1980 xj650 cold start issue

Ok guys. I'm currently working on my xj650. I have checked valve clearance,went through carbs top to bottom. Replaced coils and plugs. All cylinders seem to have great compression but no gauge to give exact. Only start cold with ether. Once warm won't idle below 3000 rpm. Cylinder 4 not hitting at idle. Starts hitting about 4500 rpm or so. Runs great down the road. Just no idle and hard start. What am I missing? Any suggestions??

 

Did you bench sync and vacuum sync and check your float heights on those carbs?

 

I bench synced and set floats. Bowls are just over 3/4 full of gas. I even wrapped intakes as shown in other threads. Replaced gaskets thinking was vacuum leak. Can spray with ether when running nothing changes so shouldn't be vacuum issues.

 

What about using a vacuum sync tool on all 4 cylinders, Carbtune or vacuum gages. Or colortune for your mixture?

 

I haven't done that yet. Will the out come be correct when I have to have rpms so high? I'll go ahead and vacuum sync see what I come up with.

 

Did you lower the idle adjustment screw behind the carbs? Check that no 4 plug and connector, if need be remove the no 4 plug connector and twist off the cap, then cut about a third of an inch off the lead and twist the cap back on and replace. Sometimes the end of the spark plug becomes corroded

 

Ok I'll check that too. I replaced one coil already. This bike been sitting god only knows how long. I bought it two years ago in Florida. Just recently got it here to Arkansas and been working on getting it running.

 

When I turn the idle screw to lower than 3000 rpm engine dies. If you just hit the throttle to pick back up dies. You have to feather throttle. Like pumping accelerator on a car. After 3000 run perfect. Throttle very responsive

 

Pilot circuit screw almost entirely closed, or more likely, pilot fuel circuit is internally clogged.

Try putting a little bit of choke on it and then turn the idle speed screw down, see if it will still keep running then ----- although, since oyu say you have to give it ether to start, then most likely the enrichment circuit is clogged, too (the little jets down inside the fuel bowls).

 

One last thought, check that vacuum line that goes to the 3rd cylinder from the petcock. Make sure no splits or obstructions and that it's connected. Good Luck with your new ride.

 

The hole in the fuel bowl is one I had a lot of trouble cleaning. I used a very small drill bit until I could spray carb cleaner through the hole if I put the choke on engine runs 5 to 6 thousand rpms even when idle screw turned out.

 

Ok did vacuum sync,cylinder four is now hitting as strong as the others. Still when starting for first time of the day have to use ether. Once warm idle set at about 1300 rpm. Isn't this still high? After warm just bump starter and fires up no choke needed. Is this still a enrichment circuit issue, or do I need to look at other issues? I read a thread about hard starting having to do with fuse panel. Head light not on till running. Sometimes the neutral light won't come on have to jump solenoid. I have a new gel battery. Could I have a low voltage issue at start up causing the problem?

 

Manual suggests 1050 +_ 50 The headlamp won't come on till it runs ,so all the power is directed to the ignition. Sounds like a faulty connection for the neutral light.
Don't have a clue about the ether.

 

interesting issue. will be following.

 

If the neutral switch or associated wiring is not functioning the safety circuit is deployed disabling the starter. So, if you don't have a neutral light then the most likely suspect is the neutral switch. You might try jiggling the gear shifter to see if you can duplicate an intermittent light. Also, a portion of the safety circuit uses the diode block, so the wiring routes up into the headlight, where a possible poor / intermittent connection exists.

Plan B when you don't have the neutral light you should be able to pull the clutch in and the starter should function, which would be much easier than shorting the solenoid.

They are subject to corrosion and the tabs securing the fuses break. Always a good idea to inspect them and consider upgrading to a blade style fuse box.

Likely... if the float bowls required a drill bit to clear the enrichment well then a good chance the brass feeder tubes that sit in the enrichment well are clogged. As Chacal suggested also, good chance the pilot circuit is still partially clogged.

 

I'm going to pull carbs again today and check the fuse panel and connections. Bike sat outside for a long time. The tank rotted completely. Carbs were in really bad shape. So I'll check them again. I'll keep updated on what I find if still can't figure out I'll be picking more brains. I love these bikes and want this one perfect for the wife. Thanks guys.