got it together and it won't stay running

[duckman86]

hello everyone, So i completely rebuilt the whole bike (mountain 90 non oil i.) and all i got it to do was fire up for 30 secs and die. It ran perfectly fine well it was running. I think the carb is messed up or the fuel line may not be right? there is a fuel filter, but it looks like gas is going into the carb. it doesn't have a gas shutoff my dad put some random thing on there but fuel comes out but not super fast. Before i completely rebuilt the bike and broke the kick s. lever it did exactly the same thing - run for like 30 secs and die and then you couldn't start it again. Has anyone had this problem? Or knows what it is? LET ME KNOW! I've spent way too much time on this thing. Also would it need a battery to stay running as i do not have one hooked up? Also if there is any new aftermarket carbs i could buy to throw on it that will work? or off a diff. bike that has a easy to find carb?

[duckman86]

update, i can't even get it to start now. If the gasket wasn't sealed good enough could it have gone out after running for 30 secs?

[rocketman]

Looking on,it does sound fuel related. You will have nothing but constant problems without a proper fuel shut off. Adequate fuel supply is a must,and if it won't shut off you will likely have a flooding problem. I'm not sure what gasket you are referring to,so I can't help you with that. Check your plug for excess fuel or dry(no fuel). Check for spark when it won't run to be sure its not giving up due to a bad condenser sometimes they can allow the engine to start,but quickly fail upon warming up. Hope some of this is helpful, Mark.

[duckman86]

I've got it to run, but.. the spark plug gave us spark at first but when we tested it later it didn't work anymore. With a new plug it fired up but won't idle. the fuel line with the petcock and filter has air bubbles shooting up. when we shoot starting fluid in it pops over wonderfully. whats that yamaha petcock that works? The carb has been rebuilt but still doesn't seem to work right unless the fuel getting to it slowly causes that many problems.

[rocketman]

Theres information under the other current petcock topic for three Yamaha numbers,etc. Fuel starvation sounds to be a likely cadidate for your troubles. Is the carb float level set correctly? Even though the carb has been "rebuilt",it is sometimes difficult to get all the junk out. Theres a couple topics on these problems too you can look at. Check the carb for blocked passages,sticky needle,etc. Reference the manual for proper carb settings and proceedures.  Mark.

[duckman86]

ya, I've narrowed it down to being the carb and fuel line setup from the tank. Cause it will run great if i drip gas into the carb opening. So i don't think it's electrical. I've just ordered a new petcock to replace my thingamajig. I took the carb apart and found stuff in there even though it was cleaned. It seems like gas doesn't want to go into the carb and into the float section, it's like it's blocked somewhere and i can't get it out, cause it will drain the carb of gas before it will refill. Is there any other carbs that will work that are cheap? also your refering to the service manual on here correct?
THANKS!!! for your help.

[rocketman]

To the best of my knowledge,parts for your current Mikuni carb are all still available. If you have determined the fuel is getting to the carb from your tank,line,and filter,then the problem would be between the carbs fuel inlet,the internal passage to the needle valve,the needle valve assy itself,or the float level too low. Remove the fuel bowl. Connect a fuel source with good flow. Hold the carb over a pan and turn on the fuel. With the float bowl removed and the float hanging free,gas should flow quickly through the needle seat. If it does not,make sure the needle is not stuck in the seat. If the needle is free,you have an obstruction in the inlet fuel passage. Read the topic on "plugged up stuff". And yes,by all means take advantage of the manuals provided on this site.  Mark.

[duckman86]

Ok, I will try that tomorrow. I took it apart again today and i got like tiny dirt and rust particles to come out of channels. I hope it will run free now.

[omega man bike]

mine was VERY fussy if anything got into the carb. even the smallest things.

[Jeff Bar]

Tank must be real clean, many guys are treating the tank to the "Kreem" system, as it really keeps dirt under control. when you start
with a nice white tank lining

Jeff Bar