SBC Tuning help needed

[808_67C10]

I have an older Mexican GM Crate 350 (dipstick hole on both sides). It is pretty basic - not a high HP motor. It has a edelbrock intake, Holley 670 carb with a 1" spacer and headers. It also has an electronic distributor.. that should be enough to help you help me.

I got the truck with the motor in it and when I pulled the valve covers, the valve train is super clean --- dont know how many miles are on it.

When I got it, I changed the plugs, wires, cap, rotor and I have never had good luck with edelbrocks and put a new holley 67 street avenger.

I found top dead center by pulling #1 plug and it is straight up on the balancer. There is a timing mark dohickey but it is off the the right of straight up like all other SBCs I have had. If I time it off the timing gauge on there, there motor is barely running and sounds awful... but, I turn it up to the mark on the balancer at straight up and she starts and runs but, it doesn't sound right. Then, I drive it and its ok till I get on it just doesnt feel right. I cant advance the timing 12 deg past the straight up because the idle will be too high n I cant bring it down with the carb. should I with this set up?

as for the carb, Its about 1.25 turns out on both air/fuel screws with 20lb on the vacuum guage (front vacuum port).

What am I doing wrong? Is there something else I can try?

[kwmech]

Roll the engine to top dead center with the timing mark at 12 0'clock as you stated. Then remark the balancer with paint to match the indicator at zero, vacuum hose removed. Vacuum to the dist should be ported. Set your timing at 8 degrees then see how it runs. Adjustment from there may or may not be necessary. Sounds like you are guessing at the moment. High idle after the adjustment may be a small vacuum leak

[geezer#99]

You’ll always be guessing until you find true tdc with a piston stop. You can use either timing tab, just re-mark your balancer.
Piston stop info here.
https://www.crankshaftcoalition.com/...op_dead_center

With more timing, if your idle is too high and you can’t turn it down enough then close your secondaries more. They are adjustable.

[68gmsee]

After doing above recommendations, also insure the distributor is pointing towards #1 distributor cap post when piston at TDC in the compression stroke. I usually center the distributor adjustment when doing this check. If it's too far off you may have trouble adjusting the timing and hopefully the cam/crank gears are aligned properly.

[808_67C10]

Why did I not think of just putting it at TDC then remarking the 0 deg then go from there... crap... I was blinded by the WTF! HA HA great advice, that is why I love this forum so much.

As for a vacuum leak, I have re-torqued the intake and the carb and there arent any vacuum lines, I dont have anything outside of the PCV valve and power booster vaccum hooked up because I had a high idle problem starting with the edelbrock and that is the first place I started. I replaced all the hoses to both too... and the PCV.

The distro is pretty close, she is pointing at #1... I think not having the vacuum line to the distro threw me off too... I will see what I can do with her this weekend. Thanks guys!

[SunSoaked]

I recently bought a 85 with the same crate engine you have. I noticed the timing mark did not align with the grove on the balancer either. I noticed there was another mark that looked like a paint marker line. I converted the engine to Vortec heads, cam, etc. In doing so, I checked TDC and it was indeed referenced to the white line on the balancer. I ended up swapping to a new summit balancer with the correct markings. The OEM "Mexican" balancer was junk from gm (stamped China btw!). The TDC markings were off and the tolerance was so tight I almost stripped the threads in the crank nose trying to get it on (yes, I used the correct tool).

[808_67C10]

Originally Posted by SunSoaked

I recently bought a 85 with the same crate engine you have. I noticed the timing mark did not align with the grove on the balancer either. I noticed there was another mark that looked like a paint marker line. I converted the engine to Vortec heads, cam, etc. In doing so, I checked TDC and it was indeed referenced to the white line on the balancer. I ended up swapping to a new summit balancer with the correct markings. The OEM "Mexican" balancer was junk from gm (stamped China btw!). The TDC markings were off and the tolerance was so tight I almost stripped the threads in the crank nose trying to get it on (yes, I used the correct tool).

Did the heads make a difference? Did you go with a cam too? Mine has a lil power but, compared to most - she is a dog. I have a 5.3/4L60 to drop in but, I have to wait till I pick up another mini-truck to daily drive while I do it. Hopefully, over the winter.

[SunSoaked]

To be honest, yes. However, I swapped heads, comp 254 cam, Edelbrock intake, roller rockers, headers, serpentine drive assembly and electric fans at the same time. Broke the cam in with the carb then installed a Holley Sniper before driving it. So yes, a huge difference but I can't say it was all because of the heads.

[toolboxchev]

I see no mention of a vac advance??? So you are setting with 12-16 degrees of mechanical and how much total at 3000??

Crankshaft Coalition has pulled me through a ton of problems. Call Edelbrock get the right springs and turn down the idle then run.

Clean that carb out also. You know the routine, ignition first, then carb. Get a decent Coil, Cap, and module, matched set. Eccel does this well.

RRrrrrrrruuuuuuuuuuuuuuuuuuuunnnnnnnn!

[808_67C10]

Originally Posted by toolboxchev

I see no mention of a vac advance??? So you are setting with 12-16 degrees of mechanical and how much total at 3000??

Crankshaft Coalition has pulled me through a ton of problems. Call Edelbrock get the right springs and turn down the idle then run.

Clean that carb out also. You know the routine, ignition first, then carb. Get a decent Coil, Cap, and module, matched set. Eccel does this well.

RRrrrrrrruuuuuuuuuuuuuuuuuuuunnnnnnnn!

I have a Chevy HEI with a new MSD Cap and Rotor. It has a mechanical advance.... no vac advance. The carb is new - Holley 670 Street Avenger. Gonna mess with it this weekend.

[kwmech]

I just changed the brake booster on a customers K5 because of a high idle

[cadillac_al]

Any stock Chevy will feel doggy without vacuum advance. I can't think of any reason not to use it.

[808_67C10]

Originally Posted by cadillac_al

Any stock Chevy will feel doggy without vacuum advance. I can't think of any reason not to use it.

This is what happens when you buy someone else's problems... ha ha I am still fixing issues and haven't been able to do the things I planned to do to it yet (other than the wheels).

Every electrical switch has gone bad, I am still chasing short in the dash and courtesy lights, the "in the column" wiper switch needs to be changed... its one thing after another... but, that's part of how we keep these beautiful trucks on the road.

I have been debating just getting a new distributor with vacuum advance. I have never messed with the mechanical ones so, best to stick with what I know. I hate just throwing new parts at problems I cant narrow down.

[toolboxchev]

The adjustable vac canisters I like the best. You can dial them to your motor or driving conditions, such as type of fuel.

[808_67C10]

Okay, so, I never ask a question without coming back and reporting what the problem was... So, come to find out, the truck has the OG 305 electronic distributor with no mechanical advance... no vacuum advance therefore - no advance. No wonder I could get it to run smooth at idle but, when I drive it runs like crap. See what happens when you buy other peoples ****... I never had these issues with my 67 because it was bone stock when I got it and I built everything ground up!

Off to the local performance shop to grab a MSD HEI with vacuum advance tomorrow.

[Ironangel]

If your going with MSD, I would suggest the 8360. They do not require the box and are fully adjustable, vacuum and mechanical advance. Very simple and straight forward tuning. Factory diameter cap allows plenty of clearance. Put one in my BB truck 3 years ago and it's still tight, no waiver or cut out at high rev.