Cold Startin' S.O.B.!!!

My '80 xj650 runs like a champ....except when I go to start it!! Every single time I start it (as in a new day) I have to spray starting fluid in it to get it to fire up! Once it is started, and ran, it will stop and start no problem, but if it sits overnight it will not start up!? Any suggestions?

 

Try putting fuel valve on PRI for about a minute before your next cold start. See if that solves the problem.

Is your enrichment circuit working? As you slide the thumb lever to "Choke" you should see the enrichment valves at the top front of the carbs rising. Make sure all 4 are lifting.

 

There is a separate Fuel Supply on each Fuel Bowl which supplies Fuel to the Cold Start~Enrichment Circuit.

That small "Well" needs to fill-up with Fuel from the Fuel Bowl.
There are Metering Jets in the bottom of the Fuel Bowl to allow this.
Those Jets are easily clogged -- because they are particularly small.

The Brass Tube which extends down into that separate reservoir has a number of the tiniest Fuel Metering Ports on the whole Carb. Those tiny Ports are the first to become clogged with any contaminant entering the Fuel Bowls.

If there is any cause for interrupting the Fuel Supply to enter and Fill the "Siphon Tube Well" or prevent the Fuel in the well to pass into the Tube to feed the opened Enrichment Valves when the "Choke" is opened ...

The Bike becomes very difficult to start.
The Bike becomes hard to start.
The Bike won't start.

The Metering Jets at the bottom of the Fuel Bowl need to be probed and blown-out with Carb Cleaner.

The Tube ... and its Inside Diameter ... need to be Flushed Cleaned.

Fill-up a Rubber Syringe with Carb Cleaner.
Fit the end of the syringe over the tube and push the syringe all the way down to the base of the Carb Body.

Squeeze and release the Syringe ~~> with the Enrichment Valves removed.

The Squeezing and Releasing will "Unclog" the Tube and its Passages to the Enrichment Valve.

Evacuate the Syringe and flush the Syringe out with some clean Carb Cleaner.

Refill the Syringe with Clean Carb Cleaner and re-attach it to the Tube.
Flush all the Carb Cleaner in the Syringe through the Tube and out the Upper Level Enrichment Valve passage.

This will cure that engine of being stubborn to start.

 

Had a similar problem with my dad's xj700 - except it would not start if on the center stand or anytime the bike was straight up and down. If it was on the side stand - it would start if the choke was on and you held the throttle wide open. Come to find out - I didn't pay close enough attention when disassembling the carbs for a much needed cleaning. The screws holding the diaprhagm covers/caps are all the same length except for one - which is shorter. The shorter screw needs to go in the hole under the linked choke lever. On the 700 - the choke lever has an arm that comes up and contacts the underside of the diaprhagm housing. With one of the longer screws in that hole - the choke plungers were not able to open (or close) all the way.

I'm assuming that before - with the bike on the sidestand - the fuel level may have been a little higher putting a little more fuel in the float bowl causing it to be able to start while holding the throttle wide open.