Most fuel/air screws are fuel screws so to give it more fuel you would need to take it out. (some are an air bleed though)

You may even have to put in a bigger pilot jet if the fuel/air screw is backed out too far.

 

I'm not sure which this one is. It's on the motor side of the carb if that makes a difference. so keep going out with the screw until the poping goes away? what if it doesn't? would we have to change something else? we'll try it in the next couple days and see what happens, I just want to have an answer for him incase it doesn't work....

 

This may help you out. I think it's the same carb but you would have to check to make sure.

http://forums.atvconnection.com/hond...uel-screw.html

If it's still too lean your going to have to change the pilot jet to a bigger size.

 

Let me throw in my two cents. I think it was all said by Bigbore on tuning a carburator. Depending on what carb you have, and what you are able to do with it, you may need to keep some poping as you let off fast. The problem is that if you are jetted up fairly rich because the motor can handle it and is requiring a large amount of fuel/air, as in high performance, and when you shut down the throttle really quick, that last gulp of vaccum sucks a bit of raw fuel (making it rich and unburned, and there it burns in the exhaust. If it is not a poppiing issue if you release throttle at a slower rate, you may just need to be with it. If the plugs look fine at the end of all rides, then you are burning efficient.

 

The air/fuel screw is in the same location, but the carb is a little different.

John1965: That makes sense too, because while we've been changing main jet sizes and needle settings one of us ride it for a 10 or 15 minutes to make sure whatever it is going to do to the plug happens and it's staying pretty much right with the exception of one side of it being the slightest bit sooty. But it's only about a sharpie line wide, which I guess could be the overly richening from backing off the throttle so suddenly. Otherwise I think we could be pretty much right in main size and needle clip settings then. We had planned on going one size smaller on the main but work has kept us pretty busy this week.

 

Now you got my brain working. Just so you know, I logged on to this site because I am helping a friend out rebuilding three carbs on some small motors and saw Bigbores story and was very impressed. I used to race cars and rebuild everything and anything for myself and fellow racers.

Here's what I don't know but would like to. Is this one carb, two cylynder and four stroke you are talking about and the modification you made was a better flowing exhaust and nw you are playing with carb adjustments to make it run right? Any difference, please post and I will try my best.

In the meantime, you said one side was suttyer than the other. How bad.

 

You're close john, it's a single carb, single cylinder, 4stroke that we changed the tailpipe(not the full system) and are trying to get the air/fuel mixture back right. We also added a revbox and that's when we figured out it was too lean, because after about 20 minutes it was WAY overheated and started to cut out and sputter when throttle was applied. As far as the plug soot, it wasn't caked on or anything but it looked like carbon buildup... it's just wasn't built up. It went away with a quick swipe of a wire brush.

 

So, it sounds like it is running fine except the few pops at a quick throttle back. The only issue other than that is some sut in one spot on the plug. If so, you can try leaning very slighly but you may not know at what rpm is the actual richness coming from. If perfect off idle to ful throttle, maybe your there. As far as the plug, we used to cut the tab off (forgot the term) with a cutoff wheel. Cut it pretty much even with the electrode so if looking straight at the bottom of the plug, you see the electrode. The clean the dust fragments and regap it. We were doing that 25-30 years ago before they came out with plugs that already have modifications.

 

I'm not sure exactly what you're talking about cutting off... if i'm looking straight at the electrode end, or from the side or what?? what would be the gain of doing this? or are most plugs these days already cut short like you're describing?

 

It's called side gapping plugs. In a high perf engine it can help a hair in performance.
It can help with flame front travel in very high compression engines. For a stock or near stock engine.......????
But it is free other than time....................

Second row down and fith from the left shows a before and after side gapping.
side gapping spark plugs - Google Search