1986 XJ700 Hard Starting, Uneven Running, Dies when idling

I have a 1986 Yamaha Maxim XJ700, and it has been sitting for about 5 years. Toward the end of last fall, the bike was running okay and after I rebuilt the clutch and checked the brakes, the bike was drive-able and road-worthy. The only problem was that the header pipes were vastly different temperatures. No. 1 seemed to always heat up and the other three seemed to alternate (sometimes 1 & 4, sometimes 1 & 3, etc.) After cleaning the carburetors did nothing to alleviate this issue, and new plugs didn't make a difference, I assumed the valves were to blame, so I measured them and adjusted them according to the spec sheet. Now, the bike won't run like it did before. It takes MANY attempts to start it, but eventually it will start. Most of the time it just tries to turn over and then it sputters out. It won't idle (no matter what you do with the choke), and if you let off the throttle it will die. However, if you rev it up a little over idle and hold the throttle completely still, the engine will all of the sudden rev up and hold for a little while, or slow down and almost die unless you crank the throttle quite a bit. It just seems to do whatever it wants, but it will sometimes respond to the throttle, and sometimes it will ignore that you cranked it and just continue running at the speed were it was. I have already checked all the plugs and they are all sparking. I really want to know what else I can try. Thanks in advance for any other ideas.

 

The carbs must be zestfully clean including setting the fuel levels and have absolutely zero vacuum leaks in order for our bikes to run good.

Gary H.

 

How can I test for vacuum leaks? And by fuel levels, you mean the carb float levels, right?

 

Sounds to me like a fuel problem. The carbs must be completely clean, the floats properly set, the pilot screws properly set, good bench sync, and no vacuum leaks. Before removing the carbs again you can use propane around the intake manifolds while it is running to see if that has any effect. If so, you have a vacuum leak. Check and make sure the "choke" cable is actually opening the enrichment plungers and allowing them to completely close. The pilot screws can be initially set at about 2 1/2 turns open, although for my 85 xj700 that ended up a little rich. Finally, open the idle screw a little in case your bench synch was bad. If non of that helps the carbs will have to come off again. Follow the "church of clean" instructions exactly, do a good bench sync, wet set the floats (do that several times just to make sure) and the bike should start easily. I found out the hard way that there aren't any short-cuts, but when I finally slowed down and did everything exactly in the order and as instructed in the "church of clean" my bike starts without enrichment, unless very cold, idles well, accelerates well, and my mpg went up substantially. I've come to the conclusion--from my personal experience and what I've seen on this forum-- that most folks just get impatient, get in a hurry, take short-cuts, and end up doing it over and over.

 

the wet setting of the floats not the dry set dry set is just a reference point .

when you go to wet set carbs or test levels fill bowls then cycle the floats a few times (drain out some fuel with new fuel flowing in) this will remove any air and balance out any overfilled carb bowls.

vac leaks use a propane torch unlit go around the carb manifold boots vacuum link even at tank them around all connections at the carbs then carb to airbox boots.
bike will speed up where you find leaks.

 

check your battery voltages keep battery charged .
did you do a compression test? if so what were your results?

 

HOW did you clean the carbs? I mean EXACTLY how did you clean the carbs? Also, when you were done cleaning them, did you bench-sync them? What did you do with the mixture screws and settings? What did you set your floats at for initial setting? Did you do a running sync? Did you colortune? Or at least do some plug chops?

What book did you use for setting valve shim clearances? you may have used the one with the famous typo:

The CORRECT CLEARANCE ranges are as follows for your bike:
Intake: .11-.15mm
Exhaust: .16-.20mm

IF YOU USED THE WRONG GUIDE, it would have told you that the intakes get the same as the exhaust

 

Burn that into your brain and you can then march to a different drummer and not have to go thru the heartache of psoriasis.......or of a poorly performing, un-enjoyable bike that just won't run properly.

Throwing money and time at the wrong problem is not the way to get ahead in life.....

 

+1

 

Except if you have a Harley then it's a must but we are smarter than that

 

I couldn't find the same book i used before, but I checked the clearances yesterday using the measurements you gave and they are well within spec.

 

Okay, so I think someone might have poured sugar, sand or something else in my gas tank O___o I pulled the carbs off again today because I checked everything I could without taking them off, and I took the bowls off to check and be sure that they aren't clogged up again for some reason and to my dismay, I found quite a lot of this sand-like material in them. It looks almost exactly like sand (same color and everything) but if you rub it between your fingers, then it crumbles into a kind of damp dust. As soon as I saw this I was floored. The gas tank has a lock on it, but I always have left the key in the ignition when I turn off the bike. I even have an idea of who it might have been, but I don't want to say anything until I see if its possible that might have been something else. It clogged up most of the smaller jets and a fair amount of it collected on the bottom of the bowls and stuck to basically everything inside that lower section of the carbs. additionally, two of the floats were difficult to move, and another one was entirely stuck until I sprayed it(with carburetor cleaner) and gently wiggled it free. The "sand" stuff is mostly in #1, but there is also some in the others as well. Does anyone know what this could be?

 

do you have a filter in your line? What about the beanies? Did you drain, dry, and clean the inside of your tank? How about the petcock?

Dave

 

It's rust fromryour tank