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I am wondering whether I have this situation or not and not sure exactly what would be the symptoms or exactly how to correct.

During the rebuild process I manually rotated the engine to get #1 to TDC. When I was sure it was in the proper location I looked down and "lo and behold" the 6 degree TDC mark was precisely on the timing point. I had "painted" this mark with some WhiteOut to make sur eit was easy to check later and was pleased to see everything lining up in the right location.

Later on I inserted the distributor and made sure the rotor was approaching the #1 plug hole and think I hit it on the mark. I did notice the distributor rotated a bit as it went on down assuring me the gears meshed properly.

When I finally got around to firing the motor with my newly rebuilt 4100 from Pony Carbs the engine seemed to fire right up and run immediately. Success! Or at least I thought until the engine warmed up and began to stumble at idle. Dont think I have vacuum leaks but I will test this closer as well. I am wondering whether the disti could be off a tooth. Even though Pony Carbs says not to use a timing light it seems like my engine is up around 12-14 degrees and the vacuum canister is rotated around and nearly hitting the upper radiator hose.

If I pull the disti and attempt to move one more tooth, logic tells me I will get the canister more forward and not interfere with the hose. Also, it seems llike I would have my timing hit more at the 6 degree mark.

Does this make sense?
 

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i think i understand.

The only important thing is the the crank and timing make point to TDC. from there you can point the distributor in any position you want as long as you can rotate the cap to match it. So if you want to pull the distributor and rotate it a tooth or 2 it won;t make any difference because you timing using a light to a fixed reference point on the engine.

The problem with the direction of the distributor is only on first start up. the #1 piston goes to TDC twice. once it is on the compression stroke and once on the purge stroke. If you think the purge stroke is the compression stroke you will point the distributor 180 degrees from correct. But even if you go that you could rotate all the spark plug wires around and it would run fine. Its just the lengths of the spark plug wires would be all wrong in that orientation.
 

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I'm a little confused about your explanation. You say "During the rebuild process I manually rotated the engine to get #1 to TDC. When I was sure it was in the proper location I looked down and "lo and behold" the 6 degree TDC mark was precisely on the timing point." Are you saying that you were checking on #1 piston top with the head off and the timing mark was 6 deg off? If so your ballancer ring has slipped and needs rebuilt or replaced.

As far as the distributor goes, if you are at the end of the range of movement then yes, pull it and move it a tooth or 2 - that's fine.

Pony carbs is right, you should time it by the "advance it 'til it pings and back off a little" method.
 

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If your front balancer is of by 6 degrees you can buy a degree tape and re-locate tdc. There are tools available or you can make a tool from an old spark plug that you put in the #1 hole and it will stop the piston before tdc. You would hand crank the motor clockwise until it stops, mark the position of the pointer on the balancer and then rotate the motor counter clockwise by hand until it stops again, mark the position on the balancer again and split the difference between the marks, that would be true tdc. Put the timing tape at the new tdc mark and you have a corrected balancer...
 

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There are tools available or you can make a tool from an old spark plug that you put in the #1 hole and it will stop the piston before tdc. You would hand crank the motor clockwise until it stops, mark the position of the pointer on the balancer and then rotate the motor counter clockwise by hand until it stops again, mark the position on the balancer again and split the difference between the marks, that would be true tdc.

Okay, this is totally my own naive analysis of the problem and should in no way be construed as actual knowledge.

Wouldn't you be able to determine TDC by inserting a long blunt object through the #1 spark hole, and rotating it to the point that the piston has crested, using the object as an indicator? Maybe I'm missing something (probably, since I've never done it;)) but the screw-in-an-object method seems overly complex to me.

Please feel free to educate me.
 

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You are correct TDC it is, however, that is not enough. TDC happens twice per cycle in four stroke engine, so you need to check that valves are shut also, which can be done with finger in plug hole. When you rotate the engine at firing TDC the valves are shut and the air tries to escape through plug hole.
 

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If you had a dial gauge on the screwdriver then you may possibly find top dead center but it still will be tricky. Once the piston is at tdc the crank is cresting and can move a few degrees without any noticeable movement of the piston. By putting the tool in the spark plug hole you gauarantee that the piston stops at the exact spot during each rotation and the difference has to be tdc.
 

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The tool can be as simple as old plug stripped of its' insulation and center electrode. Then weld a suitable length of rod to plug and that's it.
 
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