holley secondaries not opening

[shaun89]

so i went and bought a holley secondary spring kit just for fun because i had my friends 670cfm truck avenger on my engine for a while and that thing would kick when the secondaries came in and it PULLED (with no secondary spring tuning)but i never felt this with my 770 truck avenger. so i kept putting lighter and lighter springs in until the lightest one they make was in, and even now, only at about 4000rpm i feel it only start to come in, and half the time it doesnt even work any ideas?o ya its a 420hp 350 and everyone i have talked to said thats a perfect CFM for it.

 

[BILTIT]

I believe there is a small o-ring which seals the spring housing sense port to the carb housing, is it in there and everything sealed up? Double check the diapraphm as they can get torn or bunched up easily too.

 

[shaun89]

r u talking about the O ring below the cap that u take off to change the spring? i checked that and its all sealed up. im going to take off the diaphragm and check that tomorrow. thanks for the help.

 

[4X4HIGH]

For a SBC a 770cfm is way too big. A 650cfm is plenty to feed even the meanest street engine.

 

[shaun89]

For a SBC a 770cfm is way too big. A 650cfm is plenty to feed even the meanest street engine.

i was starting to think that,it only revs. to 5800 also, so the CFM's the engine is taking in isnt too high...they(hi-tech engine)tested my engine with an 850? Q-jet. im guessing thats just to get the highest possible hp rating? ill look into a smaller carb more i guess...

 

[BILTIT]

770 should be fine with vacuum secondaries, it may need to be tuned abit though. There should be an o-ring between the whole spring housing and carb which you would not have had to remove/replace but it can have a vacumm leak there.

 

[shaun89]

770 should be fine with vacuum secondaries.

thats what a lot of people are saying, but i think my heads comb. chamber are too small, (i heard that a bigger comb. chamber makes more vacuum) and my motor doesnt rev enough. if i can somehow get my carb to work then i would keep it. ive just been trying for months with no luck and my friends 670 made my motor real happy.

 

[4X4HIGH]

Engine vacuum is controlled by the cam selection and nothing else. I was the Holley Guru back in the day. Trust me when i say a 770cfm is way to big for a SBC. But what do i know, i've only been working on cars/trucks for 30 years.

 

[shaun89]

Engine vacuum is controlled by the cam selection and nothing else. I was the Holley Guru back in the day. Trust me when i say a 770cfm is way to big for a SBC. But what do i know, i've only been working on cars/trucks for 30 years.

hmm, the more you know! thanks for the help man, i put my 770 up for sale(or trade) i think i might just bump up the jets a number if i REALLY have to on the 670 but i think it will be fine. thanks again

 

[RootBreaker]

hmm, the more you know! thanks for the help man, i put my 770 up for sale(or trade) i think i might just bump up the jets a number if i REALLY have to on the 670 but i think it will be fine. thanks again

good call with the 670... I too was told 670 is way big enough and 770 is sometimes not even good on a bbc!!!!!!

anyhow you said your buds 670 ran great.. what did you do to it to get rid of the stumble?

I put the .35 discharge nozzles in mine and the pink acc pump cam (truck is off the road right now) so I havent got to try it yet but it seems alot better.....

 

[shaun89]

good call with the 670... I too was told 670 is way big enough and 770 is sometimes not even good on a bbc!!!!!!

anyhow you said your buds 670 ran great.. what did you do to it to get rid of the stumble?

I put the .35 discharge nozzles in mine and the pink acc pump cam (truck is off the road right now) so I havent got to try it yet but it seems alot better.....

i didnt really do any tuning on it, i just set the bowl levels and idle mixture screws, and it ran pretty good. but i didnt change anything other then that. i think the engine just ran much healthier with the 670. but im sure ill be doing what you did to tune it in perfect when i pick a 670 up.

 

[Mike D]

Before you get rid of the holly, remove the secondary vacuum asembly from the main carb body. There should be a small cork or rubber "O" ring ( 1/8 - 1/4" ) that seals a vacuum port. If this O ring is damaged or missing it may prevent the secondaries from correctly and fully opening. Get a blow up diagram of your carb from Holly and locate this passage. I found it by accident when I was converting my Holly with the spring kit. It was a very tiny cork gasket that fit in a recessed area and yes it was only half there. After installing the spring kit (and new gasket) the Holly ran good!
Hmmmmm ! Could it have been the little gasket after all? They include several of them in a rebuilding kit.

 

[shaun89]

Before you get rid of the holly, remove the secondary vacuum asembly from the main carb body. There should be a small cork or rubber "O" ring ( 1/8 - 1/4" ) that seals a vacuum port. If this O ring is damaged or missing it may prevent the secondaries from correctly and fully opening. Get a blow up diagram of your carb from Holly and locate this passage. I found it by accident when I was converting my Holly with the spring kit. It was a very tiny cork gasket that fit in a recessed area and yes it was only half there. After installing the spring kit (and new gasket) the Holly ran good!
Hmmmmm ! Could it have been the little gasket after all? They include several of them in a rebuilding kit.

really? hmm i guess ill take that off and take a look at it, soon as it stops pouring out...i hope tomorrow it will clear up. thanks

 

[BILTIT]

Yup, that was what I was referring to. He explained it much better though.

 

[Thunder]

Listen to 4x4HIGH.... That carb is far and away too big for a little ol SBC putting out 400 hp.You can put gaskets in and tweek till the cows come home and it wil never run right.
A 750 works great on a SBC that is cranking out 800 HP and reving 8K rpm.
But for a little popgun like you have it is killing your engine. It wont even have enough power than to do anything more than crack open the secondaries. And if it does open them up it will fall on its face.
600- 650 is perfict for your engine. Time to get real.......Bigger carb does not = more HP
BTW the reason your engine ran so good with a 800 cfm Q jet is because. Q- Jets are metered by an air valve on the secondaries. They only deliver as much air as the engine needs to make max HP. Q- jets when tuned right, are a very smart carb. The only thing better is fuel injection.

 

[shaun89]

Listen to 4x4HIGH.... That carb is far and away too big for a little ol SBC putting out 400 hp.You can put gaskets in and tweek till the cows come home and it wil never run right.
A 750 works great on a SBC that is cranking out 800 HP and reving 8K rpm.
But for a little popgun like you have it is killing your engine. It wont even have enough power than to do anything more than crack open the secondaries. And if it does open them up it will fall on its face.
600- 650 is perfict for your engine. Time to get real.......Bigger carb does not = more HP
BTW the reason your engine ran so good with a 800 cfm Q jet is because. Q- Jets are metered by an air valve on the secondaries. They only deliver as much air as the engine needs to make max HP. Q- jets when tuned right, are a very smart carb. The only thing better is fuel injection.

haha ya, i didnt no much when i was buying my motor/carb, and i went with what people said to, damn them! but thanks, i totally forgot about how q jets r regulated. but if anyone somehow wants my 770 its up for sale/trade for a 670 in the classifieds!

 

[rcamacho]

Piling on.
A 770 is way too big for a mild SBC. The vacuum secondaries are doing their job not coming in at all until the higher RPM. If you still would like them to come in earlier than you can move to a lighter spring. Also, some secondary canisters have a check ball that delays acutation until airflow picks up. It can be removed but then you will need to run a stiffer spring to compensate and it may still bog - especially on a heavy truck.

 

[shaun89]

Piling on.
A 770 is way too big for a mild SBC. The vacuum secondaries are doing their job not coming in at all until the higher RPM. If you still would like them to come in earlier than you can move to a lighter spring. Also, some secondary canisters have a check ball that delays acutation until airflow picks up. It can be removed but then you will need to run a stiffer spring to compensate and it may still bog - especially on a heavy truck.

ya, i bought the spring kit figuring that would help and or fix it but the lightest spring(white) is in there and that is when it opens at 4000rpm, well starts to open them, any other spring they dont open. but its for sale now,so im not doing anymore to it.

 

[Chevy305]

You're not supposed to "feel" the secondaries opening. If you do they open too late and you are starting to hit a slight flat spot then when they kick in it picks back up again. Its supposed to be a smooth transition that you shouldn't be aware of taking place.