Issues after carb rebuild

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BucketHead
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Issues after carb rebuild

Postby BucketHead » Mon Sep 20, 2021 4:23 pm

So, the '64 Cub had issues with the carb when I first brought it home. Basically it had either full throttle or idle and nothing much in between. I had a similar issue with the '49 Cub a while back that was corrected with a carb rebuild. So I rebuilt the carb on the "new" Cub... Replaced everything... Adjusted the float height (it was a bit high).. Opened the air screw 11/2 turns and it fired right up and idled beautifully.

When I advance the throttle, the lever moves about a quarter of the way before the RPMs start increasing and continues to increase until the the halfway point on the throttle quadrant. Then any movement past that point causes the engine to stall.

When it stalls, I noticed that the linkage from governor to the carburetor just sorta "slams" full open. So, it seems to me that rate of engine rpm increase doesn't match the throttle movement. It seems that all of the rpm increase happens between a quarter throttle and half throttle.

So, do I have a carburetor problem, a governor problem, or some other problem?

The carb is original to the tractor (based on the date stamp), it does not appear that it was ever touched before I opened it up. It was disassembled, soaked in mineral spirits, blown out with carb cleaner, and then tossed in the ultrasonic cleaner for 20 minutes before I reassembled it. The tractor sat for 16 years before I bought it.

Looking forward to your advice..
Karl

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Re: Issues after carb rebuild

Postby Bob McCarty » Mon Sep 20, 2021 4:37 pm

After reinstalling the carb, did you adjust the carb to governor linkage? Does the governor have the long or short arm on it?
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Glen
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Re: Issues after carb rebuild

Postby Glen » Mon Sep 20, 2021 7:00 pm

Hi,
It sounds like the engine, or carburetor is starving for gas. The governor will open the throttle trying to keep the engine running at the speed selected, if it is above slow idle.
It will open the carb butterfly valve fully, as the speed goes down, if the engine doesn't speed up.

Be sure the gas valve under the gas tank is fully open.

The main jet may be plugged, I showed how to clean it in my post at your other post.

If you meant you replaced everything, even the main jet, or other internal parts, I would put the original main jet in and try it.
They have said on here that some of the kits come with the wrong size jet for some carbs.

You could do a gas flow test, hold a clean can under the carb, remove the drain plug, and let the gas run out for 1 minute.
At first the gas in the carb will come out. After that, it should be a good size flow, not stop and go.
If you use a clean can, you can put the gas in the gas tank when done.

The gas strainer, under the gas tank may need cleaning, it is supposed to have a screen in it, above the bowl gasket.
Below is a page from the 1965 Cub operator's manual, showing the gas strainer.

http://farmallcub.com/rudi_cub/www.clea ... age-10.jpg

Before working on the gas strainer, move the Touch Control arms to the rear, or down position. It is easier to get to the strainer.
If the gasket is old, it may not seal again if you try to reuse it.

TM Tractor, at the bottom of the page, has a new gasket, and screen. :)

BucketHead
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Re: Issues after carb rebuild

Postby BucketHead » Mon Sep 20, 2021 8:37 pm

Thank you for the quick replies!

I have not adjusted the carb to governor linkage after the rebuild. I do not know which arm the governor has on it, I'll check it tomorrow.

I did replace "everything" in the carb, I'll try swapping out the main jet if the fuel flow test doesn't show anything. I'm now a little suspicious about the fuel flow... When I first got it started (after its 16 year nap) I had no flow through the fuel line and needed to blow it back to get any flow. I'm going to give each component of the fuel supply system some close scrutiny and make sure it's all in order.
Karl

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Don McCombs
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Re: Issues after carb rebuild

Postby Don McCombs » Mon Sep 20, 2021 9:16 pm

BucketHead wrote:I had no flow through the fuel line and needed to blow it back to get any flow.

This indicates to me that you may have debris in the tank, partially blocking the fuel leaving the tank. Take off the fuel cap and, with a flashlight, inspect the opening that goes into the sediment bowl.
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Re: Issues after carb rebuild

Postby Cubfriend » Mon Sep 20, 2021 9:29 pm

Also check the fuel inlet screen in the carburetor for additional debris.
Frank

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Glen
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Re: Issues after carb rebuild

Postby Glen » Tue Sep 21, 2021 1:25 am

Hi,
The throttle linkages need oiling at the pivot points occasionally.
There is a place on the governor where the linkage commonly gets tight.
Below is a pic from TM Tractor showing where it is.
Apply oil where the cotter key is in the pic. Work oil into it, the pivot is about 1" wide.
The shaft should be solid on the governor, and the arm turns on it.

You can get to it from the left side of the Cub, by the fan. The engine has to be shut off.
You probably need to use a light to see it.
The other side of the arm pivot can be seen from the right side of the Cub, you can oil it there also. :)
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Cub gov 4.jpg

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Re: Issues after carb rebuild

Postby Gary Dotson » Tue Sep 21, 2021 7:21 am

While I agree that this sounds like a fuel starvation issue, either within the carb. or flow to the carb, don’t overlook the ignition system. An issue with the points could cause such a problem.

BucketHead
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Re: Issues after carb rebuild

Postby BucketHead » Wed Sep 22, 2021 12:20 pm

Gary,

I'm glad you mentioned that! The ignition system was also on my radar. I had popped the distributor cap off and a quick peek didn't reveal anything grossly out of whack but I didn't look at the fly weights or check the advance. I'm going to order new ignition parts to install as well as give it a thorough cleaning and lube... Just to cover all the bases.
Karl

BucketHead
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Re: Issues after carb rebuild

Postby BucketHead » Wed Sep 22, 2021 4:58 pm

I just went and tinkered with the carb some more while being eaten by every mosquito in western Mass. I started by turning on the fuel and pulling the drain plug from the bottom of the bowl. The fuel stream seemed pretty steady and I got a couple of small globs of water. I also checked the inside of the fuel tank and was impressed with how clean it was. I then lubed all the pivot points on the governor linkage. The throttle seemed a little smoother afterwards but no big changes. I did notice that full travel of the throttle handle is only a little bit more than halfway on the throttle quadrant. I then reinstalled the drain plug and fired it up. It idles amazingly well. Then anytime I moved the throttle it would stall. I could position the handle anywhere in its travel then hit the starter, and it would fire up and run... Then immediately die if I moved the throttle. Next I started it and added some choke (about halfway or a little more) and the engine smoothed out. With the added choke, I was able to move the throttle and the engine rpm would respond immediately without dying.

So apparently I have a lean mixture issue. Either I have a heck of an air leak or I'm just not getting enough fuel. I guess my first step is to spray some carb cleaner around the gasket connections to see if I have an air leak. If that reveals nothing then I'll disassemble the fuel shutoff and sediment bowel and clean them thoroughly. I'll also be sure the fuel line is clear. If that doesn't fix anything then I will swap the old jets back into the carb to see if that's it.

Is there anything else I have missed?
Karl

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indy61
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Re: Issues after carb rebuild

Postby indy61 » Wed Sep 22, 2021 5:22 pm

It sure sounds like a fuel restriction. The IH carb main jet is likely, no need to disassemble, it's located on the side.
Double check the fuel tank outlet and screen at carb inlet.

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Re: Issues after carb rebuild

Postby Glen » Wed Sep 22, 2021 5:25 pm

Hi,
I sent you a PM, you get to the PM at the top of the page.

It is easy to put the original main jet in and try running the engine.
The pic of it is shown above. :)

BucketHead
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Re: Issues after carb rebuild

Postby BucketHead » Sun Sep 26, 2021 2:27 pm

After some more troubleshooting I've learned the following...

I couldn't find any air leaks by spraying carb cleaner near any places that could be leaking air.

I swapped the old main jet back into it and I believe it actually ran worse than with the new one.

I checked the timing and it's retarded a couple of degrees but nothing major, I'll dial it in when I have someone to help me.

I started to adjust the governor but decided to wait until it's running better.

I'm pretty frustrated by this. I know that I need air, fuel, and spark for this to operate. Clearly I have all 3... It's just the amounts I need to figure out to get the engine performance dialed in. I hate troubleshooting in the gray area.
Karl

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Re: Issues after carb rebuild

Postby Jim Becker » Sun Sep 26, 2021 3:33 pm

BucketHead wrote:. . .
I checked the timing and it's retarded a couple of degrees but nothing major, I'll dial it in when I have someone to help me.

I started to adjust the governor but decided to wait until it's running better.
. . .
I hate troubleshooting in the gray area.

Start by fixing the things you know need fixing. Don't try to troubleshoot your way around the gray area of known problems.

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Re: Issues after carb rebuild

Postby Waif » Wed Sep 29, 2021 11:03 am

There is a process after a carb removal and reinstalling it regarding adjusting the linkage , and air screw.

Where throttle performs on quadrant bothers me less than range achieved.
Follow carb install adjustments.
Running throttle lever up and down during one adjustment has a reason.


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