# 65 GTO Tripower running rough



## torpedo51 (Sep 8, 2009)

Its a 389 with Rochester 2GCs tripower, 4sp.

Car ran fine. Put into storage for two years. Now runs rough.

After chasing carmelized fuel and gaskets, and leaks sprouting up one after the other... I decided to do a full Echlin brand rebuild on all three carbs, took them apart and cleaned them thoroughly. There is no gas leaking in, on, or around the carbs. I changed the gaskets, pump valve, spring, ball bearing, Ts, etc.

I have the stock distributor - replaced the points, plugs. I've set the gap, verified the dwell and timing. All within factory specs.

Capped the vacuum ports, checked with a guage - vacuum also seems to be close to spec (a little low, but not very low). Doesn't appear to be leaking.

Has a temp controlled choke - appears to be set correctly. When I adjust the choke while the car is running - it does affect the rpm. It seems to be set correctly. After the car warmed up, I twisted the choke so that it is fully disengaged - and won't affect the rpm.

Checked compression on all cylinders - all relatively close to each other and above 80%.

Car starts fine. Runs horrible, sounds terrible, has 1/10th the power, and idles high at about 1200.

I can't adjust the idle down to normal rpm - it will simply die below 1200. 

So... I'm not sure how to get the mixture correct, or the idle down... to get that familiar deep rumble.

I bought the Rochester manuals - not the best read. Seems like I need an oxygen sniffer and a dyno at this point.

Help!


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## 1970 Lemans (Jul 25, 2009)

Well, I never had a tripower, but about 6 years back I had a problem on my vehicle (350 automatic, 2GV carb), that sounds somewhat similar to the symptoms you report.

Specifically, my vehicle idled badly and would stall if idle set to normal (though power on acceleration wasn't too bad). Timing, dwell all set correctly, new points and plugs, rotor, dist. cap. Turned out problem was in carb idle circuit; the idle pick-up tube was loose (note, this occurred soon after a cleaning and rebuild by a reputable carb shop). Perhaps in cleaning/rebuild, something got loosened in one of the carbs? Carb shop re-fastened (epoxied if I recall correctly) tube back in place ... fine ever since.


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## Gran Turismo (Jan 12, 2010)

They recommend tuning the engine on centre carb only' taking end carbs off (blank plating inlet) then adjust screws to base then 2 1/2 out. 
Check out Mike Wasson at Pontiac Tripower A great source for rebuilding and tuning tips. Used him myself for parts for top quality parts. Butterfly plates / shaft wear at edges and dont seal and can cause the problem you describe.


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## torpedo51 (Sep 8, 2009)

Here's an update:

I sent the carbs out to get the throttle plates worked on. While they were out, I dropped in a new-in-the-box holley four barrel and matching edelbrock intake manifold. The car acted the same!

After digging a little further, we found that the oil pressure is abnormally low, some of the rockers are worn, some of the valves are clattering, and when the engine is above 2500 rpm the timing skips (the timing mark jumps wildly +/- 10 deg).

We think the low pressure and worn rockers are preventing the lifters from operating at a full range, while the slack in the chain and the old distributor are contributing to timing failure.

I'm going to pull the engine for a "light rebuild": timing chain, oil pump, bearings, rockers, rings, water pump, cam & lifters. I'm not building a race motor, I just want to freshen it up.


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## jetstang (Nov 5, 2008)

How long has it been since it ran good?


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## torpedo51 (Sep 8, 2009)

I think it probably never ran good. Since I bought it, I only drove around a residential area a few times, and then put it into storage. I never tried to get it over 45mph or burn the tires. The good news is that after a light rebuild, I can use my tri-power again.


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## jetstang (Nov 5, 2008)

My 66 389 ran great but smoked bad. My pistons were gone. My car was redone in 2000? and I think they did a light rebuild but didnt' do pistons.


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## torpedo51 (Sep 8, 2009)

ok, I'll check the rods, bearings, rings, and piston heads too. I was thinking of having the entire rotating assembly balanced for karma points.


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