312-8 won't idle very well

[Catch 0]

Having trouble with my 312-8 idle. Well I don't wonder, the thing is 25 years old or better. I have rebuilt the carb a number of times, but anyway: I had to clean the gas tank recently, replace the bushing and install a new fuel line. The tractor runs ok and starts well and operates ok at high speed. I can't however seem to adjust the idle speed with the air bleed screw. It really has been a good tractor, but the idle is so rough I am considering paying the highway robbery they want for a new carb. Does anyone have any ideas about how to fix this? The throttle shaft may be worn enough to where it is sucking air. There seems to be a minute amount of play in the shaft. Has anyone used the kit that supposedly fixes this problem? Is it difficult to install? Thanks for the help and ideas..............Catch :omg:

[Docwheelhorse 2,563]

HI--I would turn the throttle stop screw in(1/2--1 turn) to SLIGHTLY open the throttle butterfly. Then adjust the air/fuel ratio until it is running smooth... then you can begin to back the throttle stop screw off until you get the desired idle speed. It could also be the case that your throuttle stop screw is several turns out of adjustment and you will have to open it more to begin with. If that is the case I would SLOWLY back out of the throttle until you get to the point that the engine will no longer idle well and bring the throtlle stop up to that point and begin making the adjustments I spoke of above.

Good Luck

Tony

[Kelly 1,028]

As a bandaid to see if it fixes it, I've pulled the throttle shaft out and put a small O ring on the shaft so it sets on top of the carb body, it will help seal the vacum leak, if it does you know you need a bushing kit and shaft, or a good used or new carb, again this is not a fix just a bandaid to get you by.

[rickv1957 70]

Make sure that the small holes at bottem end of main jet needle are clean as they are a big part of engine idol,Rick

[72morph 1]

I got beat up with an idle problem that turned out to be the float was set too low.Had no change while adjusting the idle screw all the way to 5 turns out .Set the float higher then factory adjustment was almost dead on plus or minus 1/2 turn.The high speed was factory too.

[Catch 0]

Update: Got the idle problem fixed. It idles nicely now after reading a great article about these carbs. Here is the site in case some of you have not read it.

http://gardentractorpullingtips.com/carbfuel.htm#primer

I pulled the welch plug, cleaned the openings, and replaced the plug with a tapped hole and a i/8 pipe plug. Put three o rings on the throttle shaft to prevent air leaking into the carb. Made sure that the main jet was clean. AND IT WORKED!

Thanks for all your help. I thought the recommendation about the float was especially a good idea. Catch :omg:

[Roger from southern Iowa 1]

Glad it's idling smooth for you. :omg:

[horsefeathers 15]

Catch, Sounds like you have a nack for gettin' the job done! And those new fangled contraptions (computers) help too! Bet your Swiss watch works like a (well) Swiss watch! Tinkerin' ain't just tinkerin' if yer thinkerin' too! (Thinkerin' is that a word?) I think too much! HORSEFEATHERS!