Holley transfer slots

[Godsmack635]

Hello all-  I have a Holley 4150 750dp that I've been trying to get tuned in.  I rebuilt the carb with the kit I picked up and had it set with stock jets and power valve.  After some trial and error I'm now running 72 jets primary and 82 secondary.  Not far off from stock with a 4.5 power valve as I have between 8 and 9" of vacuum at idle.  The engine is a 383 with Eddy performer intake, 2 1/2" hedman headers, stock heads with a pretty decent cam.  I do not have the specs on the cam but it sounds pretty lumpy.  Initial timing is at 24* and total at 36* running an MSD 6AL setup.  I bought this carb used on CL and it seems to be in great shape other than a few helicoils I've noticed in the main body.  Car was running pretty good until I stripped a float bowl screw.  I took the carb off and after fixing my problem I noticed the transfer slots on the primary and secondary plates were set up different. The primary was exposed about .080 versus the secondary side being completely covered.  When I had the carb mounted with this setup it seemed to run way nicer at idle.  After setting the transfer slots both primary and secondary to .025-.030 each.  Now it runs like crap. I've read somewhere that both slots should be evened out like this but its running like it hates it.   The carb now runs really rich at idle.  Do I have to drill holes in my throttle blades or should I put the transfer slots back to where they were?  Only reason I adjusted the slots from where they were is because I thought it might help my off idle stumble.  thinking I should have left them the way they were.  Any suggestions or help would be great.  Thanks!

[c00nhunterjoe]

Overall it sounds pretty close. Sounds almost like your initial setup was idling on the primaries instead of the idle circuit. Ideally, you want just enough of the slots exposed to resemble a square when you look at the slot against the butterflies. Anymore exposed then that and you can have an off idle bog. Too little exposed, and you can have an off idle bog. Based on what you are describing, you have a 4 corner idle setup correct? To keep things simple, make sure there is only a power valve in the front metering plate. The rear should have a plug in it. Once everything is setup, see if she idles at the right speed. If its too low, then you may want to look into drilling a hole for more air. But first i might suggest a little more timing. Both initial and total. Then adjust the idle mixture screws to lean it out if it needs it.

[Godsmack635]

It is a 4 corner idle setup and I know for sure the secondary power valve is blocked off.  I also tried tweaking the timing both advancing and retarding which seemed to make it worse.  The transfer slots were both set up as "squares" as you suggested.  I have to adjust the curb idle a little high when the car is in neutral but as soon as I put it in gear it starts to sputter and die.  I pulled a couple spark plugs and checked them both looked like they were really rich.  Does this sound like I have to try drilling a hole or holes?  how many?  one on each of the butterflies?  Both primary and secondary butterflies?  Right now the idle  mixture screws I have all 4 adjusted 1 and 1/2 turns out then about a 1/2 turn in.  this is where I had my highest vacuum reading at between 8" and 9" at idle.  I appreciate your help.

[1974dodgecharger]

I drilled in my primary butterflies I think 1/8th...you might have a 509 cam...that's a nice lumpy sound to them.  I have a manual so I can get away with a lot more than you...as in forgiving on the idel stuff.  I run 81 jets in rear and 72 in fronts with PV blocked off in rear of course.  With 35 squarters and 31 in the rears.

[Godsmack635]

I should have added that I have the rear power valve blocked off and I'm running a 37 nozzle in the primary with a 35 in the secondary. I'm still at odds with getting this thing to idle both in park and in gear. I've checked for vacuum leaks and found nothing. PCV valve is connected to back side of carburetor under secondary bowl.

[c00nhunterjoe]

It is a 4 corner idle setup and I know for sure the secondary power valve is blocked off.  I also tried tweaking the timing both advancing and retarding which seemed to make it worse.  The transfer slots were both set up as "squares" as you suggested.  I have to adjust the curb idle a little high when the car is in neutral but as soon as I put it in gear it starts to sputter and die.  I pulled a couple spark plugs and checked them both looked like they were really rich.  Does this sound like I have to try drilling a hole or holes?  how many?  one on each of the butterflies?  Both primary and secondary butterflies?  Right now the idle  mixture screws I have all 4 adjusted 1 and 1/2 turns out then about a 1/2 turn in.  this is where I had my highest vacuum reading at between 8" and 9" at idle.  I appreciate your help.

if you raised the idle by opening the primary butterflies AFTER setting the idle transfer slot, then you negated the purpose of doing it in the 1st place. one trick you can try, prior to drilling the plate, is pull the carb back off, flip it upside down and slightly open the secondary butterflies a little more then the squared slot appearance. its trial and error, too much and the mixture screws will be ineffective on the rear metering block. the most crucial is the front slot, put it back to the square appearance and dont touch the screw.if you open the primaries to raise the idle, you will have too much transfer slot exposed and get an off idle bog. i was able to set my idle without using the drilling method on my 383 with a decent cam. mine idles at 1250-1300 rpm and i do not have a drilled plate. 4779 holley 750 dp.
  if its got anything near a 509 cam in a 383, she should want 25* initial at least, and probably closer to 40 total. another question regarding timing, what distributor do you have? vacuum advance? my next suggestion is block the vacuum advance if you have it, and also depending on the distributor, you might want to check the advance springs. ive seen alot of the mopar distributors cause idle issues due to the springs either being incorrect, or weak from age. when this happens, the car will not idle because the advance curve changes by a few degrees when you go from park to drive causing a big rpm difference. same goes with the vacuum advance canisters.

[Godsmack635]

So I should try setting my idle only using the secondary adjusting screw while leaving the primary blades in the position so that the transfer slot is square..... I will give this a try. Also my distributor is the MSD pro billet with mechanical advance. I'm assuming that because I'm only getting 12 degrees of mechanical advance someone has modified the bushing used to limit the mechanical advance. I can also shoot for 25* initial and see of this helps. Setting my total and curve I will try after I get my results. If there's anything I'm missing let me know. I will try to get this stuff during the weekend coming up. Thank you again everybody for your help.

[c00nhunterjoe]

So I should try setting my idle only using the secondary adjusting screw while leaving the primary blades in the position so that the transfer slot is square..... I will give this a try. Also my distributor is the MSD pro billet with mechanical advance. I'm assuming that because I'm only getting 12 degrees of mechanical advance someone has modified the bushing used to limit the mechanical advance. I can also shoot for 25* initial and see of this helps. Setting my total and curve I will try after I get my results. If there's anything I'm missing let me know. I will try to get this stuff during the weekend coming up. Thank you again everybody for your help.

Yes try using the secondary to raise the idle. Open the secondaries the max they will go while still leaving a decent looking pattern on the transfer slot. If it isnt enough to get the desired idle, then look towards drilling a butterfly. Odds are it will idle too high, which is good, then you can close the secondaries some to obtain the desired idle speed.
 Thats a nice distributor. The advance curve kit is only about $15 and lets you change the total amount of advance and the curve. based on what you initially posted, i would advance it 2 degrees giving you 26 initial and 38 total. That should be pretty close to the sweet spot on your 383. Be sure to have someone there when you set the timing. Set it in park 1st, then verify that the initial timing doesnt change when you put it in gear. If it does, then you need to change the springs in the distributor.

[Godsmack635]

alright thanks again I will post my results as soon as I can.  I just ordered one of those secondary idle adjustment brackets from eBay.  Should be here within a week.  I hope this isn't a dumb question but I'm just curious how does setting the idle speed using the secondary throttle blades help me more than using the primary throttle blades?  Hoping someone can explain to me the advantage of using one over the other. 

[c00nhunterjoe]

The primary blades are what move 1st from an idle so they are the most critical to have perfect. The secondsries are also important because the slot still affects the idle mixture and if it gets opened too far it will cause problems too, but you have a little more room to play with on the secondary blades and it is usually enough to bring th idle under control. When you open the primary blades to raise the idle you are overexposing the transfer slot and you will get a huge off idle stumble/bog/dead spot in the throttle that 90% of holley owners complain about. The transfer slot being overexposed to correct a low idle is usually the culprit.

[Godsmack635]

It all makes sense thanks again. 

[c00nhunterjoe]

here is a good watch.

https://www.youtube.com/watch?v=gag-Bg-X8cM

[Godsmack635]

I watched the video, paid special attention to the idle portion.  What stumps me still is I know my secondary transfer slot is already exposed about .030" if I can only go to .040" I don't have alot of room left on my secondary transfer slot.  I hope by bringing it to the max at .040" my idle will stabilize leaving my primary slot at .025"-.030" and not touching it.  If this doesn't help  I may be bringing out the drill. 

[c00nhunterjoe]

what are you trying to get it to idle at?

[Godsmack635]

800-900 in gear.

[c00nhunterjoe]

If you cant get it to idle at 8-900 in gear without over exposing the transfer slots on both sides then there is another problem. What is it idling at in park?

[Godsmack635]

its at about 1000 RPMS in park but I have to keep it running by hitting the throttle in park.  It smells and acts like its way too rich and loading up.  My goal is to have it idle between 800 and 900 in gear but I can't even get it to idle in gear................YET!

[c00nhunterjoe]

1000 in park should be no problem between the primary and secondaries. Check for vacuum leaks and the idle circuit.

[Godsmack635]

even at 1000 rpms in park, it won't stay idling unless I keep blipping the throttle.  idle mixture screws did nothing to help.  I haven't been able to identify any vacuum leaks.  I will still bump up my timing from 24 to 26 initial and 38 total see what happens.  If none of this helps, I'm thinking my plan is to remove the carb, set primary transfer slot to .020-.030 and measure the gap between the bore and the blades on the primary.  I will set the secondary blades with the same gap measurement between the bore and blades as the primaries.  If I have to adjust my idle any, I will use the secondaries.  I will also note how many turns on the secondary idle screw it takes to go from baseline to .020-.030 into the secondary transfer slot.  If I have to exceed the amount of turns to reach .020-.030 in thte secondaries I may have to drill holes in my primaries.  If anything I can JB weld them back together if I don't get the results I want. 

[c00nhunterjoe]

even at 1000 rpms in park, it won't stay idling unless I keep blipping the throttle.  idle mixture screws did nothing to help.  I haven't been able to identify any vacuum leaks.  I will still bump up my timing from 24 to 26 initial and 38 total see what happens.  If none of this helps, I'm thinking my plan is to remove the carb, set primary transfer slot to .020-.030 and measure the gap between the bore and the blades on the primary.  I will set the secondary blades with the same gap measurement between the bore and blades as the primaries.  If I have to adjust my idle any, I will use the secondaries.  I will also note how many turns on the secondary idle screw it takes to go from baseline to .020-.030 into the secondary transfer slot.  If I have to exceed the amount of turns to reach .020-.030 in thte secondaries I may have to drill holes in my primaries.  If anything I can JB weld them back together if I don't get the results I want. 

If you screw the mixture screws in all the way and the engine wont die right away, then you are idling on the primary circuit. like i mentioned before, set both blades so the slot looks like a perfect square and fire it up, if the idle is too low then you willprobably end up drilling. Do not use jb weld!!!! Use a pop rivet. If the jb weld were to break off you would be in big trouble.

[Godsmack635]

Ok thanks again.  I'll post my results as soon as I can get a day to test things out.

[don duick]

I have same carb and same problems. I followed above advice now it runs well, low float levels were also a part of the problem.

a big thank you for this topic 

[BSB67]

 When I had the carb mounted with this setup it seemed to run way nicer at idle.  After setting the transfer slots both primary and secondary to .025-.030 each.  Now it runs like crap. I've read somewhere that both slots should be evened out like this but its running like it hates it.   The carb now runs really rich at idle.  Do I have to drill holes in my throttle blades or should I put the transfer slots back to where they were?  Only reason I adjusted the slots from where they were is because I thought it might help my off idle stumble.  thinking I should have left them the way they were.  Any suggestions or help would be great.  Thanks!

Honestly, I did not read all of this thread but a couple of things jumped out at me here reading you initial post: 1) If it ran better before, you were probably closer to correct before than now, and 2) The transfer slots do not need to be exposed the same between the primary and secondary sides.

In most applications the secondary's are completely closed.  The start position for beginning your idle tune is with the secondary's closed.  Adjust them a very very little bit in a stepped approach as needed to acquire decent primary idle circuit control.  That is it.

If the cam is huge, you may need to drill the primary throttle plates.

You cannot have your timing change from idle neutral to idle in gear.

If your cam is huge, and have a stock converter, you might not be able to get where you want to be.

[Godsmack635]

This weekend I set my primary throttle blades to expose only .020" of the transfer slots.  I closed the secondary throttle blades and just barely cracked them open from their seated position.  I picked up one of those secondary idle screw brackets and mounted it as well.  This way once I get the car running I can set my idle using the secondary idle screw from the topside and leave the primaries alone.  I do plan on checking the timing again as well and seeing if there is any change at idle while the car is in gear and put into park.  I hope to get all this done Halloween weekend.  Thanks for your input. 

[c00nhunterjoe]

Only problem doing it that way, now you wont know how much you are opening the secondaries... too much and you will get a bogwhen they open and have more idle issues. Thats why i said to open both to the max safe limit of .020-.030 and put the carb on. Start it up and see how it idles. If the rpm is still too low like that, then you will need to drill the plates. If the idle is too high, then you can start backing then down.