93' TRX300FW running rough

[82winger]

Greetings all. All of a sudden my atv started idling terrible. It will start and run best with the choke on. If I throttle up it does ok but does spit a bit. If I let it return to idle it will die. Restarts are the same. I have checked the compression and it reads 150. Pulled the carb and everything looks fine. Has my timing chain jumped? One thing I have not checked yet!!!
Is there anything else I should check?

Many thanks,

Jerry

[Here 2 help]

It's unlikely the timing chain jumped. It is almost certainly a carb problem, but you might want to check the valve clearence. If you use premium fuel from a brand name source, then water contamininated gas is unlikely, but don't rule that out either.

[82winger]

I did check the timing, it is good. I thought my slo jet was clogged so I took a small drill bit to open it up. I think that was a big mistake, now it really runs poorly. Black smoke and puking quite a bit. I have ordered a new #40 jet and will install it when it arrives.
I've also added seafoam to the tank in case there was any moisture. I run regular unlead. It's just odd that all of a sudden it will not idle.

Many thanks,

Jerry

[Here 2 help]

Many times sudden poor idling is caused by a change in fuel or long (30 days or more) periods of un-use. Whenever I park my machine, I drain the carb. If it sets more than 30 days before I ride again, I drain the tank and put in fresh fuel. I always use premium (because it typically contains less alcohol than other grades) and I always use Shell or BP. I have not had any carb issues for over 10 years.

Yes - using any size of drill bit to clean a jet is bad news. I have some micro-drills I use to drill out main jets on certain Chinese quads that you can't buy individual jets for. The largest is .00260 - 5 different sizes of these micro drills cost $20 and I needed a special mandrel to hold them. The good news is you don't need a drill to turm - just use your fingers. Ordering a new jet was wise.

[82winger]

Do you still think it is carb related and not a broken valve spring or something? As I said before, it starts fine with the choke on, would rev up but not idle. It had to stay around 2K rpm to stay running.

Many thanks,

Jerry

[Here 2 help]

A broken valve spring usually affects high speed operation more so than low speed, but if a valve has only a single spring (not a dual spring set up like yours has), then a broken spring can prevent starting or cause bent valves upon failure.

Failure to idle - I belive will be either a carb issue or valve clearence issue - could be an ignition problem, but answer this: can you hold the throttle and make it idle?

[82winger]

Yes I can.

[Here 2 help]

If you can hold the throttle and make it idle, why don't you just adjust the idle speed screw to set the idle speed? Or would it be idling too fast if you did that? If it won't idle down to an acceptable speed, I would check the carb low speed circuit for a blockage.

[82winger]

Replaced the slow idle jet and it idles great. Thank you again.