Farmall Cub Forum -- Questions and answers to all of your Cub related issues.
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my '48cub is still fowling plugs after an extensive maintanece upgrade: rebuilt magneto (has great spark now) including the cap and wires, checked out the carb, everything looks nice and clean including the little idle curcuit passages , the neddle and jet look new as the p.o. said he just replaced them. The float is set a t 1.6 in. which gives a gas level of about .7 in. below the gasket which is a little low compared to the book level of 9/16 (.56). and yet it still ran rich had black smoke and ran for about 20 minutes a stumbuling and a missing before it just DIED! With new plugs it starts right up (in fact without the choke on a chilly day.) but then goes into it's fits. You know I kind expected for this old tractor to be a little different then modern eq. but this is getting down right ornary (my kids named it grumps cause it's like the old man hard to get moving in the morning) I have been wondering why the spark plug only has a .023 is it because the ignition is so weak most magneto ignitions I have worked on (outboard motors, lawn mowers, motorcycle, ect.) usally have a gap of .028 to .032 has anyone tried opening the gap up or would a surface gap plug work; the mag seems to put out enough current to fire one.
Or is it the carb? I did a search on this forum and got a couple of hundred post back on carbs and running rich so this is not a new topic here and I'm wondering if anybody has made any break throughs and found somthing that really works?
thanks for any help you can send on this I have a landscaping project on hold and a wife tapping her toe as I promised her it would be done last month.
This has been talked about alot on this forum. I've had a terrible time with it. Some have no trouble at all. I'm glad you posted and I will be wanting to here what fixes it for you. Everyone is going to tell you its rich mixture for sure. I'm not so sure there is some element that hasn't been stumbled upon yet because these old tractors in general seem to me to be sensitive to overfueling (I don't know if thats whats really happening or not). I tried to fix it on my H for months before using an alternative fuel that completely cured it for me. I've got a key question, try this some time. With your engine running loosen the mag and rotate it ( it won't go far) either way and see if the engine responds. If its doesn't or very little then your at the root. I to hava a mag ( and actually tried 3 diff rebuilt ones) till I noticed one day the ignition wasn't was igniting the fuel. Thats why I think I was fouling so bad. It appears your overfueling when in fact ( for some reason) the fuel thats there isn't burning correctly. I know we have 2 diff animals but maybe something is similar here.
Iignition is a pretty simple thing, really! The plug either lights the charge or it doesn't. It's really a chain reaction. If it lights it reliably at the right time, there's NOTHING more it can do... kinda like the fuse on a fire cracker. Nothing you can do to a reliable fuse will make a better or louder bang. If the "bang " isn't what you want, move on to the fuel where it will make a difference.
If your mag is timed correctly, it will be retarded slightly from the setting that produces maximum RPM at a given throttle setting. This is for safety reasons... to prevent injuries when cranking. Advancing it from the correct setting may be laying a trap for the next guy who doesn't know it's advanced. Please don't do it!
The most affectionate creature in the world is a wet dog. Ambrose Bierce
I have been wondering if there is and connection between my cub running rich and the top of the carb being wraped. when I took the carb apart I noticed this and following the threads on wraped carbs I tryed to straighting it with some success but was afraid to go to far and with the gasket on it seemed tight. But---- if it wasn't could air get in and shoot thru the main jet and act like an injector causing the rich mixture.
What are the symtoms of a wraped top besides leaking gas.
-----------Old man + Old machinery = New @#$$%^&! vocabulary
George-I think your missing something that is very critical here. Timing is everything and the volitility of todays fuels is different. Therefore the timing requirement has changed. Last summer I had an Oliver 550 that would not run right after carb rebuild and ignition tune-up. It was suggested I time the tractor by ear to see if that would help. BINGO! It ran smooth just by advancing the timing. The factory timing no longer would work for that tractor and I'm thinkin its the change in fuels.
I'm not sure what happens inside the carburetor bowl when there is an air leak. I guess it depends on location and size and power demand. But I do know the carburetor depends on air pressure differentials in order to operate properly, warped or misfitting components mess up that gradient and your carburetor won't perform properly.
My Cubs all run fine with the timing set to the original specs and burning the cheapest gas I can find, magneto or battery ignition.
If they won't run right that way, something else is wrong.
You may think I'm missing something, but I'm not having trouble with the way my tractors run. I don't experiment with the vital conditions like fuel, compression ratios, and timing and then blame the fuel for my troubles. I do think if you get the manual and read and follow it your troubles will be much less.
BTW, don't try to hand crank that 550... it might bite you!
The most affectionate creature in the world is a wet dog. Ambrose Bierce
Well something is up. I'm having trouble with eguipment fouling plugs that is less than 10yrs old and I've never touched any adjustment on them. My commercial mower fouled out last Dec when I started it up to put it in storage. I'm saying that (at least for me) it seems to be an issue with a variety of things unrelated other than they are all carburated. This has really got me intriged to figure out what is going on. As I mentioned in some earlier posts my neibor was having the same trouble in his quadrunner and so was a guy here at work. I'm not the only one even though I sometimes think so.
I remember when I bought my first car ('55 Ford), I had to repair it when it broke, which was often. And I remember reading that before changing the ignition timing on your car, one should make a note of the original setting so that you could go back to that setting if you got in trouble. I think it stated something about worn parts, etc. making it necassary sometimes to adjust the timing for these changes. I never did that though. And I always got in trouble. You learn more that way. In saying that, I believe the Master (George) is right, in that you should always go back to the original settings of timing, and in your case especially, the original carb float level, air/fuel mixture settings. I have had carb problems many times and I was always helped by systematically going through the posts on this website.I love to speculate on things, but when it comes to my tractors, I rely on the facts! Opinions are like patooties, everybody has one! My $0.02.
Is the air cleaner clean?
Are all of the gaskets in place inside the carburator?
That's the only thing I can think of that hasn't already been suggested.
Yes I agree with all the comments made, just one more, have you got good compression, that's to say is the engine making the most of it's gas and spark to compress the mixture enough to whirl the old pistons around efficiently or is the loly compressed mixture just giving off a pheuf, just turning the piston and chucking the rest of the partly burn't fuel up the pipe?
From avgas posts I have the impression that you have poor quality gas over there, here the sans plomb 95 actually burns!
do you add lead ersatz additive to your unleaded 95?
I was told to do so to protect the valve seats.
what makes my cub very rare is that it's the only one I've ever owned.
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