Xj700 ran a few weeks ago but now doesn’t.

Fuel, air, compression, and spark. I’ve been working through these to get my grandpas old bike running once again. It was riding a few weeks ago but slowly went downhill. Loud pops from the exhaust rough idles, and killing in traffic. Sometimes it would all of a sudden go from boggy (feeling like it’s running on two cylinders) to bucking like a horse and all of a sudden I get full throttle. Now it won’t even run. I’ve had the carbs out many times cleaned them very well replaced plugs to find out two were pretty covered in carbon. I’ve put thousands of dollars into getting this bike to run and it did not long ago but I’m running out of answers. I could go on and on about all the things I’ve done to get a clean fuel delivery, and proper electricity getting to the plugs. Does it just need a running sync? Has anyone had this weird acceleration/idle/starting problem??

 

Did you send those carbs to hogfiddeles to get rebuilt?

You can get that bucking, poor running from a weak spark or plug, or from a carb that isn't working correctly. A poor or weak spark is exacerbated when putting the engine under a load and delivering a rich mixture, but firing might improve as RPM's go up and the throttle is backed off a bit.

Usually, a good bench sync and the bike will run OK, they just get much smoother after a running sync.

It's a pain to write it all but it might help to identify something you haven't done that is worthwhile.

 

So I looked back and you did list some parts in this thread like coils and TCI. It's best to keep to one thread on your bike so members can easily review history.

https://www.xjbikes.com/forums/threads/help-xj700-n-carburater-problems-first-post.132854/

So details like where did you get the coils, brand, new plug wires, new boots / caps included, etc are important. Have you done electrical testing of the pickup coils and the new coils to see if they are in tolerance for the specified resistance readings?

 

Yes I sent them to hoggiddles and it ran good for a few weeks only had to screw with the idle mixture screw a bit and that’s it but it slowly started getting weird on me. I figured it was rust in the carbs so I took them off and cleaned them all out twice I even had the gas tank coated so I wouldn’t have to worry about that.

 

do the running sync since that step seems to be missing.
how many turns are on the mixture screws?
There is a very fine adjustment point where these run well at idle.
Both of my Seca's seem to idle best at the leaner end, don't be afraid to start at just 2 turns, then try 2-1/8, 2-1/4....., synchronize them at each adjustment.
Keep going richer until it returns to idle when blipping it.
You need an auxiliary tank (or the tank just supported out of the way + fuel hose) and the carb synchronizer while you do all this.

 

Need to look at that fuel tank. Sounds to me like there is something in the fuel, and it is slowly making its way to the carbs and plugging them up again. Do you have a fuel filter after the petcock before the carbs? Take a close look at the fuel tank and see if there is anything in there. Might just have to clean, seal and add a fuel filter. At this point, them carbs need to be looked at again.

 

I had the tank professionally coated and I washed all extra residue out of it after cleaning my carbs. Now she doesn’t wanna keep running

 

I would suggest checking the wet fuel level on each carb on the bike to be sure you have fuel, and to be sure you don't have one or more carbs overflowing. You can ballpark it on the bike on the center stand, just put the clear tube at the middle of the outside carb. You may not get the exact spec here, but it certainly should be close and not overflowing.

You will need to use the prime position on the petcock, and if you haven't checked the petcock you should do that too verifying it flows freely in prime position and only flows with vacuum in the on position.

Here is a procedure for wet setting:

https://www.xj4ever.com/setting fuel levels.pdf