3.5 V8 Holley 390 tuning issues - Defender Source
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  #1  
Old May 31st, 2016, 01:19 PM
GRJ
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Greg Johnson
1989 110
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3.5 V8 Holley 390 tuning issues

1989 3.5 v8, electronic ignition, originally fitted with dual crabs, retro fitted by previous owner and now has an Edlebrock Performer intake and a 390 Holley carb.
Distributor has 2 ports on the vacuum pod, outside facing port connected to venture vacuum (where Holley says to connect the vac advance), the inside facing port has been left open. I tried connecting that to manifold vacuum and it ran like a real POS. So I have left that open as it was when I bought the Rover.
Good cold start and idle.
Hard hot/warm starting.
Requires major finesse on the pedal when starting off and up shifting, too hard on the pedal and it bucks.
Hunts/misses when running along without load.
Runs smooth in 5th gear at 75/kmh when just above lugging.
If running along and it’s hunting/missing a slight grade in the road that causes the engine to work a little harder will smooth it out. Basically runs great when working hard(ish) but when it should be running in more or less the ‘enco’ easy going window it runs crappy.
Carb was cleaned by a local hot-rod shop and tweaked by the guy that cleaned it. No improvement. Same scenario after new cap and rotor. “HotRod guy” is totally intimidated by the fact it’s a Rover and has told me “I’m on my own.”
I could use some advice. Thanks
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  #2  
Old May 31st, 2016, 01:25 PM
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Red90
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John B.
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It probably need to be jetted. The easiest way is to get someone with a wide band oxygen sensor to check the current A/F ratios and then change jets until it is correct.

Not sure why a shop would care if it is a Rover. It is just a regular old, but small American V8.
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Old May 31st, 2016, 01:43 PM
slorocco
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Dan Prasada-Rao
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Did you leave the port open as you stated or is it just capped off and not connected to anything. Just tell the shop to think of it as an old Buick.
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Old May 31st, 2016, 01:45 PM
GRJ
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Greg Johnson
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Just left it open, didn't cap it
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  #5  
Old May 31st, 2016, 02:04 PM
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J. Michael McCaig
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Jeez, it's a Buick V8 with a 4 barrel carb, Must not be much of a "HotRod Guy". Sounds to me like a vacuum leak as when in econ mode, as you say, the engine should be producing maximum vacuum. Hard to tell without putting a vacuum gauge on it but pull a spark plug after a run and look at the color. If it is real white it is running lean which probably confirms a vacuum leak. If it is sooty black it is probably flooding or running rich. I wish I could help more but I know Edelbrock/Carter carbs. Never had much luck with Holleys off-road. The 390 is a popular carb, I am sure there must be tons of stuff on the net about tuning it on a GM engine.
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Old May 31st, 2016, 02:33 PM
slorocco
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Dan Prasada-Rao
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Quote:
Originally Posted by GRJ View Post
Just left it open, didn't cap it

I'd try to cap it and see if that has any effect. Without being capped it's sucking a lot of air through that may be causing it to run real lean at low throttle and idle
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Old May 31st, 2016, 02:42 PM
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Quote:
Originally Posted by slorocco View Post
I'd try to cap it and see if that has any effect. Without being capped it's sucking a lot of air through that may be causing it to run real lean at low throttle and idle
The port under discussion is on the vacuum advance of the distributor, not the carb from what I understand.

Maybe some pictures would help...
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Old May 31st, 2016, 02:45 PM
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If it's suckling air into the vacuum advance unit than the diaphragm is us. Give us a picture where your engine breather is connected to the carb.
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  #9  
Old May 31st, 2016, 02:51 PM
slorocco
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Dan Prasada-Rao
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Quote:
Originally Posted by Red90 View Post
The port under discussion is on the vacuum advance of the distributor, not the carb from what I understand.

Maybe some pictures would help...


Got it, my error in not reading better.
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  #10  
Old May 31st, 2016, 02:54 PM
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Thomason, Max
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I think its the ignition. Something is getting hot and messing up. Could also be vapor lock.

Have you put a timing light on? If she is missing, then that leads me to believe something is up in the ignition department.

Also have you pulled the plugs? What do they look like? If they look like crap, then I'd say get a colortune to see what is going on in there.
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  #11  
Old May 31st, 2016, 07:17 PM
GRJ
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Greg Johnson
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pics show... Plugs are black but not crazy fouled, the unused vac port on the cao side of the vac advance and the port used to run the vac advance on the carb.

With the mention of a vacuum leak and being asked if I plugged the open port or not, I did plug the open port and it made no difference, neither did cleaning the plugs.
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