Engine cutting out.??

VMAX  Forum

Help Support VMAX Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

kalbo

Well-Known Member
Joined
Dec 26, 2016
Messages
109
Reaction score
0
Location
Angeles City
Wasn't sure if this should be in Electrical or Carb/Tuning?
Just recently, my bike has been cutting out. It starts first time and runs great with full power through all gears, but....after about a half hour riding, it just cuts out. I only have to leave it a few seconds and it starts straight back up again. and runs fine, for about another half hour, then it happens again. Sometimes, I don't even have to stop....If I have enough speed, I just pull in the clutch and coast for a few second, then hit the starter and she fires back up.
I thought it was the plugs, so I've changed them, I thought it may be the gas, so I drained and changed that. But, the problem is still there.
Like I said, If a journey is less than a half hour, there is no problem. It never happens unless the engine has been running for more than a half hour.
It's almost as if it has run out of fuel
Any ideas?
 
Thanks Bill Seward. I have checked the gas cap and it doesn't appear to have any obvious vent. Is the gas tank vented other than through the cap?
My mechanic wants to do a full strip down to clean the tank, fuel lines, filters and carbs. I was hoping that there may be a more simple and cheaper solution. Fuel starvation would appear to be the cause, and if I could check out 'the tank not venting', it may save me $$$$. were should i start??
 
The "other" line coming out of the tank is the vent line. If that's clogged or pinched, the tank won't vent properly and will fuel starve the bike. Does it stumble or just quit? It could be coils doing dumb stuff and opening up when they're hot (unless you have COPS, I can't remember).
 
Thanks, but 'WHERE IS THE VENT'. It may be a blocked vent, but do I have to remove the seat to find it? I can't find anything online showing where the breather vent is?
 
OK....Thanks guys....Found the fuel tank breather tube. It appeared to have touched on the exhaust, which had melted the end of the tube sealing it closed and wasn't venting. I have cut an inch off the end of the breather tube and it appears to be venting now. Will run it today and see if the problem is solved. thanks...what a great site this is !!!!
 
I had the same problem. Vent hose melted. When you open the gas cap, can you hear a whooshing sound? That would be a venting issue. I cut mine off near the tank and stuck a fuel filter to catch any exiting gas/vapor.

However, if you run the bike and it dies and then starts right back up, dont think its a venting issue as will take a few minutes for air to go back into the tank. Also check your fuel filter and fuel line. I had a pin hole leak, but again, if your bike starts up right after it dies and runs fine for another 1/2 half hour, dont think its a fuel issue.
 
Took her out again this afternoon....and the same thing happened again. No problem with the gas tank venting. it's venting fine, but is still cutting out after a half hour riding. Starts up again immediately. I have to admit that the bike hasn't been ridden hard for a long time. I mostly just cruise around town and hardly ever get her out of 3rd gear. When I go for a longer run, I usually have my wife on the back and she doesn't like me to go over 60 mph.
The bike hasn't been over 3000 rpm for months. Maybe she just needs a good hard ride and she just needs to get her heart pumping and clear the shit out of the carbs. Maybe, this is her way of telling me to get my finger out of my a** and ride her properly. Tonight, in the early hours, I'll give her a good hard ride and crank her up to 120 mph and push her to 6/7000 rpm, see how she is after that.
 
Just go for a ride down SCTEX to Subic. I regularly run at a 100mph+. Just stop at the rest stop and wait a few minutes in case the Toll is checking time on the slips.

Maybe it is a coil issue if it only happens when hot. I prob have a extra set of COPS without resisters as I bought the wrong kind.

And leave the wife at home.
 
Thanks.Today, I'm going to remove and clean the carbs and clean the fuel filters. If I can eliminate those as a possible cause, If it still has the problem, then I will have to look at the coils. It's very hard to diagnose an intermittent a problem like this. I took it to the mechanic and we ran the bike and it wouldn't do it....so i left and it cut out about half a mile down the road!
 
It seeme highly unlikely that all 4 coils would cut out at once. This is a real shot in the dark, but is there any possibility the ignition or kill switch is acting up?
 
Do you have a pickup coil wire that's loose/getting touched for some reason? I had mine cut out just from touching the main fuse housing a couple times. The timing thing is weird, though.
 
Thanks...both of the last two suggestions got me thinking that this could be an electrical issue, rather than a fuel issue. Although, I don't think it is in either the kill switch or pickup coil. So I've been thinking about what else might be killing my engine, but would then allow it to start up and run again. Whilst, investigating the fuel tank today, found a small black plastic switch about 1''x 1'', with a two prong electrical connection, wedged down the side of the tank, so I fished it out with a pair of long nosed pliers. I showed it to my friend who said ''that's a side stand kill switch''. But, my bike doesn't have a side stand kill switch, it'll start with the stand down. I've had a look at the stand and it does look as though it may have had one in the past? Not knowing a lot about the Vmax, should an '86 have a switch? If so it looks as though mine has been removed and bypassed. if there is a loose connection it may be the cause and be killing the motor. Having killed the motor it would probably allow the bike to start again? Of course, I may be completely wrong and it never had one. Does this sound feasible?
 
They all have a side stand switch.

Thanks davesax36. Then that probably explains the problem. The cutting out of my motor is most likely a 'short' in a wiring modification from the removal of the side-stand switch. The circuit is being broken and it's as though the stand is down. I will have it looked at tomorrow and hopefully this mystery will be solved. Here in the Philippines they have never heard of soldering irons, they just twist wires together and wrap them with electrical tape. Thanks you got me thinking about a loose wire !!
 
My '85 quit on me at the end of the season a few years ago. After checking everything and using a replacement ignition box to no avail (Thanks Sean!), it turned out to be the sidestand relay. The relay fried, and wouldn't let the ignition turn on. The bike does not need the relay to operate, I just unplugged it. It lives up by the ignition box, in front of the airbox. It has a blue base. Even if you made the sidestand switch inoperable, the relay would cause problems if it is defective. I do believe the '86 uses the same system. Try unplugging it, maybe the relay is intermittently acting up and shutting things off till it cools off??
 
Thanks Bill Seward. I followed your advice and removed the airbox to get access to the relay. It was in good shape. However, I removed the CDI unit and found that the pin connections were quite badly corroded and the connector blocks were very dirty and there was water inside the CDI box !! It had been opened at sometime in the past. I opened it and dried it out and then re-sealed it with rubber cement. I cleaned the contacts with a toothbrush and some WD40 and cleaned the connectors. Whilst I was at it, I separated all the electrical connectors i could find and cleaned them all with WD40 and I opened and cleaned the switch gear and the kill switch contacts which were also very dirty. I put everything back together and 'hey presto' the problem has now gone. I did around 50 miles yesterday and it didn't cut out once. It was most likely the CDI box that was causing the problem.
 
Thanks Bill Seward. I followed your advice and removed the airbox to get access to the relay. It was in good shape. However, I removed the CDI unit and found that the pin connections were quite badly corroded and the connector blocks were very dirty and there was water inside the CDI box !! It had been opened at sometime in the past. I opened it and dried it out and then re-sealed it with rubber cement. I cleaned the contacts with a toothbrush and some WD40 and cleaned the connectors. Whilst I was at it, I separated all the electrical connectors i could find and cleaned them all with WD40 and I opened and cleaned the switch gear and the kill switch contacts which were also very dirty. I put everything back together and 'hey presto' the problem has now gone. I did around 50 miles yesterday and it didn't cut out once. It was most likely the CDI box that was causing the problem.
In the future try dielectric grease.
 
Back
Top