Farmall Cub Surging- Solved!

RunningRed said:
I do as well. I am going to try setting the throttle wide open and adjust it again. I have seen in the manuals they recommended both ways, having the throttle set to half or having the throttle set wide open. I tried half last time, this time I'm going to try wide open.
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also look for long cotter pins in the linkage. I have had cotter pins hang up and limit travel. I started using small hairpin cotter pins in that area. Did you have the hood off? If so the throttle linkage to the governor can go either way, but one way it binds.
 
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Well I double checked everything. Took the main jet out and cleaned it. I readjusted the governor linkage with the lever at full throttle and it didn't change nothing. I checked the timing as well and it's close on high and low idle. Still idles on low ok but soon as you make a adjustment to the throttle it surges and hunts. I said I can force it to run well if I adjust the yoke on the linkage almost to the end of its travel then put it in the governor linkage. It runs fine then but that's not the way it's supposed to be. I can make it quit surging as well if I grab the linkage to stop the surging the let go real easy it will quit but soon as I move the throttle again it picks back up surging.
 
I would take a look at the main jet size since you said it sooted the plugs both before and after the work was done. Stan
 

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staninlowerAL said:
I would take a look at the main jet size since you said it sooted the plugs both before and after the work was done. Stan
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1000002338.jpgwell Stan, I should have said it wasn't an original IH carb but and after market one I got last year and it's what I have been running. I still have the original carb so I pulled the main jet out of both to compare which I have never done. The jet on the right is from the after market carb and the jet on the left is from the IH carb. I am missing a few of my small pin gauges but my .078 gauge fits into the aftermarket carb. The IH carb is very small, I have a .036 pin gauge and it is to big.
 
Check the aftermarket jet to make sure it doesn't have a smaller orifice inside the large hole. I've never seen one that was .078, usually .040 or smaller... Also, did you open the Chinese carb to make sure the float height and drop were set correctly and it had the hole from the curved groove drilled into the air outlet.
 
Bob McCarty said:
Check the aftermarket jet to make sure it doesn't have a smaller orifice inside the large hole. I've never seen one that was .078, usually .040 or smaller... Also, did you open the Chinese carb to make sure the float height and drop were set correctly and it had the hole from the curved groove drilled into the air outlet.
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Yea you were right, the Chinese jet taper down to .039. I didn't have the carb apart but that was a year or more ago. I put the IH jet in and that stopped it surging continuously but it still surges a few times before it levels out.
 
So are you saying that you're running the smaller IH jet now and it seems to help the surging? If so, it will be interesting to see if the plugs also continue to soot up after use. The list that I attached previously is from a pdf file IH .75 carb orifice sizes located at the Resources tab at the top of this page. Stan
 
staninlowerAL said:
So are you saying that you're running the smaller IH jet now and it seems to help the surging? If so, it will be interesting to see if the plugs also continue to soot up after use. The list that I attached previously is from a pdf file IH .75 carb orifice sizes located at the Resources tab at the top of this page. Stan
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Yea it helped with the surging, I was in the middle of setting to low idle rpm when my tacometer quit working. Once I get everything set I'll clean the plugs and see if it helps with the soot.
 
Is it possible to take off the governor linkage that has the holes for the springs without taking the tractor back apart? Mine isn't terribly worn but it does have a bit of an oval shape. I'd like to take it off if possible and fix it. The governor rock shaft doesn't have lot of play but it might help eliminate another variable with the surging. It only surges 2-3 times before it levels out after swapping the original IH jet back into the carb.
 
RunningRed said:
Is it possible to take off the governor linkage that has the holes for the springs without taking the tractor back apart? Mine isn't terribly worn but it does have a bit of an oval shape. I'd like to take it off if possible and fix it. The governor rock shaft doesn't have lot of play but it might help eliminate another variable with the surging. It only surges 2-3 times before it levels out after swapping the original IH jet back into the carb.
AgriculturalEquipment
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I do not see how that is possible, without some disassembly. There is a small pin that secures the rockshaft, coming out of the governor, to the collar with the hole for the spring. Enlarge the first photo to see the pin hole. Getting the pin out is the hard part. And you cannot pull the rockshaft out of the governor, because it is connected to the tension fork with set screws. Also, removing the spring throttle lever, which has the other hole for the governor spring will be equally tough.
 

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Bill V in Md said:
I do not see how that is possible, without some disassembly. There is a small pin that secures the rockshaft, coming out of the governor, to the collar with the hole for the spring. Enlarge the first photo to see the pin hole. Getting the pin out is the hard part. And you cannot pull the rockshaft out of the governor, because it is connected to the tension fork with set screws. Also, removing the spring throttle lever, which has the other hole for the governor spring will be equally tough.
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So all I need to do is get that pin out and it will slide off the shaft.
 
I second what Bill V said. If the goal is only to eliminate the surging, I doubt it will make much difference. Since you have already addressed (and I assume corrected) the usual tune-up items, vacuum leaks, and carburetor shortcomings, there are not a lot of things left to check. The remaining rockshaft play (anywhere from the governor to the carburetor) should be reduced as much as you can. The only remaining item is to check the condition of the bumper spring and turn it in until the surging goes away. Don't turn it in any more than absolutely needed.
 
Jim Becker said:
I second what Bill V said. If the goal is only to eliminate the surging, I doubt it will make much difference. Since you have already addressed (and I assume corrected) the usual tune-up items, vacuum leaks, and carburetor shortcomings, there are not a lot of things left to check. The remaining rockshaft play (anywhere from the governor to the carburetor) should be reduced as much as you can. The only remaining item is to check the condition of the bumper spring and turn it in until the surging goes away. Don't turn it in any more than absolutely needed.
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Yea I was just going to try and fix the spring hole but it's not terribly oblong anyway. Only thing I have left to do set timing and rpm, which my timing light and rpm tool should be here today. I went through all the distributor again, cleaned everything and checked the static timing while I was there. I was just leaving the bumper spring till last
 
Well I got the rpm and timing light today and tried it out. I got the low idle to between 475-500ish. Here in the interesting thing when I move it to hight idle I'm getting 1650rpm and 13° BTDC. I let everything warm up real good before taking any readings.
 
Well I went ahead and raised the high idle to 1830rpm. I have to push a little to get the throttle leaver the last hair to get it into a notch. The low idle was set to 475ish rpm as well and the timing on low is 0° and at 1830rpm it's dead on 16°. I doubled checked to make sure the linkage was against the governor stop as well. It only surges a little but I will take the bumper spring out tomorrow and make sure it good and adjust that. Kind of nervous to adjust the bumper spring though, I don't know anything about them. Now it actually sounds like it's on hight idle, it almost sounds like it's too high a rpm but I checked the rpm I was at snow plowing last year and it was only about 1500-1600rpm. The notch below high idle which I used occasionally was only 1400rpm.
 
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