Kelby,

What I have found is there are a lot of different thoughts and opinions on everything you mentioned.  First things first, can you give more information such as:

1) Where are you located?

2) 99 or 01 cylinder?

3) Which pipe and silencer are you using?

4) What fuel delivery system do you have?  Swedetech GFS?  Pump around?  Single pump?

5) Air filter or airbox?

6) What type of carb do you have?

Kelby,

That starts to help us out.  Is this a stock or modified cylinder?  Is the Keihin carb a PWK or PWM (if you don’t know the difference you can do a quick search as there are some pretty easy visual cues)?  Did you buy this kart/motor combination used?

If you wouldn’t mind, snap some pics of various angles of the motor and send them to me at proth0303@gmail.com.  I have a gut feeling and rather than speculating on the forum I’d rather just confirm my theory and go from there.

Back to jetting… My references are probably not going to mean much given a number of differences between my setup and yours; however, at the end of the day your best bet is to learn how to read the spark plug and piston.  I highly recommend taking a look at “Firestone Kart Info” and consider purchasing his articles.  A few of his articles discuss specifically how to read the spark plug and piston and include some very good photos.

Patrick

Water temp 130 F. Max egt 1280 (and I mean max. 1300+ and the piston becomes one with the cylinder). Egt should be measured 10cm from the exhaust side of the piston. Get the CR125 jetting app that is avaiable. It is great for sprint tracks, and more or less dead-on (Keihen carbs only, mind you). Add 15 to 20 sizes to the app’s main jet for road racing. If the engine revs to max rpm on the stand at wot and doesnt go blahhhh, its too lean. Never go more than 5 hours on a piston and ring. All of this learned by me the hard way.

firestonekartinfo has some great info about running stock moto. Good luck!

Josh,

I’ll admit to being a novice but I am on my 3rd season of road racing (5 races/year)+several sprint track and even some practice days and I STILL have not changed pistons/rings.  What happens when you run them too long?  I run 2 karts (my father and I).  Stock Honda CR125s.  ’99 cylinders.  I built both motors myself.  One with a used but good ’99 cylinder, the other with a brand new cylinder.  All OEM Honda stuff.  Was planning on running another season before rebuilding. :)

Todd, when we were still running Stock Honda we’d run about 3-5 events.  Figuring about 1.5 hours for a two day and 2 hours for a three day national.  Road racing that is.  So the 5 hours Josh mentioned is a pretty good guide.

For a 5-6 event season, we’d put a piston in it half way through the season, and of course a new one to start the next season.  Every other season we’d put a crank in it.

We only ever broke one piston and that was breaking the engine in!!!  Go figure??!!  And I never found a crack in any we replaced, so it’s more of an insurance thing.  BUT, if a bottom end bearing goes it can make a huge mess!!!

So in your case, I suspect both your motors are ready for a crank and piston.  Hope that helps.

Clark Sr.

Our engines have been getting harder to start.  I wonder if we are starting to lose some compression now.  I’ll go ahead and do the piston/rings in both motors before we get started this season!