Tri-power carbs question
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Tri-power carbs question

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    Member Romper Stomper's Avatar
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    Default Tri-power carbs question

    Ok, a friend of mine just bought a 65 GTO and is having me go through it and clean it up some (plugs, wires, clean the carbs, blah, blah). It ran pretty well before, but he wants to freshen it up anyway. The only issues he had were: sometimes it would idle high (1200-1500), but, only when he had been driving at highway speeds for awhile, and it would flood pretty easily when it was cold. Its a factory 3x2 Rochester setup and I'm not too familiar with that. I'm pretty much convinced the high idle is from all the throttle linkage probably hanging up somewhere...I'll check that out later. I've got the carbs torn down and I just wanted to bounce some stuff off you guys and see if I'm in for a headache.

    Here's my questions- The secondary (outer) carbs have small holes (one per blade less than 1/32) in the throttle blades but no provisions for idle circuits. Is this normal?

    On the primary Carb, when the throttle blades close, there is about 1/8" of the transfer slot showing. Is this too much? Also, the throttle shaft seems a little sticky when turning it with the throttle plate off the Carb. Any good fixes for that or do I have a trip to the swap meet in my future?

    Also, he said the car would sometimes idle like shit when he came off the highway, then would kind of clean itself up after a little slow driving.

    I know it ain't a boat, and its a bunch of questions, but I'm hoping some of you guys have dealt with this and can help me out. I know these are probably the reason why everybody runs single carbs, but it is what it is lol. Thanks in advance.

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    I've got my '59 Impala 348 3-2 setup over at C&J (other thread here) right now. The setup that came off of the car (which I sent) were not right. They were three regular two barrels, not true tri-powers. I have learned alot from this deal.

    I thought it would be great to have the idle mixture circuits on the end carbs as well as the center. Thinking like how the new Holleys and such have 4-corner idle circuits. Well, that's not the case.

    The END carbs are supposed to have zero idle. No fuel or air circuits. Otherwise, they become a vacuum leak when closed. They are supposed to have thicker-than-normal blades to fully SEAL when shut. So, there can't be any rust pitting or abnormalities in the barrels.

    We ended up shit-canning most of the setup and ordered the bases from: Automotion Rochester Carburetor Service They have lots of info there and explain how a tri-power is suppose to work.

    So, your buddy would do wise to get the setup corrected. Those end carbs should not have the holes in the blades.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


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    Member Romper Stomper's Avatar
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    Quote Originally Posted by Beer:30 View Post
    I've got my '59 Impala 348 3-2 setup over at C&J (other thread here) right now. The setup that came off of the car (which I sent) were not right. They were three regular two barrels, not true tri-powers. I have learned alot from this deal.

    I thought it would be great to have the idle mixture circuits on the end carbs as well as the center. Thinking like how the new Holleys and such have 4-corner idle circuits. Well, that's not the case.

    The END carbs are supposed to have zero idle. No fuel or air circuits. Otherwise, they become a vacuum leak when closed. They are supposed to have thicker-than-normal blades to fully SEAL when shut. So, there can't be any rust pitting or abnormalities in the barrels.

    We ended up shit-canning most of the setup and ordered the bases from: Automotion Rochester Carburetor Service They have lots of info there and explain how a tri-power is suppose to work.

    So, your buddy would do wise to get the setup corrected. Those end carbs should not have the holes in the blades.
    That's exactly what I was thinking. Why the hell would you add air with no fuel?? I just wasn't sure if that was some factory bullshit or some random yo's bright idea. Thanks for the link. I'm definitely gonna hit those guys up.

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    I have no doubt Beer 30 has great information and sent you down a good path.

    We are also very lucky on this board to have Steve Barcak (applekrate) as a member. Steve is a true die hard pontiac enthusiast whom most likely has an IPL of every part that was oem on that set-up or what is working best with modern fuels these days. If you find you need more information, you might pm him. Steve is an invaluable wealth of knowledge for all Pontiac enthusiasts. I also have a feeling he would know a few other shops that might be able to help if need be.
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    I have no experence with the Rochester 3x2V carbs so I an just tossing this out there for consideration and have a question or two [I have done many 6V and 8V setups on FE Fords] it just seems a bit strange that the sec. carbs have no provision for a idle circuit and the throttle plates would be adjusted tight in the bore. Wouldn't that cause the plates to stick? Holley 6V setups have adjustable idle curcuits on all 3 carbs and are adjusted to utilize all 3 carbs at idle. Holley and Ford's reasoning is that would allow a slight fuel flow thru each carb at all time to prevent fuel stagnation if the driver didn't use all 6 barrels. The only difference in Holley 3x2bbls is the outboard carbs have no power valves, each has different throttle lever positions to make for a 3 stage progressive throttle opening rate and no choke assemblies.
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    Quote Originally Posted by 058 View Post
    Holley 6V setups have adjustable idle curcuits on all 3 carbs and are adjusted to utilize all 3 carbs at idle. Holley and Ford's reasoning is that would allow a slight fuel flow thru each carb at all time to prevent fuel stagnation if the driver didn't use all 6 barrels. The only difference in Holley 3x2bbls is the outboard carbs have no power valves, each has different throttle lever positions to make for a 3 stage progressive throttle opening rate and no choke assemblies.
    I'll have to look on my 'Cuda. I don't know if the Mopar 440-6pack has idle on the ends? I'll walk out to the garage and look momentarily.

    I too would think it would be great to have "more corners" in the idle circuit(s). But apparently not: Automotion Rochester Caburator Service: FAQ
    Last edited by Beer:30; 12-07-2012 at 05:49 PM.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Like 058 stated, the Ford tri power carbs have idle circuits, if for no other resaon than to keep the fuel in those carbs reasonably fresh. It is entirely possible to drive a carb for months without ever getting in to the outside carbs. Between the heat and evaporation of the fuel in a vented bowl, that fuel could get ugly pretty quick, evaporating off the low end factions of gasoline and leaving the heavy products. Over and over as the bowl was replenished with new fuel to make-up for the evaporated fuel, each time leaving behind the heavy ends of the fuel.
    Not many people realize it, but all Holleys have a idle circuit on he secondary side. Early carbs it is merely a very very small fuel supply that is taken into stride with the primary fuel supply, requiring an adjustment only on one side in most cases. for no reason than to assure the fuel in the secondary bowl was reasonably fresh. They could easily made the engine idle with just the primary idle circuit. The secondary fuel supply is that small, but always moving fuel if the engine is running. It doesn't make the engine rich because it accounted for in the tuning. Its always there, and simply means you need less fuel from the other sources, idle or main circuit.



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    Quote Originally Posted by Beer:30 View Post
    I'll have to look on my 'Cuda. I don't know if the Mopar 440-6pack has idle on the ends? I'll walk out to the garage and look momentarily.

    I too would think it would be great to have "more corners" in the idle circuit(s). But apparently not: Automotion Rochester Caburator Service: FAQ
    I believe the tri power on the early bb Corvettes were the same as the 440-sixpack, I think the only difference was the springs in the vacuum cans

    the last tri power Ford I worked on seemed to have different carbs

    Like 058 said the the outer carbs use fuel at idle to keep it fresh

    My brother and I had a 440-six pack Super Bee and a Hemi Roadrunner

    Loved that Six pack
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    Quote Originally Posted by gn7 View Post
    Like 058 stated, the Ford tri power carbs have idle circuits, if for no other resaon than to keep the fuel in those carbs reasonably fresh. It is entirely possible to drive a carb for months without ever getting in to the outside carbs. Between the heat and evaporation of the fuel in a vented bowl, that fuel could get ugly pretty quick, evaporating off the low end factions of gasoline and leaving the heavy products. Over and over as the bowl was replenished with new fuel to make-up for the evaporated fuel, each time leaving behind the heavy ends of the fuel.
    Not many people realize it, but all Holleys have a idle circuit on he secondary side. Early carbs it is merely a very very small fuel supply that is taken into stride with the primary fuel supply, requiring an adjustment only on one side in most cases. for no reason than to assure the fuel in the secondary bowl was reasonably fresh. They could easily made the engine idle with just the primary idle circuit. The secondary fuel supply is that small, but always moving fuel if the engine is running. It doesn't make the engine rich because it accounted for in the tuning. Its always there, and simply means you need less fuel from the other sources, idle or main circuit.
    I agree. Every time I drive the 440, I make sure I get into the end carbs at least twice per drive. I try to keep the fuel cycled in all of the carbs. All the more reason to go EFI! This is killing me to spend this much $ on CARBS. Friggen rediculous. But I don't have a whole lotta choice in this project.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Quote Originally Posted by Beer:30 View Post
    I agree. Every time I drive the 440, I make sure I get into the end carbs at least twice per drive. I try to keep the fuel cycled in all of the carbs. All the more reason to go EFI! This is killing me to spend this much $ on CARBS. Friggen rediculous. But I don't have a whole lotta choice in this project.
    Yeah, but you won't even sneeze at 5000.00 for a EFI. And should the EFI take a dinger, and please do not tell me they don't, I am armed to the teeth with thread links for the 8.1 alone!!!! you are screwed unless your a electron junkie. I can rebuilt and tune the average 4 bbl in my sleeep, and a EFI requires a laptop and the appropriate software just to LOOK for the problem, then it can be any one of 100 pieces of electronic crap that took a shit in the middle of freek'n nowhere. DO NOT say it can't or has never happened. It has, and YOU know it has!!!!

    All that and STILL not make 1 HP more than a good carb and manifold. Not a single HP!!!!
    Milage? YES! Emissions? Yes. Power, NEVER!

    I don't give a ratz ass about emissions or milage in my boat and many many many others could care less too. EFI is only half as great as you sell it to be, and twice as expensive.



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    Quote Originally Posted by gn7 View Post
    Yeah, but you won't even sneeze at 5000.00 for a EFI. And should the EFI take a dinger, and please do not tell me they don't, I am armed to the teeth with thread links for the 8.1 alone!!!! you are screwed unless your a electron junkie. I can rebuilt and tune the average 4 bbl in my sleeep, and a EFI requires a laptop and the appropriate software just to LOOK for the problem, then it can be any one of 100 pieces of electronic crap that took a shit in the middle of freek'n nowhere. DO NOT say it can't or has never happened. It has, and YOU know it has!!!!

    All that and STILL not make 1 HP more than a good carb and manifold. Not a single HP!!!!
    Milage? YES! Emissions? Yes. Power, NEVER!

    I don't give a ratz ass about emissions or milage in my boat and many many many others could care less too. EFI is only half as great as you sell it to be, and twice as expensive.
    Really? Here again? I think everyone with EFI knowledge here has hashed out that HP-for-HP, EFI and carb will be the SAME on a given motor.

    The only thing that has crapped out on me lately is my '55 Chevy. Bone stock (rebuilt) 265, cast iron PG, original ($600 restoration) carb. A piece of crap broke loose from the tank and left me on the side of the road puking black smoke. Took the carb apart and limped it home, but fuel EVERYWHERE. Hands, shirt, now the car smells like fuel inside.

    Never would have happened with EFI. Sure, ONE INJECTOR could get plugged, but there no float to stick.

    I'm sick and friggen tired of having to custom-fab a bracket for an idle solenoid for AC. When the AC engages, I usually add an idle-stop solenoid to kick the idle up 150-200 rpm. It's a pain in my ass on the ones that NEVER came with one.

    With EFI, it's a click of a mouse to add 200rpm with AC trigger.

    Carbs are old bullshit that ANYONE can rebuild. It's upper class of evolution that ditches them and goes to something BETTER.

    I don't give one rat's ass about ANY extra HP. I know I won't LOSE ANY with EFI. I don't give the same rat's ass about emissions, either - although you do. You ALWAYS bring it up in these conversations.

    A guy came by and was looking at my '69 PU the other day. 355, FAST EFI, TH700. The '55 was right there next to it. He asked me why the EFI? Both vehicles were cold - hadn't been started. I reached in - flat footed outside the truck - and hit the key. It started idling and settled down from cold-start idle. Never skipped a beat. The '55, same program, TRIED to idle, but couldn't because the choke wasn't set. So, it tried, but wouldn't keep running. So, I had to set a foot in there and swing the throttle. Started on the high-idle from the choke, no problem. Then, I had to reach in and kick it OFF of choke once warmed up. What a bunch of bullshit.

    With the FAST EFI, you don't need a laptop - it askes you questions and you enter what is needed. So, you don't have to be afraid of it.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Default High idle after highway run....

    I can speak from experience on this issue. My problem, also on a Pontiac w/ points, (72 455), turned out to be sticking advance weights keeping the timing advanced. A little cleaning and replacement springs and "friction tabs" solved the problem. I had a 3x2 setup on an old GMC Pontiac powered pickup, originally a 316, I built a mid 60s 389 and used a 3x2 intake. Yes, the center carb is quite different than the end carbs, but I really never had any issues with stale gas because the 4 speed hydro trans was always begging for more gas pedal..... Kick ass sleeper truck.....

    Ray
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    406 tri power arrangement. Like 058 said, all 3 have idle circuits. The CAN be set to bring in the outers at different thottle positions. This particular setup has the outers coming in sligthly sooner than maximum.
    To my knowledge the only difference between the center and outer is the choke.
    I have run 3 junk yard 2 bbls on this manifold on a 410 Merc bore after jetting them and they worked fine.





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    Last edited by gn7; 12-07-2012 at 10:03 PM.

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    Quote Originally Posted by Moneypit View Post
    I can speak from experience on this issue. My problem, also on a Pontiac w/ points, (72 455), turned out to be sticking advance weights keeping the timing advanced. A little cleaning and replacement springs and "friction tabs" solved the problem. I had a 3x2 setup on an old GMC Pontiac powered pickup, originally a 316, I built a mid 60s 389 and used a 3x2 intake. Yes, the center carb is quite different than the end carbs, but I really never had any issues with stale gas because the 4 speed hydro trans was always begging for more gas pedal..... Kick ass sleeper truck.....

    Ray
    X2 That'll do it. Easy to fix too.

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