For all you vacuum guage soothsayers

[drew8mc]

https://youtu.be/qIBFEbE5SGM

I have a fresh 383 stroker from west coast engines. Alum heads, roller cam and rockers. Here are the specs.

Horsepower: 450-475
Torque: 450 lbs
Gas: 91 Octane (Premium Unleaded Gas)
Max RPM: Idle to 5500 RPM
Stall Recommended: 2300-2500
Crankshaft: Scat (Steel)
Cylinder Heads: R.P.C. / ProMaxx Aluminum (64cc/195cc)
Cylinder Head Gasket: Fel-Pro
Cylinder Head Bolts: Elgin
Valve Springs: Pioneer
Lifters: COMP Cams
Valve Size: 2.02/1.60
Camshaft: COMP Cams / Trick-Flow
Camshaft Lift: .540”
Camshaft Duration: 230° Int / 234° Exh. @ .050” Lift
Camshaft Lobe Separation: 110
Vacuum at Idle: 16″
Push Rods: COMP Cams
Rockers: Elgin SSR (1.5 Roller Rocker)
Rocker Arm Stud: ARP
Intake Manifold: Edelbrock Performer RPM (Aluminum)
Pistons: Federal Mogul (Hypereutectic)
Piston Rings: Federal Mogul (Moly)
Connecting Rods: GM Forged Powder Metal
Timing Set: Melling (HD Roller)
Bearings: KING HP Series (Tri-Metal Performance)

I saw a Utube video from Holley with what looked like my condition and it said this was an ignition issue. I put a new DUI HEI distributor in it with new wires. I will check all connections tomorrow. Anyone seen this before? Anything else I should check.
Thanks,
Drew

[geezer#99]

What carb?
What’s your timing like?

[drew8mc]

Quick Fuel Slayer 750. Bowls adjusted. Idle mixture at the starting point 1.5 turns out. Timing set to 12 deg.

[kazoocruiser]

From:
https://www.onallcylinders.com/2015/...gine-problems/

Rapid Vibration at Idle
If the needle vibrates rapidly between 14 and 20 inches of mercury, but then steadies as rpm increases, you may be dealing with worn valve guides. How fast the needle vibrates is telling of how many valve guides may be worn.

[cadillac_al]

I had a sweet running engine that did that. I never did figure it out before I swapped the combo around but I always wanted to blame the valve lash. It had very low mileage aluminum heads at the time. I don't see how timing or misfires would cause it. Good luck.

[geezer#99]

Originally Posted by drew8mc

Quick Fuel Slayer 750. Bowls adjusted. Idle mixture at the starting point 1.5 turns out. Timing set to 12 deg.

Bump your initial up to 18 and then adjust your mix screws for best idle on your vacuum gauge.

[twinturboc10]

What is your idle rpm?

[drew8mc]

idle is set at about 850.

[tdangle]

Copied this from motor.com

Idle vacuum for most engines is about 18 to 22 in.-Hg, but some may produce only 15 to 17 inches at idle. ... If the vacuum reading fluctuates within the normal range-the gauge needle bounces around a lot-uneven compression (broken rings or leaking valves or head gasket in one or two cylinders) is a likely culprit.

You may want to contact the engine builder and send them the video.

[toolboxchev]

I am no expert but here is what I have got. You have plenty of vacuum. My 80k top end rebuild with all Comp products is almost just like your reading.

First off Comp Lifters for flat tappets 7 years ago were of a fast bleed down style. I get lifter tap when cold and oil pressure is low. Did not check if you have roller style. My lifter bores are worn for the most, yet a few are very tight. Its just how they broke in. When the top end was done the bores were not checked for specs and not honed.

If that is a fresh engine I would expect it to get better with time. 18 degrees of initial advance is too much unless you have added in vacuum advance also. I go with 14 intial, 20-22 with vac and total of over 36 with low compression heads. I can do this with a 76 cc chamber with not much of a risk of detonation.

Every engine will prefer a timing specific to it own self, Carb, heads, cam, compression ratio, A/F ratio, timing all plays into how it likes to run at street speeds and different for drags or real play.

If I were in your shoes I would work on getting all the specifics dialed in. Timing first, then Carb tuning as always. Also its is always a good bet to checks for leaks around the intake and any vacuum boosted accessories.

[geezer#99]

You guys are talking vacuum readings from a stock cammed engine. Doesn’t apply with his motor.
He has 16, which is about max for his cam. His vac fluctuation is from not enough initial timing. 12 degrees is too low. You need to start the burn earlier. I suggest 18 which might be too much or even not enough. Since his idle is at 850 his 12 initial might not be accurate. Likely lower as the mechanical could be kicking in.
Everybody has a choice.
Set it at a conservative number like 10 or 12 and ignore any other conditions that arise. Conditions like black plugs, bouncing vac, rough idle, excessive idle drop into gear etc.
Or optimize your timing and have no problems at all.
I prefer to optimize my timing.

This link shows my method I’ve used for the last 50 years.
http://www.badasscars.com/index.cfm/...d=76/prd76.htm

[drew8mc]

Update:

I went through my install manual from the engine builder which recommends 14 deg initial timing, 32-33 total.

I have set my initial at 14 deg. No real change to the vacuum gauge. It did seem to drive better and sound like a big cam idle, which is what I think it should sound like. I then adjusted the idle mixture screws and idle for best vacuum, but could not totally eliminate the needle bounce. I think I had a steadier 21 with idle set at 1200. But moved it back down to 900. I have yet to check total timing. Do people use the idle screw to set it at 2500 rpm?

Now it's acting strangely. There is a strange noise from the exhaust that sounds like a puff, different that a normal exhaust pulse. It doesn't sound like pinging in the engine itself, but almost like a valve pulse at the wrong time or something. It's almost like a hesitation or bog when that sound happens. Power seems to drop.

This first tank of gas has gone super quick as well. Under 100 miles in mostly urban traffic.

If my vacuum is supposed to look like that, I'm good. Brakes work fine. It seemed to be running fine before these latest noises. I even went back to the settings on the idle mixture screws before adjustments where it worked best so far, but the noises persist.

Thanks to everyone for chiming in and helping me figure this out. I may end up taking it to a guy to who knows old school carb tuning.

[geezer#99]

Can you adjust either mix screw all the way in and the motor keep idling?
Turn them in slowly to test.

[drew8mc]

This smells like an ignition issue... literally. It smells of raw fuel big time. I will check my plugs and wiring and make sure something didn't come loose. Maybe my gap is off on one plug or something.

[geezer#99]

Did you do the test on your mix screws?

[drew8mc]

I did check that. It could stay on with drivers side screw all the way in. It started to die with the passenger side almost all the way in.

Here are my plugs. Pretty bad.


Looks like I'm running way too rich. Here is the specs on how the quick fuel was setup from the factory.

Primary- 72
Secondary-82
Idle air bleed- 70/39
High speed bleed- 31/31
Pri nozzle - 33
Needle and seat- 110
Power valve 6.5

I also tried to set total timing but my timing light just could not sense the spark at all. I had very sporadic light pulses that made it basically impossible. I put new DUI Livewires on which has like a fiberglass jacket that fits loosely around the inner silicone insulation. Is that the problem? Should I try and use a standard old wire I have lying around just to set the timing?

[geezer#99]

The mix screw thing means your idling on the power circuit. That makes it smell rich as well as the little noises you hear in the exhaust. The noises are after fire. Unburned fuel igniting in the pipes.
You need to get the primary throttle closed enough to cover the transfer slots.
Info in here about that.
http://www.crankshaftcoalition.com/w...EI_distributor
Fortunately you have a carb with an adjustable secondary. You need to open the secondary throttle a bit so you can close the primary enough to get the transfer slots working.

If your timing light doesn’t like the wires just use a stock wire in place of #1 so you can check and set your timing.

[drew8mc]

I thought I would update this thread on what what has happened since.

I took the carb off and took a peek at the throttle blades and the air slot. It was not overexposed at all. However, I just cracked the secondaries slightly more open. Turns out I can make that adjustment without taking off the carb as there is an allen key screw in that location.

It seemed to run somewhat better although that same sound of unburnt fuel in the exhaust igniting was still there.

I talked to a buddy of my Dad's who is a professional engine builder for dragsters and NASCAR. He recommended I jet 2 sizes down to a .70 and also change the power valve to a 10.5.

I did that and it really woke this engine up. I finally feel the power I know I am supposed to have. It made me laugh out loud on the first drive after the changes. However, I still hear a little bit of that same exhaust sound. I wonder if I should go even smaller in the jets? I'll be driving it tomorrow and I'll see how it feels and sounds. I was getting a steadier 17" or 18" of vacuum. The needle still bounced a bit but not as bad.

Thanks for everyone's help. You learn by experience on theses things.

[geezer#99]

Do you change the initial timing?

[drew8mc]

Sort of.

The plug wires i have on it were giving my timing light fits, so what I thought was 14 degrees was set to more like 12. Swapping one of my old wires made the light much happier and it was reset to 14. I want to check my total timing before setting initial any higher. As I understand it, the DUI distributor comes with 24 mechanical advance which puts it in the 38 deg mark for total. I'm not sure I want to push that any more, but I also have not checked it. Doing multiple 3500 rpm runs in my driveway pisses of my neighbors, so I may try doing it at work.

[drew8mc]

Ha! The saga continues.

After my great first drive after making those carb adjustments, the thing ran like crap the next time I drove it. I didn't touch a thing. I now hear some clicking out of the valve train. It sounds like the drivers side bank. That popping sound I heard before is back. It occurs under load much more than cruise and is accompanied by a loss of power. Maybe a valve not fully closed?
I haven't pulled the covers yet to check anything. I probably won't get to it until the weekend. I still have other carb related issues that I need to work out too. I think my accelerator pump needs tuning. Mashing the throttle gives me a bad bog, either partial or WOT.

Sheesh! I swapped engines so I could drive it... not have the hood open all the time.

[drew8mc]

After looking at my plugs in the above picture, I wonder if it is the #5 valves that were giving me problems all along. It's the only plug that looks different and is not fouled.

[drew8mc]

Here is a video of me going up a hill. Listen for the popping sounds.

https://youtu.be/bkvOQGH7WJ4

I took my valve cover off on the drivers side. Nothing broken or obviously out of place. The roller on the intake side of #5 did have some marks on it compared to the others but no wear spots or anything. I'll have to wait till the weekend and try to reset the lash. I couldn't loosen the hex lock nut with a small allen key so I will have get out the ratchet and loosen. The rocker was loose like the others with no load. Didn't seem bad. How would I know if its the lifters? Also, I only hear it after warm up, at least the valvetrain noise. The exhaust popping in the video happens regardless. Does the expansion of the pushrod under heat make the valve not seat entirely?

[cadillac_al]

That doesn't sound good at all. Not exactly like cam popping though. It sounds like it is running on about 6 cylinders with one kicking in once in a while. Maybe it's just running very rich. Are you sure about the firing order? Who adjusted the valves? I hope it doesn't have a bent valve. I would be bummed if all my new parts sounded like that. I'd say it's time to step back and re-evaluate the assembly.

I would hate to do a running valve adjustment on a new rebuild, so messy. I would also hate to pull the intake to get an accurate valve adjustment. That leaves twisting the push rods and hoping for an accurate valve adjustment. Tough choices. If the valves were adjusted by the builder then I would assume they are ok and do a compression check. If that all checks out then I would be trying one of my spare carbs. What a bummer. I hope it's just something simple.

[drew8mc]

I have triple checked firing order. The long block came from the engine builder. They did all of the valve adjustments. The only thing I reused in the entire build is the intake manifold and the power steering pump. I sprayed carb cleaner all around the intake and couldn't detect any leaks. Can there be an intermittent leak after warm up? I do have a spare 600 cfm carb. It's undersized but maybe will give me an idea on what is happening. I also have a spare distributor.
It just doesn't sound like its supposed to. That's why I keep checking firing order myself.