I've been trying to set my timing and advance curve and have noticed that when I approach 3000 rpm, the timing light seems to be dancing around on the timing tape. I'm also getting a little bit of backfire letting off the gas. This is my setup: -Fresh built 327, iron heads, 9.8:1 CR, 8.3:1 DCR, 0.035" quench solid lift cam 230/236 .490/.501" lift. Doesn't seem to ping or detonate. -3x2 intake, I'm running off the center carb only, I think it's fairly well dialed in. But I think I need my timing sorted before I can go further. - my distributor is an old delco points type converted to pertronix. I disassembled, cleaned and lubed the distributor and didn't detect any slop in the bushings. New cap, rotor, wires, coil and plugs. I measures the end play on the shaft when installed on my manifold and there is 0.023" of movement up and down. - my timing light is a no frills strobe light style I picked up a while back at a garage sale. Could be the issue, but it seems to hold steady at lower revs. -my oil pressure seems to be on the high side, it's about 40-45 at idle and quickly ramps to 60-65. Wondering if it could be pump chatter? Suggestions and advice a greatly appreciated as always. Thanks Posted using the Full Custom H.A.M.B. App!
See if you can get your hands on another timing light but it seems that they will do that unless you go with a crank trigger set up.
So this is normal? I think I'm pretty close. It seems to bounce between 30- 38 degrees. Posted using the Full Custom H.A.M.B. App!
Had one do that with a Pertronix too and figured it went bad. Timing mark tracked up and down like the picture on an old busted TV and had a miss. Chip (need louvers on here) ended up with it and I think found a bad connection then stuck it in his T and seems fine now.
8 degrees sounds a little high. Is the advance all in at 3000 ? Does it settle down at 3500? You said fresh engine is your timing chain in good shape.
An 8° spread would make me nervous..2° or so could be in the timing chain [even a new one] and wouldn't worry me that much and neither does the oil pressure..
I think what is happening is that the impulse is coming faster than your light can handle it. That is making it skip a beat now and then.
Got dwell meter? could you go back to points easily? A distributor in good mechanical condition should show dwell varying less than a degree or 2. Magnetically triggered ignitions are a lot less sensitive to clearance in the main shaft and clearance between the advance mechanism etc but there are limits. HAs perrtonix got something to say? I'd lock the mechanical advance by one means or another and with the vac advance disconnected have another look. I've had some electronic distributor engines with rock steady timing, so it can be done.
Brand new chain. TDC verified via piston stop. I'm trying to be all in by about 2800 rpm. Posted using the Full Custom H.A.M.B. App!
Kinda rare, but I had to change a distributor on one of my old OT Chevies...worn bushings in the distrib. made it run rough.
You might give the chain a double check. I rebuild a 383 Chrysler a few years back. Long story, but after digging back into the engine to replace the cam a few months later, maybe 2000/2500 miles later, the chain was trash. You could almost remove with the sprockets in place.. The second one, same brand, same part number worked and lasted fine...years later, still good...! Easy to check - Just remove the distributor cap, have someone turn the crank by hand. Rotate it a few degrees one way, then reverse the action. The rotor should turn AS SOON AS the crank is turned the other way. If it doesn't...it's chain replace time. Cam walk can also show up as the problem you seem to be having. One more, if the distributor drive gear it too high or too low in the mesh with the cam, and the distr. has too much freeplay, the distr. shaft can be moving up and down, causing havoc with the ignition. Mike
I keep a spare stock Chevy points distributor around just for trouble shooting if needed. Bought one from a CL ad for $10, and it's came in handy occasionally when trouble shooting electronic distributors. I'd borrow a good timing light first, as then you've got a base to check with. Or put the light you have on another car and see if it does anything similar. If it's OK on another car, then you might have distributor issues.
Good advise. My distributor has 0.023" up and down movement. I really doubt my chain is the issue but it's well worth checking to be safe. Thanks Posted using the Full Custom H.A.M.B. App!
I had a similar issue and it ended up being a bad plug wire. Try putting the pick up on one of the shorter plug wires and see if you still have the same issue. Even without marks you will still see the jump. Take a good look at the magnet on your timing light pick up as well.
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