1982 Seca XJ750, ZRX1200 has company now.

[Bonz]

I think the logic is a bit different than the sensor is at 12V vs the voltage on one cell. I honestly don't remember the whole story. The XJ forums can serve as a refresher. I think the sensor itself was around 1k ohm when the electrolyte was present, and the cluster reads the voltage more than the current.....or something like that.

Thanks! That's what I was trying to say in the last post. As long as the voltage is higher than what a single cell should be, the "Batt" warning will be off to my logic.

Even though it functions when all is well connected to the positive battery terminal, a single cell would never feed 12 volts to the cluster. As has been said, if something goes wonky, not sure what would happen or if I would like what happens given it's a perfectly functioning 44-year-old cluster.

Back to the question, running it off of the battery with a fuse in line and a resistor, what size fuse would you all go with? A 5 amp, 10 amp etc?

[Radioguylogs]

I would choose the smallest available fuse, like 1A or less.

This circuit will draw negligible current.

[Bonz]

Thank you for that input!

Found another inconsistency with the carburetors today. Number four is from an early XJ650, needle was also from the XJ650, wasn't paid attention to by the dealer who rebuilt the carbs for my uncle, nor by me when unracking for cleaning last fall... XJ650 needles are much richer (#Y-10) than the XJ750 needles (#Y-13). Changed it out for the proper needle today from a spare carb.

A "my bad"... In going down "one size" on the pilot jets, I inadvertently went down two sizes. Hitachi's go by one number vs most others go by 2 numbers per size. Makes sense now why 38's are too small and 4+ turns out still isn't enough fuel at idle, even at 7200' elevation. Putting stock pilots back in, #40. Slowly sneaking up on getting this thing dialed in from all angles.

[Bonz]

40 pilots back in, screws 2.5 turns out. Starts with enrichener as it did with the 38 Pilots at 4-4.5 turns. A change for the better as I have adjustments both ways now.

Been dealing with an intermittent #2 cylinder. Swapped two and three plug wires, as there's a "wasted spark". For those that aren't familiar with wasted spark, this means both 2 and 3 fire from the same coil at the same time but only one of them is on the compression stroke so the other is wasted in space so to speak. New plugs are in, new eBay coil with new plug wires on two and three produces the same result.

I've discovered it's idle where #2 pipe stays cold. Hold the throttle at 1500 - 2000 RPM or higher, number two heats up. Either sync w/o YICS block off has a throttle plate covering the number two idle hole in the carburetor throat or number two pilot circuit needs another thorough cleaning.

What does the collective say? Been talking with JeffH, he agrees those are two things to check as I've been narrowing it down talking with him over the last week.

[cajun31]

Just food for thought I had a brand new pilot jet that was just bad. I fought with that until I finally just replaced it and then all was good. Question for you and I haven't spent the time to re read the whole thread but did you have the same issue with the smaller jets? If you are sure the jets are good then I have to agree with you it's time for another clean. I know you are aware, but for the collective a good soak in a gallon can of Berryman's might do the trick.

[Bonz]

Thanks for posting up. You are correct. Went down to smaller pilots, brand new from Jets R Us yet number two was not coming online until the throttle is open to 1500-2000 rpm or more. Stock pilots in there are clean, did another soak in Berryman's can of cleaner, rinsed them with gasoline, blew them out with compressed air, holes are as wide open as they can be for pilot jets.

Did an impromptu cleaning on all 4 pilot circuits. Removed screw, spring, washer and o-ring. Sprayed cleaner in the hole while the engine was running. Then four or five seconds later chased it with gasoline from the auxiliary fuel source tube straight through the pilot hole for 5 or so seconds. I could watch the gasoline burble in the pilot screw hole itself. Something's functioning in the circuit. And it was the same response on all for pilot circuits. Number two was not weak or any noticeable difference. I've compared pilot screws, 1,2 3 are identical (#4 is the course thread for the XJ650 carb body, that is adjusted fine on number four) and are clean, smooth and no damage to the tips. Hitachi carbs, pilot screws are on top and easily accessible with the tank off and remote fuel source.

As a thought, I could pull a pilot screw from one of the other spare XJ750 carb bodies and give it a try. In any case, getting the carbs on and off is not a problem to clean that pilot circuit specifically on the bench.

[Bonz]

School year is finishing for teaching middle school kids math. Hallelujah. I had a chance to fire up the Seca and play with the sync screws. Cylinder number two was not firing so to speak at idle, the pipe stayed cold.

If you recall I used the Morgan carbtune and got them "balanced". Also I did it without a YICS type tool. Pilot circuit is clear. The only other issue I could see was the butterfly plate was closing off the idle hole the pilot system feeds #2 at zero throttle.

That could happen if sync screw is adjusted with all four carburetors providing vacuum to the system. Got the bike warmed up, adjusted the 1/2 sync screw to a smoother idle not using vacuum readings. Number two header started coming up in temperature at idle. Before it would only come online if I held engine RPM 1500 RPM or higher with the throttle. Which says the butterfly plate may have been blocking off the pilot circuit hole at idle.

Next time I fire it up will tell the story if it behaves like it did today, lol.

Then it's get the new tires mounted and get the bike on the road.

With that said, number one and four header temperature idling for a bit is around 200° F. Two and three are sitting around 170° or so. There are situations where outer cylinders and inner cylinders with the same jetting will run different temperatures. Any thoughts on dealing with that at idle? First thought is leaning out the pilot system on two and three with screw adjustment. I realize mains can contribute a bit, however to my mind not that much at idle.

[DEEBS11]

Bonz, my understanding (I had a 650 Turbo YICS) is that a YICS engine can't be synced without the tool. You will receive false readings (much like what you are seeing).


Main jetting differences from inner and outer cylinders have zero impact on the pilot circuit. Only the pilot jets and air flow, The mains do not come on line until the needles raise out of the emulsion tubes.

[DEEBS11]

https://xjbikes.com/forums/threads/carb-sync-yics-tool.12104/

https://xjbikes.com/forums/threads/carb-synchronizing-on-a-yics-xj650.14472/

https://xjbikes.com/forums/threads/yics-tool-versus-non-yics-tool-carb-sync.25520/

https://www.ebay.com/itm/12710885301...Bk9SR_zd0anFZw