Hey guys, As many times that I messed with my carb the one thing Im never sure on is my transfer slots. I know they are supposed to be .020'' exposed or make them look like a tiny square. But it seems that the common problem with this adjustment for most people is that they would have to open the butterflys too much to get there car to idle so they start drilling holes in the butterflys. My situation is the opposit, If I expose the transfer slots @.020 the car idles too high and I cant get the idol to come down to the 700rpm idle I like unless I close the butterflys to the point where no transfer slot is exposed. This is a holley hp pro carb and it came with holes already drilled in all 4 butterflys. Am i doing something wrong or what kind of problem will it cause if you dont have transfer slots exposed? sorry 4 the long post

Think of the throttle opening ever so slightly while you're driving. At that point, with no slot exposed, you could have a flat spot. The slot opening should be timed to the throttle opening for a smooth transition from idle. Can you close the secondaries slightly to get the primaries open enough? A car that idles at 700 rpm is too mild to need holes in the butterflies. I've epoxied them shut before but I don't know the right way to close them short of replacing the butterflies. Even plugging the PCV would help but thats not a good solution for the street.

There is more to it than uncovering the transfer slot, I honestly never heard the .020" uncovered for a Holley until Barry Grant started providing the info with their carbs. Now it seem like the Gospel...

Keep in mind the idle mixture (on all 4 corners on most HP series carbs), the secondary throttle blades, timing and jetting all are basic's with respect to an engines idle. Add to that the proper PCV valve as Mark has mentioned.

What's the list number on this carb (on the side of the main body)? Are you sure it came from the factory with drilled throttle blades?

its a holley hp pro and I bought it new and it did come with holes in the throttle plates. the question im asking is there a problem running the carb with no transfer slots showing or is that creating some type of other problem the carb seems to run ok but mabe it could be better.

It could just be set so rich that it covers up any slight hesitation. If you start leaning down the ifr's to get some mileage you may start getting issues. Nothing is set in stone with these things. There's only general guidelines and then you have to give the motor what it wants. If it runs good......

Flyer - I have 2 HP pro series carbs and neither have holes drilled in the throttle blades. There are many different carb within the HP pro series... I gave you reasons for why you might be having to close down your throttle blades and Mark provided problems that could come from not having the transfer slot exposed... On the primary side, the slot has to be exposed a bit, maybe less than .020" but not closed down al the way.

Back to the holes in your throttle blades, that is a fix for a carb that is not designed for an engine or cam to allow it to idle. Maybe your carb was a return... I don't know maybe you have a version that is for a much more radical cam than you have.

It's really hard to give direct yes or no answers without knowing more, like what list number the carb is, with the list number folks will know exactly what you have and combined with the info in your sig may be able to help you figure this out...

I have a HP 750 without holes and a HP 950 ultra with holes? Give it more air with the IABs to bring the idle up . You may have to open the IFRs to get the mixture right. good luck .

my problem is with the throttle plates set at .020 transfer slot showing, the idle will be too high. I dont need to get the idle up Im trying to get it down with the plates set with .020 showing.

Let's take this in little steps...

Have you tried adjusting the idle mixture?

.020 is a maximum setting, back the secondary off till they are closed and set the primary right at bottom of slot. if idle isn't low enough at that point then you may have to replace one set of butterflies with no holes or fill them. I would replace, butterflies are available separately.

Yes. I have tried ever adjustment on the carb except for the air bleeds. I also tried different initial timing. The only thing to bring my idle down to a nice level is the fast idle screw which will set the plates to just about closed with no transfer slot showing. It seems fine but everything I read says thats your first setting and once you set it you adjust everything else around it. Well everything I tried wont bring it down except the fast idle screw.

The fast idle screw is a choke thing, are you talking about the idle screw? Mike said what I was saying earlier with more detail added on the secondary side. If your carb is a 4 corner idle carb you want the primary and secondary throttle blades as close to the same (same for the idle mixture) as possible. If it's not a 4 corner idle then close down the sec throttle blades but make sure they don't bind closed and set your idle with the primary idle adjustment screw.

your right I meant the primary adjusting screw that moves the plates. yes it is a 4 corner idle carb and I guess thats what I have done which is the secondaries are alomost closed and the primarys are set so the car idles @ 700rpm with no transfer slot showing on either primar or secondary. I guess what I need to know do you think its important enough to go thru the trouble to change the plates with ones that do not have holes and then mabie I would be able to expose the transfer slots or just leave it the way they are?

So are you running an HP 950 ultra on your 350ci small block?

If the sec are set right tuning in the idle/ primaries is just adjusting the mixture and idle (primary butterflys) screw Right?
Buy if the secondarys are not right the above will not adjust into factory specs

Adjust the sec butterfly screw so the sec are just off stopping on the bore.
set the mixture screws to the middle of the factory specs
and the idle speed screw to middle of factory spec...
Fire up....it will not run at idle, but will if u screw in the idle speed screw. a bit opening the primaries...
What you need to do is 'transfer' some of the big gap in the prim butterflys to bore over to the seconaries.....
So open up the secondaries and slowly close the idle screw till the idle screw is close to the factory spec....The fine tune the mixture screws as per normal.

This all assumes you have no air leaks in the carb/inlet manifold etc and float levels, float valve seats are all correct and not leaking.

You have to understand this....the carb is 2 carbs in one...a circuit when the car is moving, foot on the accelerater, and another indepent circuit just for isle.
The mixture screws are just for the idle circuit and have NO significant effect once the car is moving...

The old school drill holes in the butterflys came from way back in the 60s and early 60s when carbs where far more primitive and generally only had primaries...today instread of getting more air into the idle mixture by drilling holes, they have secondaries one can open up to do the same thing
It is just another old wives tail that still floats around.

What engine setup are you running this 950 on? Perhaps you are running this 950 carb on a setup that does not require such a large carb? If it's the engine in your signature, I would think a 950 is too large. The reason people drill holes in their butterflies is because they want to be able to get their idle speed down below 1000-1100rpm and still run a large cam. This is really a jerry rig fix. If you have to do this, more than likely you have too large a cam for the engine/carb setup you are running. If this is a street car, then the need for holes in the butterflies indicates too large a cam. If this is a race car, then the cam should be combined with a stall converter that allows the engine to run WITHOUT the need for holes in the plates. A racecar cam will come in around 3000rpm and the stall should stall to 3200-3500rpm.

ANYTIME someone needs holes in their plates on a street car, the cam is too large.