Erratic timing reading

[thatguy]

Just got the miller started a few hours ago. 8 Months in the rebuild. 454 Chev.
Problem is this. It started right up, set it at 2000 RPM for cam break in. Ran awsome!! Put the tiimg light on it and slowly brought revs up to about 3500 before the timing leveled off. Set total at 35 deg. I know I want to change springs and go lighter, I have 25 deg. mechanical bushing in an MSD pro billet "ready to run" Dist. (No box) At idle it is at 10 Deg.
When you bring up the RPM, the timing mark jumps all around. It will come up steady with RPM and then bounce back and forth. At about 3500-4000 it stops jumpimg.( When it reaches full advance). The Dist. has a vacume canister on it with no hose to the carbs. Do I need to put the Vacume lockout plate on?
Tommy :confused: :confused:

[67weimann]

you don't need the plate. I noticed the timing jumping all over if the timing light lead is too close to other wires. When you time it, make sure the lead for #1 is away from the other wires...

[Wet Dream]

Too much slack in the timing chain, too much play in the distributor.

[bajarunner]

That is usually due to the timing light itself. I have been through many lights before I found one that does not jump around. Move your pick up as far away from other wires as you can, that will give you best results. BTW bitchin boat, I love millers :D

[thatguy]

Thanks Guys,
You know I did have the light attached to #1 wire pretty close to the #3.
Will try again here in a little while.
Tommy

[wetnreckless]

I was having the same problem, MSD 6al, Pro Billet, MSD suggests checking
the plug wire and also if you continue having problems, if your light is too
close to your battery it can give erratic readings. I used a secondary battery
away from the timing light and solved the problem, hope this helps.