Engine cuts out when front break applied hard

Did a search but can't find anything, this is a really useful forum though! Already learned how to rebuild my forks, which I need to do at some point.

I got this bike in the fall, my boss gave it to me (woohoo!) needed front brake work and battery. I ran brake fluid through the front MC and bled it out, the front brakes work very well now and the handle is nice and stiff (I've done brakes on my '80 kawi). I also replaced the battery.

I found out that this bike cuts the engine when you put the kickstand down (neat), but the same exact thing happens when I apply the front brake hard (using it lightly doesn't seem to shut off the engine). I am wondering if anyone has had an issue like this before. This bike is new to me so I don't know if anyone has been in it and screwed with the wiring in the past.

 

Talked to my boss and this didn't happen when he had the bike. However the key on the bike is very finicky, you have to get it in the exact right position for the bike to start (and the lights to come on etc.) so I'll do some more testing to see if the key is getting wiggled somehow... I need to just replace that section or open it up and find why it is loose.

 

2 things come to mind.

1. the side stand relay (green in the headlight bucket I believe) is coming on (maybe from the force of the brakes?) and killing the engine. Try disconnecting it and doing the hard braking again. Just remember to put up your kickstand before you go. I know that relay can be a pain. I've had to tear my bike apart to mess with it due to a bad connection. IF that is the problem, I'd hit it with electrical cleaner and a dab of di lectric grease. Also, on the side stand, make sure that little plunger that tells the bike if the stand is up or down is not loose or too tight. You can usually just lube it and it should be ok.

2. The ignition is cutting out. I'd pull the ignition (headlight first) and I believe it's 2 10 mm nuts that old it on. Get a good cleaner (my locksmith uses gt85) and soak that sucker from the topside. It should come out a small hole on the bottom. And you'd be amazed at the junk that'll come out. You could also take it to a locksmith and ask him what's up with it. If he's good, they'll be no charge and you'll probably buy some lubricant off him anyway. Let us know!

 

once you get the ignition switch out you can take the bottom part off and see the electrical part and not mess with the key lock part

 

I'm having about the same issue.

However it seems like mine is either a fuel or generator issue, as my engine doesn't shut off completely. I just have to make sure to give the engine a little throttle if I'm going to be braking hard. The harder I brake, the more throttle I have to provide to keep the engine alive. It seems like braking hard is emptying the carbs of fuel? Not sure what the issue is though and hoping someone has had the same issue before.

Thanks for any help.

 

Your sidestand spring is still nice and tight right? I noticed that mine was weak and if I hit a speed bump in my neighborhood the side stand bounced a little and cut the ignition for half a second,I replaced it right away and the problem is gone.Or maybe floats not set correctly?Not sure if you could get one that far out of adjustment but its an idea that sounds possible

 

That's a good thought ratchetmxr. I think you might be right actually. I do have issues with the sidestand sensor sticking, so it's likely tripping and then springing back to the safe position. I think I'll try shorting the sensor and see if it changes.

 

Too much oil?

 

i would suggest doing this also if you havent already re-wire

 

my 2 cents float levels are wrong gas is either starving or spilling into the intake. i had the exact same problem except mine was accelerating when you powershifted would nose over from the momentum if it was electrical applying the brakes slowly would do the same as fast the switch still enguages at the same time if it was a broken wire it shouldnt run at all i dont believe . if you have someone you can ride beside have them follow you hit the brakes see if it blows black smoke

 

My 82 XJ650RJ will die under hard braking but only if the choke is still on when cold.

 

***ding ding ding*** Bob, tell the man what he's won!

Correct answer, unless it's an inertially-generated electrical connectivity issue. But this is the best answer, for more than one of the responders as well.

 

Yeah I'm thinking now that's more likely than the sidestand sensor. I made sure to watch the display as I braked and the sidestand warning indicator didn't come on, so it's gotta be the float levels, or another fuel/carb issue.

Also, I have K&N filters and the exhaust baffles were removed by one of the previous owners, so maybe instead of rejetting, they raised the float levels to avoid running too lean? Does that make sense? I'm going to watch my mpg's at my next fill up, and I'm guessing I'm not getting too great of gas mileage, another indication that I need to drop those float levels, and probably rejet....

I know running lean is terrible for the health of your engine, but what are the health issues related to running too rich?

 

My bike would also die under super hard braking, turns out my choke/enrichment was slightly on causing a whole bunch of gas to drown out the spark at lower RPM. That seems consistent with your issue as you say keeping the throttle open a bit keeps the bike running.

Before taking everything apart to check the floats (still a very good idea!!) I would check that the choke can close all the way.

 

this wont solve your problem but another way you can tell if its the floats to high is to pinch off the fuel line start it let it run for a bit till it begins to run out of fuel should idle better before running out of fuel. if the floats are off after you set them i would replace the plugs sync the carbs and ajust the idle mixture screws. will be worth the effort in the end .

 

Thanks for all your help guys.

It looks like I'm getting about 40mpg, which isn't too low (is it?) considering I'm doing all city driving, and I'm not exactly taking it easy the whole time.

Yesterday I had to make a short drive, and I was in a hurry (lots of hard breaking and short lasting acceleration, not much constant speed operation) and by the end of my trip (~12 min) the engine was hobbling a bit, seemed like the cylinders had a bit of extra junk in them that didn't get combusted. The next time I ran the motorcycle, even a little choke sent the engine to 4k rpm and no choke would kill it. After messing around with the idle and some revving to clear out the cylinders, it seems to be running much better today.

I really want to take the carbs off and do a top notch job on them when I get the chance. The lab that I work at has an ultrasonic cleaner, and I can't wait to take them for a dip.

 

Thanks for all the replies guys! I hadn't come back in a while as I was having car issues so was working on that (yay ball joints..)

Anyway I am embarrassed to say that this answer was the problem... I got the bike last fall w/ some brake issues and battery issues. Fixed them over the winter so I didn't have much experience with the bike, so I'd been riding it with the choke on. Stupidly thinking it was just idling really high and I'd have to adjust that some time. I'd still like to look at the wiring for the ignition to make sure it stays on always (gotta get the key in just the right place) and maybe get the carbs off and cleaned, and reset/balanced, but that is a big job for me.

 

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Trying SEAFOAM on full tank would probably give you a better idea, if its clogged jets..the treatment would improve its performance. Whether its hardtreatment or soft..make sure you dont let the bike sit overnight with seafoam...just run it till its time to fill again.