anyone know Rochester 2 Jets?

[shmoov69]

I am putting a 3x2 setup on my 58 and am having troubles with tuining it. :hammer: First, what is the little thing in the bottom of the bowl by the jets, a power valve of some sort? Is there any tuning it if it is? Next, I have got it running (without leaks!!), but it will not idle at all. It almost seems that it has a big vacum leak or something. Is there anyway to tell where a leak would be coming from or how to verify if that is what the problem is? Is there anything else I should know about doing this?
Thanks!

[PT Goat]

That is indeed a power valve, you should only have one in the center carb. If they are in the end carbs, they are probably not original. The only "tuning" I'm aware of on the power valve is the spring, which all depends on how much vacuum you're making. You want to make sure the valve is staying closed at idle.

As for you idle problem, these things are known for vacuum leaks, often at the throttle shaft, or more commonly through the end carbs. Try cupping your hands over the end carbs while its running and see if you feel a "pull." You obviously shouldn't at idle.

Every tripower I've ever had needed different tuning to idle properly. My suggestion is to make block off plates for the end carbs and just work on the center. Once you get the center performing properly, then add the end carbs. If they are sealed-up right, nothing should change.

Good luck!

[shmoov69]

Thanks Matt. I am making plates as we speak! The end carbs I'm sure are not the correct ones, being it is a swap meet piece! But the idle screws are not in the bases and the holes are plugged. So, I need to plug the power valve holes in the end carbs right? Also, how do you suggest getting the end butterfly's to achieve a proper seal?
Thanks!

[PT Goat]

One of my GTO's has power valves in the end carbs and it drives fine, but I know they can cause problems. If it were me, I'd plug them or replace the bowls entirely.

Two options on the butterflies: there is a product which I believe is called DAG which is used to seal them. It's a sticky tar-like substance. Many carb rebuilders use it, but it is very expensive and goes bad quickly. I'm pretty sure it's on an EPA hit list and not able to be shipped, etc. So obtaining enough for just two carbs is a difficult and expensive proposition.

Another option is to see if you can locate aftermarket base plates, which should seal better than worn originals. I know there are two companies making them for Pontiacs, I assume they are available for Chevy as well. Try http://www.vintagespeed.com/. Difficult site to use, but they are very knowledgeable and should have everything you will need.

Another great resource is Mike Wasson at www.pontiactripower.com. He does great work and is great to talk to as well.

Good luck.

[vintageracer]

Do you the matched and correct 3x2 carburetors with your setup? Yes, the carbs for a 3x2 original system are specific. If you are trying to make the system work with mismatched carbs, you will have trouble. The suggestion to block the outer carbs will help to determine that problem and isolate the center carb.

If you do not have the correct carbs, there is a kit out there to take 3 regular later model 2 barrel carbs and mofify them to work on a 3x2 system. I understand it works great!

I cannot remember if Barry Grant makes the conversion system or not but an internet search should find the answer.

[shmoov69]

thanks guys, I have the outside ones blocked now and it still won't run. It seems to rev good above 3000rpm, but won't idle. Ideas?
Thanks

[PT Goat]

How about some engine specs? As soon as you deviate from a stock camshaft profile, the idle settings get all out of wack. You may need to open up the idle tubes, adjust jetting, etc. What vacuum are you pulling at idle?

Also what type of fuel pump? I see a lot of guys with too much fuel pressure pushing fuel past the needle/seat when it should be closed causing flooding. 3-4lbs of fuel pressure is plenty.

[shmoov69]

the engine is a 348 at .040 with about 9-1 cr and a stock fuel pump with a small cam 224@50 & 524 lift. It ran fine with the stock carter 4bbl. Just low on power. This is a swap meet piece, so who knows what the carbs came off. Heck, I can't get it to idle long enough to figure anything out!!
Thanks!

[shmoov69]

ok, I figured it out!! A carb guy told me that the carbs were "specific" to application. And that small engines had different vacum requirement at idle than bigger engines had. And most of these carbs were on 283's and such. He told me to drill out the idle air passages about 5 thousands and it might work. But instead of that, i had scored an early olds tri power at the swap meet a few weeks ago, they needed rebuilt tho. I was thinking that early olds' were bigger cubic inches than 283's and closer to the 348 size. So I robbed the booster cluster from one of those carbs and put it in the rebuilt carb and........
It started right up and idled perfectly!!
Never would've guessed that one!! Just thought I'd share what the outcome was. I drove it to the KC Goodguys show and it done great all weekend.
Thanks for the help.

[shmoov69]

ok, I figured it out!! A carb guy told me that the carbs were "specific" to application. And that small engines had different vacum requirement at idle than bigger engines had. And most of these carbs were on 283's and such. He told me to drill out the idle air passages about 5 thousands and it might work. But instead of that, i had scored an early olds tri power at the swap meet a few weeks ago, they needed rebuilt tho. I was thinking that early olds' were bigger cubic inches than 283's and closer to the 348 size. So I robbed the booster cluster from one of those carbs and put it in the rebuilt carb and........
It started right up and idled perfectly!!
Never would've guessed that one!! Just thought I'd share what the outcome was. I drove it to the KC Goodguys show and it done great all weekend.
Thanks for the help.

[shmoov69]

ok, I figured it out!! A carb guy told me that the carbs were "specific" to application. And that small engines had different vacum requirement at idle than bigger engines had. And most of these carbs were on 283's and such. He told me to drill out the idle air passages about 5 thousands and it might work. But instead of that, i had scored an early olds tri power at the swap meet a few weeks ago, they needed rebuilt tho. I was thinking that early olds' were bigger cubic inches than 283's and closer to the 348 size. So I robbed the booster cluster from one of those carbs and put it in the rebuilt carb and........
It started right up and idled perfectly!!
Never would've guessed that one!! Just thought I'd share what the outcome was. I drove it to the KC Goodguys show and it done great all weekend.
Thanks for the help.