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New guy with a problem (big one?)--moved

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Oct 6, 2007
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#1
New guy with a problem (big one?)

All,

I'm new to motorcycles, and have a 1990 RT100. It's been having starting problems lately, but I got it for free-how do I complain--right? My right leg is getting much stronger with the 75 kicks to get it going. Anyways after doing some reading on here (reeds(?), plug, top end, etc) I wanted to check ther plug to see what its condition is after the 6-8 rides I have made. When I got it, the plug was new, filter was mint, and oil looked crystal clear. I have since drained the gas tank, and put fresh fuel into it as well. I pulled the crankcase oil dipstick to check the condition of the oil------and gas poured out! A bunch of it was just flowing out!!!!! I'm mechanically inclined (trucks/cars), so I'm no fool, but I've never seen this before. What's this mean? I'm still in the process of getting a manual. Please help this new guy out!
 
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#2
Since I posted last, I have drained the crankcase, drained the fuel tank, pulled and cleaned the spark plug (wet and fouled). I have left the crankcase drain plug out, as gas is still dripping. The gas from the crank case was gray. I kicked it over quite a few times with the spark plug, and drain plug out to try to get more gas out. I did some more searching on this site, and found that I am supposed to turn off the gas petcock, which I did not, but this bike only sat for a week. Any ideas guys?
 

lwsmithjr

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Sep 18, 2002
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#3
Just a guess here but it sounds like the float in the carb was stuck, the overflow tube was blocked and fuel filled the throat of the carb, and eventually seeped into the crankcase. That is the only path for gas to get from the tank to the crankcase (unless the carb overflow tube is attached to the crankcase breather).
 
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#4
All,

I moved this from another spot on this forum--looks like I first posted in the wrong section. I'm new to motorcycles, and have a recently acquired a 1990 Yamaha RT100. It's been having starting problems lately, but I got it for free-how do I complain--right? My right leg is getting much stronger with the 75 kicks to get it going. Anyways after doing some reading on here (reeds(?), plug, top end, etc) I wanted to check the plug to see what its condition is after the 6-8 rides I have made. When I got it, the plug was new, filter was mint, and oil looked crystal clear. I drained the gas tank, and put fresh fuel into it as well. Today I pulled the crankcase oil dipstick to check the condition of the oil------and gas poured out! A bunch of it was just flowing out!!!!! I'm mechanically inclined (trucks/cars), so I'm no fool, but I've never seen this before. What's this mean? I'm still in the process of getting a manual.

Since then I have drained the crankcase, drained the fuel tank, pulled and cleaned the spark plug (wet and fouled). I have left the crankcase drain plug out, as gas is still dripping. The gas from the crank case was gray. I kicked it over quite a few times with the spark plug, and drain plug out to try to get more gas out. I did some more searching on this site, and found that I am supposed to turn off the gas petcock, which I did not, but this bike only sat for a week. Please help this new guy out!
 
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#6
So I'll begin shutting off the switch after running the engine, and sounds like I need to rebuild the carb as well. Should I do anything more then I already have to get rid of the gas in the crankcase? Just add new oil, run for a short while, drain, and refill with fresh oil again?

As far as overflow tube, is this the tube from through the top of the gas cap, to under the bike? Would there be another one just above the carb?
 

oldguy

Always Broken
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Dec 26, 1999
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#7
the tube on the gas cap should have a one way valve which only allows air in to the tank and prevents gas or vapors from escaping. It is there to prevent a vapor lock as the fuel level goes down.
The tubes on the carb are mostly also vent tubes but will sometimes allow gas to flow out.
Your problem could be as simple as a stuck or dirty float needle or a bit more detailed as a improperly set float level. There is also the possibility that your float itself is saturated with fuel or has a leak which allowed it to fill with gas- either condition interfering with it's ability to float up and shut off the gas flow at the needle.
Shutting off the tank petcock is just a temporary fix and won't help when the bike is running so you are going to need to check the carb.

Run some fresh oil in it and then do a oil change and maybe repeat but until you get the float working you are going to have an ongoing problem
 
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Apr 18, 2006
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#8
Most bikes have several vent / overflow tubes coming off the carburetor and then simply routed down under the frame. One of these would be the float bowl vent and it must be routed so that it does NOT raise up too high. If the vent line is clear and has no up hill sections in it then the float valve sticking open would result in gas leaking out onto the ground. If the gas has to travel higher up the vent hose than it would to get into the caburetor throat then it ends up flowing into the crankcase instead.

The float valve needs work for sure, but I suspect that someone has changed the routing of the vent line and that needs to be corrected as well.

Rod
 
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#9
I'll hit up the dealership tomorrow for a carb rebuild kit, and enough oil for two changes. Wonder if they'll also have a shop manual? If so, that'll also come home with me. Hopefully it'll show me the routing of the vent tubes as well. Thanks guys for all of the help, and I'll report the progress.