Vacuum Advance Can
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
I have been chasing the same problem for a while, and fixed the problem this weekend. I am now running 36 degrees locked out timing,and may try to go back to a mechanical setup in the future. I had also drilled throttle plates,tried different vacuum cans, even swapped my Vic Jr back to an RPM intake trying to fix this.
The fix for me was replacing the throttle base with a Quick Fuel billet base. The plates are not drilled,but the base is set up for four corner idle.(My orginal base was two corner.) I also replaced the idle feed restrictors to .035's and idle air bleeds to 70's front and rear. This worked. Nothing else I had tried previously did.
Now I'm not saying this is the magic solution,but if your 850 is already four corner idle, I'd try swapping out idle feed restrictors and air bleeds. For a couple bucks, you may fix the problem.
As it stands I have 8-9 inches of vacuum in gear, idling at 1000.(406 with 254@.050 cam)
The fix for me was replacing the throttle base with a Quick Fuel billet base. The plates are not drilled,but the base is set up for four corner idle.(My orginal base was two corner.) I also replaced the idle feed restrictors to .035's and idle air bleeds to 70's front and rear. This worked. Nothing else I had tried previously did.
Now I'm not saying this is the magic solution,but if your 850 is already four corner idle, I'd try swapping out idle feed restrictors and air bleeds. For a couple bucks, you may fix the problem.
As it stands I have 8-9 inches of vacuum in gear, idling at 1000.(406 with 254@.050 cam)
Last edited by The Money Pit; May 27, 2008 at 01:17 PM.
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
Thanks for sharing your experience and fix.
I am getting 8" at 1000 with no load in neutral. I wonder if I have a problem or if that is normal for the size cam. I had thought about the locked timing, but I was concerned about pinging if I happened to lug the engine around 2000 RPM.
I looked at the plugs today to see how rich or lean I might be running and posted a different problem.
I am getting 8" at 1000 with no load in neutral. I wonder if I have a problem or if that is normal for the size cam. I had thought about the locked timing, but I was concerned about pinging if I happened to lug the engine around 2000 RPM.
I looked at the plugs today to see how rich or lean I might be running and posted a different problem.
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
I pull 12 inches in park now. When I was trying to run with an ignition advance system I was around 10 in park,7-8 in gear, and had the same issue you describe. Ran for a bit, but as the vacuum dropped,then so would the timing, and the spiral continued till it stalled.
I want to run with locked out timing for a while, till I'm able to fine tune the carb idle, then I might try to go back to an advance of sorts. This is the biggest cam I've tried to date, so I really had no clue where to start tuning. It's all related. Carb idle vacuum,timing,timing, carb vacuum......
Good luck.
I want to run with locked out timing for a while, till I'm able to fine tune the carb idle, then I might try to go back to an advance of sorts. This is the biggest cam I've tried to date, so I really had no clue where to start tuning. It's all related. Carb idle vacuum,timing,timing, carb vacuum......
Good luck.
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
I got both the metering blocks and throttle body from Quick Fuel Technologies directly. I already had the Proform main body.
I'd give them a call and they will be able to help I'm sure.
At one point before I went with all the billet parts, I hand drilled the idle feed restrictor to .036 on the stock Holley metering block, and it almost worked. At the time the baseplate was stock,except for the holes in the throttle plates I drilled.Maybe if I went bigger it would have worked, I don't know.
These are the metering blocks. Both primary and secondary blocks have the idle mix adjustment screws, but the secondary block has no power valve provision.
I just had a thought you might want to try. With the engine running at idle,when it starts for stall,try spraying gas into the carb using a plant mister or some sort of spray bottle. Don't touch the throttle,just spray. If it doesn't stall, wouldn't that prove it's carb idle tune,instead of timing?
I'd give them a call and they will be able to help I'm sure.
At one point before I went with all the billet parts, I hand drilled the idle feed restrictor to .036 on the stock Holley metering block, and it almost worked. At the time the baseplate was stock,except for the holes in the throttle plates I drilled.Maybe if I went bigger it would have worked, I don't know.
These are the metering blocks. Both primary and secondary blocks have the idle mix adjustment screws, but the secondary block has no power valve provision.
I just had a thought you might want to try. With the engine running at idle,when it starts for stall,try spraying gas into the carb using a plant mister or some sort of spray bottle. Don't touch the throttle,just spray. If it doesn't stall, wouldn't that prove it's carb idle tune,instead of timing?
Last edited by The Money Pit; May 27, 2008 at 09:04 PM.
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
Thanks for sharing your experience and fix.
I am getting 8" at 1000 with no load in neutral. I wonder if I have a problem or if that is normal for the size cam. I had thought about the locked timing, but I was concerned about pinging if I happened to lug the engine around 2000 RPM.
I looked at the plugs today to see how rich or lean I might be running and posted a different problem.
I am getting 8" at 1000 with no load in neutral. I wonder if I have a problem or if that is normal for the size cam. I had thought about the locked timing, but I was concerned about pinging if I happened to lug the engine around 2000 RPM.
I looked at the plugs today to see how rich or lean I might be running and posted a different problem.
You can always adjust them back. Been Their, Done That
Trust me your car will idle
Thread Starter
Racer
Joined: Jul 2007
Posts: 444
Likes: 0
From: Roselle IL
Thanks for the tip. I will try loosening them up 2-3 thou. Lunati recommended a hot lash of .030, but the cam designer actually recommended .026 to recapture some high end. I set them at .022 cold (alum. heads). I will move them out to .024 cold, which should be equivilant to .030 hot and see if that helps my idle any.
