Technical holley 600 vac. secondary issue.

I have had to bend the return linkage on the secondaries to get them to manually come in earlier back when. In other words, shorten the rod. Lippy

 

Just tried it on the back road with it setup to give 50% mechanical secondary and oh boy what a kick in the pants it gave.
So now its pull the diaphragm canister and do the checks there. JW

 

Spraying carb cleaner from the outside in you can see if the passages are open

 

Take an air gun and blow right across the port, that will open the secondary's. I've done it many times.

 

Post #25, i tried that and nothing happened.
I just removed the diaphragm canister and blew air through the port in the main body and gas came out one of the air bleeds in the front and above the r/hand venturi, the one nearest the carb center.... now i am really confused. the little cork gasket was good and so is the diaphragm but i will get a new one in case this one has hardened.
Thanks for all for your suggestions. Cheers, JW
edit; photo added.

 

Make sure, that primaries open fully when pressing gas pedal to The floor.

 

The compressed air has to go ACROSS not in the port, having the throttle plates wide open allows the air to flow freely.

Venturi effect is the air pressure drop at the venturi when air flows though it that draws fuel from the fuel bowl and creates the low pressure aka vacuum in the canister. Cup style paint guns, sand blast guns and liquid spray guns that hook to an air hose and have a hose off the side that goes into a canister of liquid all work the same way.

 

I better clarify one point, i was a mechanic many years ago and i know about venturi's and the like.
Holley carbs and there systems was something i never did much with.

I have since checked the diaphragm...its ok and have vacuum tested the canister and it checks out fine.
I am now thinking this carb is a mixed bag of f@#ked up and i may cut my loses and get a double pumper. JW

 

I'd remove the secondary vacuum pod and run a piece of wire through the angled hole the should be open on the right-hand side primary Venturi.... It might be clogged..... That's the only thing I can think of if everything else is good..

 

Have you faced off all the mating surfaces?? They distort quite a bit after a while..

 

Grinding , filing ,sanding , etc on carburetor mating surfaces is an effective way of producing useless scrap ..

 

OK, im still here. I replaced the diaphragm and noticed the new one was a bit softer. Had to wait a week for the weather to clear so i took it out today with the paper clip on and took it up to 100 mph and there seemed to be a tad more (maybe my imagination) and the clip moved about a 1/4 inch, not much but something all the same. I feel that these 600 vac-secondary carbs are a bit big in the primaries to achieve sufficient air speed on motors of 302'' and under.
Conclusion is, i am getting a 600 mech-secondary carb..... there is a shortage of them in NZ and they range between $825 and $1400 for the same item.
When i get one fitted i will report back. JW

 

100 mph is what , 4000 rpm ? I'd be surprised if the secondary would be open fully at that low an rpm . Try 6000 rpm. A street carb at 4000 rpm on a 301 CI engine only uses about 300 cfm

 

Just under 5000 rpm. JW

 

Must be running a short tire ?
28" tire. 3.78 gear.
100 mph = 4600 rpm
301ci @ 4600 rpm = 360 cfm .
Calculations are not precise , but close enough for discussion.

 

At that speed on a narrow paved road with a high crown and watching for the T intersection at the end, i could only glance at speed and revs at that point. I do know its 2900 @ 60 mph (our max speed limit). On the build i was shooting for 2500 @ 60 but i only run 16 lbs in the rears to maintain good tire foot print. I would say your calcs are very close and the tire size to, 225/75 x 16''. At the end of the day i want /expect a bit more from my 301 in a light car and think the mechanical secondary carb will give this, i will need to not overload it. I would really like something smaller but this is NZ and we don't have everything at our disposal. All our performance parts store are out of mech- sec 600 unless you want to pay way too much. i should have one in two weeks and i will give a report and if not OK i can change it back. JW

 

Those of us old enough to have been involved with early z-28 camaros know that they came with 780 cfm vac sec. Carbs & that those carbs were positively opened fully at lower than 7000 rpm . I have a feeling that something is amiss with your 650 , without being there & being able to examine & run tests , it will probably remain a mystery . Sad that a carb that a few years ago went for less han $100 is now so horribly overpriced !

 

I have a Question Why are you using that Air Cleaner since it
Dosen't pull in much air to the Carb.??
I run a 327/300 hp. 373 rear Power glide AFB Carb & a Open
Air cleaner, so the Engine can Breath.!

Just my 3.5 cents

Live Learn & Die a Fool

 

You may be on to something ...

 

Has anyone mentioned that the diaphragm spring might be too stiff? They sell a kit with color coded springs to tune the secondary opening on these carbs. The lighter the spring, the sooner the secondaries open. As was previously mentioned, Holley also makes a quick change kit so you don’t have completely disassemble the diaphragm chamber every time.


Sent from my iPhone using The H.A.M.B. mobile app

 

Here ...

 

I have measured the opening and it appears to have enough of an opening size wise and i will look at it again. With an open wheeled car i am reluctant to run it open at any stage but will come up with something. Thanks for the replies guys, i appreciate it. The weather is turning bad again today so further road testing is on hold. JW

 

I don't mean Not to run a air cleaner only Change it to a air cleaner
that will allow Air to enter the Carb.
Mine is 4" thick has a top piece of Metal and a Bottom that fits the Carb.

Just my 3.5 cents

Live Learn & Die a Fool

 

You could certainly run without an air cleaner far enough to test .!

 

I will take it off and make a mesh covering. I dont have another to put on. JW

 

I'd wait till after a good rain to make test runs without an air cleaner.... A good rain will eliminate any dust particles out of the air....

 

Small stones was what i was thinking of. Its hosing down now so it may be the weekend. I was thinking of also making plywood spacer to increase the opening of the air filter just to see. JW

 

If you must use a sub standard road to make road tests, why not use an indirect gear to get your revx up instead of risking life and limb exceeding 100 mph in high gear?

 

All the roads around me are sub standard country roads. This one has no houses and has little use and is about a mile long, also i have tried a non direct gear and with no secondary action, that is also like revving it up in neutral and wanting a result. With the revs i pull and the dynamics of the carb all i have is a two bbl. I don't want to drive with a four bbl function 100% of the time, not even 5% but when i do i want it to work, not have to pull 6000+ revs to make it happen. I am changing to a mechanical secondary carb as soon as i can get one that is not way over priced, BUT in the mean time i want to try what i can with the help of the knowledge here. JW