1968 Cub Fuel Issue

[DKO]

Hello gentleman,

I inherited my grandfathers 68 cub and resurrected the machine with new radiator, plugs, head gasket, some wiring, and fluids. She can idle for extended periods of time high and low with no smoke. No water in oil and I'm using low ash rotella 15 40w. The past 2 weeks I've let it idle every day to heat it up and cool it down, so gaskets can seat. For the first time, after 2 weeks I drove it around my neighborhood in all gears. After warming up when driving, it acts like it wants to shut down on me, jerking back and forth, like I'm repeatedly popping the clutch. Drove it back to garage first gear low idle. So, I adjusted the set screw on back side of carb until it idles smooth to double check. Everything from the tank to the carb is clean. Put the palm of my hand over air intake, it sucks air good, to the point where I will almost kill it. As the cub is acting this way as I drove it, I leaned over and noticed the lever on the back side of the carb going to the governor was jarring back and forth as it was hesitating and wanting to stall. I will tear off the carb to rebuild or buy a new one, that's fine. Carb actually looks really good with no leaks. Took cap off to check points also, good there, clean. But I realize that doesn't mean anything in itself. But before I get hasty and pull it off, would any of you guys have any input on this machines condition? Any wisdom would be appreciated, thank you.

[Dale Finch]

Don't be too quick to replace things, yet! Your problem may just be a matter of making sure ALL the linkage, from the throttle quadrant to the carb via the governor, is free and correct. You may only need to lubricate things and make adjustments to the carb-to-governor rod.

Others will probably jump in with more specific recommendations. WELCOME to the forum!

[Glen]

Hi,
I had a defective condenser cause that, it was like you were turning the ignition switch on and off while driving it.
If the Cub has been sitting, the points probably need filing and cleaning, or replacing.
I take them out and file them with a large flat file. If they are burned much, it's better to replace them.
You don't have to take the Battery Ignition Unit off the Cub to replace the points, if that's what you meant. It takes a really short screwdriver, and probably an 11/32 inch open end wrench.
The timing should be checked with a timing light too.
Here is a page from an IH manual showing how to work on the points.

http://farmallcub.com/rudi_cub/www.clea ... age-12.jpg

[Gary Dotson]

The first thing I would do is to look over the wiring to check for a loose connection or a bare spot shorting to ground. The insulator, where the wire from the coil connects to the distributor is sometimes a problem. The motion you're seeing at the throttle linkage is merely the governor doing what it does best, responding to the problem. As engine speed drops, it opens the carb butterfly and vice versa. I too have had condensers act like this. It doesn't sound like a fuel issue to me.

[DKO]

Thank you guys very much for the help!! I don't know what the condenser is or what it does. I will look that up. I took the carb off today and disassembled it and ordered a rebuild kit. Wouldn't hurt anyway.
Weeks ago when I had the hood off, I noticed the linkage from the throttle control was stiff. Followed it to the governor unit, I sprayed cleaner on it, then spray lube. It loosened it up good. I will do my homework on the condenser. Thanks again.

[Glen]

Hi,
The condenser is shown in the link I posted above, it's on the left in the Battery Ignition Unit.

Since you have the carburetor apart, I would blow out all the passages with air. Wear your safety glasses when using the air. Be sure to check the float height, and float drop.

Here is a listing from TM Tractor for new points and condenser, you can look at.

http://www.tmtractor.com/new/el/367fp.htm

[John *.?-!.* cub owner]

Hi,
I had a defective condenser cause that, it was like you were turning the ignition switch on and off while driving it.
If the Cub has been sitting, the points probably need filing and cleaning, or replacing.
I take them out and file them with a large flat file. If they are burned much, it's better to replace them.
You don't have to take the Battery Ignition Unit off the Cub to replace the points, if that's what you meant. It takes a really short screwdriver, and probably an 11/32 inch open end wrench.
The timing should be checked with a timing light too.
Here is a page from an IH manual showing how to work on the points.

http://farmallcub.com/rudi_cub/www.clea ... age-12.jpg

I have had a bad ignition coil cause that problem also. If the ignition or fuel is stopping momentarily the governor action you described would be normal.

[DKO]

Thank you for the link Glen!! I see what your talking about. Makes sense now. Going to IH dealer today for points and condenser.. maybe a coil while I'm there. I'm going to try all this with the hood on and hopefully I can leave the distributer in place while I replace the parts.
Big help guys, thanks again.

[Eugene]

Going to IH dealer today for points and condenser.. maybe a coil.

Available at your nearest auto parts store.

[Matt Kirsch]

The governor moving the throttle rod back and forth is the normal reaction to a running issue, not the cause. It is trying to maintain a constant speed on the engine.

When the engine starts to slow down the governor opens up the throttle plate to speed it up. When the engine speeds up past the desired setting, the governor closes the throttle plate to slow it back down. This gets exaggerated when the engine has trouble running smoothly.

[DKO]

Hello again.
Finally got around to replacing the condenser, points, cap, wires, and threw in a new coil. I sure have spark now! I left distributer in while replacing those parts so not to deal with timing. Set points to .020 on all four lobes. The carb is last step to complete before putting this machine to work. Took carb apart days ago and installed new kit for Zenith 13794E. Carb was in really good shape when I took it apart; probably wasn't necessary to rebuild it. Anyway, I've been jacking around with float setting for three days now, I've had that carb on, off the tractor and apart many times. I should be pretty good at this by the time I'm done.... I have noticed a few things I don't understand though. First, behind the main fuel inlet, where the internal fuel filter is, there is a jet that sits behind the screen. When I went to put that jet back in during reassembly, I noticed It just sets in there, I has threads, but it doesn't thread into a female seat. Not sure if that jet is supposed to be there or not. But that's where it was when I took it apart, so that's where it is currently. Secondly, the new main needle valve is a hair larger than the original valve, not noticeable to the naked eye. I tried to put the new valve in the original jet for reference, it didn't fit. But of course it does fit in the new jet. So, the new jet and needle are in the carb now. The old jet was clean by the way. I mention this, because I guess there could be a possibility that the jet is too big maybe. Anyway, to shorten this up, I did get the tractor to run, but only at low idle. During low idle I was able to set the air fuel mixture so it idles smooth. But is doesn't like to be idled up, it stalls and falls on its face. Its either getting too much fuel or not enough. In the past adjustments I couldn't get the fuel to stop leaking out of the bottom of the carb. Now, after adjusting the floats more, it doesn't leak, but when the motor stalls it will drip out of the bottom some. I'm to the point where I don't know what direction to go with the floats anymore. I'm going to reset the floats to 1 5/32 and leave it, but I think the root cause could be the small tab setting on the axle of the float that dictates how far the needle travels in and out ( rich/lean ), I've had it where the floats touch the bottom of the bowl and the other way where the needle barely drops. Am I on the right track here? Geemany Christmas! What a cantankerous process!!

[Crimson Tim]

First, behind the main fuel inlet, where the internal fuel filter is, there is a jet that sits behind the screen. When I went to put that jet back in during reassembly, I noticed It just sets in there, I has threads, but it doesn't thread into a female seat. Not sure if that jet is supposed to be there or not. But that's where it was when I took it apart, so that's where it is currently.

You've got this mounted again, already, don't you? Pictures of this would be really helpful. Something is not right there. There shouldn't be anything in there that's not tied down, and the float/needle is the only part that should move.

Secondly, the new main needle valve is a hair larger than the original valve, not noticeable to the naked eye. I tried to put the new valve in the original jet for reference, it didn't fit. But of course it does fit in the new jet. So, the new jet and needle are in the carb now. The old jet was clean by the way. I mention this, because I guess there could be a possibility that the jet is too big maybe.

I don't think that is an issue, provided needle and seat are a matched pair, but people more experienced that I will chime in. I don't think the orifice size here is super important. This keeps the bowl full of fuel, but is not responsible for metering the fuel-air mixture. My cub came with two extra carbs, and I noticed that the needles in #1 and #2 were substantially different.

If the length of the needle coming out is different than the length of the needle going in, then the float height will need readjusting is all.

Just out of curiousity, did you go with an all metal needle or the rubber tipped? Seems like a lot of people have more issues with the rubber tipped, but then there are plenty who do not. Still undecided, myself, but leaning toward metal.

Anyway, to shorten this up, I did get the tractor to run, but only at low idle. During low idle I was able to set the air fuel mixture so it idles smooth. But is doesn't like to be idled up, it stalls and falls on its face. Its either getting too much fuel or not enough. In the past adjustments I couldn't get the fuel to stop leaking out of the bottom of the carb. Now, after adjusting the floats more, it doesn't leak, but when the motor stalls it will drip out of the bottom some. I'm to the point where I don't know what direction to go with the floats anymore. I'm going to reset the floats to 1 5/32 and leave it, but I think the root cause could be the small tab setting on the axle of the float that dictates how far the needle travels in and out ( rich/lean ), I've had it where the floats touch the bottom of the bowl and the other way where the needle barely drops. Am I on the right track here? Geemany Christmas! What a cantankerous process!!

Not sure about not being able to increase revs. I had a float rupture last weekend, and it resulted in some of the same symptoms and some of the opposite symptoms. After working hard discing up a field for over an hour, I ran out of gas. Upon refill, gas just poured out of the carb and it would not even try to fire. Once the tank was again empty, it did run fine, up until I started to refill the tank, when it stumbled and died. Yup. I took out the float, and you could hear liquid inside it when shaking it. Mine ran longer at high revs than low, but wouldn't run at all if there more than trace of fuel in the tank.

The float I pulled out was also noticeably heavier than the one I swapped in. New float solved the problem. I went out the next day and finished the job.

As an aside, I tried the hot water trick for detecting leaky floats. I put the suspect float in a bowl of water hot from the tap. No bubbles. I think it's just that there was not enough temperature differential between 95° outside and the straight hot water. So I suggest boiling water on the stove for this test, or sticking the float in the freezer for a while. In this household, however, if my wife pulled a loaf her prized spice bread out of the freezer, and it smelled like gasoline, she would kill me!

Anyway, if the carb leaks when the engine is not running, that means either the needle and seat are not seating (crud, wear) or the float is adjusted wrong. You've got the right dimension for a zenith. I discovered my first float adjustment ruptured the float, and I think this weekend's episode means I weakened the second one as well.
I think two sets of needle nose pliers are necessary to do the job safely, so as not to put ANY force on the body of the float whatsoever.

If your needle and seat are new, they should hopefully be seating ok. It would be worthwhile to check the float for leaks. A leaking float will run too rich, may flood when running and especially starting, and will dribble when the engine is off.

Also, of course, the ever present possibility of crud in the fuel tank and fuel line. It does not take much crud to mess up the needle seat or disrupt the fuel flow, and it does not take much flow disruption to cause big headaches. BTDT numerous times.

[DKO]

Thanks for the response. I did put the float in hot water a few weeks ago. I didnt notice any leaks. Tonight, i bent the tab on the float axle to the point where the needle barely drops (1 or 2mm) when the fuel level drops in the float bowl. I adjusted the tab the other way also, where the floats touch the bottom of the bowl to allow the needle fo drop further. No luck. I did pull that jet out from behind the internal filter. I didnt notice a change. The only change that was good out of fiddling with it tonight, was when i barely craked open the shut off valve from the sediment bowl. It seemed to run better, but still didnt cure the issue. Tonight i put the old needle valve in the new jet and the old needle valve wobbled around quite a bit. Best thing i can do at this point is purchase a new jet and needle to match the old one. I dont know what else to do. At least ive narrowed it down to a fuel issue at this point i think. Thanks for all the input! Much thanks!

[DKO]

I need to figure out how to post pictures here. Its not obvious where the tab is to post pics....

[Glen]

Hi,
Here are pages from the Cub parts manual showing the Zenith carburetor, if you don't have them.
If it won't speed up above slow idle speed, have you tried cleaning the main jet, it is number 20 in the parts pic.
Make sure all passages are open and clean when you have the carb apart.

http://www.farmallcub.info/manuals/cub_ ... 012-14.jpg

http://www.farmallcub.info/manuals/cub_ ... 012-15.jpg