New heads and intake, now engine bog off the line - Page 2 - Chevelle Tech
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post #16 of 45 (permalink) Old Jun 19th, 19, 10:20 PM Thread Starter
Mike
 
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Re: New heads and intake, now engine bog off the line

Well I pulled out one of the metering rods and found out its a 68-42 however I have not yet taken the lid off the carb to find out what jets are in it. I richened up the idle mixture just a bit. Double checked the accelerator pump linkage is set for max stroke. Took four degrees of mechanical advance out of the distributor and added six to the base timing, its now 18* initial and 20* of mechanical for a total of 38* with no signs of pinging. The condition has improved...but its still sucks. I think I'm going to buy a new Holley 4150 style carb for it eventually. Just doing a lot of shopping and research right now. Liking what I read about the quick fuel HR780.

Also, when I put the new intake on I used one of those edelbrock thick insulator type gaskets because I used to have heat soak issues with my standard performer intake even with blocked heat crossovers. I was thinking of testing out a standard carb gasket, maybe that extra thickness of the insulator gasket is not helping the bog either???

I think the damn carter was a great carb on a mild engine but now its time for a real carb. I think there were three different diameter accel pumps in the Carter AFB and I'm willing to bet I have the smallest one. Ill measure it if I get around to pulling the lid.

Thanks for the help
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post #17 of 45 (permalink) Old Jun 20th, 19, 3:09 AM
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Mike
 
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Re: New heads and intake, now engine bog off the line

Mark Whitener, jmarkaudio has helped a lot of people with free advice here, and he can build a great carburetor for you. You should check him out.

https://www.facebook.com/lightningracingcarburetors/

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post #18 of 45 (permalink) Old Jun 20th, 19, 6:51 AM
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jeff
 
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Re: New heads and intake, now engine bog off the line

Something else to consider is the air gap intake.
I have had terrible bog issues with one I installed on my own vehicle no matter what carb if the weather was cool out and the runners were cold it would bog a little.
Had the same tune issues with a buddies LS carb swap in the winter here.
Now that it is above 85 outside the issue is not there.

I stuck the old RPM intake back on my gen 1 350 and no more issues
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post #19 of 45 (permalink) Old Jun 20th, 19, 11:13 AM
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Kerry
 
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Re: New heads and intake, now engine bog off the line

Quote:
Originally Posted by MNmalibu View Post
Well I pulled out one of the metering rods and found out its a 68-42 however I have not yet taken the lid off the carb to find out what jets are in it. I richened up the idle mixture just a bit. Double checked the accelerator pump linkage is set for max stroke. Took four degrees of mechanical advance out of the distributor and added six to the base timing, its now 18* initial and 20* of mechanical for a total of 38* with no signs of pinging. The condition has improved...but its still sucks. I think I'm going to buy a new Holley 4150 style carb for it eventually. Just doing a lot of shopping and research right now. Liking what I read about the quick fuel HR780.

Also, when I put the new intake on I used one of those edelbrock thick insulator type gaskets because I used to have heat soak issues with my standard performer intake even with blocked heat crossovers. I was thinking of testing out a standard carb gasket, maybe that extra thickness of the insulator gasket is not helping the bog either???

I think the damn carter was a great carb on a mild engine but now its time for a real carb. I think there were three different diameter accel pumps in the Carter AFB and I'm willing to bet I have the smallest one. Ill measure it if I get around to pulling the lid.

Thanks for the help
The insulator gasket isn't creating an issue. Keep it. You simply need a larger squirter nozzle. My father in laws 350 in his 42 Power Wagon did the same thing with his 600 edelbrock. Reset floats, slightly better. Accel pump to longest stroke and stiffest step up springs, better yet again. Larger squirter, problem gone. Until these changes, especially the squirter, if you hit the throttle wide open from idle the engine would just quit. Hit the key and it would start right up again. Taking off you had to feather the clutch and the throttle to not kill the engine.
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post #20 of 45 (permalink) Old Jun 20th, 19, 1:56 PM
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Re: New heads and intake, now engine bog off the line

I am still thinking it's the sec. air valve opening too soon. Find an old one out of a factory Carter and that will cure it, that's why I always disconnect the sec side when I get one of those complaints on Eddy's. If the car runs good all the way up in the RPM then you know where to look to fix the problem.
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post #21 of 45 (permalink) Old Jun 22nd, 19, 8:34 AM Thread Starter
Mike
 
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Re: New heads and intake, now engine bog off the line

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Originally Posted by 68Chevele View Post
Maybe I can look at it for you next month, I live in the Twin Cites. Are you going out to the Summer Cruise this year with your car?
Thanks for the offer but I don't think Ill make it down for the big show.
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post #22 of 45 (permalink) Old Jun 26th, 19, 8:38 AM
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Steve
 
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I too am experiencing the same problem with my 402 BB. Ever since I installed the RPM Air Gap manifold, I have had carb tuning problems from hell. To this day. I am still trying to get rid of my off idle bog. I have spent countless hours reading and tuning and am now considering buying a different intake. I am going to try making some more adjustments this weekend and see what happens. I don't give up easily. I have heard of others having the same problem after installing a RPM Air Gap intake. Like others have said, you just have to find the right tune between carb and timing. I wish you good luck.
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post #23 of 45 (permalink) Old Jun 26th, 19, 9:58 AM
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Harry
 
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Re: New heads and intake, now engine bog off the line

Quote:
Originally Posted by 68elky396 View Post
I too am experiencing the same problem with my 402 BB. Ever since I installed the RPM Air Gap manifold, I have had carb tuning problems from hell. To this day. I am still trying to get rid of my off idle bog. I have spent countless hours reading and tuning and am now considering buying a different intake. I am going to try making some more adjustments this weekend and see what happens. I don't give up easily. I have heard of others having the same problem after installing a RPM Air Gap intake. Like others have said, you just have to find the right tune between carb and timing. I wish you good luck.
On my double pumper, I have found that reducing HSAB down to 28 greatly reduces lean bog during transitions. Jets will have to be reduced accordingly.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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post #24 of 45 (permalink) Old Jul 3rd, 19, 7:46 PM
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Steve
 
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Thanks for the tip. I'm not too familiar with those air bleeds or how to turn them down to 28 or any other value. I'm running a vac. secondary Holley and I think the HSAB's are on the primary metering block. I never played with them before. I will have to educate myself.
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post #25 of 45 (permalink) Old Jul 4th, 19, 12:22 AM
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Harry
 
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Re: New heads and intake, now engine bog off the line

Quote:
Originally Posted by 68elky396 View Post
Thanks for the tip. I'm not too familiar with those air bleeds or how to turn them down to 28 or any other value. I'm running a vac. secondary Holley and I think the HSAB's are on the primary metering block. I never played with them before. I will have to educate myself.
The High Speed Air Bleed is located on the carb. body.

The other thing that helped me a lot with lean transition is the idle-eze available in the XP carbs. I open up the idle-eze all the way, which let's alot of air in. This allows me to close the rear throttle body and set the front primary throttle body at the right spot. In addition, it lets you keep the idle adjustment screws on the metering block turned out and still have a lean idle. All of this helped clean up the lean spot at transition. The idle-eze mechanism accomplishes the same thing as drilling the throttle blades and worked very well for me.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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post #26 of 45 (permalink) Old Jul 4th, 19, 1:10 AM
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Re: New heads and intake, now engine bog off the line

Quote:
Originally Posted by 68elky396 View Post
I too am experiencing the same problem with my 402 BB. Ever since I installed the RPM Air Gap manifold, I have had carb tuning problems from hell. To this day. I am still trying to get rid of my off idle bog. I have spent countless hours reading and tuning and am now considering buying a different intake. I am going to try making some more adjustments this weekend and see what happens. I don't give up easily. I have heard of others having the same problem after installing a RPM Air Gap intake. Like others have said, you just have to find the right tune between carb and timing. I wish you good luck.
I don't think the Air Gap is the problem. I have always had way more hesitations with single plane intakes due to the large plenum area over a dual plane intake. What carburetor do you have if you don't mind my asking?
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post #27 of 45 (permalink) Old Jul 4th, 19, 1:17 AM
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Re: New heads and intake, now engine bog off the line

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Originally Posted by hjdca View Post
The High Speed Air Bleed is located on the carb. body.

The other thing that helped me a lot with lean transition is the idle-eze available in the XP carbs. I open up the idle-eze all the way, which let's alot of air in. This allows me to close the rear throttle body and set the front primary throttle body at the right spot. In addition, it lets you keep the idle adjustment screws on the metering block turned out and still have a lean idle. All of this helped clean up the lean spot at transition. The idle-eze mechanism accomplishes the same thing as drilling the throttle blades and worked very well for me.
You sure are right about the idle ease, I just played with a few of my Demons over the weekend, got the 750 Mighty Demon just right with the settings after using the idle ease. My 750 A/D booster Speed Demon's Idle ease would not work at all and felt funny when I went to turn the screw. I pulled off the baseplate and found the whole assy. loose in the baseplate, I tightened it up put the 750 back together opened the screw and the RPM went up, reset the throttle screws and that baby idles as low as 500 RPM if I want it too. Now that Holley owned demon I can see why they used the BG idle ease in the XP line, should be on all their HP stuff for what Holley charges.
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post #28 of 45 (permalink) Old Jul 4th, 19, 2:47 AM
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Harry
 
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Re: New heads and intake, now engine bog off the line

Quote:
Originally Posted by 68Chevele View Post
You sure are right about the idle ease, I just played with a few of my Demons over the weekend, got the 750 Mighty Demon just right with the settings after using the idle ease. My 750 A/D booster Speed Demon's Idle ease would not work at all and felt funny when I went to turn the screw. I pulled off the baseplate and found the whole assy. loose in the baseplate, I tightened it up put the 750 back together opened the screw and the RPM went up, reset the throttle screws and that baby idles as low as 500 RPM if I want it too. Now that Holley owned demon I can see why they used the BG idle ease in the XP line, should be on all their HP stuff for what Holley charges.
Yeah, I played for years with my HP carb body...., then, I bought the ultra XP body and drilled out the middle of my base throttle plate - I made the hole bigger. Note: The holley base plate has air channels going from the middle hole to all 4 throttle holes on the manifold side. Then, after I turned the idle ease fully open, I could close the throttle plates more, which is the right way to solve the lean stumble. Two main things were key to me getting rid of my lean stumbles when tuning for an efficient carb (ie. not too rich settings to cover up lean stumbles).

1. Using vacuum advance at idle, so, I am idling at 22 deg. initial plus 16 deg. of vacuum advance for 38 deg. of total timing at idle. This allowed me to close my throttle blades more at idle.

2. Idle-Ease. Open all the way allowed me to close my throttle blades even more at idle.

For me, when I got my secondary throttle blades basically closed and my primary throttle blades just at the beginning of the T-slot, my lean stumbles disappeared -- even with a lean idle.

Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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post #29 of 45 (permalink) Old Jul 4th, 19, 11:28 AM
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Harry
 
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Re: New heads and intake, now engine bog off the line

Quote:
Originally Posted by hjdca View Post
Yeah, I played for years with my HP carb body...., then, I bought the ultra XP body and drilled out the middle of my base throttle plate - I made the hole bigger. Note: The holley base plate has air channels going from the middle hole to all 4 throttle holes on the manifold side. Then, after I turned the idle ease fully open, I could close the throttle plates more, which is the right way to solve the lean stumble. Two main things were key to me getting rid of my lean stumbles when tuning for an efficient carb (ie. not too rich settings to cover up lean stumbles).

1. Using vacuum advance at idle, so, I am idling at 22 deg. initial plus 16 deg. of vacuum advance for 38 deg. of total timing at idle. This allowed me to close my throttle blades more at idle.

2. Idle-Ease. Open all the way allowed me to close my throttle blades even more at idle.

For me, when I got my secondary throttle blades basically closed and my primary throttle blades just at the beginning of the T-slot, my lean stumbles disappeared -- even with a lean idle.
So, you can add the idle-ease to your existing double pumper by replacing your body with a ultra XP body (approx. $200). You can reuse your existing base plate, bowls, metering blocks, etc... I validated this by calling Holley. For the base plate, just make sure the hole in the middle is big enough. The old zinc holley base plates 116-112 has a big hole in the middle, but, the new holley aluminum 116-112 base throttle plate has a small hole. Both versions have air channels to route the idle-ease air to all four throttle holes. I drilled the middle hole of my new aluminum 116-112 holley throttle base to the largest size I could without hitting the air channels on the manifold side of the base. This was a good move because it gave me a lot of tun-ability with the idle-ease. In the end, I used all the idle-ease adjustment, so, I was glad I drilled out the hole in the throttle plate to the bigger size.

Here is a pic of my stock DP 116-112 base plate with the ultra XP body (hard core grey) and my QF DP metering blocks and the chrome bowls off my old DP. The carb. works great. Much better than my HP.



Note: there are no bosses for Nitrous on the Ultra HP body, so, you need the nitrous bracket that mounts to the carb stud. I had to drill and tap the second screw.


Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers

Last edited by hjdca; Jul 4th, 19 at 11:53 AM.
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post #30 of 45 (permalink) Old Jul 4th, 19, 12:41 PM
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Harry
 
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Re: New heads and intake, now engine bog off the line

Quote:
Originally Posted by hjdca View Post
So, you can add the idle-ease to your existing double pumper by replacing your body with a ultra XP body (approx. $200). You can reuse your existing base plate, bowls, metering blocks, etc... I validated this by calling Holley. For the base plate, just make sure the hole in the middle is big enough. The old zinc holley base plates 116-112 has a big hole in the middle, but, the new holley aluminum 116-112 base throttle plate has a small hole. Both versions have air channels to route the idle-ease air to all four throttle holes. I drilled the middle hole of my new aluminum 116-112 holley throttle base to the largest size I could without hitting the air channels on the manifold side of the base. This was a good move because it gave me a lot of tun-ability with the idle-ease. In the end, I used all the idle-ease adjustment, so, I was glad I drilled out the hole in the throttle plate to the bigger size.
Here is a pic of my 15 year old un-modified Holley 750 Double pumper zinc body (116-112). I broke the ear off tightening it, so, it is garbage now. You can see the big hole in the middle with the air channels. This is the perfect size for the idle-ease. This is an unmodified throttle body. If you buy a new aluminum 116-112, it will look exactly the same, except the hole will be half the size or smaller, which gives you less tuning ability. Fortunately, the air channels are the same size, so, you can just drill out the hole to the same size as the old zinc baseplates. This is what I did, and I ended up using the "whole hole" for the best tuning of my cam - idle-ease turned counterclockwise all the way.


Harry
1970 Chevelle SS396 (408), Fathom Blue,
Original Block & Forged Crank, KB Pistons, Edelbrock 6045 Heads,Comp Cam 292H, March Serpentine, RPM AirGap,750HP,100hp Nitrous
A/F Wideband,Tremec TKO 600, 12 bolt,
30 spline Moser Axles, Richmond 3:73's, Hotchkis control arms, swaybars, springs, Wilwood 12" rotors D/S, 4 piston calipers
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