T500 revs taking off

[mnellis]

Last night I forgot and left the fuel petcock in the "prime" position. Today, I realized it and started the bike only to have the engine run away and rev to 9K. I disconnected the vacuum line to the petcock but it continued to over rev until, apparently, the bowls ran dry. As the motor was starting to quit I quickly put the vacuum line back on only to have the motor take off again.

By leaving the petcock in the prime position, is there the chance that the crankcase filled with fuel causing the over rev condition? The throttle seems to be working fine as I didn't do anything to mess with it.

Any ideas? If the problem is excess fuel in the crankcase, can I drain it with one of the bolts on the bottom of the case.

[Dead Boy]

That happened to me with my GT550 the other week. I cleaned the carbs and adjusted the throttle screw incorrectly and when started she shot up to 9-10k and wouldn't shut down until she ran out of fuel. Pulled the plug wires, hit the kill switch and key multiple times, finally ran dry when I pulled the fuel line completely off the petcock. Make sure your throttle is adjusted correctly and isn't sticking at all.

As far as fuel in the crankcase, it's a possibility. I would change the oil just to be safe. If there's enough fuel in the oil, it could wash out a bearing.

[mnellis]

Ok, I found the problem. I didn't touch the carbs at all while trying to get this oil injection pump working correctly. I pulled the air filter boot and stuck my finger in the carb throat to check the slide position. The right carb slide was about half way up for some reason. I rotated the slide and it fell back down. The problem is that I shouldn't have been able to rotate the slide. I pulled the slide out and felt around for the guide pin and couldn't feel it. Crap! I pulled the carb and couldn't see anything except a small hole in the side of the carb where something used to be. I looked around and saw a small pin sitting on the top of engine case. Eureka! all is not lost.

It turns out there is a pin that goes in the side of the carb to guide the slide and keep it from rotating. Apparently it had fallen out.

Sorry for the crappy picture. It's a pretty small pin.


You can't see it but the pin has two steps in it and might be tapered a bit. Here I pushed it back in about half way.



Here is the pin all the way in and I used a small punch to 'peen' the carb body so the pin wouldn't back out on it's own.



Well, I got the idle and throttle working correctly again but I still don't have any injection oil out the left side of the pump. It's dark and the mosquito's are eating me up so I'll have to play with it some more tomorrow.

[parksie]

Use some locktite on that pin. It happened to me on a busy highway. Somehow finding the ignition key in a panic with the backs of cars and trucks approaching fast is a whole new experience.
This is a common problem with that pin for old Mikuni carbs.

[Scorch]

Last night I forgot and left the fuel petcock in the "prime" position. Today, I realized it and started the bike only to have the engine run away and rev to 9K. I disconnected the vacuum line to the petcock but it continued to over rev until, apparently, the bowls ran dry. As the motor was starting to quit I quickly put the vacuum line back on only to have the motor take off again.

By leaving the petcock in the prime position, is there the chance that the crankcase filled with fuel causing the over rev condition? The throttle seems to be working fine as I didn't do anything to mess with it.

Any ideas? If the problem is excess fuel in the crankcase, can I drain it with one of the bolts on the bottom of the case.

Next time, kill the engine! Then fix the problem before restarting, don't let it rev out of control and throw a rod.

Wait, you're saying it continued to run even with the ignition cut???

[mnellis]

Last night I forgot and left the fuel petcock in the "prime" position. Today, I realized it and started the bike only to have the engine run away and rev to 9K. I disconnected the vacuum line to the petcock but it continued to over rev until, apparently, the bowls ran dry. As the motor was starting to quit I quickly put the vacuum line back on only to have the motor take off again.

By leaving the petcock in the prime position, is there the chance that the crankcase filled with fuel causing the over rev condition? The throttle seems to be working fine as I didn't do anything to mess with it.

Any ideas? If the problem is excess fuel in the crankcase, can I drain it with one of the bolts on the bottom of the case.

Next time, kill the engine! Then fix the problem before restarting, don't let it rev out of control and throw a rod.

Wait, you're saying it continued to run even with the ignition cut???

No, I didn't let it sit and rev till it's hearts content. I controlled the rpm with the ignition switch. The problem is fixed.

[Scorch]

Ah, gotcha.

[evol02]

Use some locktite on that pin. It happened to me on a busy highway. Somehow finding the ignition key in a panic with the backs of cars and trucks approaching fast is a whole new experience.
This is a common problem with that pin for old Mikuni carbs.

This is exactly what happened to me. 80mph+ on the Bay Bridge and one cylinder was racing. The first time I ever wished that I had a engine kill switch!

My pin appeared to be falling INTO the carb, which would have been a horriffic way to destroy the engine if it had!