1971 400 question
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From: N/W Montana
1971 400 question
I am having trouble tuning my 400 engine.
it is a 71 car engine I transplanted into a 97 f150
it is modified with flat top pistons, 280 summit cam and a 600 holley.
it has v2 heads ( shaved,guides,valves,springs and relieved for the lift clearance)
the cam timing is strait up (69 cleavland timing set )
when i put a light on it, I get best vacuum @ 20 deg. adv.(
with vac line disconected ) 15 Hg. lowest smooth idle speed is 1200 RPM
there is 2 Hg vacuum on timed port. borderline kick back on start when I set the timing mark on 4 deg. with the stator pointing at pickup, rotor pointing at #1 in the 1/2 past 12 position. it runs best with crank case vent line open ( smooths out but still high idle speed )
carb is 0-1850 w/ #69 jets and #9 power valve ( recently rebuilt )
float levels adjusted to spec. air/fuel mixture(11/2 turns out) adjustments slow to respond.
( butterflies past idle circut ? ) secondaries adjusted to spec.s
throttle adjustment 11/2 turns from closed
sorry for the long first post, I'm hopping there are some old school hot rodders here that can provide some in sight.
it is a 71 car engine I transplanted into a 97 f150
it is modified with flat top pistons, 280 summit cam and a 600 holley.
it has v2 heads ( shaved,guides,valves,springs and relieved for the lift clearance)
the cam timing is strait up (69 cleavland timing set )
when i put a light on it, I get best vacuum @ 20 deg. adv.(
with vac line disconected ) 15 Hg. lowest smooth idle speed is 1200 RPM
there is 2 Hg vacuum on timed port. borderline kick back on start when I set the timing mark on 4 deg. with the stator pointing at pickup, rotor pointing at #1 in the 1/2 past 12 position. it runs best with crank case vent line open ( smooths out but still high idle speed )
carb is 0-1850 w/ #69 jets and #9 power valve ( recently rebuilt )
float levels adjusted to spec. air/fuel mixture(11/2 turns out) adjustments slow to respond.
( butterflies past idle circut ? ) secondaries adjusted to spec.s
throttle adjustment 11/2 turns from closed
sorry for the long first post, I'm hopping there are some old school hot rodders here that can provide some in sight.
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Joined: Mar 2006
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not sure i'm old-school enough, but i'll try.
you cannot (or should not, at least) set initial timing by vacuum- so forget that you get the highest vacuum @ 20 degrees advanced. that's unimportant.
likewise, forget the 2" of vacuum on the timed port. that port is closed at idle.
jets & power valve don't matter at idle, either- neither are in play.
what is the "crank case vent line"? are you referring to the PCV line?
if it runs better with that line open, i think your idle setting is way too rich (you are creating a massive vacuum leak by unplugging the line, so if adding air makes things better, you must have too much fuel).
gently turn the idle screws all the way in, then back them out 1.5 turns.
if it still won't behave at all- try turning them *all the way in*.
that should shut the engine down. if it doesn't, you are leaking fuel somewhere inside the carb. (power valve, etc).
good luck- and don't worry, somebody smarter than me will be along shortly.
you cannot (or should not, at least) set initial timing by vacuum- so forget that you get the highest vacuum @ 20 degrees advanced. that's unimportant.
likewise, forget the 2" of vacuum on the timed port. that port is closed at idle.
jets & power valve don't matter at idle, either- neither are in play.
what is the "crank case vent line"? are you referring to the PCV line?
if it runs better with that line open, i think your idle setting is way too rich (you are creating a massive vacuum leak by unplugging the line, so if adding air makes things better, you must have too much fuel).
gently turn the idle screws all the way in, then back them out 1.5 turns.
if it still won't behave at all- try turning them *all the way in*.
that should shut the engine down. if it doesn't, you are leaking fuel somewhere inside the carb. (power valve, etc).
good luck- and don't worry, somebody smarter than me will be along shortly.
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From: N/W Montana
got it fixed, it was the power valve. heres what happened. a couple of days ago
I switch the ignition back from gm HEI to the dura spark box and put lighter springs in the distributor, while timing it it backfired. I didn't think too much about it.
all the newer Holley's are backfire protected.
However, I started it and turned the air/fuel mixture screws all the way in and it didn't stall
so I shut it off and looked up the numbers on the horn of carb and discovered it was made in 1969 ...... before the backfire protection spring/BB.
so, I pulled the float bowl and metering plate and sure enough..... the power valve diaphram had a small tear in it.
I put the #6 one back in until I get a new one.
I switch the ignition back from gm HEI to the dura spark box and put lighter springs in the distributor, while timing it it backfired. I didn't think too much about it.
all the newer Holley's are backfire protected.
However, I started it and turned the air/fuel mixture screws all the way in and it didn't stall
so I shut it off and looked up the numbers on the horn of carb and discovered it was made in 1969 ...... before the backfire protection spring/BB.
so, I pulled the float bowl and metering plate and sure enough..... the power valve diaphram had a small tear in it.
I put the #6 one back in until I get a new one.
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From: N/W Montana
Thank you !
this am I timed it @ 12 deg. (timed it by ear then put the light on it)
its right on the edge of hard start. trimed the air/ fuel (in just a little from 1.5). it idles good @ 950 rpm. off idle quick and clean. I took it for a spin and about a mile out remembered I forgot to reconect the vacuum advance.so I stoped and connected it and it stalled as soon as I gave it just a little fuel. so I unpugged it. I ran it through the gears ... Yee haa
I'll watch the temp guage and check the plugs this pm.
I'll post some pictures soon.
this am I timed it @ 12 deg. (timed it by ear then put the light on it)
its right on the edge of hard start. trimed the air/ fuel (in just a little from 1.5). it idles good @ 950 rpm. off idle quick and clean. I took it for a spin and about a mile out remembered I forgot to reconect the vacuum advance.so I stoped and connected it and it stalled as soon as I gave it just a little fuel. so I unpugged it. I ran it through the gears ... Yee haa
I'll watch the temp guage and check the plugs this pm.
I'll post some pictures soon.
Posting Guru
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if so, either the advance canister is pulling in way too much advance, or the canister's diaphragm is torn, and you're getting a vacuum leak.
just guessing, though-
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From: N/W Montana
line was conected to the top . it won't start with line conected to either one.
I drove it about 90 mi. today (round trip to town) I stoped at the local watering hole and put in 4 gal.s of reg. ethonal fuel just to be safe and noticed some detonation.
I use 93oct conventional, on the way back same thing. I added 1/2 bottle of cheap octaine booster to 22gal.s. I'm only running between 9.3 & 9.5 CR. (Flat top Badger pistons, block not decked ) 2v heads shaved just enough to true them up.
temp ran 180 around town and on hiway. my fuel presure is between 3.5 & 4.5 #
I was @7# with the electric but changed back to mechanical last week when I was having fuel / carb problems. second canister , 1st one adjustable. ?
I drove it about 90 mi. today (round trip to town) I stoped at the local watering hole and put in 4 gal.s of reg. ethonal fuel just to be safe and noticed some detonation.
I use 93oct conventional, on the way back same thing. I added 1/2 bottle of cheap octaine booster to 22gal.s. I'm only running between 9.3 & 9.5 CR. (Flat top Badger pistons, block not decked ) 2v heads shaved just enough to true them up.
temp ran 180 around town and on hiway. my fuel presure is between 3.5 & 4.5 #
I was @7# with the electric but changed back to mechanical last week when I was having fuel / carb problems. second canister , 1st one adjustable. ?
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Posting Guru
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strange.
there shouldn't be any vacuum on the timed port with the throttle closed (your first post says there is 2"). also, 950 is a little high for curb idle rpm.
i'm wondering if your butterflies aren't closing completely.
to determine how much advance the vacuum canister is adding:
do you have a hand-held vacuum pump? if so, try this:
start the truck with the vac advance disconnected.
hook up the handheld pump and apply 2" of vacuum
check timing and see how much advance
there shouldn't be any vacuum on the timed port with the throttle closed (your first post says there is 2"). also, 950 is a little high for curb idle rpm.
i'm wondering if your butterflies aren't closing completely.
to determine how much advance the vacuum canister is adding:
do you have a hand-held vacuum pump? if so, try this:
start the truck with the vac advance disconnected.
hook up the handheld pump and apply 2" of vacuum
check timing and see how much advance
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