Red cub vs yellow cub round 2

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Shadow_storm56
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Re: Red cub vs yellow cub round 2

Postby Shadow_storm56 » Sun Jul 11, 2021 7:50 pm

inairam wrote:I would adjust the valves and the timing and the governor to carb linkage. If you have a tach or get an induction tach (~20 bucks on amazon) and see what the RPMs are at idle and full throttle for both cubs. Maybe the governor itself ( not just linkage) needs some adjustments but do that very last. It is also never the governor. I would also change the screen in the top of the fuel bowl, and clean the oil bowl in the air filter, check for air leaks between the cab and the manifold by spraying start fluid on the outside and listen for an RPM change. These are little things but if you are going back and forth between tractors they become noticable. I have also been having problems with IH and no names points and condensers. I started using NAPA ( I do not know where to get the equivalent in Canada)

My signature is "When you only have 9 horsepower you need to know the names of all of the ponies!" a difference in HP/performance between the cubs can be a lot of little things that are off just a little. Doing a complete comprehensive tune-up of all systems may help iron this out.


I ordered a timing light, I have a tach and the rpm seems just fine.... I definitely plan to go a little more in depth on the little things. Timing, valves and linkage is somthing I'll have to learn. It appears to have good compression but maybe the valve seats are bad in a way that makes it have less vaccume for the carb?

Shadow_storm56
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Re: Red cub vs yellow cub round 2

Postby Shadow_storm56 » Sun Jul 11, 2021 9:38 pm

I used acetylene to check the intake for leaks, causes rpm to drop when sucked in.... didn't expect that but still. No change in rpm anywhere except the actual intake. Both the red and yellow cub had their engines rebuilt years ago, red is slightly higher rpm max because I wanted it that way but not by much and it was still far more powerful even at the same setting on both. Probably take the distributor off tomorrow and see that everything is good there in deeper. The spark plug wires coming off of the cap are terrible but I can't see that inhibiting the engine only under load.

Wouldn't it be funny if when they rebuilt the yellow cub engine if they had to sleeve it and it simply just has less displacement and less HP. So many possible reasons for it being so much weaker, the overheating is what I can't figure out..

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Glen
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Re: Red cub vs yellow cub round 2

Postby Glen » Sun Jul 11, 2021 10:50 pm

Hi,
If you meant you found an air leak at the intake manifold gasket, the gasket surfaces need cleaning, and the gaskets need replacing.
You could use a straight edge on the manifold surface while it is off, if it is warped it needs flattening at an engine shop.
TM Tractor has new manifold gaskets.

There's no difference, the 1955 and 1974 distributors advance the same amount, as far as I know.

You didn't say what the compression readings are.
Open the throttle fully when doing a compression test, so the engine can get air.

Good you are getting a timing light. The timing is important, and needs setting right.
Below is a page from the Cub service manual showing the timing marks a 1974 Cub should have.
Align mark number 1 in the pic with the pointer when the engine is running at slow idle speed , which should be 500 RPM.
Use only the pic and the words under it, they are talking about other things on the page.

http://www.farmallcub.info/manuals/gss- ... 001-43.jpg

The timing should advance about to mark number 2 as you speed the engine up to full speed, which should be 2000 RPM for a 1974 Cub. You can look at it with the timing light and see if it advances as you speed up the engine.

Below are pages from the 1965 Cub operator's manual, showing how to adjust the valves.
The valve cover can be hard to remove, you may need to remove the air cleaner intake pipe at the carburetor, and the governor rod, ahead of the carb, so the cover will come out.
Be sure the valve lifters are fully down when checking the clearance.
The valves can't all be closed at the same time, you need to turn the engine some to check them all.
The hand crank is handy for that.
You need a feeler gauge to check the clearance.
The valve cover has a gasket, it may need replacing if you disturb it.
TM Tractor has a new valve cover gasket.

http://farmallcub.com/rudi_cub/www.clea ... age-41.jpg

http://farmallcub.com/rudi_cub/www.clea ... age-42.jpg

The spark plug cables and spark plugs need to be good for it to run good.
If the cables look bad they might not work well when the engine is under load.
If the spark plugs are dirty, they might not work well under load. :)

Shadow_storm56
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Re: Red cub vs yellow cub round 2

Postby Shadow_storm56 » Sun Jul 11, 2021 11:19 pm

I meant the only place rpm changed was right in the intake whare it's supposed to pull air. Plugs are all new but the plug cables are very much not... I thought I did say the compression but maybe not, yellow cub is 105 and red is about 100 but has a weak starter so far less engine speed for the reading.

Shadow_storm56
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Re: Red cub vs yellow cub round 2

Postby Shadow_storm56 » Sun Jul 11, 2021 11:26 pm

Thanks for all the information btw :) I didn't think spark plug cables would act any differently under load but if they do that could be an issue.... I guess more fuel means more fuel to ignite and more current needed?

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Re: Red cub vs yellow cub round 2

Postby Rick Spivey » Mon Jul 12, 2021 6:10 am

Shadow_storm56 wrote:Thanks for all the information btw :) I didn't think spark plug cables would act any differently under load but if they do that could be an issue.... I guess more fuel means more fuel to ignite and more current needed?

In short, yes. A weak spark may idle just fine, but will show up under a load. Change the wires and adjust the valves. Cub engines are almost never sleeved, but when they do, they bore out the block and install sleeves that meet original specs. You don't lose cubic inches over factory spec.
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Re: Red cub vs yellow cub round 2

Postby Gary Dotson » Mon Jul 12, 2021 7:07 am

Under load, cylinder pressure climbs dramatically. A good spark in open atmosphere can turn to poor spark under the pressure of cylinder compression and if you have a bad plug wire, can become no spark. Under load is precisely when faulty plug wire usually cause performance problems. I’m not saying that’s your problem, just saying you should replace them, if they’re in poor condition.

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Re: Red cub vs yellow cub round 2

Postby Bob McCarty » Mon Jul 12, 2021 8:52 am

Make sure you replace the plug wires with solid copper core wires, not carbon core wires like newer cars use. TM has the solid core.
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Shadow_storm56
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Re: Red cub vs yellow cub round 2

Postby Shadow_storm56 » Tue Jul 13, 2021 7:56 pm

I'm thinking I'll order the tune up kit I ordered for the red one a while ago. It sure helped it alot, new coil, plug wires, rotor, distributor cap and it does come with points, plugs, condenser....ect but thoes are still good on this one.


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