First off, JB weld is not the product to use. You should have used Dag213. Also backfiring out the carb, popping is a lean condition. When you keep feathering the gas, you are squirting fuel in each time to keep it going. After it warm up, an engine doesn't need as much fuel and that's why it runs better. So back to basics. get the JB weld out, use Dag 213 and follow the directions, drill the idle air bleeds. Done and be happy. I wasted a bunch of money on an aftermarket base plate off of Ebay, then bought the Vintage speed aluminum /brass butterfly baseplates. Even holding these up to light, I saw a gap of daylight. It didn't run good until I worked on the idle air bleeds to make up for the slight vacuume leak. Finally after getting it going I thought I'd try some Dag 213 on the extra 4 baseplates I now had sitting on the shelf. Well it fixed all the baseplates, even the crappy fitting Ebay one. I held them up to light and no air gap. I never installed them on the one that I drilled the idle tubes out on because Im afraid that it would be pig rich with the sealed base plates and would need new idle air bleeds ect. I'll use the Dag213 base plates on my other Tri-power or when the current one needs rebuilt. Basically all the work I did was just a bandaid because of not using the Dag 213.
I know the jb weld isn't the correct stuff to use but I had it and others said it worked for them so I thought I'd try it. Not to sound like an even bigger idiot than I probably already do, but can you tell me why it runs so rich when I put the outer carbs back on? I didn't ask the guy when I bought these carbs if he'd done anything to the air bleed already, maybe already drilled and the better seal on the end carbs causing it to be too rich?
Let's start from scratch; If you had a motor in good condition, without a noticable "cam", then when you block off both outboard carb openings with an air tight plate...the engine should idle as smooth as a brand new car. Get your center carb to behave just like that first. This also means you'd have a perfect ignition system and idle timing, etc. Get it perfect. Then work on ONE end carb at a time. If you put just one end carb back on, and now lost your perfect idle, you know which carb is at fault. Test each end carb, one at a time. Back to some info posted on this thread, some is incorrect in a big way. The factory outboard carbs did seal completely, and a post said they shouldn't because the plates would stick. That is not true. As you know, the factory used very thick plates so they won't "dig-in" and stick. Other bad info is "compensate for outboard carb plate leaks" by screwing around to make them leak fuel internally. That's a poor way to build a tri=power. I have run factory Olds J2 carbs on a bone stock, tired out 303 motor, (compression varied from 60 to 95 PSI)......with NO FUEL LINES hooked to the end carbs, and idle is mint. So nobody on earth can convice me that you need fuel leaks in the end carbs. I don't know anything about the aftermarket bases...maybe someone here can give advice if they ran them over a long period of time, to give a honest opinion. .
Just some ideas before you give up on your carbs.. (in case your sealing job is NOT the problem...) I can put up a pic of a real outboard carb base from the top gasket area. Then you can compare what extra holes you have....and maybe experiment with a homemade gasket to block extra holes. One pic I think was yours, showed a fuel log; is there a way you can run a single center carb with no fuel to just one installed end carb? In other words, get car running mint with both end carbs blocked with a block off plate or solid base gasket. Then put only one real base gasket on ONE end carb on with no gas line. If that one end carb is still not causing a problem, That means your sealing on that carb is good. So then hook the fuel line to it, and now see if the rich condition returns? I'll get a pic later today. .
Working with one end carb at a time is a good idea. I'll try that this weekend. At least to see which one does what. The engine does have a little cam, but it was still pretty smooth with just the center. Ive got some things to work on this weekend! Thanks for the help.
Just talk to Mike.http://www.pontiactripower.com/shop/throttleblade-sealer-dag He's a good source. I wish Id have found him 2 years before I started figuring all this out myself. Again, the factory used Dag 213. Its most likely all worn off from carb cleaner. My Tri power ran awesome when I first installed it but then after a couple of seats coming loose and letting fuel flow past the needle though the threads, I decided to rebuild them all. That was an error on my part as I took carb cleaner to the bases of the front and rear carb. Ooops!! From then on I was like you , chasing my tail. I did everything possible as I couldn't find DAG 213 anywhere at the time. The only way you can get them "Even the aftermarket aluminum/brass plates to work is drill the idle to get more fuel to compensate for the minute vacuum leaks. Dag will cure all this! Unless of coarse you are dealing with other issues. http://www.pontiactripower.com/shop/throttleblade-sealer-dag
Thats some good info! Thanks! I can block off one carb at a time or whatever. So I will try that this weekend. It seems like it should be fairly simple to fix and get running decent. At this point I'm more concerned with idling and "regular" driving than I am with WOT. I'll dbl check my jb weld job, even though its not the right way to do it, and see if its still sealing like it was, and go from there.
Make sure when you test one carb at a time, that you first do it with no fuel line. You want proof that you don't have a very large vacuum leak first. If that works, even if you have to slightly adjust the center carburator mixture screws, then finally hook up the fuel line to that carb to see what happens. Pics of a 1957-1958 Olds factory end carb. First thing to understand, is that all 3 main castings are the same as the center carb. The three casting differ from the center carb in the way that many things are not drilled out/machined. look at the top surface of the cast iron base; there are no holes except for the screws to hold it on the carb center section. GM blocked the ports that are still in the bottom of the center body casting, and the ones that are vacuum ports, fed the power piston and also the vacuum part of the automatic choke. on the middle main body casting; there is no power piston. It's not drilled or machined. The stock GM tri-powers all had a mechanical vacuum switch on the center carb. That was either "on or off" . It sent vacuum to a very large diaphragm can mounted to the front carb, which opened both outer carbs full on. There is not really a point where the outboards will be cruising at part throttle, so that is probably why a mid range/transition power system was not needed on an outer carb. But they did have a different main jet size to compensate. This carb has 66 jets. I've never had to convert a regular 2GC..so this is just what I'd try, being that you said the outers seem to cause it to run rich at idle? I would try to copy GM's design, and block all the extra holes "between the base and the middle body". I think it's worth a try. But this is not going to work if your plate sealing JB weld is still leaking a lot. If making a new blocking gasket is too much work for a quick test, could you lay something over the holes on the top of the base plate, and still re-use the same gasket? Maybe some thicker plastic sheeting or even black tape? Just to last long enough for a test. As long as whatever you use is not too thick, the stock gasket should still seal over it OK. The carb top casting is also the same, but like the main body, they differ in that many holes are not drilled out. The nozzle ass'y that is screwed to the top of the main body really looks the same as a center carb. But I never studied them side by side. Sometimes carbs can be misunderstood. If you took two of those stock tri-power bases, and bolted them to your intake, the engine will still run just fine with no main body or top ! As long as the plates stay shut, you could drive it that way.
I forgot something to ask you... When you converted the two outer carbs, I assume these were vacuum assisted choke setups, so did you block the vacuum holes when you stripped the chokes off? .
I bought them already "converted". all the outer holes were plugged, and the little plugs where the choke flap in the top went are there. The idle passages in the baseplate weren't blocked, so I did that. Other than that and messing with the butterflies, I haven't done anything else to them.
Where is the ball supposed to be? I don't see one in the exploded view that came with the carb kit. This a 2g or GC I'm working on. I pull the top off and the accelerator pump comes out and then there's a spring in the main body and thats it.
^^^ This. Definitely get the car running well on the center carb with the secondaries completely blocked off and the. Add 1 carb at a time. I had issues with one of my 2gs dribbling fuel. It wound up being a bunch of crud blocking the bowl vent tube. Even though the carb looked nice and clean. I re-rebuilt the carb with a new kit and cleared out the tube and problem solved.
My trouble now is that it runs fine and when you stop and come back after a few minutes it is hard to start.I mean like it is no gas have to crack throttle about half way to get to crank.Then it seems to be like it is flooded.Had this set up for 8-9 yrs.Have Hot Rod Carb end plates.Almost like vapor lock but will put electric pump on this week.This set up on my Model A with SBC.MSD ign with 6a.Thanks for help
Ive done some checking on the check ball/accelerator pump and it appears that not all of them used a check ball, just the ones that have two holes at the bottom. One hole is discharge, one is to the bowl, thats the one that needs the check ball. So mine only has the one, the discharge one. From what I've read, this is what I understand anyway.
I was thinking about RJONES tests to make sure each outer carb throttle plates are sealed good enough, before hooking up the gas line. What I mean is that he could have vacuum losses at the plates, and he says the outboards seem to make it idle too rich. That makes it hard to find out if you have possibly two problems at once.. So, what if he puts a block off plate where the rear carb was, then only install the base plate casting on the front, with the rest of the carb not installed? If he has a good return spring to keep the plates shut, now you can find out if you really have a vacuum leak bad enough to begin with. He has plugged all the vacuum/idle ports, so it should idle if there is not a bad leak. Plus you could hold something over each of the two throttle bores to tell if just one plate flap has a leak, or both. If it does not leak enough to ruin the idle, then go ahead and install the rest of that carb, hook up the gas line and see if the richness comes back. one step at a time approach. . QUOTE from Flatmotor: "New My trouble now is that it runs fine and when you stop and come back after a few minutes it is hard to start.I mean like it is no gas have to crack throttle about half way to get to crank.Then it seems to be like it is flooded.Had this set up for 8-9 yrs.Have Hot Rod Carb end plates.Almost like vapor lock but will put electric pump on this week." I would try to look down all three carbs as soon as you get the "no start hot" problem. You are looking for gas leaking down the carb bores, and could be just the center carb, or maybe outboard carbs. It should look dry in all three. If the car runs good at idle, and driving, and this only happens after "heat soak", this might be fuel pressure building too high in the lines to the carbs. That extra pressure can open the needle valves, despite the floats working properly. That is if you feel that it is flooded .
Yeah I guess I could just bolt the baseplates on and see how they each seal and see if it effects the mixture.
F&j I have removed the lines to the outer carbs and it still does it like vapor lock.Have installed electric pump just waiting on regulator.Had the same trouble with the 40 with 2 97's put heat spacer and regulated to 2 1/2 psi solved that problem but I could hear it boiling.So some of it is this sorry gas we have to buy.But I've been buying non-ethanol.Seems to help Thanks
Okay. Took the ends off, got the center running pretty good. Took the end carbs apart and plugged the power valves. I wasn't totally sure, so I cut the end off the vent valve and removed the spring too. Good idea? Bad idea? Anyway Ive only done one. Put one end back on. I don't know, seems to run fine. Doesn't seem to be overly rich. Before I took the carbs off I lowered the fuel pressure a little too, down to 3.5-4. The ends have 48 jets, not sure about the center, I haven't looked.
QUOTE: " I wasn't totally sure, so I cut the end off the vent valve and removed the spring too." If you mean the part right above the valve that you plugged? That is the vac operated piston to open the valve. It must have been non-op if the base vacuum ports are sealed off. I would be OK with removing that. I'm pretty certain your outer carbs will need jet drilling, but get all three stable first. No sense in going in two directions, especially as you are making progress. Later on, when you get to cruise steady speed with outers at part throttle, I'd assume the engine will be holding back, or like a "lean surging". No big job really, but either go with the recommended jet size for a 348, or go the more tedious way of redrilling the jets a bit at a time. .
Question about the secondary springs on the accelerator pump, do these get adjusted in any way when used for secondary carbs.?
Thanks! I cut that thing off, THEN I thought about it.... This is just gonna be a cruiser. I'd probably be fine just making the outer carbs dummies, but where would the fun be in that. Yes making progress!! Kinda slow going, but thats okay. Ive got just one end carb on now, I'll put the other one on tonite, or this weekend maybe. Then hopefully go for a test spin and see if everything else works like it does in my head!!
I forgot to think about the fact that your end carb jets might already be drilled out by the last owner. So, I would wait to see how it runs when the outer carbs are opening up.
Yeah I thought about that, and of course can't get in touch with the guy I got em from. I figure I'll wait and see how it does driving and go from there. I appreciate the help!!
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. There are the four(?) holes in the throttle bores, the bottom hole has a little piece of something sticking out of it. Its metal, looks like its supposed to be there. It also has only 48 jets.
The thing sticking out of the bottom hole is the idle mixture needle. You can pull them out of the base and plug the holes with set screws. Also, if you look close it appears that the throttle blades are not open the same on each side....could be an optical illusion.
Ha!! I didn't think about the mixture screws!! Thats kinda funny! Thanks!! Thats the center carb, the ends don't have those. It is an optical illusion. They're the same. I'm thinking I need bigger jets in the center carb? Or maybe its just a matter of messing with the mixture screws more.
I had a huge reply going, but lost it when I tried to post. Do some research on drilling your throttle plates to allow more air through the center carb. Your plates are open too far and you have no adjustment with your mixture screws (that's why you can see the points of them poking through).
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