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So I bought my first vette last week, a project car. Woot! Or so I thought. Now I am having an issue I can't seem to narrow down. I've read through posts, but not really finding the answer. Here's my problem.
I've set the timing to 12 deg. BTDC with vacuum advance plugged. In gear, idle RPM to 700. Car idles fine with this setup in park. However, I am now getting a cough back through the carb when staring it, and in gear it sounds and feels like it is missing. Idles very rough and shakes the car. I replaced cap, rotor, plugs and plug wires. I adjusted the carb as well. I sprayed carb cleaner around the intake manifold, but didn't really notice any performance difference.
What you are missing is the factory distributor, the 1981 distributor did not have vacuum advance. In 1981 the whole mechanical and vacuum advance systems were replaced by computer control. Can you provide more detail about this distributor, perhaps a picture?
Make sure that the vacuum advance is reconnected. Make sure all other vacuum lines are connected.
Prior owner probably had the timing too far advanced to compensate for a vacuum leak.
All are connected. When I set the timing to 8 deg. BTDC it starts quick and doesn't spit back through the carb. Idles fine too, but still have the load performance issue.
What you are missing is the factory distributor, the 1981 distributor did not have vacuum advance. In 1981 the whole mechanical and vacuum advance systems were replaced by computer control. Can you provide more detail about this distributor, perhaps a picture?
I've looked up distributors for that year and all of the ones claiming to be for a 1981 do show a vacuum advance on it. Not sure if that is an after market thing or not?
So I bought my first vette last week, a project car. Woot! Or so I thought. Now I am having an issue I can't seem to narrow down. I've read through posts, but not really finding the answer. Here's my problem.
I've set the timing to 12 deg. BTDC with vacuum advance plugged. In gear, idle RPM to 700. Car idles fine with this setup in park. However, I am now getting a cough back through the carb when staring it, and in gear it sounds and feels like it is missing. Idles very rough and shakes the car. I replaced cap, rotor, plugs and plug wires. I adjusted the carb as well. I sprayed carb cleaner around the intake manifold, but didn't really notice any performance difference.
That may be the original engine but it's not the original carb or distributor.
Have you verified TDC? It could be your balancer has slipped.
Also try setting the timing all in to about 36 degrees ( plug vac advance and set whilst revving engine to around 2800rpm ) Don't worry too much about initial timing for now.
...Now I am wondering if it is even the original engine.
Can't say. Someone has been under your hood. The Accel is not stock, the valve cover breather and the Holley are not stock. The engine has been repainted. Check the pad at the front of the right head. You should find two numbers stamped there: one for engine identification and the second should be the VIN derivative of the car the engine was originally installed in.
Last edited by Easy Mike; Aug 12, 2015 at 02:15 PM.
verify your plug wires are on correctly. looks like you replaced some, not all. your vacuum lines look wonky. what jets and settings are in that Holley? put a vacuum gauge on the motor and do some tests, post what you find. whjat's with the Accell coil? there are known issues with those, especially as old as that one looks.
The intake is an Edlebrock with a Holley carb. I'm guessing they changed the distributor after changing those. I do have what I believe is the original intake and carb, pictured below. most of the emissions stuff is still there, except they cut off the exhaust lines and welded the holes closed. Wouldn't I need those if I went back to the original dizzy, intake and carb?
verify your plug wires are on correctly. looks like you replaced some, not all. your vacuum lines look wonky. what jets and settings are in that Holley? put a vacuum gauge on the motor and do some tests, post what you find. whjat's with the Accell coil? there are known issues with those, especially as old as that one looks.
Yes, I replaced all but two. I need to get the car on ramps to get to the wire guides. I replaced one at a time so as to not get them mixed up. I guess my next step is to go to square one and set TDC and adjust from there. I also need to get a repair manual. Going to visit my father this weekend. He may have one since he has owned several vette's and retired from GM.
That may be the original engine but it's not the original carb or distributor.
Have you verified TDC? It could be your balancer has slipped.
Also try setting the timing all in to about 36 degrees ( plug vac advance and set whilst revving engine to around 2800rpm ) Don't worry too much about initial timing for now.
This is sound advice......HEI distributors have a crummy stock advance curve.
Rev to 3000rpm......and set timing to 36. The only way to do this with a stock balancer is to install a MSD timing tape.
Many Chevy engines suffer from a spun outer shell on the balancer...this will leave the mark in the wrong place.
It will also be wrong if an early balancer is used with a late cover and vice versa as the "0" was in a different spot.
My advice? Get a new balancer with marks on it...like a Professional Products #80000 http://www.summitracing.com/parts/PFS-80000/
and a new pointer....find true "0". Now you know where it is. Set to 36 degrees total as stated and report back. Mr Gasket makes a curve kit for HEI that helps.
So I bought my first vette last week, a project car. Woot! Or so I thought. Now I am having an issue I can't seem to narrow down. I've read through posts, but not really finding the answer. Here's my problem.
I've set the timing to 12 deg. BTDC with vacuum advance plugged. In gear, idle RPM to 700. Car idles fine with this setup in park. However, I am now getting a cough back through the carb when staring it, and in gear it sounds and feels like it is missing. Idles very rough and shakes the car. I replaced cap, rotor, plugs and plug wires. I adjusted the carb as well. I sprayed carb cleaner around the intake manifold, but didn't really notice any performance difference.
I checked the float level and it looks good. I reset the idle screws to 1.5 turns and adjusted until idle was smooth. In park it idles at about 1,000 rpm and 700 rpm in gear. Seems a bit more responsive, but I am still getting a rich fuel smell from the exhaust.
Then I would e-mail Lars at v8fastcars@msn.com, and ask for a copy of his Holly rebuild paper.
They are an easy thing to rebuild when armed with the correct information.
Then I would e-mail Lars at v8fastcars@msn.com, and ask for a copy of his Holly rebuild paper.
They are an easy thing to rebuild when armed with the correct information.
Just got done crawling under the car for a plug wire change and noticed a fuel line seemed to be kinked. Could something that simple be causing this issue? Heading out of town for the weekend, but will be replacing in next week.
1981 Timing Issue...maybe
