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Topic Review (Newest First)
07-28-2013 10:55 PM
68NovaSS Just take the information in this thread and run with it...
07-28-2013 07:38 PM
starrscreations
Quote:
Originally Posted by 2_Late_I_Won View Post
My secondary isn't opening on my old school Holley 625-600 cfm carb. I don't know jack about carbs. but I know the diaphragm is good. I took it off and put a vacuum test to it and it stayed down. So I know that is good. I started it up and didn't feel any vacuum where the diaphragm goes and didn't feel any vacuum. I put the air hose to it to blow out any thing that might be blocking it but nothing came out and it blew freely. Like I said I don't know that much about Carbs so any help would be greatly appreciated.
I'm having the same problem on my 600 cfm holley 4175. I'd like some ideas too.

Robin
04-03-2007 03:26 PM
2_Late_I_Won
Quote:
Originally Posted by NXS
jet extensions with high gears and PG...on a carb that will barely open the secondaries, LOL! don't make him spend any more than he has to, k??

2-late, can you get me a good pic of the primary/secondary linkage off the driver side of the carb?

Yeah I'll do my best may take a day or two but I will try to take lots of pictures all the way around so everyone can see what I'm talking about.

It feels smooth the whole time I can just hear and feel the extra "boost" when the secondaries open up.

Thanks Guys talk to ya tomorrow Brian
04-03-2007 01:58 PM
NXS jet extensions with high gears and PG...on a carb that will barely open the secondaries, LOL! don't make him spend any more than he has to, k??

2-late, can you get me a good pic of the primary/secondary linkage off the driver side of the carb?
04-03-2007 01:50 PM
MIKE FROM SM With high gears and pg the secondaries should open very late. The engine should rev up smoothly. If it doesn't, the secondaries are opening too soon. Keep putting in a stiffer spring until it does rev up smooth. Or put some low gears in that thing.
04-03-2007 12:41 PM
F-BIRD'88
Quote:
Originally Posted by 2_Late_I_Won
Well it's a 2 speed powerglide and I'm already in the upper rpm's when it starts to open. I would say around 4,000-5,000 rpm. Around 4-5K rpm I'm already doing close to 50 in first gear. ( I know I have really tall gears) But I was hoping with the other two barrels opening earlier. That that would help me off the line more. With a white spring ( the lightest) I would expect them to start to come on around say 2,500 rpm or so. I don't know maybe this is right where they are supposed to come on at.
What you are feeling in the seat of your pants while driving is not the secondaries starting to open.
They are actually opening right off idle (with the white spring) and opening too, too fast.
When they open too fast the engine airflow thru the carb is not fast enough. The carb cannot meter the fuel. (lean bog,soft acceleration). Then once the engine airflow ( speed) thru the carb catches up, the fuel flows properly and makes power. You feel that as a power surge.
Remove and reinspect the diapharm and diaphram housing seal for a leak. Use the thumb over the holes method.
make sure the little check ball is in the housing vac passage. Try a stiffer med tension spring. Try raising the float level a little on the sec side. (faster fuel metering reaction)
You really need to switch to a secondary metering block with jets and rear sec jet extensions. The fuel in the sec bowl gets pulled away from the sec jets on acceleration.
04-03-2007 12:29 PM
2_Late_I_Won
Quote:
Originally Posted by F-BIRD'88
Check the little cork donut shaped gasket that goes between the carb body and sec vac diaphram. If it is missing or leaks
between the vacuum housing and carb body, the vaccum signal that opens the secs at WOT, will be too late.
It will not build fast enough.
Usually when things are working right, No vac leaks, the lightest white spring is way way too light causing the secs to open too fast.
Generally a medium silver ( plain), yellow or purple spring is best for performance use.
That's what I thought. I thought the White one was way to light to be functional for most situation and car set up's

I checked cork gasket it's there and intact but I'm not saying it isn't leaking from there. I'll probably will replace it just because if it's not a problem now it soon will be. Thanks
04-03-2007 12:18 PM
2_Late_I_Won
Quote:
Originally Posted by MIKE FROM SM
What makes you think the secondaries are opening late?


Well it's a 2 speed powerglide and I'm already in the upper rpm's when it starts to open. I would say around 4,000-5,000 rpm. Around 4-5K rpm I'm already doing close to 50 in first gear. ( I know I have really tall gears) But I was hoping with the other two barrels opening earlier. That that would help me off the line more. With a white spring ( the lightest) I would expect them to start to come on around say 2,500 rpm or so. I don't know maybe this is right where they are supposed to come on at.
04-03-2007 12:11 PM
F-BIRD'88 Check the little cork donut shaped gasket that goes between the carb body and sec vac diaphram. If it is missing or leaks
between the vacuum housing and carb body, the vaccum signal that opens the secs at WOT, will be too late.
It will not build fast enough.
Usually when things are working right, No vac leaks, the lightest white spring is way way too light causing the secs to open too fast.
Generally a medium silver ( plain), yellow or purple spring is best for performance use.
04-03-2007 09:37 AM
MIKE FROM SM What makes you think the secondaries are opening late?
04-03-2007 07:54 AM
NXS you can pull the spring out and either push it inside out to soften it so the secondaries are open sooner and stay open

or

cut the bottom off, this will give an initial hit at lower rpms then slowly open in the upper rpms
04-03-2007 07:16 AM
2_Late_I_Won Well I went home last night and bought a vacuum secondary spring kit. I put the white one in ( the lightest/less tension )and my secondaries open up yeah the only problem is it opens up in to high rpm. Right about the time I want to let off the secondaries open up so I don't get to enjoy the extra power. Is there a way to increase vacuum so it will open up sooner or a way to adjust when it opens up? I know usually you would adjust when the secondaries open by getting a little bit stiffer spring but since I have the weakest on in there now I don't know what to do. Do you think I can run it with out a spring at all or do I have to have one to push the diaphragm back down?

Thanks again for all the help now I just need to fine tune this thing
04-02-2007 10:42 AM
2_Late_I_Won AHWWW HAAAA I think I found my culprit Sweet thanks I'll have to get another spring and see if that helps.
04-02-2007 10:37 AM
NXS White, yellow...to black....black being the stiffest and latest opening
04-02-2007 09:27 AM
2_Late_I_Won It said R75 but that doesn't sound like model number to me. Oh well!!! Anyway I took apart the secondary and noticed there was a Black spring in there it seemed kind of stiff. What color should it be and is the black one stock or do you think it's been changed out before?

Thanks again Brian
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