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Timing Jumps

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abnovak

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Tuning my 79 Midget. When setting the timing, using an inductive timing gun, the timing marks jump +/-10 degrees (may be little less). Haynes says that prob either a worn distributor or timing chain. Before I go through the mess of the timing chain, does anyone have any other suggestions?

Its also running rich, with the ZS Carb what the best way to address that. There seem to be precious few adjustments on this design.
 
Does that have points? If it does, then changing to an electronic ignition may help. On my cars, they seem to be less sensitive to wear than points triggered timing.
 
Check the dizzy bushing and also make sure the pin holding the drive gear on is tight. I had a drive gear with a loose pin that drove me nuts for a few weeks. Timing would change every minute or so.

Frank
 
If you do get into the timing chain, you can upgrade to a double row chain by using the six cylinder Triumph set up found on GT6's & TR6's. You have to change both gears and the tensioner, but you get the longer life of the double row setup.
Jeff
 
Can anyone tell me how to change the bushings on a 25D distributor? Mine is wobbling pretty bad. I took the unit apart from the top down. I am at the point where the inner springs and weights are exposed but I can't figure out how to go further. Does one need to gain access from the bottom? If so how is this done?
 
Drive out the pin on the drive gear with a long punch.
Scratch a mark on the gear and dizzy because it is slighly offset and you can get it 180 out on replacement.
The gear pulls off, there is a bronze washer under it, and gently push the guts out.
You will have to press out the bushing or use a larger punch (deep well socket works too) Be sure the new bushing has an oil hole drilled in it. I had one come without this oil hole and it didn't last long. Line up the oil hole with the drilling on the dizzy shaft and gently beat it back in.
It may need to be honed, test it using your shaft, it should move freely with no wobbles, it it binds, you might try running a drill up and down the bushing. Ot some sandpaper wrapped around a slightly smaller drill bit. Or the machine shop.

Frank
 
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