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  #16 (permalink)  
Old 05-20-2016, 08:58 AM
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Quote:
Originally Posted by rob_isr View Post
I set inital timing at 16* + 10* vacuum = 26* at idle
With low throttle high rpm I get around 50* max
Does it sound right?


Vacuum has gone up a little to 14.5" at idle (@ 26*)
I tried adjusting the idle mixing screw, they dont make much difference, either much too lean and then engine choke or after I pass a cirtain richness it does not matter to vacuum if I give it an extra turn or 2 extra turns.


This is the video I made a few min ago, with the new adjustments.




Sounds about right to me. So crank it on up to 34 at idle with the vacuum advance disconnected and read the vacuum (not to leave it this way). Cam manufacturer might have been playing games with timing to list the max vacuum they could obtain. Your improvement from less than 10" up to 14.5" is huge. Also what is the max vacuum while engine is decellerating with throttle closed?

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  #17 (permalink)  
Old 05-20-2016, 01:23 PM
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Quote:
Originally Posted by hcompton
I can also see by your video the vacuum gauge moves very slow iss this some type of stabilized gauge or is it from an air leak thats your problem to resolve
It's a pretty normal vacuum gauge, I dont think it is stabilized (it is not filled with liquid). I hooked it up to the manifold and not to the carb, maybe that is the reason it moves slow.... I dont know....


Quote:
Originally Posted by RWENUTS
is your timing tab/balancer correct.
I built this engine, I can tell you that the timing tab is spot on!
I set it with a lathe dial while the heads were still off.


Quote:
Originally Posted by T-bucket23
Do you know anyone with an AFR gauge
I do, and I looked at the gauge while doing the adjustment on the mixing screws. It is now set on the lean side while idle.


Quote:
Originally Posted by T-bucket23
have you tried disconnecting and plugging every vacuum line except the one you have the gauge on
I did, no change.


Quote:
Originally Posted by 2001Blazer4x4
crank it on up to 34 at idle with the vacuum advance disconnected and read the vacuum

will try





Quote:
Originally Posted by 2001Blazer4x4
what is the max vacuum while engine is decellerating with throttle closed


Around 18"


----------------------------------


Another thing I noticed, when the initial timing was set at 14* and I hit WOT at idle, it would back fire and rise a decent fire up the carb, when I gave a little more timing (16*) the backfire stoped and you can see in the video how rpm goes up and no fire from the carb.
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  #18 (permalink)  
Old 05-20-2016, 02:12 PM
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Another thing I noticed, when the initial timing was set at 14* and I hit WOT at idle, it would back fire and rise a decent fire up the carb, when I gave a little more timing (16*) the backfire stoped and you can see in the video how rpm goes up and no fire from the carb.

Don't do this it is very hard on the engine and the redline RPM is easily exceeded with a lot less than WOT throttle when there is no load against the crankshaft.

I built this engine, I can tell you that the timing tab is spot on!
I set it with a lathe dial while the heads were still off.


Unless you appreciate that the crankshaft and damper pass the timing tab twice in a revolution which puts different events happening at each place because the cycles (of the cam) are happening at half the rate of the crank. So for argument starting at a point where both the number 1 and number 6 pistons are at TDC lets say this in cam (thus distributor position) is ready to fire number 1. At this same time the cam has number 6 also at TDC of crankshaft but it is finishing the exhaust stroke and will commence the intake at the same time number 1 is on a power stroke. At this point if the timing cover was to be removed the timing mark of the crank gear and the mark of the cam gear would both be in the 12 o'clock position.

Now rotate the crank one full turn, both number 1 and 6 are back at TDC but number 1 is finishing exhaust and about to start the intake cycle, while number 6 has finished compression and is about to fire and start its power cycle. The timing mark on the damper is at TDC as the example above, however, with the timing cover removed the crank gear mark is again at 12 o'clock but the cam gear mark is facing it in the 6 o'clock position.

This quirk of the SBC catches a lot of engine builders including experienced ones. the reward is an engine that seems to want to run but doesn't quite get there.

The other is the distributor being off a tooth, this is forced by alignment of the oil pump drive which rotates with the distributor any time it is removed. This drops what seems to be the TDC point by 27 and some fraction degrees. The engine will start and run but has no power and backfires a lot yet appears to be timed correctly. This also bites a lot of people.

I'm not excepted form either and have my biggest problems when "I" know I put it together right.

Bogie
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  #19 (permalink)  
Old 05-20-2016, 03:46 PM
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""That guage is very very lazy? Why?"" X2


""I am starting to think maybe I did something wrong while putting in the cam, I never checked at what deg it opens the valves, I just set it in as the book said – dot to dot.""


if the cam was never degreed in when installed?? I would check it..
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  #20 (permalink)  
Old 05-20-2016, 08:10 PM
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Your gauge is not responding properly. When you snap the throttle from idle the gauge should snap to almost zero just as quickly, and when you drop the idle from open to close quickly the gauge should jump to 30+ in a blink of an eye.
Someone asked where do you have it hooked to, I'd second that question. Also, that is the steadiest vac reading I've ever seen. It doesn't look like it's even wiggling at idle (but maybe it's the video quality) - I've never seen that before. Check it on another vehicle or against a vacuum pump of some sort like a Mighty Vac or similar.

Degreeing the cam, of course, is never a bad idea, but I really think that your issue is gauge related as the motor sounds smooth and seems somewhat reasonably responsive IMO
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  #21 (permalink)  
Old 05-21-2016, 12:38 AM
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how big is the orifice/hose/fitting going to the gauge??
it needs to be a 1/8" or so..
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  #22 (permalink)  
Old 05-21-2016, 06:22 AM
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Looks to me like he's T'd the power brake line for the vac gauge. I'd connect the gauge to the front of the carb......




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  #23 (permalink)  
Old 05-21-2016, 11:48 AM
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I tested the engine 2 hours today, and I can't say i'm happy with the results.


At cruise, 65mph flat highway 4th gear with lock up, rpm at around 1500-1700, very light foot on the throttle - vacuum reads 5"


Idle timing all the way up at 36* - vacuum reads 15" (this was done once for testing)


Initial timing 16* + 10*(vacuum advance) and the starter can hardly crank the engine if it's hot.


Initial timing 10* + 10*(vacuum advance) and the truck can hardly drive out of idle, it chokes and I had to put my foot very very light on the throttle.


My right idle carb adjustment screw seems to make much more of a change then the left one.


I hooked the vacuum gauge to 2 places, to see if there is any change, there was not. first at the back of the manifold and second on the lower port at the front of the carb.


I disconnected the vacuum hose that is used for the ac/heater and pinched the hose that goes to the brake, tested at idle, no change around 14-15"
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  #24 (permalink)  
Old 05-21-2016, 12:20 PM
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Engine Idle at full timing advance 36*
Vacuum does not rise over 15"









Cruising an open flat road, 65mph, initial timing set at 16* + 10* vacuum advance.
Vacuum around 5"


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  #25 (permalink)  
Old 05-21-2016, 12:36 PM
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Last one for today, this time you can see how I set the idle mixing screws.


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  #26 (permalink)  
Old 05-21-2016, 01:31 PM
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if one of the idle screws is not responsive?

when you screw them in they should try to kill the motor..
if you can screw one all the way in its plugged..

engine off, take the screw out and blast some carb cleaner or
a quick shot of some low air pressure thru the port..
watch out for flying gas tho, maybe do it on a cold motor,, and put a rag over the carb..

check the screws see if there both sharp/pointed the same..

i'd probly blow them both out..
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  #27 (permalink)  
Old 05-21-2016, 03:12 PM
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any way the exhaust/cat could be plugged up??
did you retorq the intake after the breakin??

5in vac at cruise is low, unless you going up hill..
that's probly into the enrichment circuit if the springs not been changed to a smaller one..
and probly getting a lot less vacuum advance..

if you have a timing tape or your balancer is marked off in degrees,
I don't take very long to quick/ruff check the intake center line..

I always double check them now after I got 2 cams or timing sets that were way off..
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  #28 (permalink)  
Old 05-22-2016, 08:20 PM
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What's the actual compression ratio of the engine?

What's your idle RPMs? That cam should be able to do a slightly lopey 550 - 600 RPMs idle in neutral if your compression ratio isn't too low for it...

I'd suggest a compression test on all 8 cylinders to make sure an incorrect valve lash adjustment isn't allowing pressure to leak back past an intake valve into the intake manifold, which is my biggest concern at the moment...

Your dot to dot timing install isn't likely to be any problem...

Disconnect and plug the line for the vacuum advance for now... don't reconnect it until later after we've gotten the engine running perfectly... it's only for better steady speed cruising MPG...

Last edited by BuzzLOL; 05-22-2016 at 08:26 PM.
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  #29 (permalink)  
Old 05-22-2016, 09:51 PM
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Looks like cam is extremely retarded.
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  #30 (permalink)  
Old 05-22-2016, 10:13 PM
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JJLT1
If I screw any of the carb idle adjustment screws all the way in, it kills the engine.
Car does not have cat and the exhaust was made new only 3 years ago (3" stainless tubes).
At first car was cruising at the power circuit, I replaced the springs and now it cruise at the cruise circuit.

BuzzLOL
After the break in, max compression was 145psi and min was 127psi.
I did a valve adjustment and now max is 145psi min is 140psi.
Why shouldn't I connect the vacuum advance?

Greg T
I also suspects the cam, but you have seen the timing dots, it looks fine.
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