Cub hard to start

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Dave2017
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Cub hard to start

Postby Dave2017 » Fri Jun 02, 2017 7:31 am

I did a complete engine rebuild on my 1949 cub and fired it up for the first time yesterday. It was very hard to get it started to the point I thought it was out of time. Frustrated and knowing it wasn't the best thing to do on a fresh rebuild I cheated and gave it a very tiny shot of either and it finally fired right up on the first crank and ran for 10-15 minutes just fine. After shutting it down it fires right back up if started immediately but if allowed to sit it is very hard to Start. I pulled the carb apart and blew it out still no luck. I did notice that the idle air screw makes no difference when being turned. It is a ih carb. Any suggestions?
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Glen
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Re: Cub hard to start

Postby Glen » Fri Jun 02, 2017 5:04 pm

Hi,
You could try checking the spark, it should have a strong blue spark. If the spark is weak, it probably won't start good.
To check it, pull the center ignition wire out of the distributor cap, turn on the ignition switch, and hold the wire by the insulated part of it, with the end of the wire 1/4 inch from bare metal on the engine, run the starter and see if the spark jumps the gap. It should be blue, yellow is weak.
If the spark is weak, the points might need filing, or replacing, or the condenser could be bad, or the coil could need replacing. Magneto coils in Cubs commonly get weak when they are old, and need replacing, so do Battery Ignition coils. :)

Dave2017
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Joined: Sun May 21, 2017 8:17 am
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Tractors Owned: 1) Farm all cub. 2) farm all M's
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Re: Cub hard to start

Postby Dave2017 » Fri Jun 02, 2017 9:44 pm

Glen, I checked the spark and it was good, the mag was rebuilt in 2004 and appears to be working well. Before I gave it a shot of either I pulled the plugs and the were all dry. If I gently crank if a few times then give it a good half crank it will start but if I use the starter it has to crank awhile before it starts. It has a 12v battery and I'm concerned the excessive cranking may burn the starter up.
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staninlowerAL
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Re: Cub hard to start

Postby staninlowerAL » Sat Jun 03, 2017 6:35 am

Dave2017 wrote:I pulled the carb apart and blew it out still no luck. I did notice that the idle air screw makes no difference when being turned.
Did you check/clean the main jet?

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Re: Cub hard to start

Postby Eugene » Sat Jun 03, 2017 12:54 pm

Assuming that this is a magneto's spark position/location when hand cranking and then with the 12 volt starter engaged. Same procedure if the tractor has a battery powered ignition system.
I have an excuse. CRS.

Dave2017
Posts: 29
Joined: Sun May 21, 2017 8:17 am
Zip Code: 62851
Tractors Owned: 1) Farm all cub. 2) farm all M's
Circle of Safety: Y

Re: Cub hard to start

Postby Dave2017 » Sat Jun 03, 2017 3:41 pm

I took the carb completely apart and cleaned it out. Put a rebuild kit in it and when going back together I seen that where the bowl meets the base was severely warped. I filed and ground on it until it was close to flat. I also noticed there was some slop in the throttle shaft maybe allowing it suck extra air. I put a o-ring on it to help seal it. It now fires up very easy. The air/fuel screw is very loose as if the threads are worn,even with the spring on it. It idles with the lever pulled back but as I move it forward click by click I get no response until about halfway and it then goes half throttle then two more clicks it's wide open. The lever is at the end of its travel at this point but is only 3/4 of the way forward. It seams to be usable and the governor responds when mowing. Is this now a governor adjustment issue?
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