69 L68 Tri- Power tuning?
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Joined: Feb 2002
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From: ATLANTIC HIGHLANDS NJ
69 L68 Tri- Power tuning?
Hi all. I just bought a 69 L68, engine rebuilt but previous owner put in a Comp Cam 280 Magnum.
I am just in the beginning stages in tuning but here is the question:
1. Not sure of total timing but I have it set at 12 degrees idle.
2. Choke works fine, carbs are new, and fast idle is set around 1500 rpm's.
3. Starts but runs rough until warmed up, but still a little sloppy when warm. Idles around 1,000 rpm's at idle to be decent for now.
4. Cruising and running thru the gears is really quite nice. No vaccum leaks I can sense at the moment.
Now, if I stop for gas and shut it off, restart it is hardly running at 600 rpm's, within a minute the idle is up to 1,000. Just seems odd. The choke is not hanging up.
Could the stock center carb, and I assume it's out of the box stock, just not be right for the 280 Magnum cam?
This car sat for many months I think, so I put some 93 Sunnoco in it and added Torco Octane Boost. I'm hoping a good run down the highway with fresh fuel will help some. I also put in fresh plugs, cap & rotor are new.
So, I know long winded, but any thoughts from the Tri-Power gurus?
I am just in the beginning stages in tuning but here is the question:
1. Not sure of total timing but I have it set at 12 degrees idle.
2. Choke works fine, carbs are new, and fast idle is set around 1500 rpm's.
3. Starts but runs rough until warmed up, but still a little sloppy when warm. Idles around 1,000 rpm's at idle to be decent for now.
4. Cruising and running thru the gears is really quite nice. No vaccum leaks I can sense at the moment.
Now, if I stop for gas and shut it off, restart it is hardly running at 600 rpm's, within a minute the idle is up to 1,000. Just seems odd. The choke is not hanging up.
Could the stock center carb, and I assume it's out of the box stock, just not be right for the 280 Magnum cam?
This car sat for many months I think, so I put some 93 Sunnoco in it and added Torco Octane Boost. I'm hoping a good run down the highway with fresh fuel will help some. I also put in fresh plugs, cap & rotor are new.
So, I know long winded, but any thoughts from the Tri-Power gurus?
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Check the float levels, lower the hot idle speed to 800 rpm, and adjust the mixture screws. Invest in a dial back timing light and a spring kit with stop bushing and set your total mechanical advance to 36 with vacuum disconnected. Hopefully you are always using 93 octane.
Thread Starter
Pro
Joined: Feb 2002
Posts: 734
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From: ATLANTIC HIGHLANDS NJ
Check the float levels, lower the hot idle speed to 800 rpm, and adjust the mixture screws. Invest in a dial back timing light and a spring kit with stop bushing and set your total mechanical advance to 36 with vacuum disconnected. Hopefully you are always using 93 octane.
But, I did notice percolation, so I'm giving some thought to a think heat shield and / or Phenolic carb gaskets.
I may also need an adjustable Vacuum Advance pod.
Thanks again.
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Joined: Feb 2002
Posts: 734
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From: ATLANTIC HIGHLANDS NJ
I know, it's kind of odd. I'm hoping it's just clogged fuel filters in the carbs building up pressure. I shut it off after a good ride yesterday and I could hear a hissing. Pulling the air cleaner lid off and gas was dripping off the boosters onto the butterfly, center carb. The float level is just at the bottom of the site plug hole. I do hear that the crap oxygenate gas has a low boiling point, so a few things to check out I guess.
Race Director
Joined: May 2006
Posts: 18,710
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Assuming you checked the float level with the engine running, you could have a slightly leaky needle/seat. Does your fuel pump or fuel filter have a return line to the tank? That return line would relieve the pressure in the line when the car was turned off. The center carb has a bowl vent, is it correctly adjusted?
Last edited by MelWff; Nov 7, 2011 at 05:27 PM.
Thread Starter
Pro
Joined: Feb 2002
Posts: 734
Likes: 51
From: ATLANTIC HIGHLANDS NJ
Assuming you checked the float level with the engine running, you could have a slightly leaky needle/seat. Does your fuel pump or fuel filter have a return line to the tank? That return line would relieve the pressure in the line when the car was turned off. The center carb has a bowl vent, is it correctly adjusted?
I'm gonna pull the carbs, do new filters, check needle / seat, clean and blow out the venturi's , etc. Check the tank pick up screen for gum, etc.
Just get a clean starting point, everything rebuilt with good components, so I think just lack of use and stale fuel.
Mine is a January 69 build, so no return line. Unvented tank but with the correct vented cap.
Tuning may be a little trial & error as it is stock except the guy rebuilt the engine with a Comp Cam 280 Magnum. If everything is right it should idle fairly smooth at around 850 rpm I would think.
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