Hi everyone,

The C3 corvette has been my dream car since I was a kid, and I finally bought one about 4 months ago. Granted, it's a pretty beat down 79 that had L82 badges on it, but its really an L48 with 80,000 miles. Just want to let everyone know I'm very new to muscle cars and mechanical stuff!

It's got the quadrajet and a 4 speed manual, so here's my problem. It's got plenty of torque at low RPMs (700-1300 ish), but anything beyond that it just stumbles and sputters and won't go. It revs up fine in neutral though.

I rebuilt the carburetor recently and the problem persists. I also removed the cam that locks the secondary air valves. I know the secondary air valve vacuum break is working because when I turn it on, it goes into the lock position, but I am not sure if it ever unlocks when the vacuum changes.

I've timed the engine three times now, once by me, another time a mechanic did it for me, and then I timed it again myself. Each time, I think it was done without a tachometer, so I've just installed an after market one and I'll time it again to more precise specs.

I noticed when I was timing it though, as the engine revs the timing retards pretty significantly (my timing marks only go to 8 deg BTDC and 8deg ATDC) so it looks like its retarding to about 14 BTDC when reving up to about 3-4K, but I have no way of telling exactly. Not sure if that is normal. The vacuum advance was disconnected and plugged.

I'm really in love with this corvette and it's been bothering me that I can't drive it!!

You'll have to forgive me if this is a noobish question, thanks in advance!

- Micah

 

Get a dial back timing light, remove the springs from the distributor, remove and plug the hose to the vacuum advance canister and see what your total timing is. Ideally, it should be about 36 degrees.

 

Thanks for the reply. I've never heard of such a timing light, but I'll purchase one soon.

https://www.summitracing.com/parts/s...o8mxoCBfjw_wcB

This has some bad reviews, but it's cheaper than the $80 my mechanic charged me to do the timing, and he left the bolt holding the distributor loose! lol.

 

Another member posted this video, I found it very helpful. Lots of other videos on his channel too.

 

Thanks! I was using the wrong terminology, as he described in the video that movement is normal.

I read there is a way to do this total advance timing without the dial back light by measuring the harmonic balancer's circumference with a sewing tape and dividing that number by ten. Supposedly that will give us exactly the distance of 36 degrees from the original timing mark which makes sense, 360/10 is 36. So, we add a mark that distance in the clockwise direction from the original mark.

I tend to get myself into things I'm not qualified to do, but if this seems legit I'd like to do it today since I can use my regular chinese timing light to do it lol. My question is, will I line this mark up with the 0 line on my timing chain housing tab? And is 36 degrees too much, since the fellow in that vid you linked was suggesting more like 30 degrees for a "street chevy 350", and is 3500 rpms a good rev range to do this timing calibration? Thanks!!

Thanks for your help!

 

Personally I wouldn't use any youtube video.

Lars is the man when it comes to timing and q-jet setup/rebuild. Use the search function and check out his posts on the subjects. He also has a paper on it which would help you.
email him at V8FastCars@msn.com and he'll send it to you.
Good luck

 

You need to start at the beginning. Get motor up on number one compression stroke pull cap and look to see where the rotor is pointing. Often peeps do this and get it off quite a bit.

You preferably want the rotor to point at the number 1 plug when the motor is at TDC compression stroke. Once you are sure that is set and or pull distributor to get it set then work out the timing,

If YOU DO NOT have marks in the balancer BUY a vacuum gauge. Disconnect vac adv plug vac gauge in Start motor. to adjust timing turn distributor until you have the highest vac reading then road test car and make small adjustments.

 

You just need to go get a timing tape at the parts store, and then you can use your timing light. they are about $10

 

Ok, so I hopped down underneath the vette with a sewing measuring tape, the harmonic balancer was 54cm, so I measured 5.4 cm clockwise after my timing mark and made my own mark. Disconnected the vac advance and started reving until it didn't move anymore, and I noticed it was way off. It was way off by at least 13-16 degrees.

Once I started moving the distributor in the correct direction, I noticed it took less RPMs to "peg out", and now when I shut her off, I hear loads of lifter or valve ticking. Never heard that before in this engine.

Kinda worried I haven't done it right, so I haven't tested it yet haha. I'll let you guys know if I've fixed or blown up the engine!!

Thanks.

 

Great, I think ignition timing was definitely my problem. I know I haven't adjusted it right yet though because I'm hearing actual backfires in the intake manifold, but I have definitely fixed that stumbling problem. Also, she wants to diesel when I shut her down now. Not sure if I need to advance it more or less to solve this. I'm also not sure if I should be worried about that ticking sound.

There is still a minor stumble right as it starts backfiring in the manifold at the medium-high range rpms.

Thanks a ton for all the help!!

EDIT:

I think it may be too far advanced due to the backfiring in the intake, my question is now that I have this new mark, to retard the timing, does this new line need to be on the BEFORE side of the tab or the AFTER to retard it? I'm guessing the AFTER side, but I don't want to damage my already old engine.

 

Back the timing down u should be fine