in the driveway will not open the secondaries (maybe just a little bit.) Try it with load (on the water) and they should open.
im talking about on the water wot for as long as the 455 can hold it

[SmokinLowriderSS]

im talking about on the water wot for as long as the 455 can hold it
Then see what I said above.

[roostwear]

It's highly unlikely this carb is too big for a 455. Although we don't know the list # to identify the size, even if it's a 750 that's not too big to kill the vacuum signal. If his engine has issues that would affect the secondaries (valve timing, ignition/timing issues) it would have to be thoroughly diagnosed.

[SmokinLowriderSS]

I didn't intent to insinuate he was overcarbed (unless he's running an 850, but I don't know). Was just noting the effect that they will only open enough to give the engine what it wants, no more. IF an engine IS overcarbed, they are sort-of "self-resizing/downsizing".
Lets say he's running a 455 what, 4500 RPM flat out? That inhales 600 CFM, at 100% efficiency, and it isn't going to be 100% efficient, MAYBE 90%. That makes it suck 540 CFM.
A 750 vac secc under those conditions will only open enough to supply 540 cubic feet of mixture flow per minuite, no more.
A 900CFM vac secc. under the same conditions will flow the same, 540CFM, no more.
Just for the sake of comparison, 5,000 RPM still only inhales about 650 CFM @ 100% VE.
590 @ a more realistic 90%

[SmokinLowriderSS]

i have a holley carb with vac. sec. on it and they arent opening all the way at wot ive put a lighter spring in but still not opening all the way any ideas can this be adjusted in the jets i really dont know how to adjust the carb its pretty much right out of the box as far as jets and adjustment any help would be great thanks
What I was really saying was, per the above question, "there may not be a darned thing wrong with the carb, and carb adjustments may not help it."
Jetting changes will do nothing unless the jetting is wrong in the first place. Holley's tend to be a tad rich, but generally pretty close and run very well "just out of the box".
You should buy new spark plugs and do a WOT jetting check run before touching the jetting.
OUTLAW, the only "adjustment" that changes the opperation of the vac seccondaries is spring pressure against the diaphram. Get the entire holley spring kit, it has about 7 springs or so, and instructions.
ALSO, it MAY NOT BE THE BEST SETUP to have the seccondaries open just as early as is possible, although, the reality of no real midrange heavy load in a jetboat (unlike a prop or a car) makes this less critical.
Some people still believe they should "feel the seccondaries "kick in" " when they open. THIS IS WRONG. If this occurs, they are opening TOO SOON, reducing airflow, and power production, untill the engine recovers at a higher RPM to the unneeded airflow. Proper opperation should be seamless, impossible to detect.

[OUTLAW HALLETT]

well guys i think i got it fugured , when i took the choke off i forgot to plug the vaccume port so it wouldent open the secondaries with a leak, my dumb mistake thanks for all the help by the way im wondering where everyone gets their calcs for jet impellors vs. rpm , i hear people quoute a referance chart but i dont know where to find it thanks again billy

[SmokinLowriderSS]

Berkley Impeller/HP chart (http://www.berkeleyjet.com/impeller_info.aspx)
I use LVJetboy's Jet Performance Calculator. Same thing in electronic form, with other mfr's added in.