White tip of plug = ?

[3 on the Tree]

Hi all, I have a '71 CT90 that I am trying to get dialed in and ready for the spring. I took it for a ride tonight after I got home from work and it ran like a top until I was about 1/2 a mile away from home and then it just quit on me.

After a cold push home, I plulled the spark plug and found that the tip is chaulky-white. I just cleaned the carb about two days ago and I am wondering if I have the mixture set too lean.......I just can't remember what a white tip indicates.

It will sit and idle all day long like this; it just won't accept the slightest bit of fuel...not even 1/8 throttle. Can someone help?

[Mr_RPM]

white means lean. you need more fuel

[3 on the Tree]

I did advance the ignition timing a little bit. Could this be causing it to run too hot and simulate a lean mixture?

[tri again]

Boy, those carbs are so simple it's got to be easy.

The slow jet is tiny. MAYbe .008" guitar string will go thru to.

Sure doesn't take much to plug them up.
I just got a 90 that's never been cleaned because it never got dirty, no joke.

Tank was mucky so I took that off and steam cleaned it first.

Once every 30 years isn't too bad.

The "W" clip that holds the main piston down under the throttle cable can flip sideways
and NOT hold the main needle down..I've had that happen more than once too.

[3 on the Tree]

Upon further inspection, I think something has lodged itself in the main jet. I richened the mixture up and installed a spare new plug, plus backed the timing off a few degrees and I am still having the same problem. It idles like a dream, it just won't take any throttle.

It does take some throttle on half or full choke but that's about it; maybe 1/4 throttle at best before it begins to bog and sputter badly. Looks like the carb is coming back off again tomorrow. :(

[Mr_RPM]

I had a tt-r 90 (i think) do this same thing. it was because it had a fmf pipe but was not jetted.
It caused it to run real lean, but finding larger jets to fit was looking impossible.

make sure that main jet is not clogged as you said. if it ran fine then just stopped it could be that.

it could also be a timing problem...but im not experienced with that. I have heard of timing problems doing this same thing, thats all i can say.

[MTS]

Clean that carb again and stick a couple Inline filters in..Them old Metal tanks on them RUST!!! Not sure if the 71 has an Altitude Adjustment or not...But either way its LEAN on the main..Make sure to take the petcock apart on the carb also and clean that little screen behind it.

[3 on the Tree]

Thank you for the input. I am starting to think less and less that it has anything to do with ignition timing or bad points. I was riding it down the street giving it about 3/4 throttle and it just bogged and quit running until I came to a halt. It fired back up on the first kick but it wouldn't accept any fuel beyond idle or 1/8 throttle position as I stated above.

The main jet is small and the slow jet is smaller still. I just found it hard to believe that the main jet would get gooped up before the slow jet. Now it makes sence to me since I was getting on it a bit at the time and sending the majority of fuel through the main.

I will attempt to run two small in-line fuel filters after this next cleaning (the carb has 2 incoming fuel lines like the early us90's). I suppose I will then find out if that will solve the problem since the tank is tad dirty.

[3 on the Tree]

Clean that carb again and stick a couple Inline filters in..Them old Metal tanks on them RUST!!! Not sure if the 71 has an Altitude Adjustment or not...But either way its LEAN on the main..Make sure to take the petcock apart on the carb also and clean that little screen behind it.

Thanks MTS, that screen behind the petcock is one area I did not address the first time around. My petcock may be rivited on though, I will have to take a closer look in the morning. This carburetor does have the altitude adjustment knob which reads "pull out above 6,000 feet above sea level". I have never touched that until tonight to see if that would help me limp it home, but in or out it made no difference.