[sixt8bird]

Well I finally got the old bird fired up after polishing the tri power and changing the 1973 2 bbl center carb off of a 400 catalina to a 1968 350 2 bbl. The problem I am having is when you rev it the rpms take a while to drop and when you cover the center carb it will start to rev. The exhaust burns your eyes like a lean missfire. Covering the outside carbs dont change rpms at all so I know they dont leak. I think that I am running too lean as cutting off the air on the center carb makes it race up but if I cover it real close it will kill it. It does idle ok . So my question is, if I enlarge the center jets, does it have an effect on idle mixture or do I need to drill the idle air tubes. With the 73 carb, it ran pretty rich as I could fire it up without any choke and just drive even when around 50 degs and the exhaust had black residue after driving around for a while.I drilled the jets and the tranfer slots etc etc. The 1968 carb I have the choke hooked up so it fast idles until warm.My eyes are still burning from working on it 1 hour ago.

[sixt8bird]

Well I finally got the old bird fired up after polishing the tri power and changing the 1973 2 bbl center carb off of a 400 catalina to a 1968 350 2 bbl. The problem I am having is when you rev it the rpms take a while to drop and when you cover the center carb it will start to rev. The exhaust burns your eyes like a lean missfire. Covering the outside carbs dont change rpms at all so I know they dont leak. I think that I am running too lean as cutting off the air on the center carb makes it race up but if I cover it real close it will kill it. It does idle ok . So my question is, if I enlarge the center jets, does it have an effect on idle mixture or do I need to drill the idle air tubes. With the 73 carb, it ran pretty rich as I could fire it up without any choke and just drive even when around 50 degs and the exhaust had black residue after driving around for a while.I drilled the jets and the tranfer slots etc etc. The 1968 carb I have the choke hooked up so it fast idles until warm.My eyes are still burning from working on it 1 hour ago.

[dragracer]

i went thru the same thing when i was trying to build a center carb for my tri power which was missing the center carb. if your idle mixture screws are backed out real far to get it to idle at all, try opening up the idle discharge hole in the base plate. when you run the idle screws all the way in you will see them sticking out of the holes in the throttle bore. this will probobly get you started anyway.

[DiamondJim]

It sounds to me as if your car is very rich at idle, your power valve may not be receiving enough vacume to keep it closed at idle. When you partially cover the center carb it is increasing the vacume signal to the center carb and closing the power valve(it revs because it was so rich it is almost flooded, closing the valve corrects this problem). How much vacume(in inches) do you have at idle? You may need to cut on few turns off the spring or better yet buy one of the spring kits that Jon Hargrove sells(The Carb Shop). -Jim

[DiamondJim]

Also the float height on the center carb is very critical, be sure you have it set right. -Jim

[carbking]

Engine RPM slowly dropping after revving is a classic symptom of a vacuum leak. Would check this before throwing rocks at the carb. The engine gaining RPM with your hand partially over it tends to substantiate the presence of a vaccum leak, as it would richen the mixture.

Jon.

[Mr. P-Body]

Be certain the little "wind up" springs on the end carbs are fully closing the butterflies. We've seen this on TriPowers before. It is indeed a vacuum leak, as carbking suggests.

[Department X]

That a nice looking setup. Good to see you can put together a tripower with different off year carbs. Would like to see how it turns out. Does someone have a plan laid out to do this. If you get time post some detailed pics

[sixt8bird]

I closed off the front and rear carb and it didnt change rpms or idle quality so I dont think that the front or rear are the problem. I will try for vacume leak as this is what I was thinking, lean conditions burn eyes with that acidic exhaust. Also I will add better gas as this has been sitting in my tank for about 6 months. I can get the idle down to where the engine will just die by adjusting the idle speed and the idle mixture screws are out about 3 turns now. I started initially at 1 1/2 but it wouldnt idle and burned eyes real bad. I have backed out to highest idle/vacume.

[Old Man Taylor]

I had a similar problem one time when I had the wrong gasket under the cluster. The rebuild kits usually provide two different cluster gaskets. The later 2-bbl's have some vacuum passages towards the center of the carburetor that the older ones don't have. The old (narrow) cluster gaskets will not seal those vacuum passages adequately.

[carbking]

Jim - actually, there are 12 different STYLES of venturi cluster gaskets used in the various 2-G series carburetors. I am not going to count the actual number of different ones (thickness, material, etc.).

This is one reason I harp on having the proper carburetor number, and not trying to "mix and match" parts. And you are correct that this can definately cause a vacuum leak.

Jon.

[mikediaz]

Really old thread - did you ever figure it out sixty8bird??

[sixt8bird]

Nope, car has been sitting since last September and decided to take a break. I am now working on installing factory AC to my daily driver. Term used loosely now but 530,000 milesis on the car. AC has never been on car since I have owned it since 1980. Pretty cool to see it all back in place. getting back to the bases. My car runs like a top with the end carbs blocked off. I nstalled just the bases on the front and rear carb and when installing, I lost 3-4 " of vacuum at each base. They are definately leaking between the bores and plates. I nstalled grease at the bore/plate edges and vacuum picked up and idle smoothed. damn it Im soooooo sick of this and I havent worked on them for 6 months!!!

[mikediaz]

darn that reallly sucks. Don't loose faith. I posted some hopefully useful info for you on the other thread about another supplier for blades. Maybe that can help. check out the post.

mike

[mrtonegto]

sixt8bird: I'm rebuilding a 66 tripower set up and also need a center carb.
Would you know what Pontiac year/model 2 bbl's are alternates? Part #'s would be great if you have them.

[sixt8bird]

I used a 1973 2bbl 400 that I cut a bunch of stuff off and welded up some holes on the base that was left. It ran really good. As far as looking correct, any 2GC with the divorced chokes all look real similar. I am using a 1968 2GC from a 350 that I got for free with intake as most people dont want them when converting to 4 bbls. It ran good until the polishing on all carbs. It runs good with the front and rear blocked off. I richened it up some just as the 1973 for a great idle and nice and cool mix. I wish at this point, I had the old grimey look that they has as they worked so good for 7 years. Now they look good but I cant drive with them on!!! damn damn Damn!!! I will get it all sorted out when I get time but with my wife having a freshly broken ankle, all cars are put on hold!!