L71 Holley 2300C Spec Question
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L71 Holley 2300C Spec Question
Hi All
Does anyone know what the original diameter of the vac secondary vacuum bleed is from the venturi in the center carb? I didn't get a reply on this from Holley so maybe the only chance is if someone has one they can look at. The hole is on the RH size way above the butterfly.
My vac secondaries are not seeing adequate vaccum from this port, the rest of the circuitry tests well, I'm thinking that the hole, which looks by eye to be about 3mm, has been drilled large. Also this hole is twice the size as the equivalent hole in the end carbs.
Next question would probably be "Has anyone had to fix this and how"!!
Thanks again
Paul
Does anyone know what the original diameter of the vac secondary vacuum bleed is from the venturi in the center carb? I didn't get a reply on this from Holley so maybe the only chance is if someone has one they can look at. The hole is on the RH size way above the butterfly.
My vac secondaries are not seeing adequate vaccum from this port, the rest of the circuitry tests well, I'm thinking that the hole, which looks by eye to be about 3mm, has been drilled large. Also this hole is twice the size as the equivalent hole in the end carbs.
Next question would probably be "Has anyone had to fix this and how"!!
Thanks again
Paul
Safety Car
Joined: Aug 2000
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From: San Antonio TX
It may not be drilled large, but is instead missing the aspirator tube. I don't know if the primary carb on the L-71 had the tube -not all Holleys did, but with that big of a hole, it's about the same size as the brass tube that would be there.
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Thanks!
Whats' an aspirator tube? Is this a tube that would have been pushed into the port from inside the venturi?
I'd still need to know what the ID should be.
I do know the end carbs have no such tube - the hole is about 1/2 the size!
Thanks.
Safety Car
Joined: Aug 2000
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From: San Antonio TX
The aspirator tube is a small tube with a 45-cut on the end that protrudes from the top of the venturi. I can tell you if the hole you now have is at the very top of the venturi, you should have the tube. Yes, it does fit from the venturi side of the carburetor. If the tube is missing, there is no way you will get the secondary to open. The way it works is a pressure depression is created in the tube on the primary. Once the secondary starts to open, there will be velocity in the secondary venturi. You will see a small hole deep in the venturi on the secondary and where air flow is fastest pressure is lowest. This is why the hole is in the narrowest part of the secondary venturi. This hole is supposed to help pull over the secondary by adding additional vacuum to the vacuum motor.
I'm sorry, but I don't know the OD of the tube. But that shouldn't be too hard to find. Just google for Holley aspirator tube. When you install the tube, make sure the 45-degree cut is facing straight down and you epoxy the tube in place.
I'm sorry, but I don't know the OD of the tube. But that shouldn't be too hard to find. Just google for Holley aspirator tube. When you install the tube, make sure the 45-degree cut is facing straight down and you epoxy the tube in place.
Safety Car
Joined: Aug 2000
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From: San Antonio TX
I found this link on Speedtalk that will instruct you on what you need to do to add the tube: http://speedtalk.com/forum/viewtopic...36615&start=15
Burning Brakes
Joined: Jul 2016
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From: Blaine MN
I will measure mine this evening and post finding. I don't think my center Carb had the tube being mentioned, I sealed the hole with my finger during leak testing and it was smooth.
Sorry for the delay, my fuel leak on the front Carb took precedence (needle/seat assy. moving fuel level up as I tightened lock screw), if you do any screw tightening on your Carbs use the Holley torque specs and inch pound torque driver.
Sorry for the delay, my fuel leak on the front Carb took precedence (needle/seat assy. moving fuel level up as I tightened lock screw), if you do any screw tightening on your Carbs use the Holley torque specs and inch pound torque driver.
Burning Brakes
Joined: Jul 2016
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From: Blaine MN
The center Carb. (list 4055-1, date 842) port (next to Booster Venturi) measured 0.085-0.088". The outboard Carb. (list 3659, date 841) port (same location) measured 0.04x" (didn't have wire the right diameter) but less than 0.050". So it sounds like your port size is correct, I recall reading somewhere tht you installed o-rings between the Diaphragm Housing and Main Body? The correct item in that location is a cork gasket. You can verify operation of each Diaphragm by using a piece of rubber (or a friend with small fingers) to cover the internal port and apply Vac. with a hand pump, it should stay open until you release the Vac. Get a hand pump with a gauge, this way you also will see your opening Vac. pressure and rough spring curve. Hope this helps.
Burning Brakes
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From: Blaine MN
Regarding my Carbs, they are the correct date code Carbs for my 1968 L71 (I can't swear they are original but I swear about them enough due to all the internal corrosion damage to believe they are). I can also tell you that the Secondaries take a fair amount of mass air moving through the Center Carb. before they begin to open (volume and time). I'll be putting mine back together this week and I'll give you some Vac. and RPM numbers off of the Center Signal Port on the weekend.
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Regarding my Carbs, they are the correct date code Carbs for my 1968 L71 (I can't swear they are original but I swear about them enough due to all the internal corrosion damage to believe they are). I can also tell you that the Secondaries take a fair amount of mass air moving through the Center Carb. before they begin to open (volume and time). I'll be putting mine back together this week and I'll give you some Vac. and RPM numbers off of the Center Signal Port on the weekend.
Actually im in the UK, the car was bought in MA in the spring, I imported it, it is really beautiful.
But now I'm really stuck - the hole using your wire test, has maybe a 0.5 mm clearance around a 2mm wire, so even though its a bit bigger than your measurement its not like night and day, so I'm not convinced this is the root cause.
So many thanks for your help, sadly I may be going 4 bbl as I've spent far too much time getting nowhere. I'll keep the set as the original fit. I can't seem to find anyone in the UK who knows these, short of buying a completely remanufactured set I have no where left to go now!
I may buy a vac gauge so if you do take your readings please let me know. Obviously you realise these have to be driving values, even more of a challenge unless you happen to have a rolling road at home!
But thanks again!
Paul
Last edited by ti9ere; Aug 17, 2016 at 03:49 PM. Reason: added text
Burning Brakes
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From: Blaine MN
Actually I will be doing it while driving, I'm also going to use a usb bore scope in the engine compartment to see the throttle shaft movement and temporarily attach a TPS to one outboard carb so I can correlate my logger data. It''l be this weekend, so don't give up yet. (I was in UK this spring for work and a little play, I really liked the place).
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Actually I will be doing it while driving, I'm also going to use a usb bore scope in the engine compartment to see the throttle shaft movement and temporarily attach a TPS to one outboard carb so I can correlate my logger data. It''l be this weekend, so don't give up yet. (I was in UK this spring for work and a little play, I really liked the place).
I don't like to be beaten by a mechanical thing - so I did buy a vac gauge so I can measure the output from the centre port.
I did a bit more digging today - I have to say that the secondary butterflies don't need a whole lot of 'suction' as applied by mouth at the end of the tube to move them.
I also checked that there are no blocks or leaks in the whole circuit from the venturi hole downstream.
Maybe they are working, in which case I don't get why the car behaved so differently above 3000 rpm when the manifold vac was pulling the secondaries!
Look forwards to you update, thanks.
Burning Brakes
Joined: Jul 2016
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From: Blaine MN
I would discount any behavior you experienced when hooked to manifold vac. The secondaries are not meant to operated that way. I most cases manifold vac. is very low at WOT (volume of air thru throttle bores is high and creates the signal to open the secondaries)) but at part throttle it can be quite high (Cam and Load dependent) which would likely pull the hard on the secondary diaphragms and the closing linkage. The thing to remember is that the signal port is above the throttle blades which tends to be at a higher pressure than the manifold and it relies on mass and velocity to create said signal. (side note: theoretically a larger signal port should (location would be critical as it's near a venturi transition) provide a stronger signal).
Burning Brakes
Joined: Jul 2016
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From: Blaine MN
I didn't write the WOT/Part Throttle section very well, my parenthetical note about volume was in relation to the signal port. My main point was that a manifold signal would be very different from a throttle bore signal that is located above the throttle plates. Describing air velocities and pressures inside the carb. bores is a science beyond my knowledge, I just wanted to assure you that using a manifold port for the Secondaries is a bad plan. I think some folks figure if you can switch the Dist. Vac. Adv. from one to other other why not the Carb.Secs. as well.
Melting Slicks
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