89 kx 80 fauled plugs ?

[Daggs]

my sons kx 80 fauls plugs (b9egv &b9eg)during training ,he is a new to 2strokes and m/c ,at the end of the day after 6 or so plugs  we go home clean the bike and we have found that the air cleaner is full of what looks like 2 stroke oil . it runs 30:1 fuel was using "shell" replaced jets ,repacked muffler as was oiled to max today ,after cleaning it starts first kick every time until he rides it and the trouble starts again havent ran it since jets & muffler been done . any idea ?

[LWC82PE]

i would recommend setting it up as the owners/workshp manual suggests, with the stock jetting, the recommended fuel ratio and oil. Try a different fuel. Shell is known to be a bit sus. try and get it to run on factory specs and then if needed make fine adjustments to suit rider and rider conditions. Any alterations to fuel /oil ratio WILL require adjustments to jetting. the 80cc MXers like to be ridden hard and fast and like plenty of revs and are not suited to continuous slow running/low revs stuff. I would say its a combination of the state of tune/set up of the bike and the riders ability/style. 80cc full blown motorcrossers have never been known to be ideal 'first bikes' It sounds mostly like a fuel/jetting problem and the way the bike is being ridden to me so dont think its an oil problem as reduce the amount of oil in the mix as most people mistakenly do. Set it up as per the book and ride it like a bat out of hell and i reckon it should be fine.

[lc4]

Check that all the petals on the reed valve are sealing. Pull the reed block off and look up through it and you should not see any light coming through. If petals are leaking fuel mix may be getting back and saturating filter with oil which then is being sucked back in and causing the plug to foul.

[holeshot buddy]

should be running about 40to1
synthetic use bp ultimate fuel
if its not running high speed all the time switch to a 8 series plug
air screw1 and a half turns out needle on middle clip

if it still loads screw in mixture if it improves
your pilot jet is too big

[lc4]

One other thing to check,is it blowing a lot of smoke? . If so it might be a leaking crank seal drawing in gearbox oil.

[dirttracker]

check the needle jet, if its worn you wont be able to tune it no matter how many different size main or pilot jets you put in it. if the needle jet is worn you can bet the needle is worn also so replace both.

[Big John]

If the air filter looks like its got 2 stroke oil on it I would be looking at the reed valves if there not sealing the air/fuel would be getting forced back to the filter.

[evo550]

Daggs,
Are the plugs foiled or do they stop sparking after a small amount of use??
A mate of mine had this problem with the new ktm 65's after pulling his hair out for weeks, ktm released a bulletin saying the 65's should not be run using Premium unleaded instead owners should use 93/95 octane, he did so and not a problem since.
It turns out that the premium fuel additive's cause small deposits on the plug and allows the charge to travel over the isolator instead of jumping the gap.

[LWC82PE]

It turns out that the premium fuel additive's cause small deposits on the plug and allows the charge to travel over the isolator instead of jumping the gap.
 

is this problem only unique to the KTM? i have never heard of that being a problem on other bikes. Premium or high octance fuel is usually a good fuel to use as it burns at a lower temperature. To use lower octane fuel you will often have to use hotter plugs and ride the bike much harder just to keep the plug from fouling.

Daggs, yes check your plug cap/wire. perhaps the cap is vibrating loose when riding. You need to eliminate all possible problems one by one sytematically as part of the fault finding process. No point leaving it like it is as you will always be thinking 'oh the plug cap is a bit loose.....i wonder if its that'

i would be seeking a second opinion on the 40 to 1. i wont say its necesarily wrong but what i would like to know is what the MANUAL for that exact bike says it should be. Because if it (40 to 1) is less oil than what the book says, then your still going to have problems with a rich fuel mixture with std jetting. The std jetting is for use with the oil ratio the manufacturer recommends for that bike and not for use with more or less oil.

[evo550]

Leith,
I have had the same issue with a Maico I used to own, although at the time  didn't know of a cure and I always ran premium fuel thinking it was best.
The plug would fail after a couple of hours of use with no visible signs of carbon build up between the gap, it could be cleaned with some acetone and a good scrub and plug would be fine again. It turns out that there was a build up of carbon from the tip, over the insulator and back to the inside of the thread, this build up would allow the charge to run from the tip, over the insulator and earth out on the head, instead of its intended path from the tip across the gap.
This is what ktm are saying the problem is with the 65's and running the lower octane fuel fixed his problem instantly. The manual even states 95 octane fuel to be used.
I haven't had the problem with any other two strokes I've had running premium fuel, so I don't know what triggers it in different bikes, there was also someone else on the forum who had the same problem with a kx125.

Daggs,
So the jetting is standard, fuel/oil mix sounds about right and you foul 6 plugs in a day....sounds like a crank seal, does it blow a lot of smoke?

[LWC82PE]

thats interesting. i will keep a look out for that possible problem in the future.

[holeshot buddy]

daggs yes 40 to 1 motul will be fine
and try an 8 series plug like i said
and also bp ultimate
if jets are in the standard spec ballpark
it should be ok

if its still dodgy check your float level is not too high
and if its still ratshit you may have a low speed coil weak
in your stator

easy really

[runutz698]

Change the plug to a none racing one, NGK B8ES will fit in place and is more like a lawn mower plug. Will make it harder to foul. The plugs you are are running only have a small point to make it a strong spark but hence have less surface area so they foul easier. Not good for learning in the low rmp range.

Nutz

[Ji Gantor]

This probably does not relate to your problem but it is a similar tail.

A fellow VMX racer has been bringing his 1976 Maico MC400 to the races but only completes one lap and is back in the pits. I usually go over and offer some advice and service help. At the last race he did not even make it to the line. I offered my services in between races but nothing at the track seemed to help. We changed out spark plugs, tried different fuel to oil mixtures and adjusted the fuel mixture screw.
Symptoms,
Plug fouling (wet looking),
white smoke out of exhaust'
spark breaking down while just revving it.
I suggested to the owner that he bring it over to my place and we spend a day on it trying to track down the problem.

During the week the owner installed a new spark plug, new crank shaft seals, Mikuni carburettor and points and still it made no difference.
He also filled the tank with fresh fuel and an in line fuel filter.

When he arrived we started by checking the ignition coil under the fuel tank and found that it had 5.7million ohms of resistance when it should have 3000ohms. We did a continuity test on the lead and plug cap and found that some one had replaced the original cap with a resistor type. I had an old Maico ignition coil with lead and cap so we installed that. When that ignition coil was detached from the frame we noticed that most of the metal around the earthing bolt hole was gone, so we welded that back up to provide a good fixture and earthing platform.

We then took a look in the magneto cover and discovered that the primary winding was lose, the capacitor or condenser was wired so it was bypassed and the points were new but not seating flat. We replaced the primary coil with another that was not rotating, replaced the capacitor with a new one and wired it in like what the manual suggested and set the timing and points.

We then fired the bike and it ran great. I am not sure if it is totally fixed as we could not take it for a test ride, but I will keep you posted.

Ji

[frostype400]

good to hear i am after a similar vintage kx rm yz cr with at least front disc for my little brother know whta to do if the thing fouls up ask the guys on ozvmx thanks Michael.