runaway maxim! ahhhh please help

so i finally decided it was time to put some gas in the bike and get it ready to take a spin tomorrow i put gas in and sprayed a little starter fluid on the pod filters and fired her up.... suddenly and with no regard to my repeated demands that it stop, the engine started to redline and it didn't take any scenic routes to get there i'm talking wide open throttle straight to the redline i finally caught a hold of myself enough to flip the killswitch... i sat there for a moment trying to comprehend what was happening... well... maybe it just had to burn some fuel out of the float bowls i thought... i started it again and the same thing happened. suddenly i notice a funny bubbling noise and look down and probably a quart of oil has shot straight from the crankcase breather to my pant leg i absolutely cannot figure out why this is happening... i cleaned the carbs right before i put it away and left them with heet in them as to not gel the gas inside them... i checked the petcock for leakage and on the prime setting it flowed like a siv and on res or on it didn't leak a drop... figure that means its working well. i checked the throttle and it all seems to be attached and working properly i just can't think what it would be..... would like some input.

 

p. s. i have pod filters and a mac exhaust on my bike... thats about it as far as mod's are concerned...

 

how was the oil level after it shot a bunch of it out?

 

near empty, it spat just about all of it out

 

Was the bike running properly when you put it away, or is this a new project for you? Why did you feel the need to use starting fluid, did you try it first without? Has the tank been off since the last time it was running correctly?

Sorry for all the questions but as far as I know, the only way to get that kind of pressure out of the breather would be serious piston ring damage, as it would then transfer the combustion chamber compression pressure into the crankcase, and vent out of the breather. I ask about the previous running of the motor because if the rings were in particularly bad shape to begin with, then managed to detonate in a violent fashion (ether), I suppose the rings could have broken up. If you are new to this bike I suppose that poor maintainence and bad filtration could wear the rings and cylinder bores enough that these pressures could exist from past neglect as well. Have you done a compression check? Dry? Wet? What are the numbers?

Forgive me if I overlooked something else obvious. The last thing I want to do is worry someone unecissarily.

Best Regards
XJ750Guy

 

the bike ran fine when i first got it, it has around 15000 miles and i started it up the day i bought it drove it around and then decided that it was time to start modifying. i stripped the whole thing down and did some modifications to the frame to change it to my liking and have since put it all back together. i tried to start it a few times unsuccessfully with just the choke and rolling on the gas a tad but i figured since it had been a while since it had any gas in the tank or anything a little starter fluid wouldn't hurt. it started right up after i sprayed that and then proceeded to take off on me. i have had the tank off for quite some time now as i've been stripping it and painting it and such. i haven't done any kind of compression test as i don't have a tester, i plan on doing that tomorrow first thing... I'm kind of thrown off by the whole thing because i'm pretty darn sure it has good compression, i obviously can't verify that til i have numbers but i really think it does the crank case fluid (yes its no longer oil) i've decided is a mixture of gas and oil since it smells like gas and doesn't really look like just oil... that would lead me to believe that the petcock is leaking but i tested that right before i put it on the tank and started it up today... i don't know if there is any other way to test that besides just switching the valve as i did (if you know a more in-depth test please inform me) that being said the next thing is the carbs not functioning properly... that is more a possibility than the petcock i believe since i haven't seen the internals since i cleaned it a couple months back, but i took my time and got them spotless as to avoid this kind of thing, i stored them as best i know how and i don't think any gas has gelled inside of them (i could be wrong still) after that the next question i thought is the vacuum line that goes from the intake to the petcock... is there some reason this would produce too much pressure (or vacuum) so that gas was dispensed too freely? i can't really think of a way to test this so again if you know of a way please inform me. i really think it has something to do with the fuel system since there was little to no throttle response and the engine was going straight for redline (meaning, i assume, that the engine was taking in gas at its own accord) those are my thoughts... feel free to share any you might have... hopefully a solution can be found! thanks so much guys. -07spacker

 

After cleaning my carbs and reinstalling them, I fired it up and had the same thing happen. WOT, redlining, turned it off after a split second of "whoa!" shock. Turns out I hadn't secured the throttle cable to the carbs correctly. Secured the cable, and she purred like a kitten. I don't mean to question you or anything, but you might want to double check that throttle cable (make sure it naturally goes back to idle) is secured properly on the carbs.

 

well i did tear the whole thing apart, so it is possible but looking at the whole throttle body they move in unison and return to a nuetral position after rolling on the throttle... i dunno how to explain it better than that... i'm mostly worried about the oil for the moment... ick... it makes me sick just thinking about my dirty shoe

 

Did you bench-sync the carbs before you put them back on after the teardown? I had a similar issue on my bike, except it only went to about 5K rpm "idle". I pulled the carbs and bench-sync'd them and the problem was gone.

I was really surprised how subtle the sync adjustment was. Just looking at them I thought they were fine. But when I shone a flashlight in the intake side and observed from the outlet side I could see slivers of light around a couple of the throttle valves. So I adjusted them until all were of equal darkness. Then it ran fine when I re-installed.

 

hmmmm i did not think of that... i think i'll have to add that to the list of things to do tomorrow.. is there a write up anywhere on how to do that?

 

I think this post might have something to do with that topic: How To Bench Sync Your Carbs :wink:

I prefer my flashlight technique to the paperclip. It seems to me that one could easily scratch things with the paperclip. But the basic procedure is the same, only the measurement device is different.

 

awesome i just read that and read the comments afterword and rick said he used a strip of a business card... that seems less abrasive than a paperclip... then again i could just go to autozone and get a set of feeler gauges and be legit. either way i'm doing it tonight in the wee hours of the morning after i've partied all night. any thoughts bap3826 on where the oil may be coming from? could there be a relation between the sync of the carbs and the profuse leakage of gas/oil from my PCV? and is there any chance the valve itself could be failing? i know its kinda farfetched but it seems like that'd be an easy thing to verify and i like easy!

 

I suspect it is related to the gas contamination of the oil. Once you change the oil I wouldn't be surprised if it went away.

If you have the carbs off tomorrow, you should check the float levels. I believe that high float levels (or plain stuck floats) are the prime way to get gas flowing into the cylinders and contaminating the oil. Might also contribute to the crazy rpms.

There was a post the other day about how to check float levels while carbs are on the bench.

Not sure if feeler gauges are necessary for bench sync. You are just trying to get all the throttle valves the same. I don't think it really matters whether that's all set to 0.0 or 0.1.

I'm a newbie though. So be suspicious of my advice. ;o)

 

hahah i'm willing to trust your advice, you seem to know your way around thanks so much for the help, i'm going to get to working on it right now... yes i'm starting at 12:48AM but thats how we do it.

 

alright....... i've returned from my venture to the shed... its now 2:37 AM... and i've realized that i'm an idiot. i went about syncing the carbs and i think i made some improvement in that sense but i found out why my throttle was screaming... in my haste to rebuild the bike (or due to the carb cleaner fumes) i attached the choke cable to the throttle body and the throttle cable to the cold-start body... ya... so pretty much when i started it with full choke (or so i thought) i was at WOT. that explains why it was screaming.... as for the oil... thats tomorrows project. still looking for any input from anyone as to ideas.... a question:

-if i suspect that my petcock may be leaking can i add an additional fuel shutoff in the fuel line? would that contradict the original leaky petcock? i think i've read somewhere that someone did it but now i can't seem to find the post.

 

If you added a manual shut off in the fuel line between petcock and carbs, it would prevent bad petcock from leaking fuel into carbs. It would also serve as a kinda theft prevention device. Nobody would think to look for it. Check the petcock, make sure that no drips (disconnect fuel line from it) when in "on" or "reserve" position. It should flow when in "pri" position. If it doesn't drip in the "on" or "res" position, then it checks out as good.

 

see thats what i was thinkin and thats how i tested it originally but i'm still going to add an extra inline one as it is so much cheaper than rebuilding the whole petcock.

 

I would rather fix the petcock. I just got mine to stop leaking - finally - by following some of Chacal's advice. I opened it up and lubed with silicone grease plus removed a burr on the o-ring seat. Not a drip since.

Until you get the time / parts to rebuild, when you are not using the bike just pull the carb supply hose from the petcock and replace with some kind of plug. I used a small chunk of hose sealed at one end.

 

hmmmm..... alright i suppose i'll give that a shot before i spend a few bucks and get a new shutoff... i suppose i'm kinda the opposite of most people here, i'm not opposed to spending some money if i can get it done quicker (thanks to the fact that my living expenses involve only a cell phone and i work 45 hours a week at 14 bucks an hour) the thing i don't have much of is time... so i'd like to get it done quickly. but i like your idea and i'll give that a shot here before i go get one.

 

Maybe just get a tube of silicone grease and try that. I think it is pretty cheap ($5?) and really useful for anything carb related.

 

Sounds like you h ave a handle on the problem.
I Bench Sync with the sliver of Business Card because it conforms to the circumference of the throttle plate and carb body without marring anything of causing a scratching situation.

High revving after the Carbs are off is usually due to hooking up the linkage wrong ... or, in many cases, capturing the Carb Linkage Throttle Cable Connection beneath the Cylinder Head.

If you do catch the Carb Cable Linkage hook-up under the Cylinder Head it forces the throttles almost wide open.
This is a very common thing to happen when the carbs have been off.

Just don't try and pry that connection loose. Bending it enough to free it might break it or cause the linkages to bend and then you'll have throttles that will stick open.

Also, giver yourself some slack at the Knurl up on the front control lever perch. A little slack goes a long way to bringing down rpm's and getting the carbs ready for a proper tuning.

 

alright i've returned from my trip to autozone and have a tube of silicone grease a inline fuel shutoff and enough oil to change it twice... i'm hoping that will clear out all the gas that may have seeped into the crankcase and fix my possibly leaky petcock... i'll be dammed if this doesn't fix the problem! i feel like such an idiot over the throttle thing still... one of those times you wonder where your brain was.

 

I'm a little surprized the Choke Cable End-Stop (Bullet end) didn't slip right out from the Carb Linkage Holder.

The Bullets for the Choke Cable are smaller.

 

Just goes to show what a good night's rest can do for you Spacker. A clear head is a necessity to win the battle...
I'm not sure what might be the problem with the oil. Good luck on that one!

 

hahaha ya... i'm still kicking myself over it. alright so after installing the inline fuel shutoff greasing and cleaning the petcock and changing the oil twice i've got the bike up and running with no more projectile oil spraying... (crossing fingers) but i've come across a new problem..... I went to ride my bike out of my shop (after an hour and a half of shoveling snow/slush to make a path) and i can't seem to shift into any gears besides neutral... it would seem that something electric is keeping it from shifting gears i thought it would be possibly:

Clutch Engagement Sensor

Kickstand Sensor

i'm thinking it's probably the clutch one since i have removed the entire switch of the kickstand one but maybe that is my problem... i just figured if i disconnected the quick connect and removed the switch it would just let the bike ride fine in case you accidentally broke it off or something and needed to ride home (mine was of course removed intentionally) I visually inspected the clutch switch and from what i can tell it looks to be intact but i do not know where the actual relay is.... ya.... so if anybody has any ideas as to what else could cause this problem or has had something similar feel free to chime in! Thanks so much for all your guys' input, i really wouldn't have a functioning XJ without all of you

 

<fx: Pops head over parapet>

Is it going into gear when the engine isn't running?

Try for first, then push the bike forwards to check it's in gear. If that works, try going through the rest of the gears. If they all select happily from there, I'd suggest (assuming the cable is free and adjusted correctly and the actuating lever is happy) sticky clutch plates.


HTH?

 

For clarity: do you mean that it mechanically won't shift into gear or that when it pops into first gear, the bike dies as if it were shut off?

 

i suppose i should have specified, ya it will mechanically go through all the gears buttery smooth buit something electrical is killing the bike once i do.

 

It sounds like one of your safety switches (or relay) has malfunctioned, but which one? That's a question you'll have to suss out for yourself. Better get your tester out and start testing.

 

The Prime Candidate is the Side Stand Switch and the Safety Relay.

The Side Stand Switch is prone to being a problem. The Switch's placement makes it easy for dust and dirt to sneak in and keep the Switch from opening and closing.

The mechanical part of the Switch ... the Rod that extends through the Side Stand Hinge ... often gets dirt-fouled and fails to move within its full travel fooling the Switch.

Remove the Switch
Remove the Dust Cover
Remove the Rod
Spray-out the Switch with WD40 of Electric Contact Cleaner
Clean the Rod.
Clean the Expansion Boot
Clean the Port the Rod extends through at the Hinge.
Lube the Port.
Reassemble and test for starting and function.

Similar issues are involved with the Clutch Lever Switch.
Clean
Insure that the switch is firmly mounted within its holding port.
Lube
Secure with a small plastic tie inserted within the bracket holding the switch
Use the tie wrap as a shim to keep the switch from moving.
Remove excess plastic
Insure its tightness
Test function with Meter or Test Light.

 

Spacker you said you removed the kickstand switch, it that still so? You will need to short the connector on the bike that the switch plugged into. At least you do on my bike. The PO on for mine had made up a short piece of wire with two female spade connectors. It was formed into a U shape and plugged in where the kickstand switch should connect.

 

ya i did remove it... i tried just splicing the two cables together but that didn't change anything so i think the clutch one is my next move... i'll get on that tomorrow as i have a lovely half-day at work

 

so my bike still won't shift out of neutral... any ideas? i pulled apart the headlight to get to the main wiring and unplugged the clutch sensor and still no luck on getting it to shift....

 

The problem is a mechanical one ... not an electrical one.

When the transmissions on these XJ-Bikes get bound and the shift drum won't rotate it's > usually < because there is foreign matter clogging-up the gear exchange channeling on the shift drum.

Namely: Particulate from the Primary Chain Guide.

There is a "Quick Fix" that allows you to pull the Shifter Cover and probe through an opening into the Tranny and try to extract the material clogging-up the works.

I don't remember the exact wording of the Thread ... but, someone will come along shortly and have it.

I have never done the Primary Chain Guide Chunk Removal procedure.
The few that have ... have enjoyed some success.
Search the archives along with me and let's see if we can locate the emergency procedure.

 

Unless the wiring is way messed up the clutch switch won't kill it. That's to prevent starting in gear without the clutch pulled.

This sure sounds like a sidestand switch issue. To clarify - the bike will not run with the sidestand down unless the transmission is in neutral. Even with the clutch pulled.

You can see if the sidestand switch is your problem by unplugging the sidestand relay. The sidestand relay attaches to the wiring harness just behind the coils.

If you have the Yamaha service manual the picture on page 13 of the J supplement is the relay (The caption says Starting-circuit cut-off relay, which is incorrect).

 

i pulled the shifter cover and didn't notice anything... i'll do it again and make sure that i don't see anything. to clarify, the bike will shift into gear just fine the engine just dies when it does such. the clutch is engaging because there is no jump or lurch forward when i do it it just instantly cuts power to the engine. (or so it would seem) i have no sidestand, sidestand switch, or sidestand relay, they've all been removed and now there is just two wires 1 green 1 red .

 

If you unplug the starter circuit cut-off relay and jump together the two red/white wires together, will the bike keep running after going into gear?