randommj

So the corvette has had a small timing issue, at a solid RPM (the best way I can describe it) it sounds like rrrrR-rrR-Rrr-rrrr......just very un steady

well, I finally got a timing light to find that its timed to +2 (the gague going to +2, +4, +8 from top to bottom) so I put it to +8 like my 74 L-48 should be, now it sounds AMAZING, a steady LOUD sound, VERY nice, but it runs like utter crap!

I went in today to pick the car up and take it for a short drive to see how it runs now, well it took 6 tries for it to stay running, and at about 150* I tried to pull it out of the garage, well it died, so I waited till it warmed all the way up, it BARLEY made it out, my idle RPM was at 500, so I adjusted it to 700-750, like its suppesed to be, in park I could rev it fairly fast to probably where ever I wanted (I stopped at 3000), under a load (in drive) it wouldent make it past 1000 with out cutting out and almost dying

the only mods Im aware of are my headers and free flowing side pipes, other thatn that, Im not sure what the previous owners hav put into it, but power wise it feels almost the exact same at my dads 72 L-48, a little more sluggish

so whats wrong? should I de-tune it?

thanks for the help guys

Miles

randommj

O yea, when I was timing it, I turned the dist in the wrong direction (further away from +8) and it seemed to smooth out, when it was about on +0 it sounded pretty smooth, it was off of the gague though

Miles

Jeffery73

Hi Miles,
When you say +8 do you mean before TDC or after? You want it on the before side. Putting more timing into it should make it run better. I had mine at 15 (per Lars instruction) and I wasn't really happy with how it was running so I just bumped it up to 20. I haven't driven it since the change to see if it's any better.
Are you sure that the timing light lead is on the #1 plug wire?
Also, did you disconnect the vacuum advance on the distributor and plug the hose when you were checking the timing?

redman76

Have you read through BarryKs sticky at the top of this forum? I used his and Lars docs for my reference and got mine running pretty good. I still need a better vacuum advance module, but it now screams (for an L48 ) and starts easier.

randommj

Im not fimiluar with "TDC", the gague in the crank shaft, Im sittin on the 8 that is above/closer to the drivers side, it seems the closer I get to the drivers side, the better it runs

and I did not unplug that vacuum hose, Im 95% sure I know wich one it is, so Ill unplug it when I go back to fix it

and yes, I put the lead on the #1 plug wire, at least Im sure if that! lol

Im not up to par with my termonology, I know how it all works, I just dont know the names of anything

Miles

TimAT

If you have a stock timing tab, there will either be a hole in it or one "V" notch that's bigger than the others. That's "0".

BKbroiler

You have got to unplug the vac hose. Its the only hose connected to your distributor. Plug it with a small bolt. Then set the timing. Reconnect the hose when you're done.

randommj

deal, Ill try to re-time it after my classes today! do I need to plug both ends of it? the hose and where it plugs into the dist?

and should I still be shooting for the upper 8 on my timing tab?

Miles

Chandler

Hello, unplug the vacuum hose, plug the one end of the hose, with the engine idling set the timing to 12 (some use 15 and some 20) After you get it drivable experiment till your happy. You might have to adjust the idle speed after you set the timing them check timing then check the idle. Enjoy

Chandler

mdj21

if your reading 8* btdc with the vac advance hooked up, you timing is way retarted.

pull the hose off of the advance can and plug the hose with a golf tee or something else like that. now set your timing to a minimum of 8* btdc, hook the vac can back up, and readjust your idle as required.

better yet, if you want to get the most out of your engine, read and follow the sticky post by BarryK on timing at the top of this forum or email Lars for his paper on timing.

good luck,

Mike.

BKbroiler

The vacuum hose should be left connected to the carb. Then plug the end that came off the distributor. This pevents a vacuum leak into the carb.

baxsom

if the hose is hooked up to a ported vacuum source there isnt any vacuum at idle anyway so does it really need to be unplugged.

randommj

I think there is the most vacuume at low RPM, and less to none at high RPM

unless I have got another thing screwed up in my head...

Miles

TimAT

Vacuum advance can be set up either on ported vacuum or full vacuum. Ported, there's nothing at idle, but it comes on just above idle. Full vaccum, well, full vacuum.

Looking at your dizzy, picture in your head what happens when you apply vacuum to the advance- it' pulls. Thinking of that, then turning the dizzy CCW advances the timing. CE retards it.
If you set the timing with the advance hooked up, you're running between 10 and 20* AFTER TDC (retarded). Pull the line off the vaccum advance can on the dizzy and plug it. If you play golf, a tee works well. Set the timing to 10-12-15, whatever you like. See how it runs now grasshopper.

aussiejohn

randommj,
Regardless of what has been done to your engine, the amount of vacuum you have at virtually any RPM range depends on load. If you're in top gear and climbing a hill, your carb's throttle blades are maybe wide open, and you have almost no vacuum, so your distributor only has centrifugal advance (plus 10-12-15 static) and therefore retards (from a light throttle position) somewhat.

When you get over the top of the hill and coast down the other side, your throttle blades are closed, and your engine therefore has heaps of vacuum so that your distributor gets full advance, up to maybe 55 degrees. So it's a fallacy to state that there is "no vacuum at high RPM".

Do what the others have suggested and listen to the experts like Lars. Read the paper, disconnect the vacuum line at the distributor and plug it with a golf tee, not a bolt as air can leak past the threads. Then, with a good timimg light connected to the forward-most plug lead (#1) set the static timing at about 10 degrees BTDC. Then re-connect the vacuum line and set your idle speed.

Then go for a nice drive.

Regards from Down Under

aussiejohn
9 months to go

BKbroiler

Not to split hairs over this but, a snug fitting bolt will work every time. The goal is to take the vacuum off the distributor. Not everybody has golf tees laying around.

randommj

I disconnected the hose yesterday and timed it to 12, the car actually runs now, and rund well, but ive still got a really un-even constant RPM sound, maby its something Ill hav to live with untill I can get home durring christmas break where all my tools are

BUT at least the car is able to be driven again, Thanks guys!

Miles

BKbroiler

You might have a bad spark plug or wire that is causing a "miss".