Moody Throttle

[WReXie]

OK, so I've had my '80 XS400G for a whole 10 days now, and it's moody throttle is my only complaint and I would love to be able to fix it.

When I start my bike and take off, the first time I get on the throttle (turning out of my driveway and onto the street most of the time) the throttle responds in a weird way. I crank it about halfway with no response at all (not even increase in engine speed) then it's like the engine stalls for a half second, then kicks in and it pulls like crazy to the redline.

My husband is a mechanic turned machinist and has no idea why this is happening, but he also doesn't ride so hasn't experienced it, either.

Warm up time doesn't seem to make any difference. I let it idle for 5 minutes the other day and it still happened.

Any thoughts?

 

[WReXie]

Adding that it only happens the first time I get on the throttle and take off for the day. I'm sure if I worked a normal job and it sat for 8+ hours it would happen again, but 1, I don't work 8 hour days (I'm a photographer) and 2, I ride to ride and the longest it sits while I'm out is 2.5 hours for roller derby practice.

 

[drewpy]

sounds like it bogs down. I would check the timing etc first, then synch the carbs.

If that doesn't work you'll have to play with the pilot mix/clean out the carbs

drewps

ps lets have a ganders at some of your photos?

 

[szymaszkiewicz]

I've had simular problem with my xs400 from 1978, when I've bought it it had a problem to pass 5-6t on rev meter, soon I've realized that vacuum hose used in my bike is a piece of fuel hose, i've bought proffesional rubber vacuum hose for 1 dollar and the bike runs like new! Try it!

The fuell hose used as vacuum started to become elastic while getting temperature from the engine, and started to colapse!

Replace it!

 

[WReXie]

Carbs were just done before I purchased it (I have the paperwork), so I don't think it's that.

Will check the vacuum lines this weekend.

Thanks

 

[WReXie]

Small update;

Had a spacey moment and pulled out of the driveway with the choke still on (in the warm up position, not the start position, if it even makes a difference *shrug*) and it didn't cut out. Got to the stop sign a block away, heard the engine reving high, pushed the choke in (I'm familiar with the symptoms, my dad threatened to have "Choke In" tattooed on my arms when I had my dirtbike, oops), and took off again. Still no cutting out/moodiness.

So, in an effort to avoid moodiness from the beloved xs400, I've considered making this a habit, leave choke out one click, push in after shifting into second for the first time, but want to know if I'm going to do any damage by doing so? Or does this accidental experiment further clarify whatever problem is causing the no power/cutout situation?


(For some reason I LOVE parentheses today, sorry)

 

[drewpy]

the bike doesn't really get warm till its used properly, so that may be the way it should be with your set-up.

 

[OliverB]

You say you know the carbs are OK but was the idle mix screw on top of each carb set to 3-3.5 turns out? As Drewpy said, it does sound like a lean warm up issue but my '80 never does this. I do run it for a couple minutes before I take off - as I gear up. In warm weather I never need more than 1 notch of choke unless the bike has sat for a while. When it starts to have a loping sound, I push the choke in. When I pull off (engine not fully warmed yet), no issues like you describe. I know each bike can behave a little different but I don't think it should do what you are experiencing.

 

[HoughMade]

So, in an effort to avoid moodiness from the beloved xs400, I've considered making this a habit, leave choke out one click, push in after shifting into second for the first time, but want to know if I'm going to do any damage by doing so? Or does this accidental experiment further clarify whatever problem is causing the no power/cutout situation?

Cause any damage? That's the way it is supposed to work. Been using this procedure for a long while.