Choke problem?

Hey everyone,

I've been having a problem with my 1982 xj650rj. When I start the bike under normal conditions, I usually set the choke to about 3/4 or full. After riding for a few minutes, I gradually turn the choke off, and the bike runs fine. However, when it rains or is very humid, I have to leave the choke on all the time at about 1/2 or 1/3. This is absolutely killing my gas mileage. The reason I have to leave the choke on is this: when I try to accelerate at low rpm's (i.e., below 5 or 6 thousand) it hesitates or sputters or coughs or something, as if the mixture is wrong. This problem is completely fixed by leaving the choke on. When the choke is off, I can rev the engine while in neutral without any problem, and cruise without noticing any problems, but as soon as I twist the throttle to accelerate, the problem comes back. Any ideas? Thanks.

 

What's the tempature? Does it matter if it is warm and humid or cold and humid?

I've heard of this happening on smaller engines when it gets colder - carb icing... a buddy of mine actually rigged up carb heaters so he could ride his ninja250 year round in Kingston Ontario. Carb icing occures when it gets cold and damp. The more humid it gets the more it happens.

Now the only other options I can think of are:

- the humidity is changing the air density enough to frig up the mixture

- it's so wet and/or the carb boots are damaged enough to let water into the carb side of the system

- your spark plug wires are damaged and are shorting out when they get wet. As the revs pick up they have a stronger spark and work. A weak spark and a full shot of gas probably causes it to flood or definately run rich.


That later I think is the most plausible. To test this theory go ride on a wet day. Leave the choke off and try to get somewhere. Pull the plugs after it has done it's nastyness for a little bit. Are they black or getting more black than when you started?

Are their obvious marks/damage on the spark plug wires? Can you see sparking? Can you hear arcing?

New plug wires on an old bike isn't uncommon... but if you could find the break in the wires first you could make sure. Remember the spark on plug is a massive jolt so don't be sticking your fingers on the end of the plug to test it!

 

Woot,

Thanks for the advice. It's in the lower 40's most of the time, so not cold enough to build up ice on the carbs. The colder it is, the more affected the carbs seem to be, but the humidity has a much more profound effect on them.

- I think the air density might have something to do with it. It is always VERY humid because it is always raining, but I don't think I can do anything about that.

- Damaged carb boots - I know the boots are getting pretty worn out, but would water actually have to be sitting on the carb boots to cause this problem, or would the admission of humid air through a crack in the boots be enough?

- The plug wire problem sounds like something that would be easy to test, so I'll probably check it out tommorrow (it will be raining again, as usual). Thanks again for the help, and I'll let you know about the spark plug wires.

- Jason