Low Boy sputters under load

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dano6807
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Low Boy sputters under load

Postby dano6807 » Mon May 16, 2016 11:50 am

Hello, I have one of the yellow and white low boys...63-67 I believe. She starts right up and purrs like a kitten at any rpm. But as soon as there is any load on the motor, it sputters and loses power, also seems to run hotter now. I've rebuilt the distributor, new plugs and wires, and cleaned the main jet. I'm assuming that it is starving for fuel under load, but I'm concerned I might be chasing the wrong problem. Should I be looking at the valve train, timing...etc. Any help would be greatly appreciated.

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gitractorman
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Re: Low Boy sputters under load

Postby gitractorman » Tue May 17, 2016 8:23 am

Sounds to me like the timing is off, and/or the governor is not working properly. Also, with the early Lo-boys like this, the moderators should move this to the standard Cub forum. You'll get more eyes looking at it that way, and they're the same tractor up till 1968/69 when the number series starts.
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tbear
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Re: Low Boy sputters under load

Postby tbear » Tue May 17, 2016 6:23 pm

May be running lean. Check carb. adjustment, intake manifold gaskets, carb to intake gasket, cracked intake, adjust timing by ear (not with the light), make sure points are opening and closing all the way, weak coil?, water in the gas?
There is a finite number of things to check until you find the problem, just keep at it, you'll find it.

dano6807
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Re: Low Boy sputters under load

Postby dano6807 » Wed May 18, 2016 11:26 am

Well I completely tore down the carb and cleaned it. Then I adjusted the timing, which was quite a bit out. But when I put it where it should be, it didn't run good at all. How exactly do I adjust it by ear? Just advance it until it sounds like it's smooth? The distributor was good and tight, so I'm not sure how it got that far out....but even with it close to TDC on low idle, (where it sounded good) it still sputtered only under load. The advance is working properly as well. Any timing tricks I could try?
Thanks.

dano6807
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Re: Low Boy sputters under load

Postby dano6807 » Wed May 18, 2016 11:27 am

I also just ordered a new coil. Hopefully that will help?

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Re: Low Boy sputters under load

Postby Eugene » Wed May 18, 2016 12:32 pm

dano6807 wrote:I adjusted the timing, which was quite a bit out. But when I put it where it should be, it didn't run good at all.
Distributor timed to engine.

Used the 2nd pulley mark to line up with the pointer to time the ignition? 1st pulley mark to match the pointer is the distributor advance mark.

Roll engine over until pointer lines up with the 2nd mark to line up with the pointer. Mark the distributor base to line up with the center of the #1 spark plug tower on the distributor cap. If the rotor isn't close to the mark on the distributor base, roll the engine over 1 complete turn until the TDC mark and pointer line up. The center of the rotor should be pointing directly at your mark on the distributor base.

Edit: Frankly I don't know what you are doing wrong in timing your engine. Something is wrong. You should not have to time it by ear. There are You-tube videos on how to time the Cub engine.
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dano6807
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Re: Low Boy sputters under load

Postby dano6807 » Wed May 18, 2016 2:48 pm

Exactly.....I used the first mark at low idle, then ran throttle all the way up and it advanced to the 2nd mark. I have no clue how that couldn't be right, but it didn't like being there (rough idle and slight backfiring). So I advanced it slightly, and it sounded great. That just doesn't seem right, unless the cam is out of time, but even then I think I would have bigger problems. Plus it ran perfect last summer, so again it makes no sense to me.

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Re: Low Boy sputters under load

Postby Eugene » Wed May 18, 2016 5:39 pm

dano6807 wrote:I have no clue how that couldn't be right, but it didn't like being there (rough idle and slight backfiring). So I advanced it slightly, and it sounded great.
Ignition timing problem. I'm sure I mentioned that a couple of times. Did you run the checks I posted?

Did you check to see that the distributor wires are on the correct spark plug?

That just doesn't seem right, unless the cam is out of time, but even then I think I would have bigger problems. Plus it ran perfect last summer, so again it makes no sense to me.
Yup. No comment.
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dano6807
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Re: Low Boy sputters under load

Postby dano6807 » Wed May 18, 2016 7:53 pm

Yes, I performed all of those checks after I used the timing light and saw how far out it was. Plug wires are correct, points are new, gap is correct. Like I said, she starts and runs perfect....just not under load. I'm going to run through the timing process again, and try the new coil. Hopefully the problem will arise.

outdoors4evr
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Re: Low Boy sputters under load

Postby outdoors4evr » Mon May 23, 2016 8:31 am

Check the crank pulley with the timing marks on it. There is a keyway that sometimes gets wallowed out and allows some slop. This may have your timing marks off a bit.
You can see it best with the timing light. If the keyway is sloppy, the timing marks seems to jump around a bit.
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dano6807
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Re: Low Boy sputters under load

Postby dano6807 » Mon May 23, 2016 8:41 pm

I will definitely check that out. That makes sense because I have gained some power back by messing with the timing, but the marks still don't line up with the pointer.
Thank you everyone for your help!

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gitractorman
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Simplicity Conquest
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Re: Low Boy sputters under load

Postby gitractorman » Wed May 25, 2016 6:12 am

Since you're messing with the timing, I'd double check that the crank shaft pulley is still attached properly. It is VERY common for the key way to wear allowing the pulley to spin on the crankshaft. In many cases it turns just a little then becomes wedged in place but now your timing marks are not correct. It's a pain to fix but it could be a big problem if your tractor has lost power and you're trying to get it back in time, and the marks aren't in the right locations.
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Re: Low Boy sputters under load

Postby cricket142 » Fri Jun 17, 2016 7:28 am

Could you also be trying to time by a different cylinder? Is your timing light pickup on the right plug wire?


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