Technical Intakes.switching a 3x2 to a single 4

The outer carbs as it is only dump,I'm pretty sure just my center is what's not running right. But yes,my outlets could be blocked off with a plate.

 

Listen hooligan, tune your carbs properly and your problem will go away. It's not a quick process and requires a lot of learning, but you are plenty capable. A dyno shop would take at least a couple hours at over $100/hr, so figure 4-5 times that amount of time I trying to do the drive/adjust/drive/adjust/drive and so on.

You have to treat each circuit as its own problem. If you have 3 carbs leaking air but only one with an idle circuit, you need to richen that single carb up enough to compensate.

I do not advocate tuning the center carb with the outside 2 capped off because once you uncap them, all the air leaking through them makes your first adjustments useless. Adjust your carbs in the exact setup that you run them. But seriously, if you think this project is over your head, there should be shops in your area that will do it for relatively cheap. Just understand that tuning is always time consuming.

 

That suggestion is a precise way to know if the center carb is really OK, or not, and then find out if the outboards are Ok or not.

You can get the center dialed in perfect, and then only have one outboard put back on, to know if one or both outboards are OK
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EDIT to Add: When using progressive trips and end up with a problem, you must verify first, that the primary carb is perfect. You would be wasting time if you had the opinion that a primary carb can be re-adjusted to compensate for a "known" throttle valve vacuum leak....or compensate for a throttle plate that does not seal each and every time it closes.

That is why each carb needs to be tested at idle, after the primary is perfect. If you add just one outboard back on, and see that the idle is poor or inconsistent, you must fix that outboard air leak, and then test again, before adding the last outboard.

The OP stated that "sometimes" the car wants to take-off at a light. That is a good indicator that "sometimes" one of the outboards is not sealing perfectly each and every time.
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3 x94s= about 425 CFM's
So after all this tuning your still only going to have 425cfm total, at high rpm your going to run out of fuel anyway. If your intake has dual pattern carb mounting holes, sell the 94's get some Rochester 2g small base they will be close to 675 cfm from all three, should run much better. Just a thought.

 

High rpm? Why does everyone act like this guy is going to be running this thing around 5,000 all the time or asking for 100% of the available power? Seriously, this guy is trying to tune his car for drivability which has absolutely nothing to do with making sure the engine has every CFM that it can use. For gods sake, the OHV V8 survived many many many years in millions of cars with a SINGLE 2bbl carb and no one complained of drivability problems.

 

^^^^^^"My setup is,355 chev,headers,comp 268xe cam,3000stall converter,3.08 gears in a pretty light fender less A coupe. (And yes I'm pretty happy with that gear in this particular car) yes the 3x2 looks good,but I'm over the issues it is causing,it even tends to 'go' when I'm sitting at a light. and I do like the look of tunnel Rams. I know it may not be everyone's cup of tea. Also thinking on a nice duel plane air gap style intake.ill perhaps go back to 3x2 later but for the summer I just want to enjoy the car...and hear the cam again!"

So you think that with this car and engine that he will never go over 5000 rpm, what rock have you been living under? It really makes no difference weather he goes over 5000 rpm or not, I thought the reason we build these cars is to get the most performance we can out of our combinations.
With the 94's on there the car will not run the best that it can. OP already said he is going to remove the tri-power because the single 4bbl runs better, the 2g's will get closer the the 4bbl than the 94's.

 

I could tell my story again about the friend who bought a "3 deuce" setup (with 94's) for his '55 Chevy in 1961. Didn't run for ****. I looked it over and saw that we could drill the manifold for 2GC's. That, and a trip to Carmichel's in Excelsior : problem solved. But I won't. (Ooops, guess I did.)

 

Hooligan "The punters are not leaking air,I have used the special glue to seal the blades at idle." What special glue did you use and where did you get it? Any tips for applying the stuff? Thank you.

 

I forgot that the OP said he was disappointed with the dyno numbers of his motor and not his drivability........ HA


Anyway, you guys can keep pushing him in any direction you want. I'm all done arguing with people trying to fix a CFM problem that the OP DOES NOT HAVE. I'm sure his car will drive better with an improperly tuned 4bbl or an improperly tunes set of Rotchy 2bbls. Yeah buddy.

 

Damn, I missed the dyno numbers, what were they?

 

Hooligan, what does the person who sold you the tri power rig have to say about your situation? You obviously paid good money for it.

 

Jib, his original post wasn't complaining about the flat out performance of the setup. Therefore getting him more CFM's won't solve his problem. It's as simple as that. He could put a single 2 bbl on there and if it was tuned properly, it would solve what he is experiencing. YES, it would severely limit peak horsepower and torque numbers, but again, he was never having a problem with those, his problem was drivability.

 

I think that @porkn****** came with some reasonable observation! Again, except that optimal burn is lambda 1. Lambda 1 is 14.7 gram air to 1 gram of fuel.
15:1 to makes it lean, 14:1 makes it fat. But lambda 1 ain't good for old motors/valves, a little fat is good for your car. And please not fat people jokes!

The most common way to measure for the right amount of fuel wild be CO. The more you get, the more unburned fuel is in your exhaust 3-4 % is good for an old car, less then 1% is lean (dangerous). 4-7% is fat and will cost you money, but if you can burn it you can drive it. At some point it will wash your cylinders and break you engine.

You can check your exhaust temp. That will give you good indication on fuel ratio 1200-1500 degree Fahrenheit is good, above is lean. Lean hurts your engine, and makes it hot.

You can go untraditional and buy a young boy racer fuel ratio gauge and put a bung in your exhaust.
But infrared temp gauge is way cheaper and will more all round tool for your shop/house/boat/settling/roadside repair box and the list go on

You are definitely in the lean part of the spectrum!
More fuel is what you need, not a four barrel! Putting a 4bbl on is just giving up!

I see no reason for that you should run three small carbs on a fairly big motor. I would recommend that it will need more fuel fast then where you get it now. Like more fuel on the center carb, and the two other most must come shortly of idle, nut at 2000-2500 rpm, it needs to come in above idle (in the work zone)

A remember in this game; one change, needs one test, and a reaction!
Last one will be a cold one in the shade.

How does you plugs read? Plugs ain't the most perfect method, but it's simple and all available fact should be counted in!

Maybe pics and running progress reports, the ac***ulated knowledge of the HAMB can make that baby run and fun again.

 

That tri-carb should work just fine on your engine. Your problem is the outside carbs are set up wrongly, put the idle circuits back in them and run them as proper carbs complete with power valves - do you know what jets and power valve are in the centre carb?. I've been running my set up for 15 yrs now and never had a days problem from it and it runs as a progressive system.

 

Update- not really but. I've been sick and busy with work. Haven't messed with the car. But to clear something up. I'm not looking for peak hp. This car already is/was quick. I just want my drivability,as a few have stated. I'm still confused on what the idle restrictors is. I do have the drill bit to drill it now. Don't really have the time or money to set up my outer carbs to be functioning idle carbs yet

 

I definitely don't know as much about 3x2 setups as some of the guys here, but in the process of setting up my setup, I learned a lot. I'm using Rochesters, so that part is different, but I went round and round with trying to get the end carbs to seal. Took them both off, tried tuning just the center, and then reinstalling, one at a time, different ends, filing and sealing the ****erflies..... I ended up getting new baseplates for the end carbs that really do seal well. I could get my old ones to seal "ok", but not great. The shafts leaked, I think was the main problem. My ends have no idle circuits, no powervalves. After I got that part figured out I started messing with air/fuel. I drilled out all the jets, centers bigger than the ends, which let me be able to adjust the mixture better with the adjusters, whereas before that I couldn't. I read alot about drilling out the idle mixture tubes(or whatever they are actually called!), ended up not needing to do that. Not to say that on a dyno, maybe tuning those would make a difference, but for me, for driveability, it's right on. Starts right up, sits and idles super smooth, stop and go traffic not a problem. I'm glad I stuck with the 3x2, it looks so cool.

 

If you'd like I can drill a set and send them to you. let me know how long your tubes are, there's more than 1 length.

 

Did you use the aluminum ones?where did you get them?

I notice that my rear carb does leak fuel out of the throttle shaft. I ***ume that it's also leaking air there as well.

 

Yeah, the aluminum baseplates. I got mine from Vintage Speed, but Speedway sells them too, as I kit I think. Made a huge difference.

 

Well that's a problem.
It's going to be the cause of chasing symptoms which leads to agrivation and a shelved 3x2 setup.

 

Hooligan "The punters are not leaking air,I have used the special glue to seal the blades at idle." What special glue did you use and where did you get it? Any tips for applying the stuff? Thank you.

 

Yeah so do I get new bases and run the idle circuits? Or just seal them off as I have mine?

 

I don't remember,it's a special shellac type stuff from a Pontiac guy,it's the real deal stuff from back in the day. Tho he only gives you a swab of it for 15$ it's just enough to do the end carbs. You apply it,let it dry,then snap the blades back open. It should leave a nice buildup ring

 

Hooligan, thanks. I had read somewhere that you had too heat it to about 350 degrees for about 40 minutes to cure it. Sounds like you had success with just letting it dry. Now I have to find some.

 

I talked to the guy and he said either heat it or it will dry naturally in 2 days. So I left them out in the hot sun for 2 days. It seemed to of dried pretty well.the guy has a Pontiac web site or something. Forgot his name,he's in the Midwest I believe. Also keep the stuff cold until you want to use it,supposedly has longer shelf life that way

It's just my throttle shafts that are hanging me up I think

 

It's called DAG 213, it was used by the factory on all Pontiac Tri-Power secondary carbs.

I'd be looking to replace the tiny Ford/Holley 94s with 3 small-base Rochester carbs. Pontiac used the 3 small-base Rochester carbs on the first two years of Tri-Power engine production, on the '57 347 and '58 370 engines.

After the introduction of the 389 in 1959 they went to using the large-base secondary carbs while still keeping the small-base center carb, Tri-Powers used this same configuration all the way through 1965 on 389 and 421 engines. In 1966 which was the final year of the Tri-Power production all three carbs were the large-base Rochesters on both 389 and 421 engines.

1959 Pontiac Tri-Power setup for your viewing pleasure. The Rochester carbs when nicely recolored/re-plated can be some pretty nice eye candy.





The small-base Rochester center carb is much better suited for the fuel/air needs of any vintage Chevy small-block, after all they did come from the factory with one of these if you ordered the base 2-barrel engine. Cruising around on the street you'll be running on only the center carb 99% of the time and it might as well be sized correctly for your engine.

This all has nothing to do with all-out performance at 5,000 RPM, it has everything to do with having good manners on the street. However good top-end performance will be there as well with the 3 Rochester carbs, it IS a hot rod isn't it?

That's my story and I'm sticking to it.

 

Dag213 yeah

I can't afford to go that route. My intake is not drilled for those,nor do I have any of those carbs

 

Hooligan and Draggin' GTO: Thanks for the info. I am in the same boat as Hooligan, I have 94s and would consider the small based Rochesters except for the cost. This thread has some very good information that is new to me. I went and checked my stock of spare parts for some idle tubes. I found 2 different diameters in the 4 spares I have. Since I have the same driveability issues as mentioned previously, I am going to start by checking and replacing the tubes if they are the small diameter. If that doesn't change the condition, I guess I'll buy the #31 drill and see what happens. BTW, I am running 6 Holly 94s with the 4 end carbs currently blocked until I am happy with it on the 2 center carbs. (401 nailhead, homemade log manifold) This thread would be a good addition to Dreddybear's collection of Holly 94 threads (search for Holly 94 info)

 

Apparently you missed the leaking end carb even while looking for something amiss.
That overlook is exactly why it's often suggested to block the end carbs off and get the engine running properly on the center. Then when the end carbs are added back in any new problems are easily found or at least the direction is pointed out.

With progressive linkage, You're end carbs should not be wet with fuel or pulling a vacuume across the top of them and I'm sure you know this. I've found that end carbs that don't do much or often like to develop problems with the needle and seat valve or the accelerator pumps. The first will give you sloppy slobber idle (wet carbs and leaking shafts) and the second will give you a lean under throttle condition.

 

The drill does not work,I bought a .035 bit and it slipped right in,so I drilled it out to .060 because it's what I had and I'm frustrated. It made hardly no difference at all