Running ok, but...
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Joined: Apr 2006
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From: Ridge NY
Running ok, but...
Replaced broke L48 w/new GM crate 350-300hp w/mild Lunati cam. Bolted on my original edelbrock performer rpm intake and edelbrock 750 cfm carb. New Taylor wires and ac delco cap/rotor/plugs. Put about 180 miles on this setup. It's running ok but could be better. Vacuum is low at idle fluctuating 13-15" off idle is 18"+. Timing set at 10deg. Engine shakes slightly at idle, some hesitation on acceleration, hard starting when hot. Acceleration from 2500 rpm and above seems fine, but not as strong as I expect from a fresh motor. Fuel mileage is 10 mpg. Will some of this correct itself as engine breaks in?
Looking for advice as to where I should look first to correct these issues.
Thanks in advance
Looking for advice as to where I should look first to correct these issues.
Thanks in advance
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Joined: Mar 2007
Posts: 3,652
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From: Bridgewater nj
With any new engine, you have to play with it!!! Bump the timing up a few degrees. Test it out. Adjust the fuel air mix on the carb. And test drive after every adjustment along with a notation of where you started and what you've done. It could be as simple as timing adjustment or a PITA like valves being too tight... Just be methodical.
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Joined: Apr 2006
Posts: 75
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From: Ridge NY
With any new engine, you have to play with it!!! Bump the timing up a few degrees. Test it out. Adjust the fuel air mix on the carb. And test drive after every adjustment along with a notation of where you started and what you've done. It could be as simple as timing adjustment or a PITA like valves being too tight... Just be methodical.
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From: anchorage ak
Replaced broke L48 w/new GM crate 350-300hp w/mild Lunati cam. Bolted on my original edelbrock performer rpm intake and edelbrock 750 cfm carb. New Taylor wires and ac delco cap/rotor/plugs. Put about 180 miles on this setup. It's running ok but could be better. Vacuum is low at idle fluctuating 13-15" off idle is 18"+. Timing set at 10deg. Engine shakes slightly at idle, some hesitation on acceleration, hard starting when hot. Acceleration from 2500 rpm and above seems fine, but not as strong as I expect from a fresh motor. Fuel mileage is 10 mpg. Will some of this correct itself as engine breaks in?
Looking for advice as to where I should look first to correct these issues.
Thanks in advance
Looking for advice as to where I should look first to correct these issues.
Thanks in advance
Last edited by bluedawg; Jul 22, 2014 at 09:34 PM. Reason: Hookers and blow!
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Joined: Apr 2006
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From: Ridge NY
With out knowing what the cam specs are, this is a shot in the dark but set your initial up to 13* to 16* initial and idle rpm set to about 650 rpm in gear. some break in might help some but for the most part it should be broke in. get it out and put 200 or so miles on it. The only thing of concern in your post is the vacuum sweep and although not a lot of sweep still I'd like to see a more consistant and steady vacuum reading. Is your rpm flucutating at the same time? What rpm is this occuring at and do you have your vacuum advance hooked up? Like I said step your initial up to 13 to 16 degrees and set your idle rpm and then look at your vacuum again then if it don't settle and steady out then well look from there.. Cam specs would help in the next post. Good luck and let us know how it goes.
Rpm is steady. Cam specs: lift is .443 intake/ .465 exhaust. Duration @.050 is 214 deg intake/ 224 deg exhaust. Lobe separation is 112 deg.
Will try advancing the timing as suggested.
Drifting
Joined: Apr 2007
Posts: 1,970
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From: Cameron Park CA
Mine really woke up after I had my distributor set up by an expert and set the timing accordingly. Yours should too.
There are lots of posts about ignition timing - try search.
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From: anchorage ak
That's not really that big of a cam and shouldn't detract from the vacuum. Try the timing first. But as was said a rocker might be out of adjustment.
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Joined: Jun 2013
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from my experience, the timing bump to 12 to13 degrees will help a ton. you also want your timing all in by 3000 rpm. once you have it timed, try running manifold vacuum, it does wonders for idle quality and temp. finally, you might look into replacing that carb with something more performance oriented. the edelbrocks just aren't that great. summit just came out with a holley styled annular booster carb that comes in a 600 and 750 cfm for under 300. I just installed one and it screams with it. annular boosters just atomize fuel so much better and always do well with longer duration camshafts.
give the timing and the vacuum a shot, but you may wish to look into a better carb and sell that one off. edelbrocks are old tech.
as far as rocker adjustment goes, when one valve on any one cylinder is at full lift, adjust the opposing rocker assembly. this way takes time, but you will know its right. tighten till no play in the pushrod (stop the moment you cant move the pushrod up and down) and tighten the rocker nut one half turn.
heres the link to the 600 (there is a 750)- notice the reviews http://www.summitracing.com/parts/sum-m08600vs
here is a video review I did of mine that I didn't even intend to keep originally
give the timing and the vacuum a shot, but you may wish to look into a better carb and sell that one off. edelbrocks are old tech.
as far as rocker adjustment goes, when one valve on any one cylinder is at full lift, adjust the opposing rocker assembly. this way takes time, but you will know its right. tighten till no play in the pushrod (stop the moment you cant move the pushrod up and down) and tighten the rocker nut one half turn.
heres the link to the 600 (there is a 750)- notice the reviews http://www.summitracing.com/parts/sum-m08600vs
here is a video review I did of mine that I didn't even intend to keep originally
Last edited by 81vettehelp; Jul 22, 2014 at 11:59 PM.
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Joined: Mar 2007
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From: Bridgewater nj
On a Monday engine, it's not hard for a tech that's hung over from the weekend to give a few or all the valves an extra 1/4 turn. A few thousands of a inch can have an engine doing exactly what you describe. A little ruff running, hard starting when hot and down on power. If a few valves are being held off their seats a tiny bit, it bleeds off compression. Results in everything described above.
Timing too far retarded will also cause similar problems and since timing is the easiest, you start with that first.
Timing too far retarded will also cause similar problems and since timing is the easiest, you start with that first.
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From: Ridge NY
Thanks for all the replies. I guess it's narrowed down to ignition, fuel or compression.
I'll start with the timing as suggested. If still not good I'll go with a running valve adjustment. That should narrow it down to the carb. Scott, I did adjust the idle mixture to try to help the idle and vacuum. Didn't play with jetting or anything else although I do have the kit.
I'll start with the timing as suggested. If still not good I'll go with a running valve adjustment. That should narrow it down to the carb. Scott, I did adjust the idle mixture to try to help the idle and vacuum. Didn't play with jetting or anything else although I do have the kit.
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Joined: Apr 2006
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From: Ridge NY
I'm a bit concerned now, guys...If the valves are too tight and not seating properly is it a terrible thing to drive it a couple hundred miles or even at all while I'm trouble shooting?
Drifting
Joined: Apr 2007
Posts: 1,970
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From: Cameron Park CA
If you do a compression test, do a second test after squirting engine oil into the cylinders. That'll seal the rings; after that any low cylinders would be leaking past the valve(s).
Pete
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Joined: Apr 2006
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From: Ridge NY
Back on it today after a break...Again thanks for all the help so far.
I re-adjusted the valves running from 5/8 turn down after zero lash to 3/8 turn after zero lash to be sure the valves were seating ok. Engine ran the same but I feel better now. I adjusted initial timing to 14deg BTDC and it started waking up. Vacuum still fluctuating but slightly better (14-16) and running smoother at idle. Guess I'll work on the timing some more, before looking at the carb? Saw l good reviews on that summit carburetor that 81vettehelp recommended. Any other thoughts? Need to be ready for the Carlisle trip!
I re-adjusted the valves running from 5/8 turn down after zero lash to 3/8 turn after zero lash to be sure the valves were seating ok. Engine ran the same but I feel better now. I adjusted initial timing to 14deg BTDC and it started waking up. Vacuum still fluctuating but slightly better (14-16) and running smoother at idle. Guess I'll work on the timing some more, before looking at the carb? Saw l good reviews on that summit carburetor that 81vettehelp recommended. Any other thoughts? Need to be ready for the Carlisle trip!