I bought a used 1979 SBC 400. Seller told me it was a good runner. I pulled it from a motorhome. After some checks it did shown pretty decent. I bought and cleaned it up. Did some maintenance and upgrades and put it in my 1980 Vette.

I installed a new timing gear and chain set.
Installed headers.
I installed an Edelbrock performer intake manifold.
I cleaned up and installed a 1975 Quadrajet.
I installed an MSD Street Performer HEI dist. Assy.

After assembly and installation the engine fired up quickly but sounded pretty rough. We played with the timing and air idle mixture screws. Things improved but it still ran pretty rough. It wouldn’t rev up smooth or make good power. I double checked all my spark plug wires, all are new and in proper position. More screwing with the timing led me to believe that’s not the issue.

The quadrajet definitely is problematic. It’s certainly over fueling. Even leaking fuel. Pooling in the manifold divots. I checked fuel pump pressure its a new pump. It makes 7.5-8 psi. I will get the Quadrajet dealt with. Yet I was thinking maybe I am out 1 tooth on my timing chain? A few times while adjusting the timing, when cranking the engine over to start, it pushed a good shot of compressed air up through the carb. Spraying raw fuel out of the venturi into the sky. Hmm. Again I am thinking, maybe valve timing is out.

I just pulled the front end apart and checked my timing marks. Seems to be bang-on. With distributor rotor pointed to #1, timing marks are lined up (spread apart, both dots at the top of their gears, lined up). I took valves cover off and confirmed valve movement. Checked tension at rockers. Both valves are definitely closed. #1 is at TDC. I feel like my distributor and timing gears are all lined up.

Here’s the weird thing: with the timing light connected to spark wire #1, when the engine is running, the flash of the timing light is picking up the harmonic balancer mark at about 11 o’clock when viewed from the front of the engine. It should be over al about 2 o’clock. I’m thinking, hmm. Harmonic balancer has maybe slipped? Or maybe slipping while the engine is running? I can see the rubber has a few small cracks in it. No obvious signs of it coming a-part or slipping. It is the original 1979 balancer. I have ordered a new balancer. It’ll arrive in a few days. That should eliminate that variable. The timing light I am using is old school. On off. No adjustments.

With the balancer removed here, right now #1 is at TDC. Gears lined are up. When I slide the balancer on the crankshaft the timing mark is at 2 o’clock. Where I expect it to be. Weird. Why does my #1 spark plug seem to be firing so early? My distributor might be out one tooth? Am I on the right track here? Yet we twisted the distribution a lot in both directions when trying to clean up the rough running. Engine running didn’t improve much.

Next point:
I am looking here at #1 TDC all lined up. Harmonic balancer is at the 0 degree timing mark. That all looks good. I locate and find #1 spark wire boot at the distributor. I remove the distributor cap. The Rotor is about half way between wire 1 and 2. Well past where I think it should be. I believe it should be at #1. I thinking I need to pull distributor and set it back a tooth. Am I on the right track here?

2 things going on here and are separate issues. The carb will also be addressed.

Your comments are appreciated. Thx.

 

It sounds like you have it assembled correctly. Might the poor engine performance be caused by the overly rich fuel delivery and who knows what else is going on with the carb?

#1: I think you should borrow or rent another timing light to make sure your light is working properly. No dissing intended: are you testing TDC and connecting your light to the plug wire on the forward-most driver's cylinder?

#2: When you said the rotor was half-way between 1 & 2, I want to make sure I'm understanding: The #2 cylinder fires immediately before #1 - was the rotor between these two? #8 fires immediately after #1 - was the rotor between these two? The only time I'd restab the distributor is if there isn't enough room to swing the distributor to get the proper timing.

Maybe post a photo of the top of the engine without the air cleaner.

 

Thank you for the reply. I mistakenly said my rotor was between 1 & 2 distributor lugs. I meant to say it was about half way between 1 & 8 distributor lugs.

I was reading timing off of cylinder #1. Front left drivers side of the engine.

My problems could very well be 100% carburetor induced. I ordered a new rebuild kit. I’ll give it a shot this week. If it is still a problem, they stock brand new Edelbrock carbs just down the road. If I get yo the point of having enough of the quadrajet, that’s what I’ll probably do. I’ll try posting a photo of the top of my engine tomorrow.

 

damper for 400 sbc is unique unto itself. Its outer ring has a large cast-in imbalance that should be prominent.

Do you have access to the OE 79 Qjet for your 400 ?

 

The timing tab needs to match the mark on the damper. Some original applications moved the timing tab and marks closer to 12:00 where it would be easier to see during service on other ( non-Corvette) chassis. You may have a mismatched pair.

 

A few photos as requested:

 

The engine was pulled from an 1980 1T Van (RV) chassis. The 6.6L was dated 1979.


My 1980 Corvette was purchased with a blown engine. I decided to use the carb that was on the blown engine. That Quadraject SN indicates its from a 1975 Corvette with manual transmission. My 1980 has an auto transmission. I do have the original 1979 Quadrajet carb that came on the 400. I could try using it.

I am in Canada. I could send either carb to Lars. It may be cost prohibitive. Also down-time considerable, during prime cruising season. This is why I am leaning towards a new Edelbrock here locally. I’d be up and running in a couple hours.

 

If it were mine (it's not) I'd limp-thru this season w/ best carb on hand. Then, post-season: send best Qjet out for Pro overhaul. Nothing stops you from DIY freshening what's on-hand.

From my perspective, bolt-on Edelbrock seem to be a crap-shoot. Some are great; others rather not.

 

Check out @stingr69's answer to this other '79 timing mark question that sounds just like what you're asking.
https://www.corvetteforum.com/forums...post1597274107

When aligning timing chain marks, I find it easiest to place the engine on #6 TDC compression stroke. This puts the crank dot at 12:00 and the cam dot at 6:00 and just an inch apart. (also from the thread link above)

 

Thank you. Yes I confirmed dot to dot line up with both dots close, about 1” apart. Also the dots spread wide apart and lined up.

Reading the articles about people having mis-matched harmonic balancers and timing markers. I agree I likely am experiencing this. What tool are people using for a tool to stop the piston travel in forward and reverse? To manually confirm TDC. Feels like that might be a fun project.

One other point I thought about. Might have Inset the valves too tight. With each valve closed, I turned the rocker bolt just enough where I could not feel any movement in the push rod. Then I turned the rocker nut another ½ turn. Effectively pre-loading the hydraulic lifter I assume? Thx.

 

if that’s where the rotor button is when you’re at TDC you’re off a tooth. It should line directly up with the post on the cap. You should be able to lift the distributor just enough to disengage the cam gear but still have the oil pump shaft follow along. ‘Walking’ it to where it needs to go.