Idle problem, transfer slots

[BelvedereSatellite1966]

Hi,

Holley 850 DP(4781), 383 BB.

Yesterday i did some tuning( and got really good and crisp response in Park, dead stop to WOT in gear is a whole other story, some job ahead with accelerator pumps, but first i need to sort this problem as i think it will help my problem with hesitation.

My problem is and was that i got a really lean tip in.
Open my throttleblades by barely a millimeter(im from sweden) gets my AFR up to 17-22+.

My t-slots was not exposed at all so i took of the carburator today and adjusted to get the square.
My new problem now is that when i opened the primaries to get the square i get to much air in that my idle is way to high.
As my secondaries already is fully closed i took down initial to 10 degrees(from 15), and lean out idle mixture to 16 in Afr.
That got my Rpm on idle down to 950-1000.

The hesitation now is unbelivible, even in park the hesitation is big.
I also got problem that rpm takes a long time to go down to idle-speed, when letting of the gas it goes down to about 1500 rpm and after that slowly decrease to rpm-speed(several seconds).


As im never touched a carburator before three months ago im a rookie, and the only thing i can come up in my mind is that i gets to much air on idle.
My idea is to cut and extend the t-slots, is it any idea?
Or do i need to face that my carb is too big for my application and head for a 750?

As for now i do not have a pcv for crankcase ventilation, only a breather.
I got a tip that you always want pcv from crank installed if you want to get the t-slots working correct.

So, not exposing t-slots give me hesitation and lean tip in.
Exposing t-slot give me more hesitation and wierd idle.
Could not tell if tip in was better or worse as my idlemix was really lean and initial taken down.

Every tip i can get is gold worth.
Thank you!

 

[coloradodave]

First of all, do not cut and extend the transfer slots. All it will do is ruin an expensive carburetor. I would do the following in order to diagnose the problem.
1) Move your initial timing back up to +-16* Check at what RPM your total timing is in and record the total timing figure. Try to not go over 36-38* depending on fuel octane and compression ratio. Heavy pinging on loaded (driving) acceleration is a sign that your timing needs attention.
2) Check your float levels. With the car on level ground, remove a site plug on the side of a bowl and adjust the level until the fuel 'barely weeps' from the hole. Repeat for the other bowl. The Holley site has 'How To' information.
3) Check the adjustment on the accelerator pump arm. ANY movement of the throttle should move the arm and produce a good, hard squirt from both nozzles. With the engine off, slowly push the throttle to wide open and make sure the accelerator pump arm is not bottomed out, that is, make sure there is a tiny bit of movement left.
4) Close both idle mixture screws and then back them out equally 1 1/2 turns as a starting point.
5) Remove your distributor cap and turn your rotor by hand until it stops. Let go of it and it should 'snap' back. If it doesn't, or returns slowly, you need to clean and lubricate the weights in the advance mechanism. This could account for the slow return to idle.
6) Check for vacuum leaks. You can Google several methods to do this.
7) After checking, use a vacuum gauge to set your mixture screws correctly. If no improvement, there are other checks that can be done. Keep us in the loop.

 

[texas69bee]

I certainly don't claim to be a carb guru but why are you playing around with the AFR so high or is that in different units as well? Try between 13-13.5

 

[BelvedereSatellite1966]

Hi, thank you for your answers.

First of all, do not cut and extend the transfer slots. All it will do is ruin an expensive carburetor. I would do the following in order to diagnose the problem.
1) Move your initial timing back up to +-16* Check at what RPM your total timing is in and record the total timing figure. Try to not go over 36-38* depending on fuel octane and compression ratio. Heavy pinging on loaded (driving) acceleration is a sign that your timing needs attention.
2) Check your float levels. With the car on level ground, remove a site plug on the side of a bowl and adjust the level until the fuel 'barely weeps' from the hole. Repeat for the other bowl. The Holley site has 'How To' information.
3) Check the adjustment on the accelerator pump arm. ANY movement of the throttle should move the arm and produce a good, hard squirt from both nozzles. With the engine off, slowly push the throttle to wide open and make sure the accelerator pump arm is not bottomed out, that is, make sure there is a tiny bit of movement left.
4) Close both idle mixture screws and then back them out equally 1 1/2 turns as a starting point.
5) Remove your distributor cap and turn your rotor by hand until it stops. Let go of it and it should 'snap' back. If it doesn't, or returns slowly, you need to clean and lubricate the weights in the advance mechanism. This could account for the slow return to idle.
6) Check for vacuum leaks. You can Google several methods to do this.
7) After checking, use a vacuum gauge to set your mixture screws correctly. If no improvement, there are other checks that can be done. Keep us in the loop.

1. If taking my initial up to 14-15, my idle land on about 1300-1400 RPM. I have a MSD Pro Billet with fixed advance via a bushing. My advance is always 18 degrees, so total of 32 degrees has given me best throttle-response from idle in park.
2. Float is checked, removed bowls and adjusted both primary and secondary with drill-bits.
3. Touching the gas give a squirt, the arms are nice and tight.
4. As for now i have them about 2 turns out, can't go further in i think, my AFR is 16-16.5 now i do not think i can go leaner on idle-mix.
5. I cleaned the distributor yesterday, but i can give it one more shot. I have no problem with slow return when closing of the throttles a little bit more.
6. No vacuum leaks, checked several times.
7. I use a vacuum gauge when i set mixture, i get 15 inches.
The problem is when i expose t-slot my RPM is to high, the only way to get down my idle to 1000 RPM is to lean out idle-mixture and decrease inital.

I certainly don't claim to be a carb guru but why are you playing around with the AFR so high or is that in different units as well? Try between 13-13.5

Hi, same unit!
I cant get any lower AFR on idle-mix as my RPM is to high then.
Only way to get down RPM on idle is to retard initial and lean out idle-mix if i expose t-slots



When i expose my t-slots i get bigger gap at the throttle-blades, it must be that the bigger gaps give me to much air?
Maybe my Throttle-blades is to worn?
Would a picture of the gaps help?

 

[furryfrog]

Sometimes getting these style of carbs sorted can be a fiasco. I think the off idle, slow cruise circuit (transfer slot) on these carbs is archaic and stupid, but its the way it is. It took me a fair amount of work getting mine sorted, (750 DP set up for blow thru) ,I had the same problem your having. It is a good thing you have an AFR guage, I could not have tuned mine without one.

Here is some helpful info to add to what Colorado dave mentioned.

http://www.hotrod.com/how-to/engine/ccrp-0807-holley-carburetors-basics-guide/

Your Main problem I think is getting your Idle down with the correct amount of t slot exposed. Without sorting this out, no point going further. Backing your timing off to slow your idle will just make your hesitation problem worse, the most inital timing you can run the better. Perhaps your carb is too big, guessing you have a mild cam. Adding a pcv will just raise your idle more. If you have no problems to explain your high idle, only couple things I can think of to help.
-bevel the back off your throttle plates to expose your transfer slots when they are closed enough for a lower idle.
-changing your idle air bleeds and idle restrictor feeds to suit, may not be enough though.
- extending t slots is an option, but risky like colorado dave mentioned, but people do it, last resort kinda thing.

To get mine sorted I had my carb off about 6 times, I changed idle air bleeds, Idle feed restrictors, bevelled the back of all 4 throttle plates to expose more transfer slots, drilled small holes in all 4 throttle plates, changed main jets, pump cams, accel pump nozzles, and moved the location of the IFR in the main metering block. Also running 20 degrees initial timing. The holley blue gaskets may be a good investment because they are reusable.

As I was tuning my carb to run better and get over the lean tip, I set my idle AFR rich to compensate, a temporary measure.

good luck

 

[Xp29h]

Looking in on this, I don't have a ton to offer. However, I did find this product that bolts right on easy and worth every penny in time.

https://www.summitracing.com/parts/pro-67237

Allows you to adjust secondary transfer slots without removing the carb!

Good luck!

 

[lewtot184]

some good tips here. i wonder if someone has taken the throttle blades out and didn't put them back centered in the bores? has someone messed with the air bleeds? lazy/slow pump cams and big squirters can cause hesitations.

 

[AR67GTX]

You may have something weird going on or someone has Bubba'd the carb. At warmed up curb idle with your dwell and timing set right, your primary throttle blades should be in the middle of the transition slots. If the blades sit above the slots at curb idle, the old school approach was to drill a 1/16 to 3/32 hole in both blades on the rear side to let more air pass and allow closing the throttle to where it rests in the middle of the slot. Instead of this, pull the carb and look underneath it in the area of the secondary throttle blades. There should be a small adjustment screw there - it's purpose is to keep the secondary blades just very slightly open so they don't sieze in closed position. You can adjust that screw and allow a little more air to pass the primary side which allows closing the throttle on the primary side so that they rest in proper position. It may take a little experimentation.

The caveat to this is if a DP 850 has 4-corner idle mixture settings. I don't know what a DP 850 has on it. If by chance it does have 4-corner idle mixture adjustments are you adjusting all of them?

 

[BelvedereSatellite1966]

Thank you all again for the tips!

Sometimes getting these style of carbs sorted can be a fiasco. I think the off idle, slow cruise circuit (transfer slot) on these carbs is archaic and stupid, but its the way it is. It took me a fair amount of work getting mine sorted, (750 DP set up for blow thru) ,I had the same problem your having. It is a good thing you have an AFR guage, I could not have tuned mine without one.

Here is some helpful info to add to what Colorado dave mentioned.

http://www.hotrod.com/how-to/engine/ccrp-0807-holley-carburetors-basics-guide/

Your Main problem I think is getting your Idle down with the correct amount of t slot exposed. Without sorting this out, no point going further. Backing your timing off to slow your idle will just make your hesitation problem worse, the most inital timing you can run the better. Perhaps your carb is too big, guessing you have a mild cam. Adding a pcv will just raise your idle more. If you have no problems to explain your high idle, only couple things I can think of to help.
-bevel the back off your throttle plates to expose your transfer slots when they are closed enough for a lower idle.
-changing your idle air bleeds and idle restrictor feeds to suit, may not be enough though.
- extending t slots is an option, but risky like colorado dave mentioned, but people do it, last resort kinda thing.

To get mine sorted I had my carb off about 6 times, I changed idle air bleeds, Idle feed restrictors, bevelled the back of all 4 throttle plates to expose more transfer slots, drilled small holes in all 4 throttle plates, changed main jets, pump cams, accel pump nozzles, and moved the location of the IFR in the main metering block. Also running 20 degrees initial timing. The holley blue gaskets may be a good investment because they are reusable.

As I was tuning my carb to run better and get over the lean tip, I set my idle AFR rich to compensate, a temporary measure.

good luck

Very good information, thank you.
Do you have any article or more information on how to relocate the IFR?

 

[BelvedereSatellite1966]

some good tips here. i wonder if someone has taken the throttle blades out and didn't put them back centered in the bores? has someone messed with the air bleeds? lazy/slow pump cams and big squirters can cause hesitations.

Took out all blades and tried to readjust them for less gap, but if they are not adjusted correctly and i bolt on the carb the blades are getting stuck when open the throttle.
So i don't think i can readjust them in any other way.

I do not think they are to worn either, the blades on secondaries look much newer but when i measured them i can't see any difference in size.

 

[BelvedereSatellite1966]

You may have something weird going on or someone has Bubba'd the carb. At warmed up curb idle with your dwell and timing set right, your primary throttle blades should be in the middle of the transition slots. If the blades sit above the slots at curb idle, the old school approach was to drill a 1/16 to 3/32 hole in both blades on the rear side to let more air pass and allow closing the throttle to where it rests in the middle of the slot. Instead of this, pull the carb and look underneath it in the area of the secondary throttle blades. There should be a small adjustment screw there - it's purpose is to keep the secondary blades just very slightly open so they don't sieze in closed position. You can adjust that screw and allow a little more air to pass the primary side which allows closing the throttle on the primary side so that they rest in proper position. It may take a little experimentation.

The caveat to this is if a DP 850 has 4-corner idle mixture settings. I don't know what a DP 850 has on it. If by chance it does have 4-corner idle mixture adjustments are you adjusting all of them?

The secondaries are fully closed now, opening them up more in the state i am in now would just make the problem worse as more air would go in.
I can't close off the primaries more as the t-slot will be closed of then.

My carb do not have 4-corner idle mixture, secondary meters is missing the holes.

 

[lewtot184]

Took out all blades and tried to readjust them for less gap, but if they are not adjusted correctly and i bolt on the carb the blades are getting stuck when open the throttle.
So i don't think i can readjust them in any other way.

this is probably the high idle problem. too much air leaking past the throttle plates. with the large venturii/throttle bore area and a small engine things can get stupid quick. i know, i've been here and done this back in the day. remove the throttle plate assembly from the base carb body, loosen the throttle blade screws, back off the curb idle screw, and hold the assembly up in some light and manipulate the blades until they are perfectly closed, then tighten the screws back up.

 

[BelvedereSatellite1966]

An idea i had was to add a small bushing between the throttle-blades and shaft, it should have the same effect as bevel the blades?

 

[AR67GTX]

I misunderstood and thought the blade was above the slot. I guess you have looked for any possible vacuum leaks. Throttle shafts can wear and leak air but I wouldn't guess your carb has that much use on it.

 

[BelvedereSatellite1966]

Update.

I will probably get banned now when i tell what i done.
I took a small bushing and did my own small gasket with milk carton and put between shaft and blades.
When this was done i could expose t-slot without having to much throttle-opening , turned inital up to 14 and idle mix to 13-14 afr.
Result, tip in problem gone!
Rpm is still a bit to high, 1000-1100 and slow return to idle is also there.

Hesitation on WOT did not change, same problem.
If I hit hard 0-30% throttle at 6 mph it ripping tires thogh(295 tires)
Pulling more then 30% throttle bring afr to high and it starts to hesitate.
It seems that accelerator pumps not giving enough, its wierd as i got 35 squirt and White cam(position 1) on primary and 40 squirt with orange cam(position 1) on secondary.

Tomorrow i will try and add little more between shaft and blades and see if i can bring idle down and head for little more timing.

My big question is if you guys think the gap between shaft and blades affects the fuel and air going through?
As seen in the picture, only bevel the blades would not helped me enough.
Maybe bevel the blades with this gap make the magic, the question is how the gap affects the air/fuel going throught it.



Have a nice Friday!

 

[furryfrog]

Adding a shim like you did is a good solution to your problem, not sure what they make mild cartons out of in Sweden, but the wax cardboard they use here would not work well and gasoline would dissolve it quite quickly. I hope you used locktite on your throttle plate screws? I don't think the extra thickness of the assembly after adding the gasket will affect your flow much, you probably have too much carb as it is.
Glad your making progress.

 

[furryfrog]

Thank you all again for the tips!



Very good information, thank you.
Do you have any article or more information on how to relocate the IFR?

I read somewhere that having the IFR in the bottom of the metering block makes the carb more consistent when it gets hot. My carb did heat up quite a lot and "acted" up when it got hot, so I tapped the lower location and made screw in bleeds from small machine screw threads, and removed the orifice in the upper part of the metering block. It did help in my case. It seems the lower location is where they used to put the IFR's but now they put them in the upper part of the metering block. I can dig up pics if needed.
Another hot carb problem I had is the fuel sitting in my primary accel pump circuit would foam up so my pump shot would not be effective if I had not changed the gas pedal position for a bit, like after sitting at a light for a few minutes. The fuel in the bowl gets a constant refresh of fuel, but the fuel can get stagnant and warm up more quickly in the accel pump circuit. Doesn't help that my rad fan blows hot air directly onto my primary bowl. I made a "sock" for my primary bowl out of some thick heat resistant material, seems to be working well.
I do have higher under hood temps than average, due to a twin turbo setup. Good chance you won't have these specific problems, but just throwing It out there.

 

[BelvedereSatellite1966]

Did a more permanent solution today. Idle-rpm is ok now with 14 inital timing, and slow idle is gone.

But when i did the same on secondarys my idle is to rich instead.

Problem now is to get it leaner on idle.
Idlemix screws one turn out give me 12 afr.
Turning them further in just get my idle-rpm higher without any difference in afr.

Will try to grind down the "washers" tomorrow.

 

[BelvedereSatellite1966]

Picture

 

[BelvedereSatellite1966]

Picture