running with choke

ok i just cleaned and recleaned my carbs.set mixture to 3 turns out float height is ok.reinstalled, will run but with choke on.looked at plugs and found 2 left plugs black and two right plugs tan. why will it only run with choke only.revs up fine but doesn't sta at idle until i give it a little throttle.any thoughts on this one?

 

Check the exhaust pipes to see if they are all the same temps,if not switch the leads on the ignition coils. I just went through this,but the coils were good and I have a bad pickup coil or tci. See my post rickomatic helped me.

 

Did you bench sync the carbs?

Warm the bike up and set the idle to 1050 using the idle screw. 3 Turns is just a starting point. Look up plug chops to get your tuning right.

Idling with the choke on for a good bit of time will turn the plugs black.

 

Choke on means you are starving the engine for fuel, and making up for it by starving it for air. When the air to fuel ratio is right the engine runs.

Step one is to make sure you have spark on all cylinders. I fashioned a spark plug tester out of a hose clamp and an aligator clip and a known good spark plug. This wont tell you that your coils are 100%, but it will tell you that they are somewhat working.

Step two is to sync the carbs with vacuum gauges and YICS tool. Small twists of the idle screw will make a big change in how your engine runs at idle, and the mixture in each cylinder at idle. This will take all of about 5 minutes, but unfortunately $100 or so worth of tools.

If you are still having trouble, or this doesn't fix the problem, I would pull the carbs and check your idle jets very carefully. Last time I pulled my carbs, I took my jets to work and cleaned them under an electronics microscope to be sure they were clean. Varnished gas can look clean. A clogged idle jet is the most common cause of the symptom you are seeing.

Good luck

 

cobra

had the same issue with my bike when I first got it. turned out the Idle adjust screw was all the way out and would only run with full choke. turned off the choke and adjusted the idle screw and bam it started normally

 

The carbs on the XJ do not "choke" the airflow in any way. They "enrich" the air mixture with additional fuel. Additionally, when you choke a classic carburetor, you are restricting the airflow creating a greater pressure differential which causes more fuel to be drawn into the mixture.

Since the two on one side seem to be working fine and the other two are running rich, it is not a coil issue since one coil fires 1 and 4 and the other coil fires 2 and 3. When you rebuilt the carbs, did you replace the throttle shaft seals? It is a lot more work but well worth the effort when it comes to this. Any where there is an air leak creates a more lean mixture.

I do agree with another poster though. I would check to see that the throttle blades are actually propped open some. If not, you need to turn up the idle so air can get past the blades. When I first fire my bike up, the idle speed will go up to about 2000-2500 rpm with a part "choke". Decrease the enrichment to maintain a 1200-1500 RPM idle (at least that is what I do). After riding a while, the idle will increase up to about 2000 RPM which is when I eliminate enrichment. I only do this if I am going stoplight to stoplight. If I am riding the roads, I'll turn off the choke right away once I take off so I don't forget since it really is only needed to maintain idle when the engine is cold.

Good luck to you. These are very fun bikes to ride but the carbs can be very tricky once they are dirty/old.