Timing for Rebuilt L48

[1978L48jafo]

Bob My time was limited last night with the vacuum line off and plugged I had about 28 mechanical advanceat approx 3600 RPM. The wife was a bit cranky so I didn't get to try as many different RPMs as I would have liked. Again I want to run through this on saturday where I can take my time. Let me know if the reading does not make sense. I am also going to fill up with higher octane on the way home just in case regular gas has caused some of this grief.

John

John,

Did you measure with the vac advance disconnected and what was your total advance?

Bob

 

[Bob Chadwick]

Sounds like you need to adjust the springs to get the total advance in a little earlier and adjust the weights to get the total mechancal advance a little higher. According to the paper that Lars wrote, 36 degrees at 300 rpm is just about right.

 

[1978L48jafo]

Bob I down loaded the paper and also read through some excellant posts by Johnz. Doesn't the total 36 degrees of recommended advance include the vacuum advance too? I had this off and plugged duing my checks. I assumed the total advance equaled mechanical + static = vacuum. With this asked, the concept is beginning to make much more sense.
John

Sounds like you need to adjust the springs to get the total advance in a little earlier and adjust the weights to get the total mechancal advance a little higher. According to the paper that Lars wrote, 36 degrees at 300 rpm is just about right.

 

[Bob Chadwick]

My understanding is that it is without the vacuum. It is the initial advance of 8 degrees plus 28 mechanical. The vacuum kicks in when there is no load, such as cruising, and further increases the advance to somewhere around 50, if I recall correctly, and then falls off back to 36 when you put the engine under load.

 

[Bob Chadwick]

OK. Everything I know about timing is theory. The last time I timed a car it was a 65 VW beetle and you didn't even need a timing light.

I got my timing light out tonight and was futzing aroud with the existing distributor in anticipation of replacing it. I don't have much common sense but thought I should figure out how the existing system works before I repalce it and possibly get into a troubleshooting situation.

First problem was I couldn' t get to the #1 plug wire to hook up the timing light. It runs under the header and with the heat I was going to loose some skin.

Can some one confirm that the #1 piston is the front most piston on the drivers side?

So I have read that you can use the #6 piston for timing as well, which I understand to be the third piston back from the front on the passenger side. Can someone confirm both of these things.

I checked the timing on the using #6. I had 4 degrees at idle of about 750 rpm and about 20 degrees at 3,000 rpm. This is not good considering I paid someone to recurve the distributor last year.

 

[1978L48jafo]

Bob # 1 is the first piston on the drivers side and # 6 is the third from the front on the passenger side. I am also a little short on skin from attaching the inductive pickup.

No Idea on using 6......
John

OK. Everything I know about timing is theory. The last time I timed a car it was a 65 VW beetle and you didn't even need a timing light.

I got my timing light out tonight and was futzing aroud with the existing distributor in anticipation of replacing it. I don't have much common sense but thought I should figure out how the existing system works before I repalce it and possibly get into a troubleshooting situation.

First problem was I couldn' t get to the #1 plug wire to hook up the timing light. It runs under the header and with the heat I was going to loose some skin.

Can some one confirm that the #1 piston is the front most piston on the drivers side?

So I have read that you can use the #6 piston for timing as well, which I understand to be the third piston back from the front on the passenger side. Can someone confirm both of these things.

I checked the timing on the using #6. I had 4 degrees at idle of about 750 rpm and about 20 degrees at 3,000 rpm. This is not good considering I paid someone to recurve the distributor last year.

 

[curtis]

found a nice explanation of timeing and vacuum. www.corvettefaq.com listed under carburetor vacuum ports. by Lars

 

[Bob Chadwick]

Thanks Curtis. I think that paper is one of the two I have linked on my web site.

I heated the car up tonight and was checking the timing. A little off, about 2 degrees.

I was going to adjust it before I marked the rotor spot on the firewall but the last guy must have been a 500 pound gorilla. I couldn't get the darn distributor retaining bolt loose. I took off the valve cover and it gives me a little better access but it is just too darn hot to work on right now.

Oh well, another day and another beer.

 

[curtis]

didn't mean to reitereate what you already knew. guess I didn't read your previous posts close enough .............BEER sounds like a damn good idea. Hot here today 90 degrees and humid. gonna put in new overflow tank tonight when it cools off. old one was yeloowed and real ugly.

 

[Bob Chadwick]

No problem. I appreciate your pointing me in the direction of another possible source of info.

 

[Robin7TFour]

Jafo, the 'dial-back' is a nickname for a timing light with a dial(on the back) for adjusting the advance of the ignition.if you don't have a sears close by. harbor freight has an inexpensive model that does a great job.

Robin

 

[Bob Chadwick]

What are you guys using for a dwell/tach? I bought one from Sears and am considering taking it back. It's a pain with the coil mounted on the distributor. You have to pull the negative wire, add a jumper from the coil to the wire and then hook the tach to the jumper.

 

[Robin7TFour]

Bob, i made a Y wire assy and plug it into the tach lead on the distributor. i mounted a cheap auto tach on a board ,with a terminal strip for connecting the power leads.
on the bottom of the board i put some rubber padding so it doesn't slide around.plus i can lay it anywhere without scratching.

Robin

 

[Bob Chadwick]

I may have to try that. The thing wasn't cheap and all I really wanted was the tach function. The cheap ones only went to 2000 rpm.

 

[1978L48jafo]

Thanks Robin, I usually check with Harbor freight love their prices but hate their customer service......I pick up a light from sears it was only about 60 dollars.
John

Jafo, the 'dial-back' is a nickname for a timing light with a dial(on the back) for adjusting the advance of the ignition.if you don't have a sears close by. harbor freight has an inexpensive model that does a great job.

Robin

 

[Bob Chadwick]

Help me out guys. I marked the orientation of the old distributor, the orientation of the rotor and pulled the old distributor.

I am trying to put the new one in but can't get it to go in the oil pump slot. For the last hour I have been turning the oil pump to try and line it up. It appears that I can get it to match one tooth of the distributor gear to either side of the mark on the firewall. With the pump at a certain point it lines up to one side of a my rotor mark. If I move the pump less than a quarter of a turn, the rotor line up point falls back to this spot when I try to line it up. A quarter turn and the rotor lines up with what appears to be a gear on the other side of my mark.

I can get the rotor to line with the mark when the distributor is not in the oil pump groove.

Am I trying to hard. This is only about a 1/2 inch move in either direction. Is this close enough and I can adjust it by turning the distributor to make up the difference?

 

[1978L48jafo]

Bob I was waiting hoping that one of the motor heads would reply. I believe the distributor gear engages the cam gear before it sits down on the oil drive so what I have done many times is get the distributor where I want it and crank the engine, while maintaining light downward pressure until the distributor drops the rest of the way (when the oil drive lines up) I do this with the distributor unplugged of course.



Update.... My vet has never run better, the timing changes now allow me to slip in the 6th at around 55. I have been reading through posts on carbs and ordered a new Edelbrock Performer carburetor. I think and hope it will improve the economy as well as performance.

Help me out guys. I marked the orientation of the old distributor, the orientation of the rotor and pulled the old distributor.

I am trying to put the new one in but can't get it to go in the oil pump slot. For the last hour I have been turning the oil pump to try and line it up. It appears that I can get it to match one tooth of the distributor gear to either side of the mark on the firewall. With the pump at a certain point it lines up to one side of a my rotor mark. If I move the pump less than a quarter of a turn, the rotor line up point falls back to this spot when I try to line it up. A quarter turn and the rotor lines up with what appears to be a gear on the other side of my mark.

I can get the rotor to line with the mark when the distributor is not in the oil pump groove.

Am I trying to hard. This is only about a 1/2 inch move in either direction. Is this close enough and I can adjust it by turning the distributor to make up the difference?