deerslayer1979
New member
I have had sleds before and am a mechanic by trade, (actually and instructor now), and have bought 2 Blue and Silver Yamaha Exciter 300 twins for my kids. One was a runner but it didn't run all that well. Got em home, pulled the carb and cleaned it up, also installed new plugs. Wasn't all that dirty and didn't really fix the hard start issues. After toying with it found the choke cable was loose under the dash and sticking in the carb. I got that cleaned up and the cable moving freely and it starts and runs really good! 
Downside, after a hard run at WOT the engine dies out and needs the choke to keep from dying. With the choke on it runs like a champ and only requires a small amount of throttle play to keep it running in the powerband. I tried adjusting the screw on top starting at 1 turn out, and went both directions a full turn, in 1/4 turn increments. None of which seemed to help, actually made it less responsive while sitting in my garage. The last bit of info I can give you is sometimes when i try and get it to take off from a stop the engine bogs and will not rev. Even if I keep it pinned I get nothing. Flip the choke and let the idle stabilize it seems to get going just fine. So, what is going on? I has good spark, new fuel pump, new plugs, a clean carb, and runs great when it wants to. Once I get it to run decent I will be looking at other things to make it a bit more little kid friendly, but I need to know it wont leave my kid stranded and make me walk out into the field to get it running again.
Thanks,
DS79
Downside, after a hard run at WOT the engine dies out and needs the choke to keep from dying. With the choke on it runs like a champ and only requires a small amount of throttle play to keep it running in the powerband. I tried adjusting the screw on top starting at 1 turn out, and went both directions a full turn, in 1/4 turn increments. None of which seemed to help, actually made it less responsive while sitting in my garage. The last bit of info I can give you is sometimes when i try and get it to take off from a stop the engine bogs and will not rev. Even if I keep it pinned I get nothing. Flip the choke and let the idle stabilize it seems to get going just fine. So, what is going on? I has good spark, new fuel pump, new plugs, a clean carb, and runs great when it wants to. Once I get it to run decent I will be looking at other things to make it a bit more little kid friendly, but I need to know it wont leave my kid stranded and make me walk out into the field to get it running again.Thanks,
DS79
Throttle Junkie35
New member
You either didnt get all the passages in the carb completely clean, or the rubber plug in the carb is hard and leaking, or you have a base, head, crank seal or carb boot air leak.
deerslayer1979
New member
Well I am almost positive the carb is clean, there is only 5 different ports on that carb, and I can get good flow through all of them. I have another carb I will try but theres a chance that one could be dirty as well, I did have to clean this one and have not had it on anything as of yet.
What rubber plug are you talking about? I didn't see any rubber plugs in this thing.
If I need to find one if one those seals is leaking whats the est way to find them? Ether or carb/choke cleaner?
If all else fails I may try and swap all the parts onto the other sled and see if I can get that one to run correctly. I guess that would tell me its a motor issue and not a carb issue. Just make one nice sled out of the 2.
What rubber plug are you talking about? I didn't see any rubber plugs in this thing.
If I need to find one if one those seals is leaking whats the est way to find them? Ether or carb/choke cleaner?
If all else fails I may try and swap all the parts onto the other sled and see if I can get that one to run correctly. I guess that would tell me its a motor issue and not a carb issue. Just make one nice sled out of the 2.
Throttle Junkie35
New member
Nevermind about the rubber plugs. I was thinking it had a different style carb like I had on my 340. I would check a couple of things. One being float height. Two, the cylinder base gaskets. You can spray carb clean or the like around them to find a leak....last would be crank seals...also, check the carb again. Sometimes things can show up from being sucked in from a dirty tank or lines if they have been sitting for an extended period of time. I would also check for water in the fuel.
opsled
Active member
Make sure the in tank fuel filter is in good shape.
I've had them come apart from sitting dry for to long and the pieces can pass through the pump and plug the needle seat or jets. I even had one that plugged the inlet side of the fuel pump. Run symptoms can be erratic and come and go. Blockage on the inlet side of the fuel pump can cause starving at WOT but may be fine at normal speeds. Small pieces that can pass through to the bowl can plug a jet while it's running then settle down to the bottom once the sled is shut down and it runs fine after it's started again (for a while)
Also had filters that are plugged (or partially) with varnish from old gas.
Anyway, eliminate the filter as a possibility before you mess with other stuff.
When cleaning a fuel system on these old sleds do it all from filter to carb and make sure the tank is clean too.
opsled
I've had them come apart from sitting dry for to long and the pieces can pass through the pump and plug the needle seat or jets. I even had one that plugged the inlet side of the fuel pump. Run symptoms can be erratic and come and go. Blockage on the inlet side of the fuel pump can cause starving at WOT but may be fine at normal speeds. Small pieces that can pass through to the bowl can plug a jet while it's running then settle down to the bottom once the sled is shut down and it runs fine after it's started again (for a while)
Also had filters that are plugged (or partially) with varnish from old gas.
Anyway, eliminate the filter as a possibility before you mess with other stuff.
When cleaning a fuel system on these old sleds do it all from filter to carb and make sure the tank is clean too.
opsled
deerslayer1979
New member
I am swapping the other carb today to see if the symptoms stay with the sled or with the carb. Unfortunately i do not know for certain that the swapped carb is a good runner but I could get the jet out of this one and verify that it was not plugged when I cleaned it. So that alone gives me hope it will cure this. If not, how can I check the floats? I set the last carb by putting in a vise and adjusting the tab until I had the floats level with the body just as the needle was getting pushed up to the seat. Now, I had it running in the garage with the track up. I ran it up to about 1/2 throttle, just before it would die out and need the choke, I shut the engine off and let it die while holding the throttle still. I pulled the plugs and they decent. I bit darker then what I see online, but very little wetness if any at all. I did notice that the intake boot was very damp when I removed the carb, is that normal? Anyways, I'll post back once I know more with this different carb. If this doesn't fix it I'm swapping parts to the other sled and seeing if that one runs better.
Thanks,
DS79
Thanks,
DS79
deerslayer1979
New member
Good news, I got it to run out perfectly! The 2nd carb wouildn't even start so I did some more reading and thinking. After reading up on how the choke actually works (adds fuel to the cold engine) I realized that I had to be running really lean on top which is why it would only run @ WOT with the choke on, AKA; getting enough fuel. So I pulled the bowl and the main jet again and found I missed some scale on one side of the jet. I cleaned it out and threw it back together, adjusted the screw on the top a bit and reset my idle and went for a ride. It seems to run out pretty good now. I want to replace the belt, and figure out why the suspension is so soft, but all in all it runs great! Now to get it in an area where my middle son can learn how to control it.