So the other day my brat started idling super slow on me, like it was going to sleep on me. Sometimes it would idle slowly enough that it would quit. Before this started happening I had adjusted the idle speed so that it idled at a little below 1000 RPMs, but now it was idling around 200-300..

 

It's not overheating, but when it happened the engine was at normal operating temperature.

 

I checked the oil and that is fine. I checked all the wires on the spark plugs and they were snug.

 

I simply adjusted the idle speed screw so that it was back up to around 1000 RPMs, and it runs normally now, but at first (right after I adjusted it) the engine was hiccuping, or lapsing rather. What could be wrong with it?

 

I fear that by simply adjusting the idle speed screw I'm only treating the symptom and not the cause of the problem.

check fuel filter(s)

Vacuum leak might do this.

Hit that carb with a can of carb cleaner. Read them instructions. Can't hurt.

compression test, tappets ...resolved issues before

Worn throttle shaft will do it too.

Thanks for the replies, I will try and troubleshoot it. The weird thing is though, that just last night it started idling really high. I adjusted the idle speed screw down again. Something is changing independent of the idle speed adjustment screw that is changing the idle speed. What could it be?

Might be debris floating around in the idle circuit. Sometimes blocking it partially, sometimes not. I repeat; hit it with some carb cleaner.

I had one old carburated Subaru where the idle mixture screw and spring would wind itself out over time and fall out. It was always just sitting right there so I could screw it back in.

You have a Weber on that bad boy?  I had irregular Idle and found that my Brat was begging for a fuel regulator. They are fairly inexpensive, I think the one I got was like 30 bucks and it made a huge difference in the entire drive experience.  I don't know if anyone else has feedback on this, but seemed to work for me.

Im voting a vacuum leak without seeing it.  Ive had that happen many a time.  Hitachis when running correctly are good carbs.  The problem is most are on their last legs by now.  And they are overly complicated.  If you do end up finding its the carb i strongly recommend ditching it and all associated vacuum tubes for a weber carb.

Thanks for the input. For a while now I've been wanting to switch to a Weber Carb, so that will eventually happen. I'll hit it with some carb cleaner for now and see what happens.

So the other day my brat started idling super slow on me, like it was going to sleep on me. Sometimes it would idle slowly enough that it would quit. Before this started happening I had adjusted the idle speed so that it idled at a little below 1000 RPMs, but now it was idling around 200-300..

 

It's not overheating, but when it happened the engine was at normal operating temperature.

 

I checked the oil and that is fine. I checked all the wires on the spark plugs and they were snug.

 

I simply adjusted the idle speed screw so that it was back up to around 1000 RPMs, and it runs normally now, but at first (right after I adjusted it) the engine was hiccuping, or lapsing rather. What could be wrong with it?

 

I fear that by simply adjusting the idle speed screw I'm only treating the symptom and not the cause of the problem.

 

Sounds very much like the carb is flooding slightly because of a leaky or sticky float valve.

 

Since you have an EA-81 this is fairly simple to check.

Merely check the fuel level in the sight glass.(I love those)