Thread: center tri carb won't idle...

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I'm putting tri power on a sbc 350 - got the first and third carb openings on the intake sealed off - only the center carb on the car. Just rebuilt the engine and put it together with a mild cam. The car will start and idle ONLY with the choke blade partially closed. If the blade opens completely, allowing full air flow into the funnel, the car shuts down immediately. My guess is too much air??? Not enough gas??? Wrong ratio??? There are no known vacuum leaks. I have backed the idle screws both out about 4 turns... hoping to get as much fuel as possible into the carb. How can I get the car to run on this 2 barrel? thanks - kip

should mention this is a rochester carb with vacuum choke - thanks

I don't know all the technical names for these parts, but stick with me. I took the carb apart, and discovered that the two tubes running down out of the venturi cluster, were clogged. These two tubes have holes drilled across them, and part of why I took it apart to begin with was I noticed there was only one weak stream of fuel (on the passenger side) entering the carb when working the throttle by hand - engine off. So there was a clog somewhere that kept the fuel from coming in those two tiny holes. Perhaps I did not get all the clog out? Is it possible to remove these two tubes without breaking them? Probably better to replace them??? I read that the fuel pressure for a tri power is about 3 lb.s - is that right? Does the stock fuel pump off the block put out too much pressure? I'll check for leaks tomorrow with carb cleaner... thanks - kip

3 to 5 psi is about right. I have the J2 pack on my Olds 371 and at idle it's about 3 psi, 5 when hurrying down the road. Also I am running a SW electric fuel pump, not the stock unit.

I got the tubes unplugged using carb cleaner and a piece of copper wire small enough to up the tubes. Sprayed carb cleaner all around and found no leaks around the carb, but major leaking where the intake meets the heads. We did not use a sealant on the sides, only the gasket by itself. We did put sealant on the front and rear with the rubber pieces that come in the gasket kits. Perhaps these are not pulling down enough. Will take them out, and put sealer all around the intake and see what happens. thanks much - kip

KB

I don't know what intake gaskets you used, so what I'm about to say may be off base.

When I set my tripower up several years ago, it was recommended that I use thick soft gaskets on the intake to head surface. I was told not to use the hard gaskets like the ones that come in most gasket sets. As a matter of fact, Edelbrock had a warning on their website about not using these hard gaskets on any of their aluminum manifolds, but I can't locate it now.

Offy actually sells special thick gaskets(part # 5305 Special) for their tripower manifolds.

I used Victor graphite impregnated gaskets(sorry, no part #, been a long time) that my local machine shop had on the shelf. They were pretty thick and very soft.

I was told to torque the manifold down in several small steps, too( more steps than you would normally). The way it was explained to me is this: The tripower(and 2x4) manifold is very stiff in the main body, but still has regular thickness flanges. This makes it easy to distort the sealing surfaces and get vacuum leaks if you're not careful, especially with hard gaskets.

This info came from Hot Rod Carburetion and they said that most of the vacuum leak problems could be traced to improper gaskets and torgue. I took their advice and mine have been trouble free for about 7 years.

Hope you get it figured out.

Mike

Oh well, I used the hard gaskets that came with the kit, and did not torgue the intake manifold bolts down. I tightened them to what seems to be "tight". Is there any where to locate a larger but soft intake gasket? Is possible to make them out of gasket material??? My guess is no. I don't know that I understand what you were saying about the reason the harder gaskets are not the best to use. My guess is that there are still vacuum leaks, thus still hard to get to idle right. There are several places that sell tri carb materials, wonder if any would know of such gaskets? And what their recommendation would be? I'll check. Thanks - kip

KB

Here is the warning form the Edelbrock website I referred to:

CAUTION: Always use new gaskets as recommended. Check
with gasket manufacturer for compatibility with aluminum
intake manifolds. We recommend Fel-Pro Printoseal gaskets.
The use of Permatorque gaskets can lead to improper sealing
due to the hardness of the gasket. Don't use Permatorque
gaskets.

Here's a link to the document:

http://www.edelbrock.com/automotive_...e_Manifold.pdf

Don't blame you for being skeptical of the explination. Just passing on info from someone who had delt with far more of these manifolds than me.

Mike