B Farmall Zenith Carb

Hi all I have a B with a Zenith carb carb has the adjustable main jet, I can not get it to idle below about 1000 r's top end is at what the book says it should be 1500 no load, also with no load the gov / engine surges and finally settle down at 1000 rpm's. In gear it revs up fine to about 1500 and will idle down to about 8/900. I have adjusted the gov to carb rod per the manual, tried to adjust the surge spring on the bottom of the gov to no avail, have adjusted the idle and main jet nothing. Is it normal the when the main jet is turned co,pletely in that the engine runs just the same? Under load it will not make power but just setting idleing at 1000 r's it makes no difference.

The idle is set with the screw on butterfly rod
behind the carb. It is hard to get to.
If you have already done this something must be
binding. Butterfly, rod ?

Two things mite need to clean the carb and how much slop does the input shaft of the gov have that can make for some awful speed control. I rebush them and if the rest is adjusted and a clean carb they run and idle just like new. Adjusting the t-handle on the main jet should make a big difference in engine operation.

Yes I know about the fun of getting at the idle stop screw, it is off the stop.
The carb is clean, really no slop in the input shaft, as I posted earlier I've adjusted the idle screw the idle stop screw is not on the stop peg, I've adjusted the linkage per the manual, have tried adjusting the surge screw on the bottom of the gov but that makes no difference. And as I say screwing the "T" jet screw all the way in does not have any effect on engine revs, It does make a difference when power is required thus I turned the jet out about 2.25 turns and the engine runs good has good power. On other carbs when the main jet is run all the way in they generally sputter and stop not this one.

I have an A that sounds like it has the same zenith carb and have a similar problem. The only way it will run is with the main (t handle) needle screwed all the way in. If I back it out, it bogs down and dies. If you turn the surge spring screw in too much, it will keep it from idling down. If the stop screw is backed out, that might be the problem. I think that spring gets worn out and when you turn it in enough to work, there"s not much give left it in. I"m planning on replacing that and the governor spring in mine. If you disconnect the arm to the carb and the throttle lever arm, you might find there"s more slop than you think as well... that is the case with mine. Mine had a very similar problem to yours and I"ve worked it out a lot. Another thing that might be a problem, even though you say you set it is the shaft from the gov arm to the carb. I fiddled with mine and ended up with the engine running around the right high idle speed, but wouldn"t idle down very much at all... I ended up readjusting it to specs again. One odd thing with mine is that you can"t really turn the yoke on the shaft towards the carb enough to make the pin slide in like the manuals says it should... it runs out of threads. Makes me wonder if the governor arm could be not indexed correctly on the governor shaft? My governor shaft arm was also twisted slightly that may have put it in a bind a little. I very carefully bent it back. Hopefully we"ll both figure it out. Mine is running much better and has good power. Before, it would run good and then kind of stumble under any load at high rpm. At low rpm, it was ok... good luck

Hi jamieei, I worked on it yesterday got it somewhat better, I'm thinking some of my problem is that the throttle lever on the carb has slipped in the past someone tried to braze it and not knowing the exact location / setting makes it hard to rig right. The engine runs good under a load the top rpm's are right it's just does want to idle below 900/1000 unloaded, also when unloaded there is no rpm increase as the throttle lever is advanced untill the last 1/2 inch of travel.
Yes I read about adjusting the surge spring only about 1/2 turn at a time and that too much will cause high idle, I'm thinking like you that the spring maybe weak as any adjustments I've made has had no effect on surge or idle. I'm going to see if I can barrow a carb off my brothers tractor and see if it will run better. Please keep me posted as to what your finding and I'll do the same, thanks

Hi jamieei, I got my carb and engine running good, repaired the loose throttle shaft lever and set the carb up per the manual, while its not perfect it works good, no more surging, good power engine starts right up and now idles.