1983 XJ750 Maxim Build (Updates and Questions)

gray wire goes to the coil it is the signal wire to tach
black wire is ground
Brown wire goes to signal fuse
do a continuity test on the Gray wire from the coil to connector could be bad connector connection at tci or coil connector plug

so the ground should be good because the bulb works.
check for 12 volts at Brown wire at connector

 

It is possible for the tachometer to fail. Corrosion on the component board, or broken solder joints are likely suspects.

 

Thank you for the tips! I will try this weekend and let you know what I find.

 

I checked continuity from the coil to gray and it passed. The voltage on the brown with bike running was 14V.
I am testing the coil where it is mounted to the frame. Is this the correct way to check?

 

Well I disassembled the tach to look at the circuit board and connections. Everything looked good so I hooked it back up to the bike and it started working. I must have had a bad connection somewhere that got fixed when I put it all back together. Now on to syncing and colortune.

 

One thing to do is to go through all of the connectors, deox them, and apply dielectric grease to prevent future corrosion.

 

Yes that is on the list to do when I install the lights.

I did not have any luck syncing the carbs today. They were not drawing enough vacuum and the gauges stayed at "late valve timing or leak at intake manifold or heat riser"
The engine had a rough idle and when i would blip the throttle the rpms would hang at 4K and very slowly come back down. I have never used this tool before and I think that may be why I am having issues. I did build the yics tool I found on another thread and I had it installed during the process. Any tips would be appreciated.

I checked the compression on 1-4 and they read 120,90,90,90.
The valve clearances are in spec and the spark plugs are new. 1,3, and 4 plugs looked good buy 2 looked a little lean.

 

when using vacuum Gauges you have to put a restrictor in the hose to slow down the jumping of the needle. a hose splice with the red tube from carb spray epoxied into it works well.

 

The gauges I bought came with with bleeder screws and I was able to control the needle movement.

 

Did the gauges come with restrictors to put in the vacuum lines? The screws are for adjusting the baseline of the manometer (by connecing all of the lines to one vacuum port, and setting all of the gauges to read the same).

 

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?