Help! New annular booster carb - engine runs poorly
Thread Starter
Racer
Joined: Apr 2006
Posts: 429
Likes: 0
From: Marietta Georgia
Help! New annular booster carb - engine runs poorly
I have a GMPP 'ZZZ' in my 1974 convertible. The engine has run fine for 15 years with a Holley 750 double pumper. I just bought a Holley 830 with annular boosters and installed it yeterday. When the car is in park, the engine performs as expected (idles well, responsive throttle, etc.). However, when I drive the car (which wasn't far), it begins to stumble, 'pop' and backfire. I swapped out the 830 with a friend's 750 (w/ annular boosters) and it did the same thing. I changed out the plugs (which were fouled) and put my old 750 back on and the car ran fine.
I have the HEI distributor with an MSD coil - but no other ignition upgrades. I am using Autolite 106 plugs with a .035 gap. Any ideas from the engine and carb guys would be appreciated.
I have the HEI distributor with an MSD coil - but no other ignition upgrades. I am using Autolite 106 plugs with a .035 gap. Any ideas from the engine and carb guys would be appreciated.
Thread Starter
Racer
Joined: Apr 2006
Posts: 429
Likes: 0
From: Marietta Georgia
I do have backfire protection (Mr. Gasket product). I believe that my problem has more to do with the fuel not being "burned" thoroughly. The cylinders seem to load up with fuel (The #5 for sure) when I have an annular booster carb installed. I think that I may need to upgrade my ignition system (MSD 6 AL box, etc.) but wanted to see if anyone out there has had similar experience with annular booster carbs.
Safety Car
Joined: Aug 2001
Posts: 3,892
Likes: 13
From: Pettis Performance 565 with two stages of Nitrous Supply nitrous 1.082, 4.61 at 155, 7.17 at 192
It is not the fact it is an annular booster carb. Once it is tuned correctly it will be more responsive and more streetable than the down leg was. Check the floats level, pumps, shooters etc. Can you give a little more detail of when it starts acting up, cruising ? accelerating ? stomping the throttle, etc.
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Almost every carb I have tried over the years has always had to be tuned to run well. I have the exact carb you have and it runs great! But not without a considerable amout of tuning. It sounds like a lean condition that could be due to your jetting and accel pump set up. I have a LM-1 O2 analyzer which takes the guess work out of the tunning. Are there any Dyno facilities in your area where you could experiment with jet sizes? If you want better info from forum members, post your primary and secondary jet sizes, accelerator pump nozzel numbers and PV valve number. Engine details would also help. I don't know what a "ZZZ" is. You ignition is fine, my suggestion would be to stay away from all the ignition box stuff, just more things to go wrong. If you don't have any kind of force induction system, a good HEI is all you need. I am making 450 hp at the wheels with my 427 CID with a 830 annular holley carb and a HEI from DUI. Oh yes, and make sure your floats are adjusted, this one thing is the foundation for all other changes. If you dont know how, there are tons of stuff on the internet as well as books that will walk you through the process. Durning shipping, many times the floats get knocked off out of adjustment. And it doesn't take much to screw everything up!!
Thread Starter
Racer
Joined: Apr 2006
Posts: 429
Likes: 0
From: Marietta Georgia
Additional info
Originally Posted by KJL
Almost every carb I have tried over the years has always had to be tuned to run well. I have the exact carb you have and it runs great! But not without a considerable amout of tuning. It sounds like a lean condition that could be due to your jetting and accel pump set up. I have a LM-1 O2 analyzer which takes the guess work out of the tunning. Are there any Dyno facilities in your area where you could experiment with jet sizes? If you want better info from forum members, post your primary and secondary jet sizes, accelerator pump nozzel numbers and PV valve number. Engine details would also help. I don't know what a "ZZZ" is. You ignition is fine, my suggestion would be to stay away from all the ignition box stuff, just more things to go wrong. If you don't have any kind of force induction system, a good HEI is all you need. I am making 450 hp at the wheels with my 427 CID with a 830 annular holley carb and a HEI from DUI. Oh yes, and make sure your floats are adjusted, this one thing is the foundation for all other changes. If you dont know how, there are tons of stuff on the internet as well as books that will walk you through the process. Durning shipping, many times the floats get knocked off out of adjustment. And it doesn't take much to screw everything up!!
GM Performance Parts 'ZZZ' sb 350 crate motor. The 'ZZZ' is the original 'ZZ' family crate motor (Grand Daddy to the 'ZZ4'). It was installed in 1991. It is a 350 small block with aluminum dual plane intake, aluminum heads, 1.5 ratio rockers, HEI distributor & hydraulic roller cam. I have headers with 2 1/2" dual exhaust. I have added a Holley mechanical fuel pump and a MSD coil to the HEI distributor. I have Autolite 8.5mm spark plug wires and Autolite 106 plugs (.035 gap). No forced induction. . .yet.
My carb is a used Holley 830 with annular boosters. It was recently rebuilt with a Barry Grant rebuild kit. It has a .68 primary and .78 secondary jets. I don't recall the PV or accel pump numbers (the carb is at a friend's house, I will add that info tomorrow). The floats were adjusted.
The engine runs fine from idle through WOT when the car is not in gear. When I drive the car, it becomes sluggish and makes loud "popping"/backfire noises starting around 1,800 RPM. I also get a little bluish white smoke when idling like the car is running too rich.
There is NO smoke when my 750 DP is installed.
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Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Adjust your idle feed screws to lean out your idle, go up to 72 primary jets. Check your float level again , enigine at idle with just a tiny drible coming out of the sight plugs. Make sure you have the correct Idle transfer slot exposed .025 - .030 and on your secondary side just have a sliver of slot exposed (if any). Your PV valve should be 1.5 to 2 inches below your lowest vacuum. Make sure your air bleeds have not been messed with. I always recommend going to a 50cc accel pump on the primary side. This really beats down the lean spike that happens on all built 350's running the 30 cc pump. Trust me on that one.
Thread Starter
Racer
Joined: Apr 2006
Posts: 429
Likes: 0
From: Marietta Georgia
Originally Posted by KJL
Adjust your idle feed screws to lean out your idle, go up to 72 primary jets. Check your float level again , enigine at idle with just a tiny drible coming out of the sight plugs. Make sure you have the correct Idle transfer slot exposed .025 - .030 and on your secondary side just have a sliver of slot exposed (if any). Your PV valve should be 1.5 to 2 inches below your lowest vacuum. Make sure your air bleeds have not been messed with. I always recommend going to a 50cc accel pump on the primary side. This really beats down the lean spike that happens on all built 350's running the 30 cc pump. Trust me on that one.
Thread Starter
Racer
Joined: Apr 2006
Posts: 429
Likes: 0
From: Marietta Georgia
Originally Posted by Brettmc
Change em.
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Check out this article, even if you are not using athe LM-1 there is a lot off good info to help you tune your carb.
http://www.chevyhiperformance.com/te...une/index.html
http://www.chevyhiperformance.com/te...une/index.html
Thread Starter
Racer
Joined: Apr 2006
Posts: 429
Likes: 0
From: Marietta Georgia
Originally Posted by Fevre
Check out this article, even if you are not using athe LM-1 there is a lot off good info to help you tune your carb.
http://www.chevyhiperformance.com/te...une/index.html
http://www.chevyhiperformance.com/te...une/index.html
Thread Starter
Racer
Joined: Apr 2006
Posts: 429
Likes: 0
From: Marietta Georgia
Fixed - ignition issue
Originally Posted by gatorbcn
Good article. I got to work on the car a little last night and am pretty convinced that my problem is an ignition issue, not a carb issue. I am going to try some ignition upgrades (borrowing parts from friends) to see if I can solve the problem.
MSD pro billet distrbutor
MSD 7AL box
MSD blaster coil
Car runs fine. The annular booster carb makes a big difference (at least seat of the pants right now) over the Holley 750 DP. Much more responsive off idle! Thanks for all of the posts.
Last edited by gatorbcn; Jul 21, 2006 at 08:31 PM.
