xs400j carb question

Are the carbs on this thing trouble? I've heard nothing but complaints. Can an average guy rebuild them without buying specialty tools? I have the service manual with a step by step guide, but even the perty pictures seem scary. I've never seem to have any power with this and Yes I know its a 400!!! It just doesn't seem right. I had a yamaha dealer check valve clearance and fine tune carbs, but there was no real change. I'm too the point of taking the carbs out and going through them. Is it worth it? Is there an aftermarket carb that I should buy instead? Do I just rebuild them with an overhaul kit?

dave

 

I heard the same thing about my carbs. I had no knowledge of what to do to clean and overhaul carbs before I dove into mine. I got quad carbs and if I can do mine you should have no problems on yours. All you need are screwdrivers some metric sockets the parts you are going to change out, carb cleaner and some patience. If you do some searching there are some threads here that may aid you in going through them. I will take a look and will post one for you in a bit. I know this is not the writeup for your carbs but hopefully it will give you a guidline to follow. Good luck!

http://www.xjbikes.com/Forums/viewtopic ... tubes.html

 

I don't know of a 0-60 spec for the XS400, but a Ninja 250 -- which has 36HP like the XS400 -- makes 0-60 in 5.75 seconds. I've never timed myself with a chronometer but shifting at 9,000RPM I top out in third somewhere north of 50MPH and it probably takes around 6 seconds I'd guess.

Above 6,000RPM is where the power is at, there's not much low-RPM torque on this little twin. Roll on the throttle at 3,000RPM and nothing much happens.

Hopefully that will help you determine how 'gutless' it is.

 

Get in there and tweak them carbs, my XS 400 has plenty of get up and go....
Mine seems happiest shifting between 6 and 7K, I'm actually suprised of the power of this little critter

 

wow, looks like i need to do some work!

 

Well dave I cleaned my carbs on my xs400j and didn't have to adjust the carbs at all , lucky I guess but i made it a point not to turn any mixture screws. A good tool to use in scrubbing the bowls clean is a battery operated tooth brush, I

 

If i do this, I already have the yamaha manual. But after reassembly, there is a float level check but no real sync or fine tuning. How does one know if one carb is richer than the other? or if they are synced?

I have Mikuni carbs

 

Syncing is done with a vacuum tool, either a homemade manometer or a commercial mercury sync gauge. On a twin cylinder like the XS400, 8-12 feet of aquarium airline tubing with a slug of ATF in the middle will work quite well. Hook it up to the carb holder nipples, start her up, then turn the sync screw one or or the other until the ATF stops migrating one way or the other.

Adjusting mixtures can be done by ear and confirmed by reading the plugs, or, better, using a Colortune (glass spark plug). I tried doing it by ear and got nowhere, then I paid $50 for a Colortune and it was money well spent.

 

Do a good bench sync and you can fine tune it later if needed.
Factory has these things running lean, you can determine how they are running by checking your plugs after a good run......