742 b, carb and tune-up

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Following recent post about the carb, I found that Bobcat can get me a new one--for $1200. Plan B was to get another Walker rebuild kit from O'Reilly, and it is in, and seems to work OK. I also recently put in new plugs, points, & condenser, which was also helpful. The machine now starts and runs, but I know the carb needs adjusting--idle mixture screw. Before adjusting the carb, I want the engine properly timed. All four plugs seem to be firing as expected, the engine responds to the throttle and the choke, but there is still just a hint of a skip. After removing the big belt guard to view the entire crank pulley, I find the timing to be about 90 degrees BTDC if the divot on the face is the timing mark--there is no notch. The last time the crank pulley was off was several years ago at the dealership. It doesn't seem logical that this pulley could be attached to the crankshaft in any more than one position. This would seem to be an elementary automotive challenge, but I am baffled. Any thoughts are welcome.

 

[craigb93]

If you are sure the pulley is not bolted to the hub with the wrong indexing or if it is one piece and can only go one way, do the following. Remove the porcelain center from an old spark plug. Run a tap through it to create internal threads. Screw in an all-thread bolt ~2-2 1/2" long. You are making a Stop to find TDC. Remove the engine plugs and screw the Stop into No 1 Cyl. Turn the crankshaft with a socket and pull handle until the piston is against the stop, first clockwise and then counter-clockwise. At each stop position mark the pulley at the TDC mark on the cover/timing tab. Adjust the Stop as necessary to halt the crank such that the marks are <2" apart. Remove the Stop. True TDC will be half-way between the two marks. Now you can confirm the original mark or make a new one. Use this mark to set the timing. You did not mention plug wires or cap & rotor in your tune-up description.

 

[[email protected]]

If you are sure the pulley is not bolted to the hub with the wrong indexing or if it is one piece and can only go one way, do the following. Remove the porcelain center from an old spark plug. Run a tap through it to create internal threads. Screw in an all-thread bolt ~2-2 1/2" long. You are making a Stop to find TDC. Remove the engine plugs and screw the Stop into No 1 Cyl. Turn the crankshaft with a socket and pull handle until the piston is against the stop, first clockwise and then counter-clockwise. At each stop position mark the pulley at the TDC mark on the cover/timing tab. Adjust the Stop as necessary to halt the crank such that the marks are <2" apart. Remove the Stop. True TDC will be half-way between the two marks. Now you can confirm the original mark or make a new one. Use this mark to set the timing. You did not mention plug wires or cap & rotor in your tune-up description.

I did not replace the wires, but installed new cap and rotor. When installing the new cap, I held it close to the old one, and transferred plug wires one at a time. I will double check the pulley position, then follow your stop instructions.

 

[flyerdan]

I did not replace the wires, but installed new cap and rotor. When installing the new cap, I held it close to the old one, and transferred plug wires one at a time. I will double check the pulley position, then follow your stop instructions.

Logic would dictate that if the timing was out 90 degrees it wouldn't fire, much less run. First, double check that you have the sense wire on #1.
The book shows that the crank pulley is held on with four bolts, so it being off by 90 degree increments is quite possible.
If the other shop went into the front for a timing belt but didn't disturb the distributor, they wouldn't have need to time it, and wouldn't have discovered their mistake. Although they should have checked the timing as a matter of course.

 

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Logic would dictate that if the timing was out 90 degrees it wouldn't fire, much less run. First, double check that you have the sense wire on #1.
The book shows that the crank pulley is held on with four bolts, so it being off by 90 degree increments is quite possible.
If the other shop went into the front for a timing belt but didn't disturb the distributor, they wouldn't have need to time it, and wouldn't have discovered their mistake. Although they should have checked the timing as a matter of course.

Dan--your sense of logic is the same as mine, but sometimes stupid mistakes trump logic. I removed the four bolts holding the pulley on, rotated it I/4 turn to the right, and solved the problem. You would think there would be some type of idiot-proof machining that would prevent such a mistake. It now runs as good as it ever did (for me), but would still like to correctly adjust the idle mixture. The book says turn the screw in until RPMs drop, screw it out until RPMs drop, and set it half way between. I can get it to slow down by screwing it in, but need to screw it out several turns before it slows down. My experience with 1950s -1970s carbs on cars is that the two extremes are rarely more than 2 turns different. I have mine set 2 1/2 turns out, and it runs OK, but this may be way off. I am assuming correct = better.

 

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Dan--your sense of logic is the same as mine, but sometimes stupid mistakes trump logic. I removed the four bolts holding the pulley on, rotated it I/4 turn to the right, and solved the problem. You would think there would be some type of idiot-proof machining that would prevent such a mistake. It now runs as good as it ever did (for me), but would still like to correctly adjust the idle mixture. The book says turn the screw in until RPMs drop, screw it out until RPMs drop, and set it half way between. I can get it to slow down by screwing it in, but need to screw it out several turns before it slows down. My experience with 1950s -1970s carbs on cars is that the two extremes are rarely more than 2 turns different. I have mine set 2 1/2 turns out, and it runs OK, but this may be way off. I am assuming correct = better.

It has been about two weeks since last post, and I have run the machine enough to identify problems. I suspect the carb had never been touched when I bought it ten years ago. Over time it became necessary to operate at 1/4 to 1/3 choke. After a few years I rebuilt the carb, and though operations were more reliable, it still ran best with partial choke. Since rebuilding again recently, I find the same. It has always required lots of pumping and full choke to start, but I can live with this because it is regular and predictable. Even following the rebuild and after a thorough warm-up, it won't run continuously at operating speed without some choke. This suggests to me that the idle mixture is set too lean. As mentioned in previous post, the instructions are clear, but I can't seem to affect the running except by turning the screw way in. Any thoughts?

 

[Tazza]

It has been about two weeks since last post, and I have run the machine enough to identify problems. I suspect the carb had never been touched when I bought it ten years ago. Over time it became necessary to operate at 1/4 to 1/3 choke. After a few years I rebuilt the carb, and though operations were more reliable, it still ran best with partial choke. Since rebuilding again recently, I find the same. It has always required lots of pumping and full choke to start, but I can live with this because it is regular and predictable. Even following the rebuild and after a thorough warm-up, it won't run continuously at operating speed without some choke. This suggests to me that the idle mixture is set too lean. As mentioned in previous post, the instructions are clear, but I can't seem to affect the running except by turning the screw way in. Any thoughts?

Needing to run with the choke on leads me to think that your main jet is plugged or partially plugged. Something is not right.