Can anyone read this plug ???

[Joe-405]

Lets call this read a plug day ! Kart runs like crap 3/4 throttle and down. And this plug has at least 30 min. Run time on it ! I wish it was black or white. At least it could be read correctly.

the idle air jet is turned way out so everybody said to go one size smaller on jet, BUT it ran a lot worse with smaller one so i put the other one back in. If you floor the pedal it takes about 5 to 10 seconds to hit the power band but if you stay in the power band it runs awesome and breaks the tires loose in every gear.

This is on my 1991 KX125 engine in a shifter kart with a FMF pipe. It is suppose to have a lot motor work done but i don't know what. I am running 110 race fuel @ 32 to 1 oil mix.

The carb is from a 1992 and is a Keihin 37mm from what i have found. has a 158 main jet and a 50 pilot jet.

 

[Poboy kartman]

Gap looks wide- electrode a bit worn....Try a new plug....Check the gap and set accordingly. ...Other than that. ..looks a bit rich- but not exceedingly so....

I think your problem is that plug.... Anyway- cheap and easy enough to eliminate- (and at worst you have a spare plug....).

 

[Joe-405]

that was a new plug 2 days ago.

 

[Poboy kartman]

Must be the camera playing tricks on me...Really looks alright except that last pic.... And pretty clean for a two stroke....IDK.....However-it wouldn't be the first time a simple plug change has solved an issue- or a brand new anything wasn't up to snuff.....what about the gap?

 

[itsid]

Hmmm. I agree with Doug
the gap looks a little large (check the engine manual to set the gap to specs)

Also: is this the "manufacturer recommended" plug, or did you get a plug recommended by someone else (on your own)

I do not agree though on the "running rich" part;
quite the opposite, I think it's running a bit lean ,or -more likely- too hot.

'sid

 

[Joe-405]

It is the manufacturer recommended plug. I'm here in Arizona at ride on power sports and they said it looks way lean. So I'm trying a 168 main instead of the 158 for the hell of it, it's cheap enough. I hope it works cause it's been driving me crazy not knowing what's wrong. I'm usually really good at the 2 stroke stuff but this one acts like a whole new learning curve.

 

[OzFab]

2 stroke plugs always read differently to 4 stroke plugs due to the oil in the fuel; if that was a 4 stroke plug, I would say it's just about perfect but, for a 2 stroke, I'd have to agree, it's super lean...

See how it goes with the bigger jet & let us know...

 

[exenos]

Could you do a wot chop for us? What heat of plug are you running? (Br9, Br8) When you say that the kart runs poorly in the bottom 3/4's of the throttle you definitely mean throttle and not rpm range right?

EDIT: And contrary to what fabroman and sid have said I'd almost say its fine or a bit rich. (Note, almost ) Take a peek inside the pipe if you want. Should be dry and have a very light tan colour. Also, before you change the main jet try raising the needle.

 

[Joe-405]

All of the throttle sucks BEFORE the powerband. And I'm not doing a wide open plug check cause I'm not blowing it up trying it since almost everybody is saying its lean. This engine is no where near stock and I don't have the money to fix it.

 

[Poboy kartman]

2 stroke plugs always read differently to 4 stroke plugs due to the oil in the fuel; if that was a 4 stroke plug, I would say it's just about perfect but, for a 2 stroke, I'd have to agree, it's super lean...

See how it goes with the bigger jet & let us know...

That's what threw me on my OP- I was thinking 4 stroke when I saw it. ... Not sure on 2 cycle plugs- but it sure couldn't hurt to go richer and see what happens. .....

And seeing that the oil that lubricates the engine is delivered with the fuel......

 

[itsid]

Maybe we can narrow in on your problem.

could you do a compression test?
Do you have about 140psi? if not either your reed valve isn't sealing properly or you have worn rings..
that should be fixed first of course!

Now let's get to your carb
Warm engine.
Turn your airscrew all the way in, then 1.5 turns out, start your engine and crack it a bit to keep the engine running while messing with the carb
Do not mess with the throttle, set it and keep it.
Now slowly turn the air screw in either direction to find the spot where it revs fastest!
If the airscrew is less than a full turn from closed your pilot jet is too small
if it's more than 2.5 turns from closed your pilot jet is too big.

in both cases it needs to be replaced.
once done, adjust the air screw to best possible throttle response.

Now you should adjust your needle if necessary.
that requires a bit of driving though

drive the kart around between 1/4 and 3/4 of full throttle if there's a lag between opening the throttle and a reaction of the engine you should lower the clip one notch (and by that raise the needle) .. repeat until immediate throttle response.

At this point it's safe (well as safe as it can be) to make a good plug read,
warm engine, fresh plug, long straight, WOT, killed engine... you know the deal...

since it's a two stroke the plug should be a fair bit darker than it would be on a four stroke,
but if you can peek inside the threads at the base of the insulator, you can use the color scheme of a four stroke.
white-grey too lean, tan-light brown good, dark brown-black too rich.
resize the main jet until you're satisfied with it.
(basically the color you now have on the tip, you want down at the base.. a tad darker maybe)
The tip by now should be somewhere in the chocolate region.

'sid

 

[exenos]

All of the throttle sucks BEFORE the powerband. And I'm not doing a wide open plug check cause I'm not blowing it up trying it since almost everybody is saying its lean. This engine is no where near stock and I don't have the money to fix it.

Thats what I wanted to know. I hate being the guy that seems to be offering different advice, but I think that what you are going to find is that if this engine has been worked over enough to require 110 then its going to have very little or no power until it gets in its power band no matter what you do with the carb.

You should set up the carb like sid says but if its as wild as you say it is then its always going to be a high rpm screamer.





EDIT: I know you said that you've been around 2 strokes for a bit but I figured I'd post this up.

I just pulled this plug from my sled this morning after a mile long wot pull and it looks just about spot on. Ideally that's what you want if you dont want to risk a melt down.

 

[Joe-405]

Maybe we can narrow in on your problem.

could you do a compression test?
Do you have about 140psi? if not either your reed valve isn't sealing properly or you have worn rings..
that should be fixed first of course!

Now let's get to your carb
Warm engine.
Turn your airscrew all the way in, then 1.5 turns out, start your engine and crack it a bit to keep the engine running while messing with the carb
Do not mess with the throttle, set it and keep it.
Now slowly turn the air screw in either direction to find the spot where it revs fastest!
If the airscrew is less than a full turn from closed your pilot jet is too small
if it's more than 2.5 turns from closed your pilot jet is too big.

in both cases it needs to be replaced.
once done, adjust the air screw to best possible throttle response.

Now you should adjust your needle if necessary.
that requires a bit of driving though

drive the kart around between 1/4 and 3/4 of full throttle if there's a lag between opening the throttle and a reaction of the engine you should lower the clip one notch (and by that raise the needle) .. repeat until immediate throttle response.

At this point it's safe (well as safe as it can be) to make a good plug read,
warm engine, fresh plug, long straight, WOT, killed engine... you know the deal...

since it's a two stroke the plug should be a fair bit darker than it would be on a four stroke,
but if you can peek inside the threads at the base of the insulator, you can use the color scheme of a four stroke.
white-grey too lean, tan-light brown good, dark brown-black too rich.
resize the main jet until you're satisfied with it.
(basically the color you now have on the tip, you want down at the base.. a tad darker maybe)
The tip by now should be somewhere in the chocolate region.

'sid

That's what is screwing me up. The air screw is all the way out before it runs, but with next size smaller jet it hardly runs. And my next guess was a compression test. I have the bigger main jet already but I won't be home for a week as I'm on spring break vacation in Arizona. There is a white line on the inside of the diode so it won't hurt for sure to richer it up. The ride on place here in Arizona said that without the air box and going to the k&n it needs to be jetted way up anyways. We will see when I get back home. The guy said it was running before but I am beginning to think they never tuned it correctly down low maybe or never road it a lot.

Edit..... I moved the needle up all the way and not a big enough change to notice it. It was in the middle slot.

 

[itsid]

I'll leave town tomorrow morning and will be gone for a week myself,
as far as I'm concerned... have a nice vacation

as soon as you're back home, check your piston rings.
worn piston rings mimic a lean jetting, and since the correct pilot
(I think it should be closer to 45 than 50) leans out your engine too much to run,
I'm afraid they need to be replaced; you might even need an oversize piston already.
But to know for sure you really should do a compression test!
Everything else is just guesswork

'sid

 

[Joe-405]

Thanks, if my posts sound like I'm pissed I'm really not. I can get that way sometimes in my wording. It is definitely frustrating tho when you been working on small engines for over 20 years and can't figure it out. I really hope the compression is good cause it has a bigger piston already. Cause I don't wanna buy a new cylinder. If that the case then I will find a bigger engine instead.

 

[exenos]

Its nicasil lined right? You should just be able to do a very light honing of the cylinder and put a new piston in. Or was it sleeved when all the engine work was done to it?

 

[Joe-405]

I don't know it was lke that when I got it. He said everything was highly ported and polished and everything was huge and forged. I was attempting to not tear it apart. So the compression check will be done when I get back first thing if the humongous jet don't fix it or change anything.

 

[exenos]

What sort of compression are you going to be looking for? 160 psi+ ?

 

[exenos]

Any luck?

 

[Joe-405]

Thanks Sid !!!!

Just tried it, no change. So I pulled the carb off to revert back where it was and yanked the reed cage out. And behold we found the issue ! The reeds are warped and are pulled away from the cage so I flipped them over and she's running way better. So I'm ordering new ones. Thanks everybody I hope the new ones fix it for good. I am gonna do a compression check when I get the new ones to check it also just so I will know. It's definitely been worked over inside. It was nice and polished and ported for sure.

With them flipped she is revving cleaner than it ever has.