# Still have issues with Tri Power idling



## timmyg (Jan 2, 2012)

Hello
I have been on the Forum asking many questions concerning Tri Power carbs. and Rear Main Seal Issues. I still have not resolved the Rear Main Seal Issue but I have set myself a goal of getting the Engine to idle correctly and perform well. Once I get that accomplished, I am going to tackle the Rear Main Seal again. I have a couple of questions in regards to the idling and performance of the engine. When I purchased the car, the following engine is what came with it. Engine had been rebuilt quite some time ago, but only had a couple of hundred miles on it since rebuild according to the previous owner. 
1970 455 HO Engine: #10 McKellar Solid Lift Camshaft – 1.65 Ratio Rocker Arms, creates a 480 lift from a 440 lift – HO Round Port Heads – Big Block Chevrolet Studs and Solid lifters – Ram Air Four Push Rods Pontiac Super Duty Rods – Forged Pistons, believed to be Standard Bore – 1966 Tri Power Set up.
I was having issues with the Engine not idling correctly and wanting to cut off as well engine stumbling upon acceleration and engine surging while driving down the road. I found that the center carburetor had quite a bit of play in the throttle shaft and also in the accelerator pump rod. This was causing the car to stumble as the throttle was being opened up before the accellerator pump was being accuated, creating an initial stumble. I spoke with the gentleman from Pontiac Tri Power and discussed with him my issues. I decided to have him build me a new Center Carburetor designed for my engine, Rear end Ratio,Etc. I recieved the Carb and put it on the engine and could not get the engine to run. I spoke with him and he built me a second one assuming that something may have been wrong with the first one. I recieved the second one and installed it. The engine will run and the accelleration stumbling and the surging are gone, however I cannot get the engine to Idle very well at all. Idles rough and will cut off if you leave it idling for a short period of time. Also, if you accellerate and come back to idle the engine immediately wants to cut off. You have to really play with the accellerator to keep it running. It doesnt seem to be loading up. It seems to be the opposite whereas it is not getting fuel properly while idling or after accelleration when you return to idle.
Would this engine inherantly have a rough idle with the Mckellar #10 Camshaft in it. I realize it should run with this camshaft, but wanted to know should I expect a rough idle even if everything is correct due to the fact that it is considered a performance camshaft. I am not familiar with this camshaft other than I have been told it is a good performance Camshaft. I have read that it was used in the early 421 engines. Also, is there any specific Fuel Pump that I should be using with the Tripower setup. I have a Carter that I purchased from Summit that was listed for a 1970 455 Engine. Didnt know if maybe there is a specific one that needs to be associated with the Tri Power set up, although I doubt it.
To sum it up, New Center Carb, with #67 Jets and idle circuit Pick up tubes modified per "Pontiac Tri Power". New Points Distributor with vaccum advance hooked up to Manifold Vacuum and total advance set at 36 degrees at 2500 RPM's. Air/Fuel mixture screws adjusted for best idle. Engine idles rough and does'nt want to idle. Adjusting the idle screw to increase idle RPM's is ineffective and does not correct the problem. Any help,ideas, or thoughts on what I should look for, etc. are all greatly appreciated.
Thanks


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## Rukee (Feb 8, 2007)

It sounds like a vacuum leak, you could spray some carb cleaner or starting fluid around the bases of the carbs and intake to heads to check for any increasing in RPMs indicating a leak. Putting your hand over the center carb choking it out slightly too will indicate a vacuum leak, if it runs better choking it out, there is more then likely a vacuum leak. Couple other things I would check, if you have power brakes remove and plug the hose going to it, if it's leaking internally it will cause your condition. Check valve adjustment. If all else fails, make a couple of block off plates and put them under the outboard carbs to completely block them off then disconnect the linkage. Vacuum leaks at the throttle plates on those can cause issues too.


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## BearGFR (Aug 25, 2008)

Don't dismiss problems with the outer carbs as posssible causes either. If they're leaking air around the throttle shafts and/or plates, you're going to have the devil of a time getting the motor to idle properly.

One semi-quick way to test would be to completely remove the outer carbs and block off the manifold openings with plates and gaskets. If that solves the idle problem, then you know the issues are with the outer carbs.

Bear


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## nineteen 65 (Jul 8, 2013)

All good suggestions, one thing you could try is disconnecting the passenger side rod that connects the outer 2 carb butterflies and ensure that they are closed. If that helps then tweak/bend the wire so that it will go into the connecting holes without moving the butterflies off the closed position. Took me some time to figure that out when I reinstalled my carbs back on the manifold. There is enough 'slop' in the manifold bolt to carb mounting holes to cause the carbs to be placed further apart and the wire has to be 'lengthened' to accommodate the slight difference in spacing.


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## geeteeohguy (Feb 2, 2008)

Here's my take: I too think it's too lean. It could be a vacuum leak or it could simply be a mis-adjusted center carb. How did you adjust the mixture screws? Also, be advised that in '66 the tripower intake used a one-year only choke system, with the choke spring buried in the manifold near the center carb. A lot of '66 tripower manifolds crack between the center carb openings, and this can be seen only with the carb removed. Check the intake for cracks in this area. '65 and earlier Tripower intakes are not prone to this due to their carb mounted choke systems. Another thing: I've owned and driven tripower Pontiacs for over 35 years, and the 'loose throttle shaft' debacle doesn't hold water for me. Loose throttle shafts at the bellcrank area really have no affect
on performance. If the throttle blades are loose and sloppy (usually as a result of being removed to re-bush or replace the throttle shaft!), then yes. I have antique cars and engines that have close to 1/8" slop in the throttle shaft area, and they run and idle just fine. My advice would be to check the intake for cracks, and if ok, then adjust the mixture properly.


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## timmyg (Jan 2, 2012)

I have sprayed cleaner around the bases of all three carbs as well as held my hand over the top of the front and rear carbs while the engine is running. I also sprayed where the intake and heads mate up. None of this makes any difference to the idling. I also could not see any cracks in the intake. Did the Tri Power intake require different intake to head gaskets? I used the ones that came with the gasket set I got for the 70 455 Engine. I wouldnt think there is any difference but thought I would ask the question just in case one of you knows different. The ones I removed looked the same as the ones I replaced with.


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## Rukee (Feb 8, 2007)

The outboard carbs should not make a difference if you cover them as they do not have idle circuits in them and no fuel is going through them until the throttle plates open. Covering them with no effect doesn't mean they are not leaking vacuum at the plates either. What does it do if you partly cover the top of the center carb?


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## geeteeohguy (Feb 2, 2008)

The intake gaskets are the same. *Again, what is your center carb mixture set at and did you adjust it properly?*


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## gtoguy389 (Jun 3, 2012)

The throttle plates on the outboard carbs need to be completely sealed off. The best way to check them is to disassemble the bases from the bodies, and use a flashlight held underneath them. There should be no light coming through the bores. I also agree with running the engine without the end carbs, use block-off plates to seal up the manifold to make sure you get the proper adjustments on the center carb. You can then add one secondary carb at a time to narrow down where the problem is. When I did mine, I added the back carb first, and ran it like a 4-barrel by using a fuel line similar to a Holley double pumper, (yes, I had to do some modifying to make it work), and then after making sure everything was idling correctly and running well down the road, added the front carb. While I was checking the idle and making sure everything was running correctly down the road, I was also checking the spark plugs before adding the next carb to make sure I got the right mixture, not too rich, not to lean. It was a good way to tell if a secondary carb was completely sealed or not.


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## timmyg (Jan 2, 2012)

*Problem taken care of*

All suggestions were great and very similar. I took all of your suggestions and incorporated all of them into my trouble shooting. I purchased a vacuum gauge and connected it to the center carb. Vacuum at idling was approx. 13 inches and somewhat erratic. I started trouble shooting with the rear carb. I covered the top of the carb. with a shop rag and this made no difference at all. I moved to the center carb. and started to cover it up and it immediately started to change the idle speed. When I moved to the Front Carb, as soon as I started to cover the top of the Carb. the engine started to pick up speed and the vacuum raised approx 3 inches to 16 inches. I had found the problem. The Front Carb was pulling air through it at idle speed. I took my hand and started to move the rod on the right side of the carb's that connect the Front and Rear Carb's. This made the vacuum change. I went to disconnect the rod from the Front Carb only, and I could feel it had tension on it. This is what was slightly holding the front Throttle Plates open. I had purchased a new Rod from Ames Pontiac and apparently it was a smiggen too short. I bent the Rod slightly to lengthen it. I hooked the Rod back up and Vacuum was good and consistent. I then went over the Air/Fuel adjustments, idle speed, and verified the ignition timing. The engine runs great and idles consistent even when in gear which is something I had not had at all previously. Once again the Forum came through for me. Thanks to all for your help with this. I am now a little bit more educated on the Tri Powers. Now, if only I could conquer the Rear Main Seal Issue!!


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## Rukee (Feb 8, 2007)

Awesome!! Yea that rod on the right is meant to be bent to adjust so both are closed and WOT at the same time. I've seen some people try to make them progressive working 1-2-3, which is wrong. Then the rod on the left can be adjusted to allow the outboard carbs to come on sooner or later depending on your liking.


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## 34Chevy (Apr 6, 2018)

*Secondary throttle plates*

I have 3 primary Rochester 2bbls. Can I simply block off idle screws to make 2 into secondaries? Do I need to change the butterflies to make sure of complete closer so that it idles on the primary only. I have a custom linkage setup that works from drivers side.


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