Yamaha dies under throttle

[KaJuN]

My XJ650 sat in a garage for 3 years before I got it. I finally got it so it idles on its own without quitting, however, the second I try to add any throttle it dies. I'm thinking the carbs are the culprits, as the floats were rusted in place when I cleaned them today. That problem is solved, but I'm clueless as to how to get the motor running properly. Any help is greatly appreciated!

[CB750F]

Sounds to me like no fuel is going through the main jets,just the pilots which control idle and real low RPM fuel metering. You can do one of two things. Either pick up some carb kits and rebuild them or pull the jets out and clean them real good.If yours has the vacuum type diaphrams on the top of the carb that open the slides up if they are broken the slides can't go up and down to give it more fuel when you open the throttle. Or you have a real bad air leak.

Try some new spark plugs too. Sometimes they get all funky with old gas and will light it off under no load but when you put a load on the engine such as opening the throttle they won't light off the air/fuel mix. In other words tune it up and get the carbs cleaned up real good then you might want to have the carbs syncronized so they work together and put the same amount of fuel into the cylinder at the same time. You can get a carb sync set up and do it yourself after you learn how or have a bike shop do it.

[KaJuN]

I cleaned the jets and now it runs real strong when I rev it. Many of the nozzles were blocked completely. Now I just need to get the engine to keep running when it gets warmed up.

[CB750F]

Yeah that happens whenever they sit around for several years.

[KaJuN]

Any idea how to lean the mixture on the carbs? The repair manuals don't say anything for fear of upsetting the EPA. The only adjustment I see is how to adjust the idle speed. My plugs keep getting fouled up and I've gotta clean them before starting it when it sits around for a while.

[CB750F]

Try some plugs 1 step hotter first. That might help. Make sure your float level is set right and the needles aren't shot also. If you pull the float needle valve out and there is a ring around it it's shot. Another thing that helps is turn your fuel valve off when you park it and let it run for a few seconds.

[KaJuN]

Sunoco's super 94 rocket fuel seems to have done the trick with my plugs. Next up is a fork seal replacement then the road. :D

[Gray]

I am having the same problem with my 1948 F.N. I cleaned out all the jets and still have the problem. Will idle but when i pull the throttle back it shuts right down...finally broke down and took it to a mechanic.

[666_wicked_jester_666]

it sounds stupid but alot of people dont check to see if they need new plugs. always do that before you stoop to the mechanic. a $25 job might cost you $125

[Gray]

Found that the problem was not the carb at all. Was actually a timing issue that has been resolved. Starts on the first kick everytime now!

[monsterjam5000]

that happens to me but now it will not run at all i do not think it is timing because some times it would run just fine. and how do you know if you need new spark plugs?

[CB750F]

They will be all black and cruddy on the tip. For 4 plugs it's not much more than $15 to $20 so it's worth the money.

[monsterjam5000]

ya i know it is just hard to get to them

[CB750F]

They don't make them to make it easy to work on them:mad:

[Uesque]

I was surprised to find that the plugs on the middle two cylinders on my XJ600 are angled outward so it's very easy to get the wrench on them. I was quite shocked.