vacuum advance issue
Thread Starter
|
Post Fiend
Joined: Jan 2006
Posts: 5,037
Likes: 9
From: Kasson, Minnesota
vacuum advance issue
My 75 supercab 460 with stock ignition is having issues with the vacuum adcance. The engine runs a bit rough with slight acceleration and slower speeds with the advance hooked up, but when it's capped off the engine seems to run much better. I have been just driving it with the advance capped off. Timing has been checked. Is my vac advance just messed up?
Thread Starter
|
Post Fiend
Joined: Jan 2006
Posts: 5,037
Likes: 9
From: Kasson, Minnesota
Yep, timing set when vac disconnected.
Laughing Gas
Joined: May 2006
Posts: 1,140
Likes: 13
From: Port Orchard Wa
I had similar problem and it was the canister. If you're connected to manifold vac (below throttle plate) and not ported vac (above throttle plate) then you only have vac advance at idle and light load. If you have a handpump vac & gage (like a mighty vac), you could pull a vac on it and see if it holds.
Elder User
Joined: May 2004
Posts: 836
Likes: 2
From: Shreveport, LA
As stated above, you can pull vacuum on the unit and see if it holds; If it does, it's a good unit but likely needs some adjustment. The adjustment probably wouldnt cause the problems youre talking about, though. The adjustments on your vacuum advance tends to be drivability adjustments under acceleration, not idle.
Has it always done this?
Unlike above, however, if you have it connected to manifold vacuum, you'll have vacuum any time the engine can provide vacuum, which is almost everything below full throttle...at least to varying degrees.
If youre hooked to ported vacuum, which you should be, you'll have no vacuum at a properly set idle; anything above idle and you'll have the same vacuum as manifold vacuum.
Having the advance hooked to manifold vacuum, with a stock adjustment, will cause the timing to be too advanced throughout the vacuum curve and could be your issue.
Has it always done this?
Unlike above, however, if you have it connected to manifold vacuum, you'll have vacuum any time the engine can provide vacuum, which is almost everything below full throttle...at least to varying degrees.
If youre hooked to ported vacuum, which you should be, you'll have no vacuum at a properly set idle; anything above idle and you'll have the same vacuum as manifold vacuum.
Having the advance hooked to manifold vacuum, with a stock adjustment, will cause the timing to be too advanced throughout the vacuum curve and could be your issue.
Tuned
Joined: Jun 2013
Posts: 438
Likes: 61
From: Craigmont, Id
Something else to consider and check is how much advance are you getting out of the vacuum advance if it is working. Most Ford advance units can be adjusted with an allen wrench. It is inside the nipple where the hose connects. You need a timing light that you can measure timing advance with or put the distributor on a distrubutor machine to run it and I have not seen one of those that worked in a good 25 years or so. Good rule of thumb on a stock engine is a total of 40-45 degrees of advance at around 3000 rpm or so. That would be initial, centrifucal, and vacuum combined.
Thread
Thread Starter
Forum
Replies
Last Post
brokersteve
1973 - 1979 F-100 & Larger F-Series Trucks
5
Sep 16, 2012 01:03 AM
1986F150six
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
10
Feb 10, 2012 08:27 PM
smoke n tires
Big Block V8 - 385 Series (6.1/370, 7.0/429, 7.5/460)
7
Apr 15, 2005 06:54 PM
darkknight9
Electrical Systems/Wiring
5
Feb 11, 2005 12:27 PM
77f2504x4
Big Block V8 - 385 Series (6.1/370, 7.0/429, 7.5/460)
5
Nov 23, 2004 01:30 PM
