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Old 07-18-2007, 11:41 AM
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holley secondary problem

Hi
I'm running a 4 cyl that is mildly worked over,bored,HC head,cam,header,bigger valves,and a holley 390.I think because of the cam I only have 14 in of vacumn. The secondaries are not opening,I have the lightest spring in it. someone told me to insert a screw somewhere on the linkage to help,but I forgot where. Does anyone know anything about this?

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Old 07-18-2007, 01:57 PM
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Do not do this you will ruin a perfectly good carb.The engine will bog as the secondaries are forced open by the screw as there is no pump shot to cover it.Also intake vacuum has no bearing on opening the secondaries it works off of air velocity thru the primaries.How do you know they are not opening? if they are working correctly you will never feel it.Try puting a tie strap around the shaft that comes from the diaphram at the base of the diaphram drive it, come back and see if it has been slid down the shaft if it has they are working. Also another thing to consider if it is a smaller 4cyl they may never open as a vac secondary automatically regulates carb size by only opening as much as the engine can use.If the velocity never comes up high enough(high demand )they will not open.Thus preventing over carburetion.
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Old 07-18-2007, 02:01 PM
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I tried the wire yie thing and they are not opening. I used to have 2 sidedrafts on this engine and they ran 4 barrells all the time
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Old 07-18-2007, 03:23 PM
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You didn't mention the cubic inch of the engine , so I couldn,t do the math .
rpm x ci devieded 3456 gives you 100% cfm . That 390 seem a little large based on 144 ci ??
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Old 07-18-2007, 03:41 PM
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Its a 2.0 bored .40 over Like I said it used to have 2 mikuni 40 sidedrafts and they had no kind of progressvive linkage or vacumn they ran on all fours all the time with no bogging or anything but I had some leakage issues and decided to go with the one 4 barrel,but I'm running on just 2
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Old 07-18-2007, 07:32 PM
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The mikunis that you were running before are a completely different kind of carb and cant be compared to the holley. Try pushing the seccondary pushrod up into the diaphragm as so they are all the way open, and cover the signal hole in the ventury with your finger or a piece of rubber, then let go of the push rod and see if they stay open. If they close you may have a bad diaphragm and it isnt holding vaccuum.
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Old 07-18-2007, 09:09 PM
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I'll try tomorrow,thanks
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Old 07-19-2007, 09:23 AM
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drop a small piece of paper in the secondary hole. drive it hard and then look for the paper.

if you are using a quick spring change kit, make sure there is a gasket on the lid. no gasket, no vacuum, no open.

the secondary works of venturi vacuum. low idle vacuum from the cam will have no effect. Air flow thru the carb is what makes the vacuum.

check the seal around the secondary diaphragm.
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Old 07-19-2007, 11:54 AM
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If your vacuum secondary diaphragm gasket has a hole or tear it will not open at all check the gasket.
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Old 07-19-2007, 03:39 PM
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Quote:
Originally Posted by 454C10
drop a small piece of paper in the secondary hole. drive it hard and then look for the paper.

if you are using a quick spring change kit, make sure there is a gasket on the lid. no gasket, no vacuum, no open.

the secondary works of venturi vacuum. low idle vacuum from the cam will have no effect. Air flow thru the carb is what makes the vacuum.

check the seal around the secondary diaphragm.
I do have the quick change spring kit I'll check it no time for a couple of days though
thanks
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Old 07-19-2007, 04:06 PM
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There is a round gasket that goes between the removable spring lid and the main body of the vacuum canister. It falls off easily and you could put the lid back on not knowing it fell off.
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Old 07-19-2007, 04:56 PM
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Have you checked you linkage it could be binding or bent and not letting your secondaries open. You can check your quick change gasket but im talking about the main vacuum secondary gasket inside the canister the one that your quick change spring sits on.

Last edited by cianide; 07-19-2007 at 05:01 PM.
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Old 07-19-2007, 05:33 PM
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Quote:
Originally Posted by cianide
Have you checked you linkage it could be binding or bent and not letting your secondaries open. You can check your quick change gasket but im talking about the main vacuum secondary gasket inside the canister the one that your quick change spring sits on.
I appreciate all of the advice you guys are giving me so monday or tue of next week I'm going to check everything u have suggested
THANKS
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Old 07-19-2007, 07:47 PM
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Quote:
Originally Posted by 454C10
There is a round gasket that goes between the removable spring lid and the main body of the vacuum canister. It falls off easily and you could put the lid back on not knowing it fell off.
Actually it's an "O" ring about 1" in diameter.

Vince
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Old 07-20-2007, 02:59 PM
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On a2.o liter engine at 7000 rpm and 100%v.e you need 247cfm the secondaries are not opening probably because the engine can't use it. If they opened all the way you would probably have a huge bog and the engine would die, the air speed thru the venturis would slow to the point no fuel would be pulled from the metering circuit.What you are doing is equivelent of an 1150 dominator on a stock 283. Ain't gonna happen now if this thing will turn 11000 to 12000 rpm it could work. Basically if the diaphram isn't ripped, seal missing etc. the carb is doing what it is designed to do the secondaries are opening in response to engine demand for more air,or in this case it don't want it and ain't gonna take it.
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