Thread: Tri-Power Carbs build.

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No problem Brian, Glad to see the post is still helping people.

Wow I missed this the first time around. Thanks for the details and pictures. I cut and pasted it to wordpad, for future reference. This one would go well with the reference pages Tech was setting up with Bill.

As I said before I'm glad people are still getting some use out of it. I remember when I did this thread, I got real tired of building 2Gs. I did the 3 for the Hemi, rebuilt the 3 that are on the FE in the 64 Ford, did 3 more on a SBC intake I still have plans for and then the 6 that are on the HEMI for the 37 Dodge. 15 Carbs at one time gets kind of old.

A correct tri power set up.

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I know this is an old thread, but I just found it. Ive got 3 of the small base 2gs on a 302. Just got it running the other day. These were carbs I bought from a guy as Tri power carbs, center has idle and mixture screws, the outers have the mixture screws removed and sealed up. The holes on the baseplate aren't sealed up. The problem I'm having is one of the outers is really sucking air. Ive taken the baseplate off and centered the butterflies best I could. Holding a light behind it, you can see a tiny bit of light. I know its hard to say without seeing it, is that enough? If I really push hard on the linkage I can get it to seal better. So I think it just needs to seal better? The other outer seems fine. I'm wondering if I can sand the edges of those plates and get a better seal, or get new ones and go from there. Is there anything else I should check/do? Thanks for all the info.

If the holes in the base aren't sealed it's probably sucking fuel thru the idle passages. Sanding and beveling the throttle plate will probably help. You need to get as tight a seal on the throttle plates as possible.


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Thanks Mike. So I really need to seal those holes in the baseplate up even though the holes on the outside of the baseplate, where the mixture screws were, are plugged? Along with getting the throttle plates to seal better?

Making some progress. Haven't been working on it as much as I should....... Plugged the power valve hole last night, and I misread the part about the vent. I plugged the power valve AND cut off the bottom of the vent valve and removed the spring. Was that bad?? Hope not. Still need to do the other carb and hopefully test drive this thing soon!! Thanks

Sorry, I missed your earlier post.

".......So I really need to seal those holes in the baseplate up even though the holes on the outside of the baseplate, where the mixture screws were......"

I would, the internal passages are the ones that pass fuel and are located under the throttle plates (which means they see a lot of vacuum) and unless sealed will suck fuel into the intake.

"......I plugged the power valve AND cut off the bottom of the vent valve and removed the spring. Was that bad??...."

It shouldn't hurt anything. Plugging the PV would have been sufficient, cutting off the power valve rod and removing the spring is just another method of doing that.


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Thats okay, I appreciate the feedback and help on this. It's a big learning thing for me!! I'm getting there though!!

Alright, this is what I did - plugged the power valves in the end carbs, got it running good on just the center, put just the front back on (ran okay, not as good as with just the center), took the front off and sealed the intake, put the back on (ran about the same as with the front on), took it back off and sealed the intake, checked it again with just the center, still running pretty good. SO, decided to put both ends on and see what happened. Kinda ran like ass. I'm still getting a slight air leak through both ends. If I cover the back one, the engine won't die, but it won't rpm at all, if I cover the front, still doesn't die but it does kinda smooth the idle out. Then I thought I should take apart the center and look at it. It also has only 48 jets.

It sounds like you are still getting air leaks. Pull the end carbs, turn them upside down and make sure the base gaskets are fully sealing the base of the carbs (I've run into this problem a few times in the past). I don't have the part number around, but I usually pick up aftermarket base gaskets Felpro at the local parts store (Hopefully you aren’t using the odd ball 2Gs that only have the 2 bolt hold down). I would suggest when you are checking the carbs that you vacuum leaks that you do not hook the fuel lines to the end carbs until you get it to idle decently.

Some of the Tri-Power setups I’ve done (including the SBC unit I’ve run for years) have been extremely cold blooded. They like a lot of choke until they start to warm up and all of them needed the heat crossover working (not blocked off). They did beautifully once at operating temp but were temperamental until then. Cold engines do not like a lot of carburetion, it’s the main reason that all the factory 4 Barrel carbs have a lock out that prevents the secondarys from opening until the choke is fully off. With most Tri-Powers you don’t have a lockout on the end carbs……you just have to keep your foot out of it until it’s warmed up.

Once the end carbs are on, you may find you also have to richen up the idle screws a bit to compensate for any minor air leaks you might have with the end carbs. When changing from a 4 barrel to Tri-Power you will also likely find that the engine will like a bit more timing than it did before. You might want to play with the timing a bit after the engine is warmed up and see what it likes.


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Ive checked the baseplate gaskets, they're good. I read somewhere else about drilling holes in the center carb throttle plates. It sounds like that what I need. At idle I need the center carb open so much that its uncovering more of the holes in the throttle bores which is letting it duck in too much fuel, which is why its running so rich. Thats what it seems like, after reading about the hole in butterfly thing. I'm thinking of switching plugs too to see if that'll help the cold running part.

I suspect you're going to find that the plug heat range will likely little or no effect on idle. One of the things that I have found will noticeably help clean the idle up would be an MSD box. I've run them on my last couple of Tri-Power engines and they can make a big difference.

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One thing I still don't entirely understand, and you can tell me I'm an idiot, but there are 3 carbs, the center has the idle mixture screws, thats the only one that has fuel going into the engine at idle. Let's say the end carbs have a little air going by, basically leaning out the mixture because they're not letting in fuel to go with the air. So I should be able to richen up the center carb with the mixture screws? Or jets? To even out the air/fuel ratio? If I drill holes in the butterflies to let in more air, isn't that leaning it out more? Is the center carb letting in so much fuel at an idle even with the leaking end carbs that it needs more air? What am I missing?