Bike still revvs out, you guys may rember this...

[MONKEYMOUSE]

Some of you may remember my bike and everything I've done to it and the problem that I had/have. My 82 YZ100 has many new parts. I have well over $400 in parts on it that have never been ridden. Brand new clutch; basket, plates, pressure plate, bearings, throw out rod everything. Fresh top not even broken in with a new connecting rod and big end bearing. Front and rear hubs were fully rebuild with new axles, bearings, breaks and wheels were trued. Bike was pulled apart and put back together with at min 50% new fasaners. New swing arm bearings in all the linkage. As well as an entire brand new carb, fully jetted and set to factory specs. All has never been ridden on and only maybe maybe 10 min of run time in total on it all. It for some reason revvs out to no end when it starts. Did a leak down test and all was well I'm at a loss. pulled the cilly and head and put new gaskets and re torqued everything still just revvs out. I'm getting very sick and tired of having all that money sitting there that is well usless. My friend just got a really nice quad and I want to go ridding! The only thing I can think of are crank seals, there about the only thing that could be causing an air leak to make it revv out, as those are about the only thing I haven't replaced. How hard would it be to do new crank seals? Although why would it pass the leak down test (granted I didn't do the test my friends father did well I wasn't present but he knows his stuff).

 

[oldfrt613]

Pull the air box off and back boot and verify that the slide is closed all the way. We had a YZ 250 which the throttle cable got "streched" in a crash. We pulled our hair out trying to find out why it revved out when we started it. We check everything - it felt like the slide was closing all the way at the throttle, but after checking every possible thing and coming up empty we found that. Go figure. If it passed crank pressure check and vacuum pulldown crank seals should be good.

 

[SirHilton17]

I know you say it has a new carb...
But clean the carb again
Double check that the jets are the same as stock..
make sure the thottle slide is down..
Umm... I bet it is somthing really simple...
You will get it worked out
I have never seen leaking crank seals make a bike rev out when it starts...
It is a old bike so it would most likely be agood idea to put new ones in, but if it passed leak down, i bet that is not it..
so, your problem is most likely in the carb.
start with the simple things, like making sure the slide is down all the way..
And even things like makeing sure that it has the right spark plug, even try new gas.

 

[MONKEYMOUSE]

Oh also it did this with the stock orignal carb. the threads for the idle screw stiped and the carb needed to be rebored as well so I just bought a new one. I've already checked the slide and it is closing as wellas you can hear it bottem, also I am absolutely positive the main jet is the same as stock. I doubt that float hight or the secondary jet would cause it to revv out but I'll recheck them as well. Oh also the bike is extremely hard to get it to start but when it does it just hits the rev limiter. I was thinking crank seal because wouldn't the excess of air cause it to revv as well as being hard starting? I really just wanna get this problem resolved after over a year of going through this bike.

 

[ps2112]

My KX does the same thing. I read once that the reason is condensation in the cylinder making the bike run real lean. What I do is fiddle with the choke. I turn the choke on, start it, it revs high, push the choke down and it settles down. You may need to feather the choke for a bit. I would also go one richer on the pilot.

 

[MXP1MP]

Used to own one of those there's some rattle noise plus it's an air cooled bike. Do you have the boost bottle setup okay? (that should be alittle black box under the gas tank with a strap holding it closed with a hose leading right down into the rubber boot between the carb and reed block. There are no leaks around the reed block? Worn main seals would probably allow oil from the crank case into the cylinder that should cause it to bog and not want to run cause it's running very rich.

I think it's time for some carb cleaner and check for air leaks rpms should drop alittle while the air leak is being blocked. unless the bike is starting up like wide open it's okay maybe hold the throttle open and kick it threw few times to try and get some lubrication don't want to cold seizure it now. (don't start it right away i mean)

When you get that bike running it will be a blast! very little bottom decent mid/top definetly ride it wide open :) was a unique 100 cause it had full sized tires. I have the MXA test in jpeg's also. I used to ride it back in the mid 80's and used to race 125's with it and beat them pretty awesome for a bike that only made about 2 more hp that a stock liquid cooled 80 of the era!!

 

[MONKEYMOUSE]

Yeah I've ridden the bike befor and it was a blast, but it sat for a year when I had my knees get all messed up and then started acting up. The boost bottle is connected correctly. I as well as I pulled the reed spacer block that was in there, and bought a brand new reed cage and rad valves. All new gaskits as well. I've tried feathering the choke that did nothing. I tried bliping the kill switch to kill the rpms, that worked once but the bike died soon after and didnt work a second time I tried that. Im afraid to let the bike sit there revving to the moon well I fiddle with things seeing how the top end isnt broken in yet. Oh and MXp1mp you said you have some tests of the bike, would you mind emailing them to me? [email protected] Thanks. I would love to stop throwing money at this bike and just get it running correctly.

 

[MXP1MP]

Well that sounds like you've elminated any possible air leaks then and compression test should tell if anything like the head/cylinder was the problem. It ran fine before parked/worked on you didn't mess up the timing did you ? but I don't think it's that either, I doubt the coil/cdi box just went out on ya all of a sudden. The only bike I ever had problems with doing that was my old '80 RM 125 it used to fray out throttle cables. I know some bikes when cold rev alittle higher with the choke on but it should stop when turned off. It sounds alot like an air leak from what you describe cause if it was electrical it most likely wouldn't run or if it did not very well. When you start it how high is it in the rev range? like a quarter throttle/half/full?

If you get sick of it you can always send it to me in boxes :p I wouldn't mind having one of those again. I'll send ya the pic's later not on me at the moment.

 

[MONKEYMOUSE]

Its justttt under full throttle when it starts, I'de say between 3/4 and 7/8 throttle.Timing hasnt been touched. I as well as a cuple local shop mechanics are stumped. If you are seriously intrested I'de like to get about $700 for it. I have all recipts as well; some are from around 2002ish but it hasnt been ridden since any money has been put into it.

 

[TD3]

I just picked up an 82 yz100 last week for $150. The motor is in apart, but is complete. I'm thinking of putting it together as a play bike. My yz450f is a little much when chasing around my 7 yr old on his xr70. I'm hoping I don't run into any strange issues with the motor, time will tell.

There is not a lot of info on the web about this bike. I would be very interested in the MXA test in jpeg form.

 

[MXP1MP]

Nah I can't take no YZ 100's right now I all ready have a hard time trying to ride my new '06's :) I could send ya them also if you like.

 

[MONKEYMOUSE]

For free! Sure!! lol I'll even pay the shipping to my door lol.

 

[MXP1MP]

haha no to TD3 the MXA test jpeg's. So have you tired push starting the bike and running it down the street to see if it doesn't just clean out after getting warmed up? I mean push start and pop it into at least 2nd gear at first try for 3rd gear. You can always stop pull in the clutch and hit the kill switch should make for turning around fun just keep it in the higher gear so when you drop the clutch it will want to bog down more and the possiblity of it stalling is greater don't need to loop it out cause it was in 1st gear. Make sure you don't have the cable to tight for the throttle housing. You should try to ride it like this if ya don't even up in the ER :) let me know if it made any difference. You should be able to get some sort of control with the throttle in controlling the rev's. I mean when you give it gas does it rev up like it should normally? only a few mins should be good.

 

[TD3]

MXP1MP: Could you send them to [email protected]. Send along any pics you may have of your old 100. Thanks!

 

[MONKEYMOUSE]

I've tried push starting the bike but it didn't work and I didn't want to loop it out and break somthing or hurt me. I haven't tried to ride it either the way it is. Also the past few days its been in the teen's and with my 55 chevy in the garage theres no room to work in there so I'll have to wait for some warm days again to try some more things. Although I really don't no what to try. I wish some more people could chime in and give some more insight. :bang:

 

[QKENUF4U]

might be to easy but did you try turning the idle adjustment DOWN. being a bike tech ive made this mistake and screwed it in to far, start the bike an up goes the RPMS. scratch your head for a bit then think "what the heck, ill turn the idle down" and whola thats it.
dont see it being a seal but then you where NOT there when it was done so you dont know if the dad even did it right. maybe he blew a seal out by putting to much pressure in the motor ??? sounds like he might have blown the stator side seal allowing it to suck air. might be worth your time to change the seals.
good luck

 

[Joeschmo]

check the pilot jet thats what was wrong wiht my gt80

 

[MONKEYMOUSE]

I've messed with the idle. I'll check the piolot jet but pretty sure its correct. The stator side I dont have to split the cases for correct? Pretty much just pull the fly wheel and what not and pop the new seal in right?

 

[MXP1MP]

Tear it down to the seal, sometimes for a qwick fix this works. take a short in length like wood screw or something that has good edge's drill into the seal part way with some of it sticking out and it should pull out with some plyers. If you got a replacement it doesn't matter if it gets damnaged.

When you install the seal put a small film of white lithium grease on the edges betwen the cases and the shaft. Try your best to make sure it goes in evenly especially at first. A good socket the close the outer diameter size of the seal works good long as it's deep enough. If it was the other seal would most likely be sucking oil.

You should have gotten mail for me also.

 

[MONKEYMOUSE]

Alright I'll order the seal when I get paid on wends and try that, hopfully it works. And yes I got your mail, thank you...I read what I could, seems like it was a hell of a bike when new.

 

[MONKEYMOUSE]

Alright I no this is an old thread but insted of starting a new one im bringing it back to life. I still havnt done the crank seal, but just this past week I pulled and cleaned the carb, pulled the rad assembly and re installed it with all new gaskits and what not. New plug, new gass, cleaned air filter. Now it wont start period. Ugh I'm so sick of this bike, im about to just sell it and take the huge loss of money in selling a non running bike. Hell even if it was running ide take a dive as I've put more money into it then its worth lol. Any ideas? I guess I should just really get the crank seal and try that. But if you have any ideas I could try that would be great.

 

[SirHilton17]

thats probably it... If you have narrowed everytihng down, and thats your last idea it has to be it...
Its an old bike so its really posable... If I were you I would give it a shot

 

[MONKEYMOUSE]

Yeah I guess I have to stop being lazy and drive up to the yammy shop.