Need "tuning" help.

Brad Fish · Joined: 03 Oct 2008 Posts: 45

We had our first event yesterday and it was a complete disaster. Not only did I strip the spark plug threads on my son’s kart head but I could not get my shifter kart to stay running. My son’s is an easy (but expensive) fix. Mine, I don’t even know where to start.

My shifter has a 2002 YZ125 shifter engine.

I realize that engine was probably never intended to run on 38 degree rainy days, however, that’s Rochester, NY and I want to make sure I know what to do if it happens again.

The kart would start with no problem at all and would idle all day long. I would start it with the choke on and turn it off after idling for about 5-10 minutes. It idled fine off idle. If I gave it any gas at all, it would die. I could blip it lightly and it would be ok, but if I gave it gas in an attempt to accelerate, it acted like I hit the “off” switch.

I pulled the jet that was in the carb (330) and compared it to the sizes of the other jets that were given me. It was on the extreme low end so I’m assuming that it was probably hot outside last time it ran and it was jetted really lean. I grabbed one of the fattest jets that I could find (420) and gave that a try. The kart fired right up but I still couldn’t give it any gas.

I never did get a run in. Add in the fact that I was soaked to the core and I didn’t have much fun.

Any advice will be greatly appreciated.

Michael Taksa · Posted: Mon Apr 23, 2012 9:08 am Post subject:

1. Which carb?
2. Has the kart been sitting over winter with mixed gas/oil in carb/pump(s)?
3. Is the gas from last year.
By answeriong Q2 and Q3 I think you get the idea of what to do:)

330 and 420 sounds like a Mikuni pump. 380 should be a safe jet on that.

Joe Ricard · Posted: Mon Apr 23, 2012 10:35 am Post subject:

Well you should consider yourself lucky that it wouldn't run.

Being that cold out the motor will need a ton of fuel. You could have done one more simple test. leave the choke on and rev it. if it revved with choke on then you can be pretty sure it needed lots more fuel.

Reason you were lucky is if it is infact super lean you would have stuck the motor by the 2nd slalom cone.

With the radiator fully taped up I bet it would still be a challenge to get it above 100 degrees at the start line.

BTW it was 80 degrees here this afternoon. Laughing

_________________
Arrow AX-8/ Rotax Sr.

Brad Fish · Joined: 03 Oct 2008 Posts: 45

1. It's a stock 2001 38mm Mikuni .
2. I bought the kart in February, so I do not know if it sat with mixed oil in the lines & bowl. It's entirely possible that it's gummed.
3. I put in a fresh tank of 110 Sonoco mixed with Motul Grand Prix.

I'm going to pull it off tonight clean it up and check all the settings.
460 is the jet listed as stock in 2001

Thanks for your help.

Michael Taksa · Posted: Wed Apr 25, 2012 7:21 am Post subject:

Clean/rebuild fuel pumps and carb.