Resurrecting the 750!

Spent some more time on the 750 today. If it was made of mostly dirt and neglect before, it's now made of mostly bike and neglect. I've said it before and I'll say it again: When you buy a strange bike, the first thing you should do is CLEAN IT.

Under all that dirt, I found some strange wiring, stiff and broken rubber mounts for relays, no air filter whatsoever... and some amazingly shiny exhaust pipes, along with a bike that actually looks halfway decent! Hooked up a damaged battery (still provides 12V, but can't crank an engine) and got the tail light to light up! Yay!

Nothing else - and I mean NOTHING - works yet, though, including the brake light switches, unfortunately. It looks salvageable so far, but chacal is going to make a lot of money, I think.

Since my training is mainly in computers, I tend to go for the electrical stuff first. The head light doesn't come on, even though the light works (when connected directly to a battery), and the fuse has been bypassed. According to the wiring diagram, the headlight is actually hard-wired into the Atari I found just above the handlebars.

Does that computer have a bypass built in, or does it have to work for the bike to be usable, or is there a testing procedure to test through it? Basically, I don't want to waste a bunch of time testing continuity of tons of wiring only to find out that the computer is bad and there's no way to get a new one.

 

Headlight ONLY comes on when bike is started, not the key. In fact I have to give my bike a quick 'rev' after its started and then it turns on. You will have to wait until she's running to tell if your relays are working alright. That's the only way I know to test, but someone will correct me if I am wrong, I am sure.

 

The headlight is fused in the headlight bucket w/ a 5 amp fuse. Pop in there and make sure it is intact.
Your bike can be made to run without the computer but I don't have my schematic on hand to tell you specifics.
Worst case you replace it with an aftermarket unit (no too difficult if you have some electrical savy).

 

my headlight comes on as soon as i turn the key to on, then goes off when the starter button is pushed, this is a xj750j

 

Polock, yup. XJ750J here as well. Still no headlight because...

...computer is definitely fried. Pulled the instrument cluster off, checked all the bulbs (none burnt) and pulled the computer. Computer is definitely fried; you can see the scorch marks on it.

Are these nigh impossible to get? Or just expensive? I'm good with electrical work, and the Haynes manual has a decent schematic. Would I be better off just bypassing it? What do I lose (other than the various warning LEDs) by doing so?

Incidentally, I did find and check the fuse in the headlight shell. It's good. Checked all the diodes in the rectifier yesterday (all good).

Somewhere on the list to do soon is to pull the plugs to make sure they CAN be pulled, spray some fogging oil in the cylinders, and let that soak in. Also want to pull the exhaust (except the headers) so I can try to find the oil leak. Also intend to pull the starter motor and alternator cover for examination. I've removed the starter before, but never actually done the renovations to it. Hopefully, it will just need some cleaning and lubing. Also need to give the steering head a quick push/pull/side/side check for worn bearings.

 

Got distracted poking around trying to improve my tool set, which for me includes a shop manual for the 750. Bought some parts to make better testing leads for my shiny new multimeter, all the better to test relays and wiring.

Didn't get a chance to mess with the 750 itself much. Started figuring out how to remove the airbox and carbs, which are probably filthy. There is a lot of mud (not just dirt, CHUNKS of MUD) in the airbox. Apparently, I just pull the rear fender, pull some bolts, and it comes out backwards. Kind of a pain, but not THAT bad, really.

If this thing is ever going to run again, everything on it will need to be lubed. I think it sat in either an outside shed, or just plain outside for a long time. There are remains of climbing plants in strange places in the engine. Been clearing those out as I find them, along with the spider nests.

Hopefully, some more progress tomorrow. Been trying not to let this project pull me too much away from the 650, which isn't entirely finished yet either.

 

I faced the same situation with my 750 find. It was leaned-up against a Pine tree. Bug cocoons, tree sap, weeds, flat tires and a completely outside for a long time look about it that made ne want to part it out, make a few bucks and forget it.

Two years later and its all painted, polished and running like an Atomic Clock!
It's so much fun my 900 got parked in the back of the garage and covered-up for three seasons.

As I put the Carbs back on the 900,, tonight, from Cleaning and Race Prepping those Big Mikunis ... the 900 could see a lot of weekend action.

Funny thing about thaht 900 ... it always ran good until I forgot to pull the Drain Screws leading to why the Carbs came off her this week.
The Original Brass Plugs covering the Pilot Screws are in the trash can.

I'm going to tune the 900 so damn nicie that who ever comes to buyingn it after it gets on eBay nest Month will want to ride it home.
I wish I could havge a set of those Big Mik's on my Maxim.

But, I do have a 900 Engine in a box getting all rebuilt real nice.
Maybe this winter I'll have to figure-out a way to put that 900 Engine in the Maxim and make it go!

 

Okay, came up with a couple of questions. First of all, how do I get the airbox off? I loosened the bolts that hold it in place, and I was able to break it loose from the carbs by slackening the clamps on the boots, but do I have to remove the carbs to actually get the airbox out?

Secondly, for those of you who replaced your fuse panels, what sort of connectors did you use? I got the female ends to mate with the blade connectors on the replacement box, but the heat shrink ends make the new connectors so long that there isn't enough slack in the wiring to actually plug into the panel. Did you guys splice in extra line, or bend the heat shrink portion while it was still hot, or what?

This bike remains something of an enigma. I pulled one of the plugs, and it was extremely fouled, but still wet. Hopefully, that means that the critical engine parts have remained lubed enough to still function. Wiring and plug boots seem supple. Throttle/choke/clutch cables are very stiff, though, found lots of spiders, there's the computer problem, and you just KNOW that the entire fuel system is full of varnish. The tires are almost entirely rot, and the brakes are a nightmare. Pulled the stator cover, and it's PRISTINE in there.

See? Wierd. Anyway, any advice on the above issues is appreciated.

 

Without bending or prying, I couldn't get the airbox out of a '82 Seca 750 parts bike (which will go in my '81 Seca 750 to replace the pods).
I've heard you have to remove the engine!!! I didn't try removing the rear fender.
One guy here removed his without a problem, but he might have a 550 ???
I can cut my frame, but that won't help me during the install.

 

solder the wires to the new fuse panel, less resistance and more room
take all the cables off, poke the end thru the corner of a baggie, tape the baggie tightly to the cable outer sheath, hook the baggie to the ceiling and put some ATF in it, and a rag under it, let it hang till the oil makes its way thru
keep it up till the cable works free
or just buy new ones

 

Soldering always sounds like a good idea, until you try it. I did some soldering the other night building myself some custom cables for my multimeter (LONG, and with mini-alligator clips). P.I.T.A! Used about three times as much solder as necessary, and even that was with all the manoeuvering room I could ask for. Trying to solder on the bike with those tight tolerances would be crazy.

I likely need more practice, but in the meantime, I was really hoping to use these heat shrink ends, since they'll at least make a good, tight connection...

ATF = Automatic Transmission Fluid? I don't have any of that, but it sounds like that idea would work with cable lube or some other not-ridiculously-volatile lube (NOT WD-40).

That would suck if I can't get the airbox out. It badly needs a cleaning to the extent that it would have been FAR easier to do OFF the bike. <sigh>

I thought about taking it backwards through the fender, but the 750 airbox flares at the front, so it can't move backwards. I thought about removing the battery box and other plastic along with the carbs for maximum room, but thought I'd ask here first for tips. MOST of the time, if you're working at something that hard, you're doing it wrong. Both of the airboxes have been removed from my 650s, but I don't know if they were just destroyed in the process.

Thanks for the advice, guys. I'll be tearing it down some more today.

 

I have taken the Atari off my Seca and what a job it was getting everything working again. It wasn't broken, just didnt suit the style of the bike with all the mods I have done to it.

 

I soldered Pigtails to the new Fuse Panel on both sides and positioned the new Fuse Panel before splicing the wires to the wiring harness. Once I had the lengths needed for a nice fit. I wrapped the wires with tape some ... soldered the Pigtails up ... heat shrinked them ... then, taped 'em the rest of the way.

I made it look like the Fuse Panel came with the bike.

 

Okay, some successes and some stuff to do later.

Successes:

Aired up my compressor and blew a lot of crap out from around the plug wires. Might be able to pull them now without getting crud in the chambers. Blew a lot of other junk out from all over the bike. Should make it easier to work on.

Pulled and tested the rear brake switch (works).

Got the starter motor loose, but didn't pull it, since I'm not quite ready to work on it yet, and didn't want to allow crud to get in where the gears mesh. Power connector is pretty corroded...

Re-assembled the instrument cluster. Still doesn't work, but it means that I can claim I know how to do it and that I won't lose parts while I'm searching for replacements. We'll call that "success" for today.


Stuff To Do Later (much more):

Still haven't managed to get the connectors on the fuse panel the way I want, and I despise soldering. Did find out that I CAN bend the heat-shrink connectors the way I want... before my torch quit working. Insert many expletives here.

Tried to remove the right side engine faceplate (what's under there?) and was able to break three of the stuck bolts loose, but haven't quite gotten the fourth. May have to break down and get an impact driver.

Tried to remove the after-market highway pegs (ugly and in my way), but space is getting too cramped to properly get at them. Need to do some rearranging in the garage. Did find all the bolts and correct wrench sizes for that, though. Hopefully won't screw up the engine mounts getting those off.

Attempted to pull the battery box as a prelude to an attempt on the air cleaner case, but after much arguing with the wiring harness discovered that I'll probably have to remove the rear wheel first. The idea now is, rear wheel, then battery box (out the back), then carbs, then air cleaner case. The air cleaner case MAY come out forward if the carbs and battery box are removed first for maximum clearance. May also have to remove the starter motor (which is fine) and the side covers from the air cleaner case.

I note with some amusement that neither the shop manual nor the Haynes manual give any indication of how the air cleaner case should be removed. They just tell you how to replace the filter. I'm tempted to just cut it out and put pod filters on it, like the 650, but I don't know enough about carb jetting to get that right, at least not yet. Something to think about.

 

Ha! First things first, I always say. Took the torch back with the intention of returning it. The guy there adjusted the fuel flow so that it actually works properly and showed me how to do it. Brought it back and got the heat-shrink connectors on the way I want...

...and they reach! I'm attaching them such that once the shrink material has, well, shrunk, I bend the wire while it's still pliable so the connector makes a 90 degree turn. That way, it doesn't add 3/4" of width on each side to the whole array, and all the leads will reach! Yay!

Only done the headlights so far, but plan to do the others tonight. I'll replace the fuse panel on the 650 when I know whether or not the 750 is going to be a viable bike. No point in buying a second fuse block only to junk the bike...

 

your torch quit ? good golly man i thought you were a computer guy, quit using plumbers tools, no wonder your having a hard time
atf is automatic transmission fluid, a quart is cheaper than cable lube, follow up with motor oil and those cables are lubed for a long long time
somebody you know needs some atf anyhow
once you get the carbs off, put plastic bags over the intakes, plugup any holes
push it outside and give it a bath, wash out the airbox and theres no need to remove it
keep the coils tci and regulator dry, and the motor sealed up and engine cleaner and garden hose it up
thats the first thing i do to a fixer upper

 

Make a 70% Solution of DAWN Dish Washing Soap and Grease Cutter.
Spray Bottle.
Spray the whole Bike and hit the nooks and crannies.
Let the Dawn work.
Keep spraying it on the heavy soil.
Rinse.
Re-apply a 2nd coat of Dawn ...
Keep it moist and spray it directly on oil and grease.
15 Minutes
Rinse.

You should have a clean bike to work on now.

 

Didn't get to working on fuses. Will tackle that tomorrow, I suppose.

Plumber's tools. Ha! Well, it's working well now. I've never been any good at soldering. There's something about it I just don't seem to "get". No good at welding either, though I'm GREAT with a cutting torch. Go figure.

I'll work on that motor oil + hanging cable trick. Cables definitely need to come off this bike.

Pulling the air box is mostly an academic exercise, since I may want to replace or remove it at some point. I will pull the carbs and give the rest a bath, though. I'll just pull (or bag) anything electronic first. It's all disconnected already anyway.

Rick, 70% solution? 70/30 Dawn and engine cleaner? 50/50 dawn+cleaner and then THAT in 70/30 mix with water? I have both (and distilled, filtered, and tap water)... and a hose.

Funny thing is, having had the air gun applied to it, plus some plain old wet shop towels, the 750's frame and engine actually look a little better than the 650! Go figure...

Thanks for the advice, guys. Time (and funds) permitting, I may just have this thing operational by the end of the summer! I've been telling my wife "next Spring" though, since she thinks I'm going to spend a fortune fixing it. ;p

 

Sorry Rhys, I have never been able to get my airbox out of the frame without pulling the engine. I've broken one trying.

 

Well, crap. At least I know NOW, before breaking it myself, so thanks.

So how much trouble is re-jetting carbs? Having taken a good look at the pod filters on the 650 and the air box on the 750, I'd kinda like to stick pods on the 750, but I know close to zilch about the way carbs work. Is there a formula one can use involving air flow through the filter, size of the cylinders, etc. to choose the right jets, and then use the mixture screw to tune it, or...?

I'm out of my depth with the carbs, mainly because I don't know any of the *theory* of how they work, other than that they use the vacuum of the engine to suck varying amounts of fuel and air through the jets, mixing both and send them into the engine through the intake valves. I also have a vague understanding that "pilot" jets essentially determine the idle mixture and the "main" jets determine WOT mixture. Jets are the "coarse" adjustment and the mixture screws are the "fine" adjustment. The carbs also need to be closely synced so that one is not providing a significantly different fuel/air volume than the rest (so the individual cylinders contribute close to equal power).

Is that about right? Way off base? Good link to learn theory? I know there are several howtos for cleaning and rebuilding carbs on here that I intend to read, but do they go into the theory as well, or just the "remove this, tighten this, read plugs" part of it? One can't assume that I have chosen the jets correctly.