Jump to content

2000 KX 80 refuses to idle, very weird symptoms

Recommended Posts

Hi guys, need some help as I am stumped. We recently bought a 2000 KX 80, it starts first kick on the choke, but dies about 10 seconds later, choke on or off.

The idle screw is turned all the way in. The airscrew does nothing and even removing it completely does not make any difference to the way it runs. I can keep it running with some throttle, but then it's about 1/4 open, and just barely running. Pulling the choke at this stage kills the bike immediately. (not lean)

I have gone from a 38 to a 48 pilot jet, no difference.

I have cleaned every orifice and blown out the carb with air, and it is clean. The jets are new. No blockage. I can't tell if the needle jet is worn, and the needle has no marking on it so I'm not sure if it's correct. I will try replacing all of this as soon as possible, but the symptoms seem worse than a bit of wear. 

The reeds are perfect. The timing is correct. The airfilter is clean and lightly oiled. There are no rags in the airbox. The pipe is clear and I repacked the silencer yesterday. I drained the tranny fluid to rule out a sucking wet side crank seal. There is no revving or high or hanging idle so it's not an airleak. It does smoke more than my other bikes but not terribly so.

The sparkplug is a perfect dry, tan colour, the top and bottom end are 3 hours old. (Not done by me but I checked top of piston and it looks new. Also checked thru intake and exhaust side ports and everything looks great.) Compression feels right for an 80 cc bike. (comparing to our RM85 which is perfect)

It has a very strong blue/white spark. New plug.

Stripped and cleaned the powervalve and made sure its working correctly too.

I have rebuilt seven 2 strokes in the last 3 years, and I have done it all. But this one has me stumped. I'm thinking because the idle screw is all the way in, it is bypassing the pilot circuit completely, but why does it not then just rev? The bike is very sluggish down low when riding, but the upper RPM's feel great.

Current carb specs are: 110MJ / 38PJ / Stock? Needle clip 2 (tried clip 3 too - no change) Float level with sealing surface / Stock slide / AS - 2 turns out / Idle screw bottomed out / 6000ft ASL / 60F / 40:1 Motorex Crosspower

I see that kawasaki changed the jetting specs when they released the KX85 in 2001 (I think) so I might be a bit off but again, the symptoms are so bad, I doubt it is a slight jetting issue. I also cleaned and confirmed the choke is sealing well when closed.

What the feck am I missing? 

Thanks in advance for any advice!

Share this post


Link to post
Share on other sites

If a crank seal is excessively leaky then it can cause the engine to die. Also check the crankcase for leaks (gasket or cracks in the metal). rig up a way to pressurize it to see if it bleeds down quickly.

a perfect tan color? I thought the perfect color was chocolate brown. If I'm right then the jetting is lean.

You didn't check engine compression.

Also put in a new spark plug with minimum gap in case your ignition is weak (and dying out as engine compression increases as the engine warms up)

Share this post


Link to post
Share on other sites

Thanks Jaguar, the plug is new and gapped to spec, it shows a strong spark, and yes the plug is a dark beige tan color, a bit lighter than chocolate, but as far as I'm concerned it looks good to me, considering the validity of spark reading with the new fuel additives etc, is not very reliable. I did not check compression no, I'm judging by the fact that it feels similar to a brand new RM85 we also have.

I will do a piston anyway as it's cheap enough and then I will know its right. I also noticed last night the waterpump does not turn when I kick the bike over, so there is definitely something wrong with the way the previous owner rebuilt the bike. If it was run like this it might have over heated and seized, been kicked loose and caused these symptoms, so I will check tonight what the insides look like. No use doing jetting on a possibly damaged engine.

Could a heat seized piston cause a low idle? I'm not sure... I know it effects jetting to a point when the compression is bad. What gets me is that the bike will start 1st kick when cold or hot. 

Another test I did last night was to let the engine run with the fuel turned off, and as expected, as the bowl got empty the revs picked up to where the bike was actually idling, and then eventually revving out as it got leaner and leaner.. the floats are to spec. This confirms to me that there are no airleaks, and that the low end circuit is extremely rich.

Thanks!

Share this post


Link to post
Share on other sites

Ok so, to follow up. Piston has been replaced with a wiseco unit, cylinder and bottom end are in great shape. Replaced the jets with the correct size per the manual. Water-pump has been repaired and is functioning like it should. Plug wire trimmed and checked, spark is strong and consistent. Bike still starts first kick choke or no choke, smokes a bit more than normal and still refuses to idle.

I checked the carb again, and it turns out there was a small stone completely blocking off the air tract in the throat of the carb. So I figured, "there's the problem!" pushed it through and saw it fall on the floor. Refit carb. No change??? Same issues persist. So, I change the plug which was again wet with oil. No change. Played with leaner jets, clip positions etc. Absolutely ZERO change. As in, going from a 55(stock) pilot to a 45 pilot makes NO CHANGE? I've never seen anything like this ever. Even completely removing the airscrew makes no difference. Carb is completely clean and all tracts are open.

I lowered the floats to 23mm (Stock is 18 -20) - No change. Drained tank to rule out bad gas, no change. Disconnected kill-switch, no change. Re-checked timing, no change.

Bike still revs up fine, seems normal after 1/2 throttle but below that it's extremely rich and will not idle even with the screw all the way in, even if I hold it steady on the throttle to keep it running it will just rev lower and lower until it dies. I am totally stumped, I know this is probably not going to get any replies because it doesn't make sense. My only other thought is to replace the needle jet, might be worn out, although in my personal experience this is very rare. I also want to double check the wet side crank seal again, by putting the vent hose in a glass of water and looking for bubbles.. although when the oil was drained it should have been better if it WAS the seal... I don't know what to do.

Thanks for reading. Please take pity on my soul.

Share this post


Link to post
Share on other sites

A leaky RH side crank seal would not exhibit pressure out the gearbox vent hose, 

on the contrary a slight vacuum is created as the crankcase sucks oil from the gearbox into the engine side (runs rich)

 

If the reeds have more than a season on them in a high-revving mini consider them worn

despite no apparent damage or chipping, you cannot judge visually if they have lost their tension.

 

Until you perform a crankcase leakdown test to confirm the engine doesn't have any air/oil leaks,

you are chasing your tail in guessing what can be wrong.

 

The Honda 2-stroke sub-forum has a how-to sticky on the subject, 'pressure testing a 2-stroke'

you can build your own tester for about 30$ worth of commonly available supplies from a hardware and auto parts store.

Edited by mlatour

Share this post


Link to post
Share on other sites

Thank you mlatour, appreciate the input. I drained the tranny oil once before as a test and ran the engine like that for about 10 minutes, ruling out "sucking oil" and the bike ran exactly the same, same amount of smoke, same problems?

On the reeds issue, I am fairly sure they are fine, (they seal perfectly when I suck on them and trumpet when I blow) but they aren't too expensive so will replace them anyway. Thanks. 

The needle jet, the hole where the needle goes in, should there be any gap between the jet and the needle when the slide is down? If I'm not mistaken there should not. It should completely block off that circuit, but there is a sight gap all around the needle, maybe 0,3mm... I still think that's the problem but the part is on 6 week backorder everywhere..

Last night I dropped back to a 38 pilot (55 stock) and a 110 MJ (125 stock) and again no difference. The bike will idle fine when it's cold (because it needs the rich mixture then) but as it warms up it idles lower and lower until it dies. It also doesn't just die, it stops dead in it's tracks, weird... might be the compression on the new slug. It has a ton of compression now.

Could this in ANY way be electrical? That would be my next set of tests, ohm readings and so on on coil, stator, HT lead etc... 

Thanks again!

Edited by ERabe

Share this post


Link to post
Share on other sites

Sitting here thinking of a way to test the needle jet, I could theoretically block off the main jet, so the needle jet cannot get any fuel, and see if the bike will idle? This would confirm or disprove my thoughts that the needle should block off that circuit completely. If I block off the MJ and the problems persist, then I won't need to bother with the carb anymore and focus on the reeds / crank seals and electrics. Thoughts?

Share this post


Link to post
Share on other sites

I've lost track of earlier posts, have you checked and adjusted the float/fuel level ?

 

Over time, floats can loose buoyancy, contact & pivot points can wear etc. 

higher fuel level in the bowl (even 2mm) will make the engine run richer on all metering circuits.

(less vacuum required to draw fuel)

Myself have fallen to this a few seasons ago on my YZ125, 'assuming' the float was ok (had set it the previous season)

my engine gradually ran richer on the bottom and had gone about 3 pilot jet sizes leaner until I realized what was the real problem.

 

With usage the needle orifice can wear creating an unmetered rich condition right off idle 

which most people either fail to realize or, attempt to compensate with leaner pilot or needle settings.

On some carb designs the needle orifice isn't replaceable, it's pressed in the body permanently.

 

Your original post mentions that removing the air screw completely doesn't affect the way the engine runs / idles.

I'd look closer at that circuit to confirm it isn't blocked (also making sure the needle or seat isn't damaged)

Edited by mlatour

Share this post


Link to post
Share on other sites

Mlatour, thanks, I have played with the float level, set to stock as well as 2mm lower (leaner) and it made no difference. I also always put the floats on used bikes under water and look for bubbles, which there were none. You are talking about 3 PJ sizes, but I've gone from 38 to 55 with ZERO difference. There is something else wrong.

By "needle orifice"I assume you are talking about the needle jet/emulsion tube, and yes, it does appear worn and it is replaceable on the PE carb. I think I'm going to block it off completely and see if it makes a positive difference, that would confirm if it is indeed the problem. When I switch off the fuel at the petcock the bike starts running "normally" until the level goes so low in the bowl that it starts running lean and revving up. This is another confirmation that the problem is at least somewhat guaranteed to be a "too rich"condition.

Thanks again!

Share this post


Link to post
Share on other sites

My son's rm85, stator will and can cause a lose of power on top end and also spark plug cap. Spends $3-5 and replace cap. when I changed his it gained several hundred rpm's, had to turn his idle down after that!

Share this post


Link to post
Share on other sites

Thanks smoking! I did measure the resistance of the plug and it was to spec, but I appreciate the input.

Last night I took an old spare mainjet and hammered a nail into it to block it off. Clipped the remaining piece of nail off flush and installed it into the carb, in order to rule out, or confirm my suspicion that the Needle jet and/or needle are worn out. All I can say is that it's definitely the problem, with no fuel flowing through the needle circuit, the bike idles perfect and is as crisp off idle as a brand new bike. Obviously with the needle circuit / MJ blocked off you can't rev the bike more than 1/8 throttle, but it immediately started, it needed the choke to start, the airscrew actually made a difference, and there was very little to no smoke once it warmed up a little.

Problem solved. 

Now to find these parts in my neck of the woods... talk about rocking horse s#it.

 

Thanks guys!

  • Like 2

Share this post


Link to post
Share on other sites

Awesome, without re reading yours, I had to drop his main jet 2 sizes, pilot 1 size and drop the needle 1 clip position to really get it cleaned out. Good luck

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×