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-   -   center tri carb won't idle... (http://www.hotrodders.com/forum/center-tri-carb-wont-idle-137914.html)

kbyounger 04-30-2008 01:23 PM

center tri carb won't idle...
 
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... vacuum operated choke - thanks

Holder350 04-30-2008 02:03 PM

alot of motors WONT run without a choke for the first min or so of idling.

run your idle screw on the carb IN until it will run and warm up.

After its good and warm idle it back down with the choke off.

then adjust your mixture screws till you get the highest idle again.

adjust idle screw and repeat till you don't get a higher idle when adjusting the mixture screws.

then the carb will be adjusted properly.

now.....the choke is not a vacuum operated device.

on the original manifold that the carb came off of had a bi-metal spring connected to the choke linkage.
The way it worked.....is

Before the motor starts the choke is completely closed. as soon as there is manifold vacuum a diaphragm pulls the choke open Slightly.
As the motor warms up the bi-metal spring releases its tension as heat off the manifold effectively changes its shape.






(BIG BREATH) :eek: and saying that.....you need a manual choke.

kbyounger 04-30-2008 03:28 PM

Thanks - perhaps I have not let the car run long enough... to warm up. The vacuum deal, may not have been stated correctly on my part. There is a small vacuum hose leading to a very small canister on the passenger side of the carb, with a lever that connects to the choke plate - thus I thought it was a vacuum operated choke of some type, but I must say, it really seems to have no control over this plate, even though the two are connected. The rod end off the canister is in a slot on the arm of the plate, and just seems to slide in this slot with no real effect on the movement of the plate. Thanks - kip

F&J 04-30-2008 06:30 PM

First thought IS a vac leak. Second would be a carb with plugged up idle circuits.

Tripowers are sweet setups, don't get flustered yet :cool:

F&J 04-30-2008 06:34 PM

Quote:

There is a small vacuum hose leading to a very small canister on the passenger side of the carb, with a lever that connects to the choke plate - thus I thought it was a vacuum operated choke of some type, but I must say, it really seems to have no control over this plate, even though the two are connected. The rod end off the canister is in a slot on the arm of the plate, and just seems to slide in this slot with no real effect on the movement of the plate.

That is called a "choke pull-off". When working right, the choke flap is 100% closed if you push the accel pedal down and DON'T start the engine. Then, as the motor starts, that vac can pulls the choke blade open just a little, so it does not flood.

Edit: You can check the vac can easy; Put a long vac hose on it and use your mouth to see if it is leaking, or if it actually will open the blade "slightly".

Chevrolet4x4s 04-30-2008 06:54 PM

Wont having the outboard carbs blocked off cause fuel distribution problems at WOT?

Shane

F&J 04-30-2008 07:28 PM

Quote:

Originally Posted by Chevrolet4x4s
Wont having the outboard carbs blocked off cause fuel distribution problems at WOT?

Shane

No. and it is a sure way to eliminate a possible vac leak in the outboards when working on a problem.

I've been thinking a little; and I wonder how well the intake manifold is sealing to the heads (if this was just put together?}. I'd look closely at the angle of the gasket surface to see if the manifold sits at the exact same angle as the head surfaces. It might have a leak at the lower parts and be drawing vacuum through the lifter galley.

kbyounger 05-01-2008 01:39 PM

Well, I got the car to run long enough to warm up, and then sprayed carb cleaner around the carb and found no leaks, sprayed up and down along the intake where it sets on the heads and the complete drivers side leaked and most of the passenger side. We did not use sealant on the sides, only the gasket. On the front and rear we used the preformed rubber pieces and sealant. Perhaps the rubber pieces are too high, and may need to just sealant there and on the sides? thanks - kip

F&J 05-01-2008 01:43 PM

Some, or a lot of people, discard those end pieces and use good sealer.

Also use a decent thickness of gasket, Mr. Gasket or maybe Felpro has something.

Don't go nuts trying to overtighten those alum manifolds. You may snap an ear.

Holder350 05-01-2008 09:08 PM

NEVER use the rubber gaskets that comes with an intake set.

ALWAYS use silicon.


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