hit bumps and bike cuts out

[Clutch]

hey all,

It's been a while since I've visited the forum. Glad to see it is still alive and kicking!

I've got a problem with my bike cutting out and/or dying completely when I hit bumps going down the road. I know it sounds like it should be an electrical problem, and I'm hoping you could point me in some places to look for common connection problems. I'm also interested in any other kinds of problems you can think of that may cause this because I have looked over the wires and wiggled them while the engine is running and haven't been able to reproduce the problem in the garage.

For example, do you think it could possibly be something in the carburetor?... I just read a post about balancing carbs and someone mentioned that the vacuum tube operated some valves to improve air quality. I'm not familiar with this but could these be causing problems?... I'm grasping at straws here.

Thanks in advance,
Clutch

[montmil]

Old Airhead semi-truth, "Most carburetor problems turn out to be electrical."

Check the ignition coil mount to confirm the metal bracket is not cracked and causing an intermittent short.

And rather than, "looked over the wires and wiggled them," it may be helpful to remove the multitude of ground wires from the main frame cluster mount -right side aft of the coil. Clean 'em up and add a smear of dielectric grease.

Check the Ignition Control Unit (ICU) wire plug-in and the transfer heat paste may need renewing where the ICU mounts to its heat sink. Both the dielectric grease and heat paste are available at the Shack.

Check the ignition switch leads; confirm none are loose or rubbed bare against a ground source.

The "bump" is more than likely causing the stop-start issue so do a very complete inspection while thinking like a pot hole. report back what you discover. Luck to you.

BTW, disconnect the battery's ground wire before making inappropriate sparks.

[Bob_Roller]

If the engine quits like you turned off a switch, it's an electrical issue .

No easy fix here, like Monte said you need to go through the bikes wiring and find a loose/broken connection .

Can you tell, does the entire bikes electrical system quit , or does the engine just quit, does the tachometer go to '0' when this happens ?

I know if you ride during daylight conditions you probably can't tell, try riding the bike with the headlight in high beam, at least you have one light illuminated in the instrument cluster for a reference .  

[Clutch]

Thanks a bunch guys. This is just what I needed to help get the troubleshooting juices flowing. It may be a while before I get to check this stuff out, but I will be sure to post any updates.

[Clutch]

Oh, and I'm pretty sure it isn't the ignition coil. I've had this cutting out problem for quite a while. After this problem manifested, I replaced the ignition coil with a new dyna from motorrad elektrik because I was having hard starting in cold weather. The dyna coil fixed the starting issue but not the cutting out issue.

[Bob_Roller]

I had a problem with the entire electrical system quitting, I was doing a lot of night time riding and all of the lights would go out with the engine quitting .

I never found the 'smoking gun' that caused the problem, I went through the entire wire harness, checked all of the connectors, found a few that were'nt pushed together all the way, this was in 1997, problem hasn't come back yet !!!!!

[nhmaf]

It could be that your kill switch or ignition switch has a loose connection (or, kill switch itself might be in the process of deterioration)   kind of hard to diagnose, but if the coil and other grounds issues don't turn up the culprint, maybe you can try point the bike on the centerstand, start and run the engine, and then try thumping the handlebars hard with your hand and/or pushing down hard to compress the front forks and releasing them to simulate hitting bumps.   If the problem manifests itself there, then I'd look into the electrical connections at the ignition switch and kill switch on the handlebar.

[tvrla]

I'll echo all of the above! Good suggestions all. Especially the kill switch. Do you hang a lot of keys hanging off your key ring? The extra weight can eventually destroy an ignition switch.

No easy fix - it's in the wiring somewhere. Let's hope it's not a broken wire in the harness somewhere that you can't see.  

[Clutch]

Thanks for all of the suggestions. It is a strange problem. I took it out last night and it died a couple of times on me while riding down the road but I was able to pop start it back up before I stopped rolling and head down the road a little further until it happened again. I was able to limp back home. There are some occasional backfires associated with this when the engine dies. It's like when the engine vibrations and road bumps get too violent then the problems start but as the engine dies and I begin to slow down I usually can get it to start again. I was only stranded once last year where I couldn't get it started in the afternoon after limping into work in the morning.

[Bob_Roller]

With your mention of 'back fires' from the engine, it is an electrical issue .


Another wild guess, check the security of the fuses, they are not the greatest design and can become dislodged rather easily .

[montmil]

I'm still on the electrical issues side of the fence but I have a question for you.

Have you dropped the float bowls and checked for water and/or debris?

[Barry]

A backfire suggests the ignition is being cut intermittently.

When you  lose the spark the engine stops firing and unburn't fuel mixture is pumped into the exhaust. As soon as you get a spark again the exhaust flame ignites the mixture and results in a back fire.

[Clutch]

I seated the fuses, and cleaned the carbs. May try to seat the fuses again. This may sound dumb, but I was actually hopeful I had fixed it the last time I looked at the bike. I found that the air intake tube connecting the airbox to the right carb was letting some air in because it wasn't fully connected. I seated that properly and rode it to the gas station last year to fill up for overwintering and the thing ran perfectly fine. Last night was the first time I ran it this year and the problem is still around. Oh well.

[montmil]

...and rode it to the gas station last year to fill up for overwintering and the thing ran perfectly fine. Last night was the first time I ran it this year and the problem is still around.

Fueled up last year. First start in March of next year. I think I'm reading this right.

Did you add any fuel stabilizer last year? Could your problem be stale gas?

[tvrla]

I'm getting a bad feeling about the Hall Sensor. I wouldn't ride the bike too far from home and keep a cell phone handy.

This doesn't sound like bad gas to me. A little like water in the float bowl, but usually that doesn't make a backfire. And stale gas doesn't either, just runs shitty.

I think a failing Hall Sensor would be the worst case scenario - an intermittent electrical short (or open) in the ignition circuit at the other end of the spectrum.