[V240Z]

1. I was wondering how everyone checks that they are at TDC on cylinder #1 for checking timing chain stretch? Is it just a matter of looking in through the spark plug hole and watch the piston?

2. I have a 72 240 and there are no timing marks. There is a pointer coming off of the crankcase and three painted white dots on the crank pulley. Were there any other marks on the 240? What do the three dots coorespond to? If I find the TDC above I may be able to coorelate it to the dots?

3. When I start out in first gear or really any low rpm load the engine breaks up or bucks sometimes even backfires through the carbs till the revs come up. Runs smooth when no load (free rev) and seems smooth when cruising. I've set the valve lash, distributor vac advance and centrifugal are free working. If I advance the timing (not sure what it is see above) it seems to reduce the tendancy but it still isn't running right. What else should I check?

 

[johnh240]

As far as your crank pulley goes, it sounds like you have one on there from some other engine (L26-28). The 72 had 5 notches in the pulley that aligned with the pointer. The first mark would be TDC and each of the rest of the marks would be 5 degrees. You can find out which one is tdc #1 by feeling through the spark plug hole with a small screwdriver while hand turning the engine. When the piston stops moving up, that is tdc. When the dizzy rotor is pointing at #1 post, that is tdc of the compression stroke (or you can remove the valve cover since you are checking the cam timing anyway and both valves will be closed).
The bucking and backfiring could be from mis-timing or more likely from misadjusted carbs. Most backfiring from carbs is from too lean a mixture. Can be caused by vacuum leaks (may be sloppy throttle rod) or too lean setting on nozzles, or too thin/ insufficient oil in carb dampers, incorrect balance.
If you find out that you have a non standard crank pulley what you could do is find tdc and mark that on your crank pulley then each 5d is ~ ABOUT 3/16" spaced around the pulley from tdc. That should get you in the ballpark as to what your timing is set at. Factory spec would be 5 d advance. But you can run 7-10 d without much heartburn, depending on fuel you use. I run regular and about 7 d adv. Idle speed should be 750 rpm.