b&s surging at idle

so i have a 16.5hp opposed twin with the nikki carb and it surges at an idle but runs better at full throttle i have cleaned the carb i know 3 times and i just took it off four the fourth time i have checked all the jets and they are clean and it doesnt have an adjustment screw . taryl fixes all said in one of his videos to drill out the jet one size bigger but which one and where is it located in the carb

Dont all carbs have adjustments?

Pics of carb?

all it has is a idle adjustment to make it idle low or high they took out all the adjustments for emmissions so now all you can do is redrill the jets but i dont know which one

I would assume the main.

I would be careful about drilling jets out. There are special numbered drill bits in very close sizes for that type of thing. Not just like the normal drill bits from your regular box o bits. You may have to knock a plug out to get to an idle jet, maybe in the side? Or like fackler says the main jet threaded in the bottom. Not sure why it would surge though after you cleaned it out. Unless something is missing like a small plug or you missed a tiny hole somewhere that is blocked off.

probably easier to just buy the better 3 screw carb that is adjustable

i knocked the welch plug out and there was no trash in it i have cleaned both jets i know what bits to use they come in one of those finger drills and if their is not one in there i have people that can get them for me because i have hogged out a kohler k series carb to like a 1.125

i mean it runs alright at full throttle but it just bothered me that at a idle it would act like it was gonna die then it come back to life i mean its fine i cut grass with it for a full year

I have the same carb, and when it starts to surge under half throttle it is almost ALWAYS the idle jet.  I attached a pictured from another site, it is the one circled in green.



taken from: http://outdoorpowerinfo.com/repairs/briggs_opposed_twin_carb2.asp

Unscrew it and check the bottom tip that it is fully open.  I would not jet this carb, I know Taryl talks about it on other carbs, but he also says this carb is junk and get an old 3 screw fuel pump version to replace it.  :-)  That is my plan when they come back down in price.

I know the other guys are probably right, but I've had this problem with a 8hp single and it turned out to be the governor was in the wrong position (on the little rod that comes out of the crankcase). It ran fine at full throttle but at idle it would surge up and down and it was really annoying. I cleaned the carb lots of times but it turned out to be the governor. Might be helpful to check that.

didnt even know we could adjust that screw! I was always told to let it be and not touch it. Buuuuuut i might now lol after i get my carb rebuilt kit for my 4 screw opposed junker

I have put it in my ultra sonic cleaner with simple green and it looks like new I I'm going to try it tomorrow if that doesn't fix it I will check the governor if that is ok I'm going to try find a three screw carb if not I might be the only one that has a mikuni carb on my grass cutter

Maybe try narrowing it down by taking the governor linkage off the carb.

One other thing but you should see it, on my Sasquatch project, my intake manifold was cracked in half causing surging.

The vat fixed it it runs like a CUMMINS now thanks for the help

Good deal, goop somewhere in there you got cleaned out!