Agree. Maybe he's talking about turns in on the idle stop screw (aka idle speed screw, throttle position screw, ...)
Pulling V.A at idle
- Thread starter Ironracer
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Timing at RPM
Example 1
Using a factory '73 318 distributor, timing at 1000 rpm is 9* BTDC, initial is zero.
Example 2
Setting a factory '69 318 distributor so the engine had 18* BTDC at 1000 rpm, the initial is 11* BTDC. But we can't measure that until the engine is slowed to 700 rpm or less.
Some examples of factory small block high performance timing curves in this post.
1968 340 timing
But bottom line is get the idle sorted out, then deal with any adjustments to the timing curve that may be needed.
Example 1
Using a factory '73 318 distributor, timing at 1000 rpm is 9* BTDC, initial is zero.
Example 2
Setting a factory '69 318 distributor so the engine had 18* BTDC at 1000 rpm, the initial is 11* BTDC. But we can't measure that until the engine is slowed to 700 rpm or less.
Some examples of factory small block high performance timing curves in this post.
1968 340 timing
But bottom line is get the idle sorted out, then deal with any adjustments to the timing curve that may be needed.
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I hate giving specific setup advice but in this case is close enough to mine so I will.
I'd try the timing where I said above.
Crack the secondary throttles either a 1/4 or a 1/2 turn further open.
Then adjust the idle mix screws. Start with them 1 1/2 turns out. Turn in and if the engine rpm drops turn out. 1/8 turns at time. When its warmed up, try turning in again. As soon as it looses rpm, or misses, turn back out 1/4 or 3/8s. If timing has changed, reset timing. Readjust mix. Now test in gear.
Try again at different primary throttle openings (within the range of .020 to .040" on trnasfer slots. Refer to your notes so as not to exceeed this.) If it strongest with at .040 or more, then try opening the secondary throttles another 1/4 or 1/2. Repeat above as needed.
If going over 1 turn on the secondary throttles I'd consider drilling the primary throttles.
You'll then need to reduce the idle air bleeds. Stick some wire in each one. You can search for posts where I've shown that as I've got to hit the road.
I'd try the timing where I said above.
Crack the secondary throttles either a 1/4 or a 1/2 turn further open.
Then adjust the idle mix screws. Start with them 1 1/2 turns out. Turn in and if the engine rpm drops turn out. 1/8 turns at time. When its warmed up, try turning in again. As soon as it looses rpm, or misses, turn back out 1/4 or 3/8s. If timing has changed, reset timing. Readjust mix. Now test in gear.
Try again at different primary throttle openings (within the range of .020 to .040" on trnasfer slots. Refer to your notes so as not to exceeed this.) If it strongest with at .040 or more, then try opening the secondary throttles another 1/4 or 1/2. Repeat above as needed.
If going over 1 turn on the secondary throttles I'd consider drilling the primary throttles.
You'll then need to reduce the idle air bleeds. Stick some wire in each one. You can search for posts where I've shown that as I've got to hit the road.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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If your VA is plumbed to the proper spark-port, then my guess would be'
wrong /defective gasket on the metering block, or pouched parts, on account of; the primary throttles would have to be way far open to activate the VA; like 1600/1800 rpm far. Which with 18* of idle-timing, and 9inches of vacuum, does not compute, for me.
Maybe this is linked to the fat mixture; as in ruptured PV diaphragm or wrong PV gasket..
In any case, I would take the M-block off for inspection.
If perchance your secondary side has a PV, then you better check it too.
wrong /defective gasket on the metering block, or pouched parts, on account of; the primary throttles would have to be way far open to activate the VA; like 1600/1800 rpm far. Which with 18* of idle-timing, and 9inches of vacuum, does not compute, for me.
Maybe this is linked to the fat mixture; as in ruptured PV diaphragm or wrong PV gasket..
In any case, I would take the M-block off for inspection.
If perchance your secondary side has a PV, then you better check it too.
Ironracer
Gearhead
Its the older. 484, 284 MP cam.
Ironracer
Gearhead
No Sir, the Lil flat head ones behind the float bowls. Primary sides only... fuel/ air mixture? Standard starting point is 1.5 turns out bottom, usually... ? At least that's what Grandpa told me
Ironracer
Gearhead
It's a 12 year old carb, I bought new, supposedly has PV blow out protection
Ironracer
Gearhead
I haven't messed w/ the secondary blade adj... it's outta the box, 12 years old
Ironracer
Gearhead
The main idle speed? No Sir, but I did set the acc pump clearance
Clarification... when I say mods I mean drilling the secondaries etc..
JMO 12* initial with a 484 cam is not the best spot. That's factory 340 cam timing specs and they were light.
I'd put 18-20 on it and see how things work at idle.
Drilling a carb is always the last resort for me. Timing usually helps clean things up if inadequate.
I'd put 18-20 on it and see how things work at idle.
Drilling a carb is always the last resort for me. Timing usually helps clean things up if inadequate.
I think he said it was on 18 most recently. That's why I asked if he has ever verified TDC with a piston stop. Something's making him get into the transfer slots I believe. Retarded timing could sure be it.
Ironracer
Gearhead
That's an old vid w/ the same engine, running points. The 340 is now electronic, in a Duster, pulled drivetrain, outta the 66 Sat, after my deceased wife wrecked it and bent the frame. Sorry for the muddy clarification! My Bad....
Ironracer
Gearhead
Yessir, you are Correct, I'm at 18° ( maybe 19°) currently. Thank You Rusty! Dude, The Truck You Built is Sick, Vixen is coming Along Nicely too! Glad You and Kittle are rollin Her! Love it!!!!!
Ironracer
Gearhead
So, I guess I have another question.. is it an Issue to Run that Way? Or can I get Detonation? Or am I screwing myself out of initial timing, therefore HP?
That one is often confusing becuase of the way it has been written.
The pump should move immediately as the throttle rotates off of slow idle.
The 'clearance' is when the throttle is full wide open there should be travel remaining before the spring bottoms out . In other words with the throttle wide open, a feeler gage can be forced in between the lever and the adjuster.
18* at what rpm? This is the key.
yes it may end up being too much at 2400 rpm to use vac advance, or way too much at high rpm and wide open throttle. Its under heavy load, like wide open throttle 2 and 3 rd gear that too much timing advance can be really destructive. But unless you need to go racing, work on idle and then off idle. You can even drive it around the block at light and moderate throttle.
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Yup. We're on the same page. What caught Mike's attention was the 3.5 turns out. That's an awful lot.
If you caught it above my suggestion was the same as your Grandpa's. Then when warmed up, adjust by turning in (leaner) until it looses rpm. Then turn it richer. Much easier to detect performance drop going from rich to lean. The reason to turn it richer once that point is established is because the test was in neutral and with load the engine will need a richer mix.
Great! So now if/when you crack them open you can keep track of how to return to factory. That's by taking notes on how many turns or fractions of the stop screw.
Same concept with the primary throttles. With the carb on the bench, measure the transfer slop length visible below the throttle plates when the idle stop screw is just touching. Then note how many turns it takes to open the throttles so .020 .030 and .040" of the slots are revealed. This way you will know how much the transfer slots are exposed by counting the turns on the idle speed screw. Saves a lot of time removing and reinstalling the carb after each adjusment.
I drew an illustration of how that effects the idle mix, along with a photo of measuring with drill bits in this post. Some other posts there about too rich issues too.
MOPAROFFICIAL
Oogliboogli
Haven't read all the replies yet but if this is a scenario where you have a little bit of camshaft and you only have 2 Corner idle as in primary, then there's a good chance you have the throttle blades open too far and the ported vacuum is now active.
If that were the case...you can lower the primary blades at the idle speed screw..then flip the carb over and you see a little flat head screw that adjusts the secondary throttle blades...open them just a hair more to compensate for the lowered primary idle speed... again if that's the case and there not some internal leak that's pushing fuel.
All assuming the timing is set right.
Ironracer
Gearhead
18-19° @ 900,in park...driving her ain't been an issue, even w/ the heavier car. Street driven in Tampa, Daily, for 2 years, but it's been a while for the Daily thing. Had the same Blue tag ( antique) for 12 years...
Ironracer
Gearhead
The only time I've tried to Tune er, was when I first started Streeting as a Daily Driver.. found an Article on FBBO, using a vacuum gauge, about 2500 Rpm, then bringing the screws in till highest idle, + best vacuum
So odds are that its already advancing. When the engine slows down (transmission placed in gear) timing decreases. How much depends on how quick the primary advance is. it can be pretty dramatic as illustrated above. If you have four hands and an extra foot you can see that in the timing light and tach. Just be careful if measuring timing in gear! The extra hands and a foot on the brake is better than relying on chocks alone.
Ironracer
Gearhead
I have a Talented gal that can watch a tach, while running the pedal.when I did the Vac GA thing, I used the idle screw and the tach, along w/ the vacc ga, solo I've had a Few of these Beasts break out on me at a high idle. SCARY MAN!!! Especially a 4 Dr D-200 w/ a Dana and 4:10s!!!!!!! Brutal Man!
Pay close attention to post 44. I bet that will fix it.
Yote
Well-Known Member
Something I haven’t seen mentioned here but does vacuum can on distributor have adjustment in inlet
(Allen screw in tube) . It is my understanding that it can be adjusted to set when vacuum advance comes into play. Possibly a new can not adjusted or one messed with.
This may have been mentioned before and I missed it.
Don’t take this information as gospel as many on this forum know way MORE than I do . Just a thought.
Yote
(Allen screw in tube) . It is my understanding that it can be adjusted to set when vacuum advance comes into play. Possibly a new can not adjusted or one messed with.
This may have been mentioned before and I missed it.
Don’t take this information as gospel as many on this forum know way MORE than I do . Just a thought.
Yote
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