weird!!!!!wants to run...or does it????

Ihave a 99' YZ400FL< JUST DROPPED about $250.00 for my forks to be rebuilt and some what of a face lift. i live in Phoenix AZ so it's kinda hot to ride in the summer. so i figure what better time than to take it apart. right before i took it apart, i was out riding, i ran out of gas, so when i got to the gas station on my way home, i tried to start it. it started but any gas givven, it dies. took the carb to my local shop, they disassembled and cleaned throughout. i put it in plastic bag, and it sat inside for a month. i figured the problem was fixed, but when i reassembled my bike (2 months later) it is doing the same thing. so right now, it will start, and idle 100%. you can give some gas, but then dies, and sometimes backfires. i found today if you take off and get into high RPM's and cruise, it will run. but when you slow down, it dies. then trobled starting until cooled down. pleeease someone help. :thumbsup:

just in case anybody may be having a similar problem, my local shop that has the bike right now says it is one of my valves. it needs to be adjusted. so they are going to get some shims and take care of the problemo!!! :thumbsup:

Welcome to TT and good luck with the bike. I hope that is all it is. Go to Motomans site and you will see how you can adjust the valves yourself. It isnt very hard after you have done it once. :thumbsup:

Let us know what happens. Typically if a valve is too tight it will be very hard to start and will not idle well at all. If it's idling fine then I would be surprised if it were a valve, but let us know. My personal vote would be the carb is still dirty. Hope I'm wrong and the valve adjustment fixes it! :thumbsup:

well right on guys, thanks for the input. well see what happens. i should have it back in a day or so. thanks again :thumbsup:

hey fast1, how do you like the power now, is it worth the dough??? i saw one the other day online for the first time. thought it was an interesting concept... let me know eh!! :thumbsup:

well right on guys, thanks for the input. well see what happens. i should have it back in a day or so. thanks again :thumbsup:

Last time I had that particular problem, I had a clogged mainjet. As soon as you touched the gas, it'd die. Pulled it all apart and cleaned the main, and it was fine after that. I'm with SirThump about the valves... hope it fixes the problem though.


well i just got off the phone with the mechanic from my shop and he checked the valves and they are to spec... so you were right guys. he said he went through the carurator again and did not find anything out of the norm... but he is going to continue to poke and pry at it. i will call him right now and tell him to be sure to take the carb apart to check everything. thanks :thumbsup:

Re: the Power Now, Yes I like it. I have run it for a couple of years now and thought it helped starting alot. It gave good low end response right off the bottom with no noticeable effect on the top. :thumbsup:

My personal advice:

Get the carb back, remove the float bowl and shoot carb cleaner through every hole. Remove the fuel screw and shoot carb cleaner through there and also be sure to hit the 2 holes on the airbox side of the carb near the bell. Then follow with compressed air through all holes. Verify that hte accelerator pump is working (do you get a stream of gas when you open the throttle with the float bowl full of fuel?). Now put it back together and try again.

Careful with the shop, don't let them rack up the hours on you.

well iwent down there to show them (they couldn't start the beast) exactly what it eas doing on my way home, and brought my factory service manuel. after he saw that it would start up, and idle 100%. we taked about the TPS (throttle positioning sensor). i guess i was not supposed to take it off, and i did before the last time i rode it, when i cleaned it. so he is going to look into that and see if maybe it is off a little, or maybe it has gone bad??? has anyone ever had there TPS gone bad???????????? about the labor :thumbsup:, he is kinda a friend of mine, he will probably only charge me one hour labor $58.00.

Unplug the TPS, it should run OK with it unplugged. If it still has the same problem then it's not the TPS, if the problem appears fixed then it's likely the TPS. Some people here ride with the TPS unplugged so it should run OK with it unplugged.

about the TPS being unplugged, do i just unplg the elecrical input, or do i take the end that goes into the carb out??? (probably not HUH??) but i had to ask. is therer an advantage to running the bike with the TPS unplgged?? :thumbsup:

Just unplug the electrical connection.

Beware: There is a second part of the carb that you SHOULD NOT touch! There is a plate under the main carb body, I think it has some funny headed screws holding it; do NOT remove this part.

Some people feel that unplugging the TPS smooths the power output, I have not tried this myself.

so, if the bike does the same thing w/out the TPS, then the problem would not be the TPS??? right. but if unplugging the TPS fixes this, then the TPS is bad. thanks for all the help!!! :cry:

what happens if i do unplug the TPS from the carb??? :cry:

I would bet that the slide is in wrong. The TPS wont affect its running that much, it would still accelerate very well through the whole range. Unplug it and try it, if you dont like it plug it back in. Tim Ferry never ran one.

Where is "the slide" is that inside the end that goes into the carburator? :cry:

It is under the cap at the top of the carb. If you took it out to clean the carb, it is notorious for being incorrectly placed back in. It causes all kinds of problems like you describe or it wont start at all. Worth a look if you happened to take it out while you were cleaning it. If you are looking into the throat of the carb and actuate the linkage, it is the part that moves up and down in the bore. :cry:

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now