Engine help

Have a 75 nova 350 small block. Changed it from a2bbl single exhaust to a 4bbl duel exhaust (new carb and intake, headers and 2.5 exhaust). The car runs like crap. It spark knocks on excelaration. Idles fine. If anyone can help just want to get it to run smooth. Not going to race the car it is a daily driver. Could the timing be the problem, if so what is the correct timing?
Thanks in advance for any advice.

Did you do the work yourself or did you have a shop do it?

Scott

Did the work myself.

Don't mean to be rude, but is this the first time you've done a project like this?

Scott

Yes, I drive a Mustang a newer model and have no experience with setting timing or the older chevys.

There could be a long list of errors...

But let's see what we can come up with here.

You say that the car idles fine (no shakes, no misses, fires right up), correct?

But then knocks while driving... what does it do when the engine is revved while in park?

Scott

When reved at idle sounds fine and no spark knock. Starts up fine. When accelerating we get the knocking.

Any hesitation when revved from idle?

Do you have a vacuum advance connected? If so, are you using a timed or manifold vacuum source?

Scott

Here's a link to setting ignition timing for SBC...

http://www.2quicknovas.com/happytiming.html

Here's a link to what the base timing should be, scroll down to 1975

http://www.tpocr.com/chevII2.html

I think that by 1975, all SBC were running HEIs, does your car have a HEI dizzy?

Scott

Thanks for your help. Working on now and it seems the timing is 180 deg off.
Trying to get it back, if you have any advice let me know.

I was kind of wondering if that might be the case but didn't mention it because you mentioned that it idles fine.

If it's 180 out, it shouldn't start or it may backfire real bad when you try to start it.

Good luck!

Scott

Set crank on "0" degrees and check distributor rotor and see if it is pointing at # 1 plug terminal position. Coulb be only a tooth off on dist. gear.

If it's 180 degrees "out", it will not run at all. It will spit and pop through the carb when cranking.

When you bring the pointer to TDC, you must also make sure you're "up" on #1 COMPRESSION. It will point at TDC twice in the cycle. Remove the spark plug from #1. Put your finger over the hole and "bump" the engine over (disconnect the hot wire from the distributor first!). When cylinder pressure "pushes" your finger off the hole, you're "up" on #1. THEN assure the rotor is pointing at #1 wire. Set the timing according to factory specs to start with. You can "play" with it after that to get optimum.

Sounds to me like it's detonating rather badly. Try a higher octane fuel (93). If you didn't change the cam, don't expect any "mind boggling" improvement in power. The 2-bbl. cam won't do the 4 bbl. "justice".

Jim