Ad Radar
Item Posts    Sort Order

650 Holley Problems?

 
av71674
I love my Chevy Chevette!
Posts: 16
Joined: 12/13
Posted: 07/04/14 11:16 AM

Have a 650 Holley Spreadbore manual secondary double pumper
List 6210-3,with the devorced choke removed completely,30cc front and 50cc rear acc pumps.
This carb was used but in good condition when I rebuilt it,but seems to have been tinkered with by the previous owner.
It idles very rich,and adjusting the mixture screws make no difference in vacuum readings.I can screw them in to the point of killing the engine,so I don't think the new power valve I put in is bad.
I've also noticed that the secondaries are closed completely,so it's only idleing off the primaries.Sometimes the secondaries hang up just a little bit and the engine idles up.
It's not a 4 corner system, but I think I read somewhere that the throttle plate position of the secondaries are still part of the idle system.
If so I could use a step by step "block of instruction" on how to get this thing back to how it should be.

Also,could the jet sizing have any affect on the idle quality?  

Post Reply
wayne712222
V-6 Camaros rule!
Posts: 90
Joined: 11/13
Posted: 07/04/14 01:17 PM

first.. may i introduce you to your idle transition slots..
Idle Transition Slots Setting Zps7bcc767a

if you have TOO MUCH of the slot uncovered at idle. .you will have an overrich condition that you cannot adjust out  with the idle mixture screws..

lets look at a basic idle circuit.. including idle and idle transition..

Idletrasnitionmains Zps1a151b85
note that the idle transition slot is NOT flowing in the left image.  as the primary throttle blade is almost fully covering the idle transition slot.  the only fuel coming into the engine is  controlled by the idle mixture screw..

in the middle.. you can see that the throttle is opening.. and the idle feed and the idle transition circuits are both flowing.. but note.. that the main circuit is NOT flowing..

the right hand image shows just the main circuit flowing and this is actually wrong.. at part throttle you have both the idle transition and the main circuit flowing..

lets look at a cutway of a holley now..

look at the image in the circles..
4150 Idlecircuit Zps725109ae

the only fuel is coming thru the idle feed circuit that is regulated by the idle mixture screws in the metering block.. the idle transition slot is NOT exposed..

this is the holley off idle.  fuel is coming out of the idle transition slots with increases as more of the slot is exposed to the vacuum below the throttle blade..

4150 Idletransitioncircuit Zps16485abb
the idle transition flow is limited by the idle feed restriction.. and the idle air bleeds..  usually carbs are set up for around a 355 cubic inch motor as far as i can tell..  so if you have a smaller motor.. you will need to possibly reduce the size of the idle feed restriction..  if you have a larger motor.. you may experience a lean flat spot off idle.. and you will need to go thru progressive increases in idle feed restriction  sizes.  this is best done with an air fuel ratio gauge and an oxygen sensor installed in the down pipe or a heated oxygen sensor in the header collectors..

you can tell if you have a correct sized idle transition circuit..  as you can take the engine to about 3000 RPMs. and ever so slowly back off  the engine should still operate smoothly.. you should be able to drop it back to 1200 rpms and be able to hold that rpm and slowly increase without any need for accelerator pump action

after market metering blocks have easily changed idle feed restrictions..
Aftermarketholleymeteringblock Zps64c2ebb7  

Post Reply
wayne712222
V-6 Camaros rule!
Posts: 90
Joined: 11/13
Posted: 07/04/14 01:33 PM

now that the theory is out of the way..

lets clean a few things...  this is a 4180 with 4 square baseplate idle screws. but the idle circuits remain the same..

please if your carb is together. remove the idle mixture screws..  spray some carb cleaner into the passage. and then follow by a blast of compressed air..

4180 Motorcraft Holley Idle Air Bleeds Zps7c98df5f

if your idle air bleeds are clogged or filled with dirt.. fibers.. dust.. fibers come from the air cleaner gasket and the air filters elements.. as there is significant airflow into the air bleeds during normal engine operation..  i have a 6" piece of 0.023" diameter stainless MIG welding wire that i have wound a loop on one end.. that i can fish down into the  idle air bleeds to check for blockage.. do not change the size with the wire.  if it don't fit.. don't force it..

next.. with the choke held open.. so you are NOT fighting the fast idle cam.. back off on the idle speed screw until the primary throttle blades are fully closed.. turn the screw in until the throttle linkage just starts to move.. take it back to the zero point and give it only about 1/2 to 3/4 of a turn..  start the engine.. how does it idle.. is it idling really slow.. you may have to open the secondary idle stop a little.

do you have a PCV valve hooked up properly.. if you have a digital tachometer or a timing light with a tachometer display.. if you have the engine idling.. when you pinch off or block the PCV flow.. the idle should drop from 50 to 70 RPMs..  if it drops more.. then you need a slightly smaller PCV ... if it drops less.. then you need a slightly larger..  there are as far as i know.. no flow charts on these..  just look into the bottom of similar shapes at the parts store for bigger or smaller..

so. if you get my drift.. you can set the idle speed using the secondary throttle stop adjustment.  as you will be setting the idle mixture using the idle screws.. the air and fuel will blend.. and we are not talking about a huge issue of mixture distribution at idle..  but you want the idle fuel to ONLY be coming out the idle feed ports .. not the idle transition slots..

let us know how it works out..
factory holley idle feed restrictions are NOT easy to change..  

Post Reply
wayne712222
V-6 Camaros rule!
Posts: 90
Joined: 11/13
Posted: 07/04/14 01:50 PM

lastly.. you may want to take the carb back off.. hold the choke open to see where the primary plates are closing with the fast idle cam off.   but i would probably remove the base plate..  back off the idle speed screw again..  hold it up to the light and make sure that the throttle plates are all centered..  if they there is random gaps around them that don't match.. you will need to loosen the throttle plate screws not more than 1/4 turn..  if you try to loosen them more you can break the screws off and ruin your day..  loosen the primary blades and hold them tight with your fingers in the bores and then snug the screws back down and recheck the alignment.. do the secondaries.. recheck them all..

what happens is the carb gets set down.. the linkage hangs out below the base plate..  this forces the linkage open and the edges of the throttle blades are exposed to the weight of the carb bouncing down on them.. this forces them a fraction of an inch off center..  driving you crazy.. as left and right side of the carb will be totally different..  

Post Reply
av71674
I love my Chevy Chevette!
Posts: 16
Joined: 12/13
Posted: 07/04/14 03:32 PM

Smile  Wow..Now that's a block of instruction.Pretty much covers everything I was looking for.Thanks Wayne.Will get it pulled off in the morning and get the throttle blades set up the way they're supposed to be, and find out why the secondaries don't close completely unless I do it by hand.Spring tension or binding probably.

Did have a problem with the air bleeds clogging right after it was overhauled.Started surging at constant throttle and back firing during deceleration.Had to go back and blow them out again.Since then no problems other than the rich idle,
and sucking down 8 bucks a gallon at an alarming rate. Tongue


You still on Gmail?

Ravoll  

Post Reply
wayne712222
V-6 Camaros rule!
Posts: 90
Joined: 11/13
Posted: 07/05/14 12:13 AM

i am here and there.. knock off a 2.  but i prefer to post here even if it is a pain sometimes as so many other people read it..  and learn..
this took me a LOT of years to put together this info..

you can use photobucket or imgur.. to upload your photos to..  and paste the links here..

i do drop thru at least twice a day looking for posts that might need an answer..

early in the nascar season the year before they went to fuel injection i was talking to a circle track carb metering block manufacturer about the excessive fuel consumed in the corners that comes out as flames in the tail pipe that is mostly from the idle feed passages and extremely high manifold vacuum during engine braking..   i talked about spring loaded sort of power valves that blocked the idle passages during extremely high manifold vacuum operation .. like engine braking into corners.. about three races from the end of the last season for carbs. the race was won by a car that the announcers noted that there were no flames coming from the exhaust.. i was jumping up and down.. everybody was running out of gas at 52 or 53 laps.. he won the race by going 57 or 58 laps without a pitstop..  i don't know if my other ideas got used either.. where the filler neck extension into the fuel tank foam goes deep into multi layers of different density fuel tank foam..so the incoming fuel fills the bottom of the tank first.. and the air is expelled thru the foam as the fuel level in the tank rises.. this prevents the burping needed during fast fills that slows down the speedy fill during pit stops.  yes.. i am very creative.. did the fuel fills get modified???  

Post Reply
av71674
I love my Chevy Chevette!
Posts: 16
Joined: 12/13
Posted: 07/11/14 09:42 AM

So.I've tried everything suggested.Have the primaries closed so far that it will barely run...400 to 500 RPM.I can turn the idle mixtures in all the way and kill the motor.The power valve is not bad,but I changed the 6.5 out with a 4.5 anyway,just to be sure
Have the mixture screws currently set at about 2  turns out pulling 16hg  steady @500 rpm.Still running terribly rich.If I turn the main idle screw  to 650 RPM,it gets worse, and the mixture screws have no effect.
I can only tear this thing down and blow passages so many time till it starts getting stupid.Did see where it has  jets with 602 markings.Don't know what these are cause I can find no info on them. Anyway I'm taking this pig off and putting the Q-Jet back on for now. Tongue  

Post Reply
tuffnuff
Moderator
Posts: 272
Joined: 01/10
Posted: 07/12/14 07:53 AM

The Holley spread bore carb has few of the good features of the square bore.,. such as external adjustable floats.
I tried a couple over the years and I was not impressed.,. your 750 or 800 CFM Q-Jet, if in good tune, should outperform the Holley.

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

Post Reply
av71674
I love my Chevy Chevette!
Posts: 16
Joined: 12/13
Posted: 07/12/14 02:37 PM

Yep,The Q-Jet does out perform the Holley...most of the time.Sometimes it come on really flat for no reason,like the power piston's not rising.Is why I moved over to the holley spreadbore.100cfm smaller with smaller primaries,it has more punch than the q-jet ever did.
Just running rich to the point that it's not acceptable.Have messed with tons of Holleys over the years and have never had problems like this one is giving me.
Anyway the Q-jet is back on with a number smaller rods and seems to have cleared up on the coming on flat problems...at least so far.Even when it did it wasn't always,so time will tell if it's ok or not.Gonna look into what this holley's problem is.Can't let it beat me,but it on the back burner for now.  

Post Reply
just try it. it might work you never know
I love my Chevy Chevette!
Posts: 4
Joined: 08/14
Posted: 08/05/14 02:25 AM

there are various power valve springs available for the quadrajet...

there is also the APT adjustment that will cure most of the off idle issues...

if you have a mid throttle flat spot.. play with the secondary air door spring tension..

1/2 to 15/16 of a turn in 1/16 of a turn increments...  

Post Reply
TO TOP