After solving my ignition problem I did a test I should have done as soon as I finished the break in.
I hooked up a vacuum gauge to the back of the intake manifold and found out I have less then 10" of vacuum at idle.
The timing was set at 16, and the more advance I set it the better the vacuum was and the higher the RPM got.
Even after I turned the dist all the way for full advance (around 25 at idle) the rpm just kept rising and the vacuum climbed a little to around 12".
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.
Something is not working right!
Idle is not smooth (now that I think about it, it never was).
Engine has 100 miles since build.
According to the cam spec the manifold vacuum should have been 18.5" @ 800rpm and 20" @ 1000rpm
Cam has
256/268 deg at 0.006"
And
212/218 deg at 0.050"
Lobe separation is 110 deg
What's the elevation where you live?
That effects your vacuum reading and your timing.
When the motor increases idle just turn it back down on the carb and adjust your mix screws.
Some GM shop manual illustration of the crank and cam sprockets show dot-to-dot on the sprockets. Meaning, the crank sprocket is at 12 o'clock and cam sprocket is at 6 o'clock but the shop manual fails to mention that indicates #6 firing at TDC.
Someone reads some shop manuals and set the crank and cam sprockets as illustrated, thinking that is #1 firing at TDC, then install the distributor in firing on #1. That will be firing "180 out", as the say in the artillery. If you set the crank and cam sprockets dot-to-dot , you must then turn the crankshaft one revolution (360 degrees) to bring the dot on crank sprocket to 12 o'clock again and the dot on the cam sprocket also to 12 o'clock or you can leave the sprockets dot-to-dot and install the distributor to fire at #6.
It is then time to adjust the valves according to the firing order, starting with #1 or #6 at TDC, and according to which cylinder the distributor is firing on.
Rob, if you have installed the timing chain cover, pull #1 spark plug, bump the engine over with a remote starter switch with your finger in the hole until you feel strong air pressure. Look where the timing marks are. They should be close, align the timing mark to zero. Pop the distributor cap, the rotor should be pointing to #1 spark plug wire. If not rewire the cap beginning with #1 spark plug wire on the post the rotor is pointing to. Loosen the distributor hold down until you can turn the distributor. Set the line on the balancer to 16* @ TDC. Now use a Sharpie to make a line on the distributor cap at #1 post down to the distributor body. It's a guide for next time. Make sure you have all fluids full. Start the engine and if you have a flat tappet camshaft run it at 2500 rpm for about 20 minutes. After breakin set the timing and adjust the carb with your vacuum gauge.
oldbogie, I went over and looked for the instructions that came with the timing chain kit, it clearly says to set camshaft gear at 6:00 and crankshaft gear at 12:00.
The picture attached is from the build, and it shows just that.
RWENUTS, I live at sea level, no elevation here.
hcompton, I'll go check for vacuum leaks and set the carb screw (haven't done that yet) together with the vacuum advance in the manifold port.
cdminter59, the engine is pass the break in procedure, I'm now trying to tune it right. The motor does fire/start when I crank it.
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.
Do you know anyone with an AFR gauge. If so if you check and it is real lean you most likely have a vacuum leak. Could be on the bottom of the manifold so it is hard to see or spray. you can introduce some propane into the valve covers and see if the idle increases. this will prove it is sucking air inside the engine.
have you tried disconnecting and plugging every vacuum line except the one you have the gauge on. i dont know much about the car but a bad brake booster or something sililar can lower the vacuum reading.
Keep in mind it not unusual to have to wait a full minute for the excess fuel to burn off before the idle changes so be very patient. As said before start at 1 1/2 out from lightly seated and if you find you have to go +or- a full turn to to get the highest reading its time to start looking at other places to tune.
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....
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.
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.
""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..
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
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"
This clue shouldn't be ignored, it may mean a vacuum leak at the under carb. gasket or an internal vacuum leak inside of the Eddy carb... Do you know how to test for vacuum leaks around the carb. using a torch flame? Do you have another carb., especially a known good Holley, that you can try? Don't have to hook up throttle linkage or anything, just install it and fuel it and see if in-driveway testing shows a marked improvement... While carb. is off, look to see if it made a uniform dent/depression depth all the way around the carb. gasket... no signs of vacuum leakage marks... Using a straightedge, make sure the underside of the carb. is perfectly flat, no base warpage from overtightening...
At cruise, 65mph flat highway 4th gear with lock up, rpm at around 1500-1700, very light foot on the throttle - vacuum reads 5"
Heavy torque loading OverDrive lockup cruising with larger throttle opening will have lower vacuum than the old days without OD, but that still looks too low...
The engine should run PERFECTLY without it... marine engines and heavy truck engines that normally operate at high HP levels all the time were often made without it... my boats don't have one... having it hooked up can cause confusing readings and results while testing... The vac advance is just mainly for better high vacuum, steady speed cruising MPG... it can also improve idle quality, but make a dirtier idle, hence ported vacuum ports were added to the carb.s during the early smog/emissions regulations years to prevent vac advance at idle...
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..
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..
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...
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.
You need to recalculate your DCR. An SCR of 9.5 and a dcr of about 8.1 is going to give you about a 175+PSI cranking pressure. If you're getting 140 to 145 your cam is way retarded. Either it's not ground properly or your timing set is not stamped properly. I'd bet the farm on cam timing.
The bottom timing sprocket has 3 keyways and 3 'dots' and you have to use the 'dot' which pairs up with the keyway you used... -0-. 4 advanced, or 4 retarded... I'd use -0-...
The vacuum advance will give strange looking numbers once it's reconnected, but that is normal... use about 12 degrees BTDC at idle with vac disconnected...
If you look at the first page of this thread, you will see the timing picture and the keyway for zero is the one i used.
At 14 deg BTDC idle, engine has hard time going from idle to wot
At 16 deg its all good
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