1983 XJ750 Maxim Build (Updates and Questions)

AlphaMoto Universal Motorcycle Vacuum Carburetor Synchronizer Synchronization Carb Sync Gauge Cb Honda Yamaha Kawasaki Suzuki Gs Kz XS 550 650 750 850 900 https://www.amazon.com/dp/B004MSJ7E6/ref=cm_sw_r_cp_apa_iOARAbDF3E1SQ

This is the one I got.

 

Those gauges are meant for cars (though they are marketed for motorcycles). The diagnostic info on the dials is irrelevant.

That is not to say that there isn't a problem somewhere.

Do you get a hanging idle without the gauges being hooked up?

Have the valve clearances been adjusted?

Was a compression check done, and what are the values?

 

I did bench sync the carbs before the vacuum sync and the readings were pretty close. Adjusting the sync screws didn't seem to make much of a change with the gauges connected.

Yes I do get a hanging idle without the gages

 

Well that confims a vacuum leak somewhere, which is why you couldn't synch the carbs.
Time to break out the carb cleaner and start methodically spraying intake components (slowly).
My guess is that you'll find it near #2.

 

While trying to locate the vacuum leak today I noticed the head is leaking oil at cylinder 1. After running for just a few minutes it began to drip onto the driveway. I'm guessing this is going to require a top end rebuild which will hopefully fix the low compression. There is definitely a vacuum leak at cylinder 2 put I have not pin pointed it yet.

I also got a lot of other little things done: Tires mounted and balanced, suspension replaced, new coils/wires/caps, battery replaced, brake lines replaced and bled, replacement tank welded and sealed.

Next steps:fix leaking head, vacuum sync, color tune.

Any information on what I need to do would be greatly appreciated.

 

https://imgur.com/a/JBARN6j

Here are some pictures of the progress.

 

Check to make sure that the vacuum line from the manifold port to the petcocknis not cracked or split.

Or

If you don't have that line installed, make sure you have a vacuum port cap on ALL FOUR vacuum ports

 

I replaced the petcock with an aftermarket non vacuum petcock from Len at XJ4ever. All four ports have caps on them.

 

I tried loosening and torquing the acorns on the head to solve the leak but it did not seem to help. I am planning on buying a replacement head gasket from xj4ever. Is there anything else I should replace while I have the head off? Do the valves need lapping?

Since I was unable to fix the leak this weekend I went ahead and chopped the frame and added a frame hoop. I started mocking up the side covers with cardboard. I also got the emgo shorty mufflers fitted. It is really starting to come together. I plan on trying to seal each of the intake boots with plasti-dip

https://imgur.com/a/tSoIRSh

 

I got the bike put back together this weekend. I am still having issues with a hanging idle and burning oil. There is a lot of white smoke coming out of the exhaust.

Here is what I have done. All new parts are from Len at XJ4ever

• Cylinder bores honed and inspected
• New piston rings and pistons inspected
• Valve seats cut and valves ground
• Valve stem seals replaced by shop that did head work
• Cylinder jugs resurfaced
• Head resurfaced
• Valves clearances in spec
• Carbs church cleaned, rebuilt, and bench synced
• Float levels wet set
• Compression 120,125,130,130
• Intake manifolds replaced
• Original airbox and new paper air filter
• All new gaskets and seals on the head

What should I check next to fix the idle and burning oil?

 

White smoke is NOT oil, its steam/water vapor, probably from water collected in the exhaust system somewhere. After a period of time it should dissipate.

Blue or bluish-gray smoke is oil, and it smells "oily".

Can you confirm what you are seeing/smelling?

 

Sounds like the old 'chain tunnel gasket' issue

There's no water jacket on the '83 xj750, so it's not going to be an anti-freeze issue

 

I was thinking it was oil burning because the level dropped from a bubble at the top of the sight glass to the very bottom of the sight glass. But I think this was from the new filter filling with oil. I started it again today and I did not see any smoke. I believe the smoke was coming from the newly wrapped headers.

I took a video of the idle. It will start climbing on its own with the choke off.

<iframe width="560" height="315" src="" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

 

Were you on the center stand or on the side stand when you saw it was at the bottom of the glass? The filter doesn't take THAT much oil to fill up...

 

It was on the center stand both times. I left the petcock "on" overnight and now I smell gas in the oil.

 

Leaky float valves in one or more of the carbs..........

 

AND a leaky fuelvalve.....

 

I replaced the petcock with a non vacuum petcock from XJ4ever. I believe just leaving it on overnight was the issue there. I also rebuilt the gas cap.

I pulled the carbs off the bike to check out the float valves. I am going to go over everything else on the carbs to make sure I didn't make any mistakes when re-assembling them. If I can't figure out the carbs I may send them over to you Dave for a blessing haha.

 

In which case, the petcock wasn just leaking......it was allowing full-on fuel flow lol

Give me a shout when you need......

Dave

 

the idle goes up because when the idle is low it's missing bad, as the rpm's go up the miss gets not as bad, it was still missing when you shut it down.
but with the petcock leak, maybe it was just flooded. it acts the same after a ride ?

 

I am not sure I fully understand what you are saying. You think that the RPMs rise because the engine is misfiring? Yes it acts the same after a ride.

 

you have 2 cylinders firing 100%, 1 firing 75%, 1 not firing at all.
the idle is set so it runs like this, but that 75% starts going to 85-90% and now the rpm's start to go up, up enough that the one that never fired before starts kicking in.
the rpm's go up some more, to the point that the 85-90% cylinder is hitting 100%.
more rpm's, now the one that wasn't firing at all is hitting 80% and your up to run away speed

 

Thank you for the clarification. If I understand correctly the idle screws are the reason this is happening?

 

Maybe....

its ONE reason this CAN happen.
Bad float levels can cause that.
Bad sync can cause that
Clogged passages can cause that
Bad TCI can cause that
vacuum leak can cause that
A flat tire can cause that

 

i hate when that happens

 

Here's a wall of text for my day working on the bike.

I did pull the carbs today to check them out. Everything looked good. I broke the rack again and put silicone lube on the throttle shaft seals. (I did miss this step on the initial cleaning) I polished the diaphragm piston and bore. The did pass the clunk test before polishing but i just wanted to be safe. I checked the diaphragm for pin holes. I did not find any holes. I pulled the bowls and inspected the float/needle/seat. The screen on on the seat was a bit dirty because I was running without a in line fuel filter.

After that I gave them a quick clean before reassembly. I used a piece of plate glass to align the intake side of the carbs. I did the bench sync according to a post I found from hogfiddles:

"For bench sync, I open til the middle hole on #3 is totally uncovered. (that way they are all open far enough that a different butterfly won't hold anything open or close too soon). Now ai adjust the remaining three to match. Doesn't matter what order. Once all match, I back the idle screw out til butterfly 3 covers half of the middle hole. Fine adjust the remaking three to match. Order doesn't matter. I snap them open a shut a few times, then check. Adjust if needed. install. Start up and do running sync."

I put the idle screws at 3 turns out from soft bottom.

I checked it set the floats and everything was good.

Also re-checked the valve clearances. I had two just out of tolerance and I swapped in new shims. Everything was in spec after that.

After putting it back together I had the same idle issue persisting.

I ran it around the block to warm up and set the idle. It still had the hanging idle.

I connected my multimeter to the battery when it was running. The volts hang around 12.3 at idle. When I bring up the rpms the volts drop down to around 9.0 With the bike off the battery sits at 12.7v

 

Your stator isn't charging, or something isn't hooked up, or your regulator is shot ( my bet)... you're running off your battery

 

Just checked the stator and it is toasted. The connector was melted together and I found debris in the alternator cover. Resistance between the three white wires was .9, 1.3, and I could not get a third reading.

On the rotor I got a reading of .253 The rings on the rotor looked worn.

Will replacing the stator improve the rotor resistance or will I need to replace both?

 

The resistance on the rotor seems quite low, are you sure of that reading? Did you measure at the lead-in wire connector or directly on the copper rings?

Alternator Rotors and Field Coils:

gp2) OEM new and aftermarket re-wound Alternator ROTORS perfectly replace the originals. Rewound rotors are sold on a "core charge" basis and you must return to us a usable, same-model rotor core in order to receive your core charge refund. Re-wound rotors will output at least the same current as an original.

Checking alternator rotors or field coil: the resistance across the two lead wires (usually brown and green) at the connector should be as follows. Note that worn or damaged alternator brushes can affect these readings, as can "dirty" copper commutator rings on the rotor face (where the brushes contact the rotor):

4.0 ohms +/- 10% for all XJ650, all XJ700, all XJ750, XJ900RK, and XJ1100 models.



Sounds like the stator and the rotor brushes (at least) need replacing, and a new set of the plastic connector shells and terminals at the least.

 

I checked resistance at the lead in wires

 

Pull the rotor. My guess is that the debris damaged the rotor windings.

 

Check the rotor resistance at the copper rings.....red probe on one of them, black probe on the other, doesn't matter which ring is which (inner or outer).

 

I am mildly surprised… I have never had a stator go bad on an xj. I know others have… But I have only ever had regulators fail

 

I cleaned the commutator rings and tried to get a reading on the rotor. I could not get a good reading. I would just go up and down and did not stop on a number for the resistance. The inner ring is pretty scratched up too.

Tomorrow I will pick up a 16 x 1.5mm bolt to pull the rotor and inspect it.

 

After I pulled the rotor I cleaned the communicator rings some more and I was able to get a good reading with the rotor in spec. I replaced the brushes and stator and now the charging system is functioning properly. I cleaned and added dielectric grease to every connector on the bike and found another wire that had been getting warm.

It is the red wire on the large connector. I believe this wire is for the rectifier.

I am still having the same issues with the idle. Is there anything else I need to check to fix the hanging/rising idle?
I have not found any vacuum leaks.

 

Just wanted to mention that white smoke can indicate aluminum burning. Might be your piston rings wearing as I had a problem with oil burning on my XL500r. What I believe happen is the piston rings were damaged when my oil drain plug fell out while i was riding. After I got a new drain plug oil began blowing past the piston head and out the exhaust. Its possible that this may be happening in your bike if your seeing white smoke. It is possible the piston rings burning and wearing. This is a fairly serious problem as this eventually lead to my piston head burning and breaking apart in my XL500r cylinder.

 

I finally got the bike idling correctly. I ended up going through the carbs with a fine tooth comb to look for anything out of place. I ended up finding 2 tiny little pin holes in #1&4 carbs. I sealed the holes with plastidip and reassembled the carbs. I put the carbs back on and the idle still wanted to climb to 3000 rpms.

I took the bike for a 15 minute ride and set the idle. With the engine warm i set it at ~1500 rpm.
I then ran a vacuum sync and the hanging disappeared. I followed up with the colortune and another vacuum sync. During the color tune #4 was misfiring pretty bad.

The bike is idling great now but will not start without the choke on. After 5 minutes of running I can turn the choke off and it will idle. It does this cold mornings or when the bike is hot in the afternoon.

The clutch is definitely starting to slip but I hope I can wait till the winter to replace it. Otherwise the bike rides great! Thanks to everyone for all the help.

Big shout out to Len at XJ4ever for all of the parts and information I would not have gotten this far without the info from him and this site.

 

Well the bike left me stranded today. After putting about 600 miles on the whole rebuild the battery stopped charging.

During the rebuild I replaced the stator with a used but in spec stator. I also cleaned the commutator rings on the rotor and installed new brushes. The bike ran find for the past 600 miles never needing to charge the battery.

Today I rode to the gym without any issues. While I was inside the bike got rained on, the rain didn't appear to get on any of the electrical components so I went on my way. At the end of the ride the bike started to misfire and sputter under acceleration. I parked the bike for a couple hours before I tried starting it again.

The bike was completely dead when I tried to start it again. I pressed the starter and it didn't have enough power to start the engine. I was able to bumpstart the engine but it only got a few blocks before dying again.

I checked the resistance on the stator and I got, 0.9,0.7,0.7 across the 3 wires.

The is the second stator I have gone through. What else needs to be checked?

 

That is a bit high for the stator, but sometimes it's hard to get a good connection and get the DMM to read that low of a resistance.

Check the brush / field coil connection at the two pin connector (Br - G wires) to see how close to the 4 ohm spec you get.

Make sure the battery is good. Is it a wet cell, does it have water in it? Will it charge and hold a charge? Once charged, will it maintain a 10V level when the bike is cranking.

 

I charged the battery overnight and brought it in to a auto parts store to have it tested. It tested good.

I checked the field coil and could not get a resistance reading across the connector. I pulled the alternator cover and checked across the two commutator rings and still could not get a reading.
I pulled the rotor and found that on one side the potting material has come off and exposed the wire. Is it safe to assume the rotor is toasted?


I also checked the rec/reg and everything was in spec. Next I checked for any parasitic battery drain and I could not find any drain.

Finally I started the bike and got a voltage reading around 11v while cranking. As I brought the RPMs up the voltage did rise to 13v indicating that the battery is charging.

 

Normally with no reading across the commutator rings yes it would be toast. The only exception might be is if the solder joint has failed on one of the terminals (not likely) it might be savable.

It that with the original field coil or with a different one? With a fully charged battery you should get a voltage of 14.5 +/- .3V at 2K rpm and up.

 

That is with the original field coil.

 

So maybe I'm confused, is the field coil still ohming open across the commutator rings, and if so why even try it?

 

Sorry for the confusion. The field coil was still ohming open across the rings when I tested it. The only reason I tried it is because I needed to ride it home. With a fully charged battery I was able to get ride the bike 20 miles home. I had no way to tow the bike and it was getting a charge intermittently.

Thanks to Joe Elliff I have replacement parts on the way. Those should resolve my charging issues.

 

I have been having issues with my clutch slipping under acceleration so I replaced the friction discs, springs, screws, and washers.

With the cable adjusted to achieve maximum throw I never can get enough free play in the lever it seems. I have read big fitz's clutch adjustment write up several times moving the pivot arm tooth by tooth.

I have checked my plain discs for flatness but cannot find a wear thickness limit. Does anyone have the spec for that?

I am running shell rotella t4 15w-40 oil.

The inner and outer basket are also showing some wear. Is this acceptable?

 

Winter update here. I have swapped the front end for 2015 R6 forks. I vinyl wrapped the gas tank with dry carbon wrap. Also I wired in a new speedo and got it to function with the stock handle bar controls. I am working on switching over to the r6 controls.

The start button on the r6 has only 2 wires while the stock XJ switch has 4 can anyone help me with what wiring is necessary to switch over.

Thanks

 

You really need all four. The L/B to B is for the starter switch to engage the solenoid and start the bike. The R/Y to L/B is for the headlight. For the headlight the starter switch has a set of normally closed contacts (R/Y to L/B) that power the headlight. When the starter switch is depressed to start the bike the normally closed contacts open so the headlight shuts off which reduces the load on the battery during the starting process.

 

Rooster thank you for the informative response. I would like to keep the stock function of the of the switch only using the newer R6 button. Could I wire in two relays to switch from open and closed to replace this? If its possible does anyone have a diagram of how this would look?

 

the R/W (red/white) and L/B (Blue/Black) wires are for the headlight
could be hooked to a switch or relay

 

So I can use the switch to engage the starter solenoid and simultaneously trigger a relay to open the circuit for the headlight? Electronics are not my strong suit but I know enough to be dangerous.