new carb

[garin1]

well,,I put the new 750cfm carb on finally.took it out and ran it,,it wants to run but still runs bad.probably needs more fine tuning.
checked the timing with a light and it seems to be bouncing around to much.any timing advice would really be helpfull:confused

 

[69vettester]

garin1
Was it running bad before the swap?
This may seem obvious but
Because of your new carb install, I would start looking for manifold leaks or possibly one of the carburators vacuum ports is open or otherwise leaking.


Were you trying to check your timing advance at idle speed(initial advance)? A good initial advance setting for general motors fairly stock engines is around 10-12 degrees to start with, you may be able to get some more advance later , but start with that(10-12).
Then If you have an adjustable light, see if your motor brings in around around 34 degrees total at 3000rpm. In other words set the light to 34 degrees and see if it shows up at 0 degrees on the harmonic balancer at 3000rpms. If it does, your motor should be running acceptably timed but maybe not optimal.
Ive learned this way of setting timing from some gurus on corvette forums and it works very well provided you dont have carb problems going on, vacuum leaks ect...

If its too erratic to check, because the reading moves around, then Id look for the vacuum leaks or carb settings to be way off.
Hope this helps..
TomC

 

[Rowdy1]

Timing Bouncing

How many miles on the engine? Does it run hot or break up and maybe pop back through the carb at higher rpm's? I had the same timing problem on my old block. Changed the distributor, still did it. It turned out to be the timing chain. What engine you running, sb or bb?

 

[garin1]

rebuilt 350cid about 250 miles on it with heavy cam(comp xr282hr-.51-520 lift)distributer is new although it could be bad and yes you are right it does need some fine tuning on the carb settings,
but with my old carb the marks were stable at high rpm:cry

 

[garin1]

I forgot to say there is a new timing chain and gears installed

 

[redmist]

If the spark bounce if only happening at high rpm I wouldn't think it is a vacuum leak I would tend to look towards the spark plug wires or the distributor gear.
What kind of cam are you running? Did you install a cam button?

 

[garin1]

when the dist was put in the mechanic missed setting it on the gear by a tooth so now Ihave all wires moved one hole c/clockways.with the light i can get 12 btdc but when i connect the vacuum advance it moves a lot.I put a vacuum guage on the vacuum advance and it functions properly and the guage holds pressure:confused

 

[69MyWay]

Gary,

Do you have an adjustable timing light to look at the max curve?

 

[garin1]

no

 

[69MyWay]

If ya want, you can use mine. I will be home Sat.

 

[69vettester]

Gary
Do the timing check and adjust with the vacuum advance not hooked up. If its ported to manifold vacuum(permanent vacuum) the timing light readings will be unpredictable.
Vacuum advance is supposed to come into play when the throttle is opened, not at idle speed.
Hope this helps.
TomC