Newbie needs help with 348 rough idle after 3x2 install

[devildog191]

Hello,

I'm a newbie on this board and also fairly new to the 348 engine....

I'm having a problem and here it is,

Installed a 348 with a rochester 4jet and the engine ran beautiful...

I then decided to install a 3x2 factory intake and go with 3 2gs...

Well after installing the 3x2 set up the engine had a rough idle...

Thinking it was the carbs I had all three completly rebuilt and reinstalled again...

I still am having a rough idle ... Have new points plugs and wires.... Installed a new coil....
Can anyone offer any advice how to get this engine running smoothly again...

I have been searching the board but haven't found anything too specific to what problem I'm having, so please forgive me if I over looked something..

Thanks In advance

[tripowerguy]

First off are your carbs the ones without idle circuits on the end carbs? Also are the carbs on the ends complete carbs for the 3X2 setup? If you have carbs that have been put together with pieces and are not true 3X2 end carbs that maybe your problem. Since the car ran fine with the 4 barrel we can assume that it isn't ingnition. I would first off take the two end carbs off and put two blockoff plates over the manifold and run the car on just the middle carb. You can make block off plates out of some metal plate or blocks of wood for that matter. Just put a gasket and the block off plate on. If the car idles fine then you know that your problem is in the two end carbs. If that is the case look at the butterflys, they are different than the center carb, they are cut at a diaginal so they seal off completely. If someone has put regular butterflys in then they leak air and that would be your problem. If you find the butterflys OK then take the carbs apart and check if they have powervalves in them, if they do then that is your problem. The end carbs have no powervalves. If that doesn't solve your problem then I would check for leaky intake gaskets. I would check that first before I did anything. With engine running spray some WD-40 along the gasket line and if the engine speeds up then it is a leaky intake gasket. Hope this helps.:) Roy

[devildog191]

Roy Thanks for your reply...

Well I just went outside and started it up.... Took it for a short drive and at higher rpms it seems to run smooth.... But it still idles rough...

I sprayed around the intake like you said with wd-40.... well I did notice a very slight increase in rpms when I sprayed it.... So could this be it? I didn't notice any cracks on the intake before the install and it had been sandblasted to bare metal...

The idle screws are blocked on the secondaries and the butterflies are closing.....

[tripower]

Roy Thanks for your reply...

Well I just went outside and started it up.... Took it for a short drive and at higher rpms it seems to run smooth.... But it still idles rough...

I sprayed around the intake like you said with wd-40.... well I did notice a very slight increase in rpms when I sprayed it.... So could this be it? I didn't notice any cracks on the intake before the install and it had been sandblasted to bare metal...

The idle screws are blocked on the secondaries and the butterflies are closing.....

With the engine running put your hand over the the front carb to see if it is sucking then do the same to the aft carb. If it is sucking you have a vacuum leak. If so remove the linkage and make sure the butterflies are closed then readjust the linkage.

[tripowerguy]

I can't tell from your reply whether you have idle adjustment screws in the end carbs or not. If you do then you probably have standard carbs for secondarys. These don't work well because the butterflys are not cut on a bias so they seal off completely. Do as tripower says, with it running check and see if there is any suction on your hand, if there is then take carb off and check butterflys. If they are standard butterflys they will not seal off sufficiently to work. If you close them tightly they will stick and not come loose. Also if they are standard carbs like you have in the center they will have power valves in them. If you shut off all vacumn to them the power valve opens up and pours gas into the intake. The secondarys must not have power valves in them and the hole for the power valve must be blocked off. Anyway if you put the new manifold on and you are sure that the gasket surface was hospital clean then I would stay with the carbs until I was sure that they are true secondarys and not all primary carbs.:deal Roy

[devildog191]

Thanks guys for helping me out here...

Well before I had the carbs rebuilt, both secondaries were definately sucking air when I would place my had over the carbs... Now that I got the carbs rebuilt, I did the same thing, I really don't feel a suction, but I do hear air... Is this normal? or does it still mean they are sucking just a little bit?

Just to clarify the secondaries do not have the idle mixture screws.... But I'm wondering if the butterflies are just standard ones and if they are, where can I get the ones for the secondaries? I have long shafts on all three carbs...

I think they do have the power valves in them still... The clarify the power valve is located on the inside bottom of the carb just in front of the jets?... Do I just remove them and find a plug?

When I sprayed the wd-40 and heard a slight rise in rpm, I'm thinking maybe the wd-40 could be entering the shafts and that I don't actually have a gasket leak but I'm just guessing.....

sorry for my inexperience but I'm learning slowly....

[tripowerguy]

The power valve is where you said and there is a plunger in the top that opens it. The plunger is held up with vacuum and when you suddenly floor the throttle you lose manifold vacuum and the plunger comes down and opens the power vavle until the engine picks up rpm and creates enough vacuum to pull the plunger back up. When there is no vacuum in the carb the plunger stays down because it is spring loaded and causes fuel to pour into the manifold causing a rich condition. Think of the 3X2 as one carb. you have two barrels in the middle that is the primary just like a 4 barrel carb. The car runs at idle and at part throttle on this set of venturis and the secondaries do nothing. When you floor the throttle on a 4 barrel you open up the two secondarys on a 4 barrel and when you do the same on a 3X2 setup you just open up 2 more secondaries. So the thing you must do is determine whether the two end carbs are true secondaries. You say you have no idle adjusting screws in the end bases, that is good. You said you had them rebuilt and who did this should know that when they took them apart that the butterflys went only one way. If the end carbs have power valves in them they need to be taken out and the plungers need to be removed. They pull out, they are staked in. You should be able to get plugs from Speedway Automotive. I know they sell a whole kit to convert primary carbs to secondary. And as far as spraying WD-40 I really meant to spray along the the manifold gasket where the manifold bolts to the heads. To sum up I think that if you don't have a manifold leak then you only have one choice and that is to take the carbs apart. Have you pulled the spark plugs and are they white or souty looking. If they are white then you probably have an air leak but if they are souty looking then you are getting to much fuel. Fixing this is just a process of eliminating the possiblitys.:) Roy