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Cub Issues

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Author  [Modern View]

01-11-2018 11:52:41

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Picked up a little cub with a magneto that has been sitting for a while. Compression is ok, rebuilt the carb and I have spark at the plugs but I can't get it to fire. I have check the timing (per the IT manual). The marks line up but it just doesn't want to pop off, this one is stumping me. Any ideas?

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01-18-2018 18:42:13

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
Had the identical problem. Turned out all the plug wires were reversed. The #1 plug wire from the distributor goes to the #1 cylinder. The #1 cylinder as I discovered was the one closest to the radiator - #4 closest to the steering wheel.

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john *.?-!.* cub owner

01-13-2018 12:13:19

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
Quoting Removed, click Modern View to seeAnd would make for an interesting show when you finally got it started. :lol:

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Jim Becker

01-12-2018 20:15:03

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
Quoting Removed, click Modern View to see

It would take a lot of oil in the exhaust to fill it to the valves.

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john *.?-!.* cub owner

01-12-2018 13:21:02

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
Cub magnetos that have set for very long are bad for the coil to get weak, and for the points to corrode. Either one can give you a weak spark. It take a goold strong spark that will jump at least 3/8 of an inch to start one. Also, the rotor has gear molded on the back and has to be timed to the rest of the mag to make sure the spark is at the right plug at the right time.
When you were cranking it did fuel ever drain out the bottom of the carb? Cubs will normally flood and drain out the weep hole near the front of the carb after 7 or 8 rounds of choking and not starting. If you are not seeing that, remove the plug in the bottom of the carb and make sure you are getting fuel. If it has an IH carb rather than the larger Zenith carb replacement there is a small stud on the side of the carb near the bottom. That stud is the load jet, and is bad to plug and carb leaner not clear it. Unscrew it and make sure you can see light through the hole in the end. If not use a fine wire, such as used in phone wiring, etc. to run through it and clean it. You can also visit farmallcub dot com for a lot of help.

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01-12-2018 12:34:32

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
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What???? Where are you getting that information from? They are ether with some top end oil added. Check the msds!

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01-12-2018 09:56:16

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
Valves may be stuck open.

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Russ from MN

01-12-2018 09:22:34

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
I agree with old, I have had the same problem with a Wisconsin and I put some oil in the spark plug holes and then it started right up. Anytime an engine has been sitting a long time it would be good to do that before even trying to turn it over. Starting fluid only makes it worse.

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01-12-2018 13:21:56

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 Re: Cub Issues in reply to Russ from MN, 01-12-2018 09:22:34  
I had put a little oil down each cylinder after I got it, haven't tried ATF. Pulled the manifold off and it is full of carbon. I plan on checking the valves tonight.

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01-12-2018 13:37:12

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 Re: Cub Issues in reply to MH, 01-12-2018 13:21:56  
I forgot about it being flat head engine. Fill the cylinders with ATF and if it has a vertical exhaust pour in as much ATF in it so as to get to the exhaust valves once you have the manifold back on. If you have much of any compression the valve had to be opening and closing or you would not have any compression

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01-11-2018 13:28:14

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
If I where you I would pour in a 1/4 cup of ATF and let it sit a day or 2. I would then pull the plugs back out be sure to put them in while it sits.. Clear the cylinder of ATF by spinning it over. Next I would have the intake tube off the carb and hold your hand over the carb while spinning it over. You should get a good suction and gas on your hand. If you do not have both then you have a compression problem or a vacuum leak. As for spark you need a good blue/white that will jump a 1/4 inch gap at all the plugs

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01-11-2018 12:19:29

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
No need to go to a Cub-specific forum for engine 101 stuff like this unless you really want to...

First off can you hear the impulse snapping when you crank the engine over? Should be a distinct snap coming from the mag. That helps make a good hot spark for starting.

Second off the timing marks line up twice. Once on the compression stroke (correct) and once on the exhaust stroke (wrong). You sure you have it lined up for the compression stroke on cylinder #1 (front cylinder, nearest the radiator)?

Do you have actual compression numbers? Can you share them? You really can't tell compression by feel.

Have you tried a sniff of starting fluid in the intake? That will tell you if it is a fuel problem or an ignition problem. Modern starting fluid (except for John Deere) has no ether in it and will not damage the engine.
What is your starting technique? Are you familiar with the operation of the choke?

Hopefully that's enough to think about.

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01-11-2018 13:01:34

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 Re: Cub Issues in reply to BarnyardEngineering, 01-11-2018 12:19:29  
Yes I can hear the impulse snap.

The timing marks line up twice and the rotor button is at #1 on ccompression.

Can't remember the order but #100, 100#, 95# and 1 is low at 60#s.

I have tried a sniff of starter fluid.

Crank it over and a quick pull on the choke, then release. I have varied the throttle position.

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01-11-2018 15:08:02

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 Re: Cub Issues in reply to MH, 01-11-2018 13:01:34  
Maybe I misunderstood that post, but you need to crank the engine over with the choke butterfly closed. You do not need or want to pull the choke closed after you quit cranking. The choke is there to increase the suction at the carburetor while you are cranking. This draws the air-fuel mix into the cylinders.

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01-12-2018 07:33:55

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 Re: Cub Issues in reply to steve_in_mo, 01-11-2018 15:08:02  
Yes I pull the choke while cranking the engine over.

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01-11-2018 12:04:09

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 Re: Cub Issues in reply to MH, 01-11-2018 11:52:41  
on face book, look for farmall cub rescue or farmall cub 1947. someone on one of these will probably help

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