K5 vibrates real bad.

[dirkster]

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.   

[umberto]

Have you checked the flywheel and ignition to see if everything is tight and in place?

[dirkster]

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.

[sandblaster]

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.

[dirkster]

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.

[Foxx4Beaver]

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.  

[Brute]

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...

[dirkster]

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.

[sandblaster]

On the VF2's you should remove all the screws and put them back in with retaining compound...

[Foxx4Beaver]

On the VF2's you should remove all the screws and put them back in with retaining compound...

+1...
I use yamabond.

[dirkster]

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.   

[Foxx4Beaver]

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.

[big green]

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. Good Luck!

[dirkster]

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.
 

[Foxx4Beaver]

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.