Tri-Power
Thread Starter
Instructor
Joined: Jan 2006
Posts: 163
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From: Simpsonville SC
Tri-Power
Can someone please explain briefly how the carb system works on a tri-power 400hp motor. Does the linkage open the front and back carbs or just vacuum? also if the linkage doesn't open the carbs what's it for. Also how can you tell if the carbs are opening. I did a search but I didn't come up with anything. Thanks
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Tri-power secondaries are opened by the vacuum diaphragms on the front and rear carbs, which get their vacuum signal from a pickup tube in the venturi of the center carb - that's VENTURI vacuum, not manifold vacuum. The function of the mechanical linkage on the driver's side is to positively close the secondary carbs when the center carb closes to prevent them from hanging open. 
Thread Starter
Instructor
Joined: Jan 2006
Posts: 163
Likes: 0
From: Simpsonville SC
Thanks John you have always been a big help.
I was thinking on the same lines but not sure, It seems mine are not opening with the vacuum but they do work if I open them one at a time with my hand. could it be the vacuum pods or maybe I have the hoses in the wrong place. I guess I could test the pods with my little hand pump/vacuum tool.I know I would love to hear them both open on the road because when I open them manualy they sound like it's getting ready to take off.
I was thinking on the same lines but not sure, It seems mine are not opening with the vacuum but they do work if I open them one at a time with my hand. could it be the vacuum pods or maybe I have the hoses in the wrong place. I guess I could test the pods with my little hand pump/vacuum tool.I know I would love to hear them both open on the road because when I open them manualy they sound like it's getting ready to take off.
Racer
Joined: Jun 2006
Posts: 309
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To check opening disconnect the hose from the center carb, block the center carb open (to defeat the linkage) and apply a little vacuum. If they open then all you need to do is insure that the venturi vacuum pick-up in the center carb is not clogged (put a hose on it and blow). The opening of the end carbs is really slow as delivered from the factory. To get them to open more aggressively you'll need to decrease the seated pressure of the spring (so it's free height is less) which is achieved by pulling the spring inside out. Then all the vacuum restrictions in the end vacuum cans need to be drilled out and finally you'll need to increase the vacuum hole in the center carb slightly. If you do this all well they'll snap right back open after you shift if you're mashing the pedal again. Recognize that the fuel distribution in the tri-power manifold is poor so some stagger jetting is inorder to get decent power. It takes a lot of effort to get the tri-power to equal the regular rat intake and a 850 Holley in HP.
Thread Starter
Instructor
Joined: Jan 2006
Posts: 163
Likes: 0
From: Simpsonville SC
Thanks 64Bob you are getting a little deep for my first tri-power trouble shooting exercise. Just kidding great information,Let me see if the pods are working tonight. I might try to get more detail on how to make them work better once I see if I have a vacuum leak or clog.
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
FYI...
All 3 carbs have a passage drilled from the outside to the venturi.
Looking down at the carb with the "D" pointing up, the tiny hole is at 2:00 just below the ridge in the venturi.
The hose-tube passage is drilled into (intersects) the first passage.
When the carb is assembled, the first passage is connected to the end carb vac cans (sealed with a cork gasket).
This "first" passage is plugged on the center carb so that the passage only leads from the venturi to the tube. The choke pull-off bracket covers the plugged hole.
If you apply air pressure or vac to an end carb body tube (no vac can attached) it will connect to both the external (vac can) hole and the venturi.
If you apply air pressure or vac to the center carb body tube, it will connect only to the venturi.
I recently (yesterday) found a 4055-1 center carb that had never been drilled completely through to the venturi. This TriPower setup could never have worked.
All 3 carbs have a passage drilled from the outside to the venturi.
Looking down at the carb with the "D" pointing up, the tiny hole is at 2:00 just below the ridge in the venturi.
The hose-tube passage is drilled into (intersects) the first passage.
When the carb is assembled, the first passage is connected to the end carb vac cans (sealed with a cork gasket).
This "first" passage is plugged on the center carb so that the passage only leads from the venturi to the tube. The choke pull-off bracket covers the plugged hole.
If you apply air pressure or vac to an end carb body tube (no vac can attached) it will connect to both the external (vac can) hole and the venturi.
If you apply air pressure or vac to the center carb body tube, it will connect only to the venturi.
I recently (yesterday) found a 4055-1 center carb that had never been drilled completely through to the venturi. This TriPower setup could never have worked.
Thread Starter
Instructor
Joined: Jan 2006
Posts: 163
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From: Simpsonville SC
Thanks Tom,
I hope to work on the car this weekend, With all this information I fill I do have a better understanding of how they work. Bob when I get them working I would like to learn more about how to make them more responsive. Anymore info is welcome.Thanks
I hope to work on the car this weekend, With all this information I fill I do have a better understanding of how they work. Bob when I get them working I would like to learn more about how to make them more responsive. Anymore info is welcome.Thanks
Thread Starter
Instructor
Joined: Jan 2006
Posts: 163
Likes: 0
From: Simpsonville SC
Well I worked on the tri-power set up over the weekend. I disconnected the center cab and blew out the opening. Now I know were that hole is located, I checked both pods with my hand pump vacuum kit and they worked as well( FRONT IS SLOWER THEN THE BACK). I then hooked up a vacuum gage to the center carb venturi opening and made sure I was getting a vacuum to the gage when the car was running,this also let me see were the vacuum kicked in in relation to the RPM's. I then hooked all the carbs back up and they all seem to work which was a cool sight and sound. My carbs are old from sitting for about seven years so the movement on the vacuum pods seem to be stiff. Could the diaphragm rubber be causing this? If so does Holley make replacement ones?
oK now does anyone have any suggestion and details on how to make this system more responsive? Bob64 talked about it,does anyone have any specific details I can work with.
Thanks for the help.
My carbs are old from sitting for about seven years so the movement on the vacuum pods seem to be stiff. Could the diaphragm rubber be causing this? If so does Holley make replacement ones? oK now does anyone have any suggestion and details on how to make this system more responsive? Bob64 talked about it,does anyone have any specific details I can work with.
Thanks for the help.
Last edited by skidder865; Jan 22, 2007 at 10:15 AM.
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Racer
Joined: Oct 2006
Posts: 489
Likes: 0
From: ormond beach florida
new rubbers for carbs
yOU CAN GET NEW rubber diapragms from action performance at 232 n nova rd ,daytona beach fl 32114. phone is 877 537 race or 3862522632 with tax was 68.00 for a pair DEan
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
That's a good price... Summit has them for about $26 each.
http://store.summitracing.com/partde...0&autoview=sku
Don't' forget, these diaphrams are a different size than normal... and the springs inside are also a different size/design.
http://store.summitracing.com/partde...0&autoview=sku
Don't' forget, these diaphrams are a different size than normal... and the springs inside are also a different size/design.
