XJ700N Spark Plugs

I wish XJ's had brass floats... the ones you have come across, have you ever had any xj carbs with brass?

 

So if floats can absorb fuel would that mean the needle valve would not shut resulting in a flooded carburettor?

 

no it would result in a bowl never getting to set bowl height. heaver float will be lower in fuel level.

Edit: correction, yes it would. dont know what I was thinking there. float would hang low in bowl, not letting the needle close as soon as it needed to. thanks @hogfiddles, I read you last post there and rethunk it.

 

Yes that makes sense now.

 

No

 

Very likely, as the float would likely not rise high enough to close the valve...... unless you’ve wet set the “heavier” float, in which case you compensated for it by setting the fuel level to the correct height

 

That is what I originally thought. If the float is sinking in the fuel the needle valve would not close because the tab on the float is lower because the float is lower. So if XJ floats did this even with the fuel not on prime at the tank valve the carburettors would flood even with good needle valves and seats.

 

If the valve is not closing all the way, the carbs will fill too full, possibly leading to flooding if it doesn’t finally close.

if the petcock is not on PRI, NO fuel should flow unless the bike is running. If there is fuel still flowing when the petcock is set to run or reserve and the bike is not running, then there is a problem with the petcock. In theory, the float valves should close tightly enough so That The fuel will be stopped even with a petcock set on prime. This is also why it is not uncommon for people to put a shut off valve in the fuel line As an added precaution

 

I have not had any problems yet with fuel getting into the crankcase and l might fit a shut off valve, good idea.

 

the petcock pump is not actually providing any PSI, its simple to assist in a faster flow under heavy throttle.

 

As I said in past post that's what fixed my uneven plug burn was replacing the floats after taking the carburetors off and on many times and checking and replacing just about everything, now they are a a light brown across all four. 50 miles to the gallon.

 

Pulled the rack off the XJ650J. The weirdness that I am chasing down is that it takes 4~4.5 turns out on the pilot mixture screws to achieve a rich mixture using the colortune. (the expected result would be starting at 2.5 turns, and then making small 1/4 turn adjustments, but probably not more than 3 turns)

I did a wet set of the floats, all are now within spec on the bench. They really looked out of spec bad when I did a quick and dirty measurement on the bike, but they were not bad on the bench, so I don't think fuel level in the bowls was a major factor.

I also verified that the proper jets are in the proper position, see below:


I can spray carb cleaner through all of the circuits without a problem. Granted, they may still be dirty, but they are not full-on clogged. Also, if one of the circuits on one one of the carbs was restricted, I would expect to only need to dial the mixture screws 4~4.5 turns out on that one carb to make it rich, not all four.

I will see if I can get a colortune done in the next day or two and see if anything has changed.

Assuming it still takes 4~4.5 turns to reach a rich mixture across the entire rack, I'm running out of ideas.

 

Another thing I noted about the XJ650J carbs are that the floats are kind of deteriorating. It looks like #1 float was replaced at some point (looks a lot newer, no deterioration).

See the below photo for a comparison of the #1 float next to the #4 float:


I don't think this would cause a lean condition - assuming levels are properly set. I do worry about debris from these floats getting stuck in a passage somewhere. Add another item to the list, I suppose.