Hi Everyone.

It has been years since I have been on this board.

A few years ago I picked up a gently used 2005 KFX80 that needed some carb work. It has been a terrific bike over the years. The kids (and adults) I ride with have loved that little bike so much that last week I picked up another 2004 KFX80 to add to my fleet.

This "new" one "didn't run" turned out it had not been run in about 5 years and had gas left in the tank and carb(was super nasty), also what appeared to be 30W motor oil in the injection tank. I cleaned the carb and fuel and oil injection tanks/lines. It is running great now except just the slightest miss at wide open throttle and a TON of white smoke. When I look at the top of the piston it has a moderate amount of black carbon on top that will scratch off quite easily. The side of the piston when viewed through the exhaust port looks shiny as new. Now with good oil being mixed the smoke is subsiding a bit.

I'm not too familiar with two strokers. My three kids bikes(2 KFX's and a china quad) are my only real experience with oil burners.

Now on to jetting questions. I have noticed my first 80 always smokes(blueish tint) a bit on trail rides at low to moderate throttle and a little dribbling out of the pipe from time to time. You can see it in the distance in this pic.


Now that I am tinkering again, I'm wondering about jetting changes. Both bikes have the stock 92.5 main. The needle is at midrange on the '05 and 2nd from top on the '04. I'll probably move the needle leaner on the '05 hoping to clean up the smoke a bit when "cruising" the trails. What are your thoughts on the main jet and needle? We primarily ride at 7000 ft in 70-90*F temps. Although come winter time I use the 80 in the snow to pull the kids on sleds at the house which is 4500ft and 0-20*F. I was thinking of dropping to 90 or 87.5 main jet. I haven't done anything with the first bike because it just runs so darn good I'm hesitant to change it.

Both bikes have 110-115psi on compression test and are OEM to the best of my knowledge.

Thoughts???

 

Yes...the smoke has little to do with jetting...they burn oil...that's what they do. Often, the manufacturer sets the oil pumps a bit on the high side to reduce failures during warranty periods. You mention the oil tank so I'm assuming you're still on the oil injector...that mechanism is driven off the crank (and is not adjustable) and pushes oil relative to RPM...not the air/fuel mixture of the carb's jet settings.


If reducing the smoke is a major concern for you there are some options:
1) Try a premium 2-stroke oil...some burn cleaner than others
2) Get rid of the pump/tank & pre-mix with a premium oil...then you can set the ratio (40:1 for example) that yields acceptable results.


Just remember that the oil being burnt is the only oil lubricating your engine...reduce that too much and you will be replacing things (like pistons & crank bearings) sooner rather than later...


I just tore into my boy's LT80...after almost 30 years on the oil pump the crank bearings (original) showed very little wear...so it works well...when it's working...


That leads to the obvious shortfall...when the pump fails (and they can fail)...the motor receives no lubrication...


I pre-mix...but I'm at 36:1 (more smoke)...some go 50:1 (less smoke)...I'd rather replace fouled spark plugs (well, not if you use iridium plugs...haven't fouled one yet) then engine parts


I'd get LT80's opinion however...he is the master of all things related to these little quads...

 

Thanks for the reply.

I run a premium two stroke oil and iridium plugs on all my bikes.

I agree with and understand the need for smoke. I like to see it to a point as it is a visual to know the oil injector is working well. I check it periodically (as per the service manual instructions) just to be sure and it never seems to change the amount of oil it pumps into the intake, this is reassuring. I like the convenience of oil injection as I don't have to keep mixed fuel separate from fuel for my 4 strokers

The more I think on it...I probably won't mess with the one that is running good.

I am confident my 'new' bike is just suffering from neglect, as my 'good one' was a bit temperamental when I first got it as well.

My main concern was jetting. I assume these are like any other bike. They are jetted for low altitude from the factory. In fact, when I bought my last quad new( 4x4 four stroke), the dealer jetted it for our elevation as part of the purchase. I've read these LT80's are jetted rich. I assume higher elevation compounds that 'richness'. I was wondering if I could do better by leaning out the jets for altitude.

I remember reading in one of Jack's post he mentioned it is possible to drop to a 90 or 87.5 main jet, but I don't recall the context or upgrade status of the bike in that post.

Thinking on this more today, since the injection pump is crank driven and not adjustable, jetting down will only decrease the fuel and not the oil. Perhaps I will leave well enough alone. The bike goes plenty fast for the kids. Some people ask about the smoke. I tell them '2-stroke' they say 'Oh...right'.

Maybe it is best to save optimization for when the bike no longer is fast enough, then start with the upgrades.

 

As with most anything carbureted, the main jet is often on the rich side as fuel itself is a cooling agent in the combustion process...I've dropped to 90 for my riding area...if you are at high altitude that may still be too rich...can you read plugs? That would be your best/safest bet...just remember running a little rich never hurt anything...running a little lean can lead to a hole in your piston...this is all assuming a stock machine of course...