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converting Holley vacum secondaries to mechanical!
I know this subject of vacum versus mechanical secondaries has been talked about before but I could use a little input.
I have dual Holley1850's with vacum secondaries now and I did the test with the paper clip on the diaphragm shaft. One of the carbs secondaries did not open all the way and its been checked and double checked. I've had enough of this vacum stuff, its time for mechanical linkage. My question to you guys is how would one convert it over from vacum to mechanical? Is there a kit or is there a simple fix and would I need to block off the vacum port or just disconnect the housing shaft? Thanks! |
Holley Tech Web Page
ST:
Go to holley's tech web page: http://www.holley.com/HiOctn/TechSer.../TechInfo.html Click on Carbuetor. This will give you a parts breakdown on your model, plus a tutorial on carb systems, and why you would use one feature over another. I think all you need is a linkage kit from them. Good Luck. BigMike |
Can't do it - with the new metering bodies that come with the kit, the carbs are now too long to fit end-to-end on the manifold.
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besides, the vacume carbs have no secondary accelerator pumps
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CobraEd is correct. The carbs equipped with vacuum secondaries do not have provisions for the secondary accelerator pumps which the mechanical secondary carbs have. I understand that the carbs can physically be outfitted with mechanical linkage, but will suffer from severe bogging when the secondaries are opened. I think the only practical solution, if you really want mechanical secondaries, is to replace the carbs with mechanical units. My $0.02
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Thanks for the input guys. I guess I'll keep screw'n around with the diaphram springs and hope for the best. I realize the 1850's are not new technology but they look so darn good up there!
Where there's a will there's a way!!!;) |
Throw some more money at it, ST....
Hell, you just haven't thrown enough money at it yet, ST... C'mon, Buddy...loosen up that moth-eaten ol' purse and throw some more money at those 1850's...! Enough money can even make you think she's in love with you....
...for a coupla hours, at least! :LOL: |
A couple of hours, geeeeze Freddie after twenty minutes it's nap time!**)
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ST:
FWIW, I have been playing around with my dual 1850 setup also, trying to tweak it a little. In the latest iteration, I have reduced the main jets to #60s, and have installed the stiffest springs Holley makes for the vacuum secondary diaphragms. This has provided the smoothest transition so far between primaries and secondaries. Not perfect yet, but the best so far. It still seems to be running just a little rich at low speed, and I'm thinking of trying to decrease the main jets one more size smaller to see if that helps. I have the small K&N filters, and I do notice a relatively large degradation with them installed versus without. I haven't seen any other options for air filters which will fit inside the ERA hood scoop, though, so I just keep cleaning them and live with the loss. |
Chopper, I'm also using K&N's but have #62 main jets and it runs without loading up the plugs. The inside of the pipes are a little sooty but the plugs are always clean. The elevation here is roughly 2300 feet above sea level but at the local drag strip some say the air is more like 4000. My main concern is that the secondaries are not kicken in 100% of the time. Oh whell I guess I'll start save'n up for some Webers.
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Holley tuning
Don't buy Webers. If you are having trouble tuning two Holleys, you'll never get four WEBERS working right. Get a vacuum gauge, mount it (temp.) in the cockpit. Observe vacuum at idle, cruise, and wide open throttle. You must tune the holleys: jets, powervalves, accelerator pumps, and secondary springs. The power valve should open at about 2" of vacuum less than cruise or idle's lowest vacuum. The jets are tuned by reading the sparkplugs after a full throttle pass through four gears without any idling after. The secondary springs should be the lightest you can get away with without feeling the transition between the primaries and the secondaries. If you can feel the secondaries "kick in" what you are really feeling is when the motor flows enough air to catch up with the over-carburation of having the secondaries already open. Put in a stiffer spring. The vacuum pots ot both carbs should be linked together with a vacuum line also, above the diaphram. The accelerator pumps are there to prevent a lean condition between when the throttle blades are opened and when fuel is pulled from the boosters. This lean condition causes a "pop" when the throttle is hit. If it doesn't "pop" when you hit the throttle, forget them, tuning them exceeds what I can explain here.
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The vacuum pot's are not equiped to have a hose hooked up between them. Is there some place to get some new tops to hook them up together? I've got a full set of springs on the way to play with and I'm not giving up on them so quick.
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A lot of times people think the secondaries are not kicking in because they can not "feel" them. My sons 390 AMX had the same problem, we could not feel the secondaries kick in even though I installed the weakest spring. The problem was that they were too lean. I took out the secondary plate and drilled out the main feed holes with a .78mm (I think this was the size) drill. After doing this, the car would really pull when the secondaries opened. So, . . they were opening all along, but they added little to the overall power because they were too lean. Once I richened them up, the car ran great.
Ed |
Vacuum pots
Holley does make the vacuum pot covers with nipples for connecting them together. They should be available at any speed shop that sells jets, etc. I usually remove the original ones, drill a 3/32" hole in them, insert an aluminun line about 1" long, flare the backside of the line, and seal it with loctite quick set epoxy. This looks factory if done on the later Holleys that are silver, if done correctly. Just buy a pair with the tubes already attached instead; it's ,much easier.
As for secondary opening rates: it's a question of airflow. Too early and you are overcarburated, too late and you could go a little faster. Too little carburation is always more driveable and fun than too much carburation. Jetting is separate, as it's a ratio of air to fuel. |
Thanks aeroace, I'll be check'n into that this weekend!
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You can't convert mechanical secondary carbs to vacuum, or vice versa. Too many differences. You can get either vacuum or mechanical secondary carbs for nearly any application.
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Problem solved!!!!!!!!! I bought two diaphragm housing covers with the vacuum ports to hook up both in tandem, new base gaskets and the heavier purple spring. What a difference, now you can feel those secondary's open up. Thank for all the suggestions, now can somebody tell me how to get better gas mileage? .....................Only kidding, who cares huh!
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