Cub Surges after Warming Up

Thu Sep 16, 2004 9:50 pm

Hello All,

I'm working on a Cub for an old farmer lady and after it has been run for about 10 minutes the engine almost stalls out and then surges, loses power, surges again and keeps goign in this pattern. I would assume it isn't the carb because it only does this after it has been run for a while. This tractor did sit almost a year without being ran. I did change the oil & gas. Can someone point me in the direction to look. I do see a small ammount of something that looks like white smoke coming out of the oil filler cap, so the engine may have problems.

Fri Sep 17, 2004 5:51 am

Before you rule the carb out entirely, you might want to check the float level and clean the main jet. Also, check the inlet strainer for dirt as well.

Fri Sep 17, 2004 10:39 am

Are you runnng it at idle or full throttle for those 10 minutes?? If the time changes to longer at idle and or if you let alone 5 or 10 minutes and it takes a while to surge again it pretty much has to be fuel starving because of dirt some where, In a filter, or the carb, it could be a sticky float, stickey float needle, a bent bowl or any such that will prevent enough fuel from reaching the engine. Emptying the tank or refilling an already empty tank will stir up all the dusty gunk on the bottom. Some of it it so fine that you will not see it but it still does the dirty deed. As you can see from many other recent postings fuel starvation caaused by sediment is a common thing in old tractors. Can you get it to run some what better with the choke? What happens if you remove the gov to carb linkage and you operate the carb by hand?

Fri Sep 17, 2004 11:06 am

Can you clean the main jet without having to remove the carb?


Fri Sep 17, 2004 12:55 pm

Yes, remove the large nut on the side of the carb body.

Fri Sep 17, 2004 1:39 pm

The same thing happens to my '49 and an old timer said that the points are getting hot and closing up and not giving strong enough spark etc. I havn't worked on it yet due to lack of time but might be somthing to consider

Fri Sep 17, 2004 3:01 pm

Gord Trail and I finally got his surging problem figured out. Couple of problems and they are all the usual ones :!: Go Figure eh :!: :idea: :?:

Anyways, start first with the fuel system. Check that your fuel strainer assembly is clean and there is no dirt in the screen. As was mentioned, check the main metering jet and ensure both the large orifice on the side is not plugged nor the small orifice on the end. (this one was plugged slightly on Gord's). It does not take much dirt to clog it. Then, check the inlet screen and look for teflon tape particles. (another problem on Gord's carb). Most of the white teflon tape IS NOT meant for gasoline applications.

If this is clean, then make sure that the side of your fuel chamber is not bowed in. If it is, then most likely the float is rubbing against the side and possibly causing fuel starvation. If this is the case, then crack the carb and while you are in there check the float for holes and all the passageways for dirt and stuff.

Also, check your rpm's and ensure that at slow idle it is around 400 to 600 rpm depending on where your Cub likes it. Ellie likes it at around 475 to 500, Gord's Cub likes it more in the range of 600 - 650.

If that doesn't solve it, then probably the main culprit is in the governor. There are two places to adjust the governor. One is the bumper spring tension and the other is the spring that controls the weights inside the governor. They may need to be adjusted.

NOTE: To be safe, make all adjustments to the governor with the engine stopped. YOU DO NOT WANT YOUR HANDS TO GET SMACKED WITH THE FAN :!: :roll: :oops: :x :x :x :roll: Don't ask :!: :!: