KX Riders
Maintenance & Technical => KX500 Original => Topic started by: dirkster on September 09, 2016, 03:29:41 PM
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just got my 1987 k5 back together yesterday. rebuilt engine, 87mm bore, full port and polish, vforce 2 reeds, fmf fatty pipe, new crank bearings. got the engine all broke in. rode the bike around some today and it ran like a dream pulled nice and hard, was surprisingly a smooth ride. then the bike just died on me so i checked the plug and didnt even spark so put a new one in and had spark but it was weak. got it started again and it vibrates like a sob now. trying to ride it is not a good idea hands just go numb after 2 minutes. checked all the motor mounts were tight and they were. could the vibration problem be from poor ignition timing or the weak spark? any ideas.
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Have you checked the flywheel and ignition to see if everything is tight and in place?
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just checked and it is solid. the timing was retarded so i set it back to the middle line it started easier but no change in the amount of vibration. might need to get the flywheel balanced didnt realy notice how small the flywheel was till now, dont even have to take it off to do the timing.
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Ah, you have the small size flywheel.
Great for getting your engine to wind up quicker.
I've been looking for one for a while..
I have the larger size flywheel and stator if you want to trade.
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some more info here after the bike started to vibrate like a sob, higher rpms are not smooth at all the as in dosent run right, like a misfires. could preigniton or detonation be the problem? the fuel that i filled it up with today could have been the regular mix instead of premium. i'll drain the tank and get some 91 octane with some octane booster tomorrow and see if that helps.
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going back to your original post....
check ALL your electrical connections thoroughly for loose connections, and be sure to use a little dielectric grease on all the plug connections. Make sure all your grounds have a GOOD CLEAN contact surface!.
if that checks out...you may need to start checking/testing your electrical components to be sure they're not failing.
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I picked up a tank of bad fuel two weeks ago in my brand new UTV. Non ethanol 92 octane. Ran Ok on the flat but acted like it had a rev limiter going up any hills. Drained it and put in new fuel and 'poof', runs like it should.
I should say here that the fuel MAY not have been bad out of the pump. I filled a brand new plastic fuel can (plastic) a couple months earlier and it had been sitting since. It is possible something leached out of the plastic into the fuel.
Try the fuel first as that is easy...
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Update. cleaned all the wire connectors, grounds, took the flywheel and stator off and cleaned up every connection on the bike. had a stronger spark. still ran the same. the bike had been fouling plugs quickly so i took the carb off checked to see if the main jet had fallen out, it hadnt, while i was turning over the engine i checked to see if the reeds were sealing correctly, put my hand over the open intake boot. and there was a lot off air getting pushed back out of the crank. took the reeds out, btw they are v force 2 reeds, took them all apart and the pedals were all sealing, however the center restrictor between the petals had a gap on the sealing surface. loosend the two screws holing it together and pushed the center section back to were it would be flush with the sealing surface, didnt quite go flush so i put a thin layer of sealer when i put it back together. the reeds not sealing would explain why the pug was always wet after it was running, and that the motor was running so badly because of an excess of fuel getting sucked in. well hopefully thats the problem anyway. post is probably longer than it should be, sorry bout that.
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On the VF2's you should remove all the screws and put them back in with retaining compound...
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On the VF2's you should remove all the screws and put them back in with retaining compound...
+1...
I use yamabond.
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the cdi box quit on me so i took one off an old yz400 and it works pretty good, the bike was running great for most of the morning no more terrible vibration, been messing with jets and needle position all day to try and get the engine in tune. after a while the bike started to run rough, wouldn't hit powerband, or it would try but fail, sputtering and kicking. now its running hot but the plug is wet? too rich maybe. went back to the setup that was working the best, 176 main, 3rd notch down on the needle. still wouldn't hit powerband. kips valves are opening and closing properly, put in a new plug, cleaned the air filter. this bike is the most temperamental 2 stroke ive ever owned. i just dont get it runs fine for most the day and then it starts to run terribly.
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still sounds like ignition/electrical problems to me...
One trick some of the sled guys use when they have electrical/ignition problem symptoms is, pull the spark plug cap off the lead wire, and cut a 1/4" off the end, then just re-install the cap. What happens sometimes, is the end of the lead/wire gets a little corroded, and by cutting off a little. you get a nice clean contact again.
you could/should do a leak down test, to be sure you don't have a bad crank seal...especially the stator side.
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I had a very similar experience to what you are describing on my sons yz 250. The thing absolutely drove me nuts! Could not find the intermittent poor running condition much like you are describing on your bike. No matter what I changed as far as jets or float height or checking reeds and plugs or timing it did not matter when it was acting up it made no difference. Mine ended up being a loose connection on the wire going to the ignition coil. I had the bike apart several times trying to find the issue including this connection and never realized it. I know it has been stated here already but make sure ALL of your electrical connections are TIGHT. You never new when it would act up but it always would. Hopefully this will save you some hair as I am now bald. :-D Good Luck!
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took the flywheel off again and saw that one of the wires from the stator, the signal coil if thats what it is called, had been against the crankshaft output and wore through to the wire. took the backing plate off and cleaned all mating surfaces and moved the wire aside where it wouldn't rub on metal and the the bike runs better now, still not running like it was a couple of days ago, decided to get a new stator since the one on the bike is a bit rough and a brand new one is $65 on ebay. Foxx4Beaver, I have a new coil on the bike and the crank seals should be good since i just rebuilt the engine at the beginning of this month with new crank bearings and seals along with the new top end. big green, i checked all connection on the bike and they are all tight and freshly cleaned.
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the bike runs better now, still not running like it was a couple of days ago. crank seals should be good since i just rebuilt the engine at the beginning of this month with new crank bearings and seals along with the new top end.
you still should do a leak down test, anytime an engine is rebuilt ...just because it has new seals, doesn't necessarily mean it's sealed up.
you mentioned it was running hot...that could indicate an air leak somewhere, causing it to run lean.
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Foxx4Beaver, i'll try and do a leak down test tomorrow to be sure they are sealing. also after running the bike, before i found the bad wire, it ran hot but the plug was wet and black. now that the signal wire isn't getting grounded out on the crank, the bike runs much more consistently at higher rpm and the plug returned to being a darker tan and not wet after riding.
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you're probably good to go now....
but still, a leak down test is always good practice on a fresh rebuild...cause there's always the chance something didn't seal, then you could fry it, and then have the misfortune of tearing it all back down, and spending all that money a 2nd time.
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update, leak down test was helpful there were 2 leaks at the cylinder base, got a new gasket and no more leaks. bike still runs bad. noticed that the exhaust was leaking quite a bit at the cylinder, got new o rings and didn't make a difference the cylinder was actually warn out where the pipe seals and i couldn't get any o-ring to seal right. used a roll of teflon tape on top of the o-rings and no more leaks. i was hoping that that would solve the poor running issues and bad vibration. no such luck. runs well at low rpms very responsive to throttle. once you try to get on it fells very dogish and rough. did a spark check seemed weak but made a 1/4" gap and it still sparked so no weak spark. hopefully its just down to jetting now. looked up a jetting chart and it calls for a 175 main at my elevation of 800 and average air temp 50f the bike has 62 idle 175 main already. any recommendation for jets. engine work is as follows, wiseco .5mm over piston, sleeved cylinder, full port and polish, v-force 2 reeds, fmf fatty, dg muffler, thin head gasket.
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That jetting sounds painfully rich for that altitude.
If it were me...I'd throw in a 58 Pilot to start, then throw in a 170 Main.
What slot is the Needle clip in?
I'm willing to bet, you'll end up having to go even a little more leaner than what I just suggested....but start with that.
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Another possibility, not to trash whomever did the port work...but it could be out of whack, and not done properly.
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Starting high on jetting and working your way down is safe..
We start at the following:
55 pilot
168 main
Middle on the clip
However, not knowing your porting specs can cause jetting issues.
So, get your pilot dialed in first.
Try a 55 and see how close your idle screw is to 1.5 turns out.
Your looking for 1.5 to 2 turns...
Once the pilot is done, then do wide open throttle chops and check your plug.
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Another possibility, not to trash whomever did the port work...but it could be out of whack, and not done properly.
Exactly what I was thinking when I made my last post.
If you open them to much in the wrong places you will need to go richer... Sometimes a lot richer because you reduced the velocity..
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Start with a 58 Pilot....as none of us on here know what your specs are. If it still feels sluggish, and blubbery, then go down to a 55 Pilot.....small increments at a time.
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I have an 88 in Goliath, and the jetting was very far off when I first fired it up. I had a lot of trouble getting it to run correctly, and eventually took Foxx's advice and bought a Lectron (which fixed the issue). Once I had the Lectron on, DoldGuy suggested I check the gasket under the main jet block. They get pretty ratty and can allow fuel around the main jet, causing issues. That was what was causing mine to act up. I found a cheap replacement on eBay. I would definitely keep messing with your jets, but it might be something to check just to make sure.
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just started messing with it put in a 170 main, ran better but was choppy up top. definitely need a smaller pilot jet, idle screw is all the way in and it still needs some throttle to run. had the needle set at 3rd notch. moved the needle position all the way down to see if it made a difference, it ran worse with the needle all the way down. moved the clip all the way to the top and it ran better than it had all month. still too rich though, give it a rev and there is still quite a bit of smoke. going to go get some different pilot jets closes place that sells jets is 26 miles. i believe the sleave job and porting was done by kustom kraft.
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also have 4 br8eg plugs for plug tests and br9eix when i get the jetting figured out
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you're on the right track.
be sure you get GENUINE Keihin jets!...aftermarket jets are no good.
I like to purchase from these guys...they're pretty quick with shipping...
http://pjmotorsports.com/
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cycle barn had genuine keihin jets got, 165,168,170,172 mains and 52,55, 58 pilot and a new air filter. putting in the 55 and 168 now.
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I have not seen this mentioned yet so let me know if I missed it.
The crank being out of true will cause a lot of vibes. I would overhaul it and get it balanced, trued and welded.
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alward, i thought about that a while ago but i just rebuilt the engine 2 months ago. the weird part is that it ran perfectly smooth, on par with my cr250, for about 3 days then fouled a plug and has been terrible ever since.
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got the jetting close with the 55 and 168 needle on second from bottom clip. (http://i32.photobucket.com/albums/d36/lazyboy246/kx/1110161532_zpsvxhlnaz3.jpg)
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how's it seem to be running now?...any improvement?
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that plug looks a touch lean...is that after a WOT chop with your new settings?
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how's it seem to be running now?...any improvement?
it does run better. but found another problem, about a 4" long crack in the expansion chamber just behind the main mount and a crack near the spring hook. think that could cause some running issues?... i can get the pipe brazed, or i can put jb weld over it since it a bit large and order a new pipe tonight.
that plug looks a touch lean...is that after a WOT chop with your new settings?
that was with the new setting a few wot 1-5 runs think i might do the 170 and set the needle on the 4th notch
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you could weld the pipe, no problem...I myself, would just take the plunge and buy a new FMF Desert, or PC2 Platinum.
Yeah, I would go with the 170, like I originally mentioned, and try a few more runs.
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I'm very close to your elevation...
I found for me, the best combo was...
168 Main
52 Pilot
N82T Needle...with clip in the 2nd from top
1 3/4 out on the air screw.
I don't think this will benefit you though.
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did the jet change and put in a new plug, decided to go a mile down the road and go up a logging road. did alright besides the vibes comin back down i stalled it and i looked down and the bike f#(king vibrated the bolt that holds the kickstarter on out so no more kick starter and no more bolts holding the muffler on either. i am realy starting to hate this bike.........
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oh man...don't give up on her...these things require love...
and lots of blue Loctite.
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finally found the kickstart in the ditch. took the exhaust off to see the crack its prety big and theres a crack almost all the way around where it connects to the muffler. gunna try and hold off on getting a new exhaust for it till i figure out the engine problem. does anyone know if the stock cdi has a timing curve? cause that could be the problem, the cdi that is on it now is off a late 70s yamaha 400 and is the last thing i can think of that could cause the poor running.
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finally found the kickstart in the ditch. took the exhaust off to see the crack its prety big and theres a crack almost all the way around where it connects to the muffler. gunna try and hold off on getting a new exhaust for it till i figure out the engine problem. does anyone know if the stock cdi has a timing curve? cause that could be the problem, the cdi that is on it now is off a late 70s yamaha 400 and is the last thing i can think of that could cause the poor running.
You need a cdi [yes it has a timing curve}
The most likely cause of vibration would be a out of true {balance}crank but i would get a proper cdi first
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can i use a 89-04 cdi or do i need the 87-89 if there is a difference. the bike is an 87
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can i use a 89-04 cdi or do i need the 87-89 if there is a difference. the bike is an 87
You would need 87-88 cdi and coil
89on cdi has less wires from stator/ think the 86 is also differant
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Finally found a 87 cdi with coil on ebay. only costed $85 100 less than most of the other cdi's that were listed. put it on the bike and what a difference runs perfectly now, just in time for the snow to start falling. gunna put the engine back in the quad frame for a fun quad for the snow. thanks for the help guys! much appreciated.
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I'm glad you got it figured out. How about some pictures of the quad with the motor installed?
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well looks like i jumped the gun..... got the motor out and installed in the quad, started it and back to square 1 with vibration so bad i cant hold the throttle........ i dont even know what it could be anymore.
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i would be double checking the crank for true , and everything else that could make a engine vibrate is everything in the clutch side correct and tight , does the main bearings fit the cases tight , go over the lot with fine tooth comb .
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You can also induce a lot of vibration through improper mounting..
If you have ANY gaps between your engine and motor mounts you need to use shims.
Shims are you friend.
Of course if your crank is not true or balanced you are fighting a loosing battle..
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i'll take the clutch cover off tomorrow and see if anything rattled loose need to fix an oil leak anyways. all the mounts are solid. if nothing shows up then i'll split the case and get the crank trued and new bearings
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i hate this godd**n bike.
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Do you have any pics of the crank?
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Any news?
Had a crank that actually went out of true once, probably due to my inexperience at the time,
Anyway, that caused some serious vibrations, the flywheel key broke in half and the ignition went all over the place...
And before everyone racks down at me, I was young, inexperienced and somewhat stupid...
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well i guess you guys could say you told me so but i took the cylinder off to inspect the crank and it looks like its out of true by 3.5mm and is pretty loose. i forgot until now that when i put the crank back in it when i was rebuilding it that it was hard to spin the crank i just shrugged it off and thought that it would have to wear in i didnt think that
maybe the crank was out of true and was putting extra stress on the bearings making it hard to spin. (http://i32.photobucket.com/albums/d36/lazyboy246/20170326_1204491_zpspjdfjfwk.jpg)
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A crank that is out of true will either wear cases or crank journals
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K5 Cranks should spin easily with only light seal resistance... and I mean light.... If it's sticky at all, you have issues..
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ordered a hot rods crank rebuild with con rod, bearings and pin. also new crank bearings and seals. should be here tomarrow