'82 Seca 750 Refresh Project: Now Scooby's Bike

No, the setting can be different. The way I do it (if I use the colortune because I found it hard to use with an X) is turn the screws out until an orange color, then turn them back in until the blue color and then turn them back out 1/4.
Are you sure the engine seized? Is the battery voltage okay? Did the carbs flood and do you have vapor lock?

 

Nice to know. I'll keep that in mind when I color tune the bike.

I did a little diagnosis to see if the engine was seized...Before I left, it was having starter motor issue, no mechanical issue at all so I replaced the starter motor and went on a 2 week trip. When I got back, the engine wouldn't turn over. So I opened the governor cover and tried to turn by hand. It would move clockwise but not counter-clockwise. I check the cylinders through the spark plug holes and I see an intake valve inside cylinder 4.

I don't know HOW it got in there and it certainly didn't happened while the engine was running or I would've noticed a huge BANG BANG BANG and my entire engine would be destroyed. My only guess is I never replaced the valve springs and they could be the originals from '82. Perhaps one of them broke under tension for so long. Luckily it didn't break while the engine was running. There's no way to know for sure until I open the engine up. But since the engine can't turn over... I can't reach the sprocket bolts to take off the chain... Which means I have to break the cam chain and replace it just to check the valve stems....

 

That's a pity the valve dropped. Splitting the cam chain is the solution if you cannot get to the sprocket bolts.

 

That's a PITA but you're also very lucky...

 

Haven't taken the cylinder head apart yet but here's the culprit. Snapped at the cotters. When I pull the valve out I guess we'll find out what happened to the lower part of the valve stem.

 

Don't know about lucky... I would say this is very rare, non existent even on a standard road bike, unless something else caused it.
I suspect you'll need a piston, maybe a barrel and head, but you never know. Rebuild carefully and go again.

 

You're right, def not lucky. As this is gonna cost a lot of cash... but lucky enough that I think there is no head damage.

Took off the head to inspect the damage. The piston is a bit chewed up. Since I'm already down into the guts, I'll probably just replace the piston. The valve guides look good though only way to know is when I put a different valve in and see if there's any resistance. The port next to the valve guide looks like it took the damage. If the valve guide is good then I'm guessing the valve dropped and chewed the piston when using the starter motor.

My only guess is the springs were installed incorrectly. So the top of the valve stem was shaking back and forth until it broke off.

 

Well I would say lucky that this did not happen to you on the highway in a corner. But for the rest, of course not lucky...

 

Sure thing there..
@scoobydew , turn the engine over to check the bore for damage - that piston looks fine to me, I've peened far worse with a ball pein hammer and left as is.
I don't know where you get the valve springs installed incorrectly - if the collets are in then that's it. I would be looking closely at that cam lobe - didn't you have an issue with cams at one point?

 

Hey all,

Bores look good. Everything looks fine from what I can see. except for the little dent on the piston. The old cams had an issue. The new ones were in spec. They turned over fine but there's no way to tell if they have bad runout. Gonna take them to a motor shop to check.

Right now I'm stuck on a little issue. Since I'm not splitting the crankcase, I split the chain and intend to use a master link. Issue is, every chain split kit comes with a pressure plate too big for a cam chain. They are obviously intended for a drive chain. Where can I find a kit that can install master link for the cam chain?

 

Why did you split the chain?

 

Trust me, I didn't want to. But since the valve fell into the cylinder, the engine couldn't be turned over. So I couldn't turn the cams, get access to the sprocket bolts, take the sprockets down from the cams and take the chain off the sprockets.

 

You don't need any special tool to install a new soft-link. Just insert the main part, close down the flat piece over the protruding pins and you'll feel them fit together nicely when the flat piece sits down properly on the shoulders of the pins.
At that point you could use a pair of fine-nosed pliers to make sure they're seated properly.
Once you're sure that's happened, take a 2lb hammer and use that as an anvil behind the chain, while with a 1/2lb hammer knock the ends of the pins down on the flat piece. Don't over do this part, you don't want the soft ends of the pins being too deformed and breaking off, but they must be deformed and spread out enough to prevent the flat piece from moving outwards, and lock it in place.

 

long time no see.
I'm fixin' to install new valves and springs myself. I handed it off to a shop but its been months and they haven't even touched it. I just feel like the likelihood of installing the spring crooked is high with my primitive spring compression tool from Amazon. Anyone else have any experience with re-lapping and installing valves?

 

Yes, loads. Its easy, you can do it and undo it over and over until youre an expert. Fine lapping paste should be all you need.

 

Took a while but the bike is finally "done". I synced carbs the best I could though not perfect, I didn't colortune yet though. I'm still a bit confused if all mixture screws must have the same amount of turns out or if each mixture screw has a unique amount of turns for that blue flame when colortuning. But I was able to get the bike to ride, starting up needs some throttle, that might be because of the carbs? Needs new throttle cable, I see some strands poking out of mine.

For some reason I'm always sitting around 4-5k rpm when in fifth gear. Rode around the block a bit, when I got back home I noticed some smoke and checked for oil, there is this little hole on the coil governor cover on the left hand side of the bike. Looks like some oil dripped out of it. What is it? This looks factory made, not a crack or anything

My rear brake seems to not even work. I stomp on it and i dont notice much. My front brake does all the work. I've never used drum brakes before. Maybe its just me

Not gonna lie. I'm not the biggest fan of this bike compared to my DRZ400. mainly because of its size. Just seems big and clunky, and syncing those 4 carbs... so annoying. I never rode a bike with more than 1 cylinder. It's a beautiful bike though. It's comfy but when I take off, I feel like my butt is gonna slide off. Not sure how to ride it, maybe more in a laid back style like a Harley

 

The color tune , you set the synch screw indepently for each carb IE one might be two turns while another might be three turns out . As long as you have the four vacuum gauge or Morgan Pro four synching carbs is relatively easy . Ideally the theory is for all four carbs function as one three are slight variations that can change over time valve clearance is one factor. You bike looks good once sorted the Seca has plenty of power 86 Hp so it is no slouch, mine I can ride all day out of all the bikes I've owned it is one of my favorite . Years ago bought my first new bike after owning just used bikes got my first "Thumper" a 2003 Buell Blast 500 supposedly 39 hp , I had a Kerker pipe on it so loud I had to wear ear plugs to ride . Cheers

 

Remove the cover where the pick up coils are. If oil is coming out of that hole you have a leaking crankshaft oil seal.

 

@scoobydew did you fit a new crankshaft oil seal during the engine rebuild? If you have one fitted without the lip that slots into the crankcase Chacal has the seal you can fit from the outside. Worth checking with him if yours is gone.

 

Hey Franz,

I don't remember if the seal had a lip or not but I replaced everything in the engine, most likely I ordered those parts from Partzilla... before I knew about this site so the parts took MONTHS to ship to me. There was only a few drops when I came back from a ride. So I took the coil governor off, cleaned it up and put a bit of Yamabond. I Idled it to 200 degree F, rev bombed a little. Doesnt seem to leak. at idle When the weather permits then I'll go for another ride and see whats up.

 

Hope it seals it.

 

Hey ya'll

Been riding the bike around, sealed up any oil leaks but there's been a lack of power. I attempted a colortune but two of the cylinders have an issue. Cylinder 1 goes dark when throttle is blipped rather than orange meaning not enough fuel is being sent in and Cylinder 4 is always whitish blue no matter how many turns out the mixture screw is. So I went to check for vacuum leaks with carb cleaner. Checking what the PO did to the carbs, I assume he replaced throttle shaft seals etc. when he tore down the carb. Everything is sealed up tight. No changes in idle when sprayed down.

So I pulled the carbs and found two issues. Carb 1 has the needle sticking up a bit? I posted a picture of it and another Carb for comparison. And Carb 4, the butterfly valve isnt completely sealed. There's a slight gap, you can see right through the bottom of the butterfly valve which would explain why the colortune never goes orange. How would I fix these issues? Do I have to break the rack to fix the butterfly valve?

 

Each butterfly will look different based on tuning… some with more/less light than others…

You shouldn’t have to break the rack… the adjustment screws will open/close the butterfly.

That rack has been rebuilt completely with Len’s full carb kit complete with throttle shaft seals.

The needles sticking is a completely different issue… each should “clunk” down nicely and completely when you push up with your finger…

Also make sure that no pinholes appear in the diaphragms… hold each up to the light to make sure. When I had that rack open, everything was A-Ok…

 

A lack of power?
Please explain - anything to do with synching and idle mixture will only be effective at idle or setting off. Real power is open throttle and 5000 rpm and above - it’s important to differentiate.
You should be able to fully close each butterfly before setting the synch - if not you need to slacken off the butterfly screws and reset.

 

It feels like I'm riding a smaller CC bike at the moment. Getting to 30 mph takes some time and a change of gears. Granted, I never rode an XJ750 with a solid running engine/carb so I can' compare but I do ride a DRZ400 and currently that bike takes off way faster and has a higher top speed than my XJ right now.

For sure the real power comes from higher RPMs. It does take off if you wide open throttle but it takes some time to get there. Just at the moment, I have idle screw all the way backed out and yet sometimes when the bike is warm, it goes to around 1400 rpm. After throttle blip, the RPMs drop a bit below 1k like it's going to stall then come back to around 1100k. There's no popping or backfire.

The carbs are synched according to my manometer, I used the blanking tool as well. The color tune isn't working right for two cylinders, I assume it's because of the two issues I mentioned, esp after Nuch confirmed he rebuilt the carbs.

I'm going to try bench synching them with a paperclip, try to close that butterfly valve so it's sealed and fix the stuck needle.

 

Well, I'm a fool. The butterfly valve is like that because it was synched with the others. It should only be an issue if it wasn't synched. So something else is causing the mixture issue.

I popped open the float bowls and a main jet fell out, that's why the needle was falling out As for the carb that is always lean, to be honest, I'm not sure. The jets look chewed up though they aren't dirty, you can see through them. I'll check the float level and maybe move up from 120 to 122 I think? Not sure, been reading a bunch of info on here. I have an aftermarket exhaust, I think it's MAC 4 into 2, the stock exhaust was rusted out.

 

It wouldn’t be the first time for a jet to get loose either.... first carb clinic I ever attended— they had a rack that was giving nothing but trouble— Couldn’t sync, Couldn’t colortune......One of the guys finally caved in to open the rack....yup, a jet rolling around in the bottom of the bowl.

 

Indeed, if all else fails. I could bring this carb over to the clinic.

Though that's a while away. I'm confident I can finish this before next riding season. Although, it's been a headache of a project, feels good to dial in on some of the issues by just tinkering with things

 

Good news,

Removed those old jets with new nice ones. Synched the carbs, colortuned as best I could and took her out on the highway. Runs great!

Finally finished after about 2 years or so. It was a trip, a huge pain in the butt when I fixed one thing and another thing broke but I'm glad I took on the project. I may not be an expert on motorcycles but I know this one in and out after taking her apart so many times. Just wanted to thank everyone for chiming in, giving some advice and information while I was stuck on an issue.

Appreciate ya'll, gonna see if this bike can make it to Michigan and back

 

If successful, next stop = Carb Clinic.

 

Hi yall,

I was having issues submitting my VIN for insurance, they were requesting a 17 digit number, my title has 9. So I called up my insurance and the guy said it might be a "leftover '81". Something about VIN numbers switching over to 17 digits in 1982

What does that mean? 1981 XJ750?

 

There's an article in the forums about VINs and the switch from shorter VINs to longer VINs, probably about that time.

 

Hi yall,

I noticed my bike needs a tiny tiny bit of throttle to start up when warm, otherwise it puffs a bit then stalls. Otherwise it runs beautifully, plugs look good, took it on the highway, doesn't stall out when coming to a stop, no high idle, holds at 1k RPM fine. I'm thinking the carbs are slightly out of sync? Of course I'll fix this but I'm in a bit of a pinch to get to work tomorrow so I need the bike for transportation and I don't have time to fix the sync today so my question is:

Does riding with out of sync carbs damage the engine?

 

Only if they're grossly out of sync.
A slight amount will make no difference to longevity, but will probably be a slightly vibey ride (buzziness through the bars) and will be annoying in presenting a lumpy idle.

 

That's a common observation on many of the XJ's if you mean after 10 to 15 minutes of sitting when hot. On mine and other posts here it seems to be normal to start easily hot is say you stop for gas and off just a few minutes, but if you have a longer errand and off for the 10 to 15 minutes then yes a bit of throttle seems to get them going

 

Hi all,

Been working on my headlight. I replaced the diode, the relay, the bulb, the fuse and still nothing from the headlight or the aux. In fact, the "fog lamp" and the "high beam" handlebar buttons don't work.

High beam on the dash doesn't light up to blue when I press high beam

Which is strange because my blinkers work and every other light on my dash, Neutral, check lights etc etc.

What else am I missing? I looked at the wiring and don't see any damage.

My odometer is also very quick. The bike says I have 600 miles when in reality, I must've only went 130 miles on the bike since rebuild

 

What are you missing? Getting a dvm and being methodical, working through the wiring diagram, looking for where the missing volts are. It sounds hard, but is easy once you apply yourself to it. Expecting a forum to diagnose what may be more than one electrical fault is just expecting too much.

 

You're 100% right.

I was just hoping perhaps, if I'm lucky, someone with a similar situation might drop in and say "hey! easy fix, replace rectifier!" and boom, problem solved

 

Yes sure, that might happen, but then you wouldn’t have learnt anything?
Keeping 40 yr old bikes going takes time, or money - and who’s going to spend shop money on something worth a few hundred bucks, two thou max?
But, here’s where we’re lucky - the electrical system on these bikes don’t need an serious kit to maintain, or even a genius. Someone methodical, logical, with a dvm can diagnose anything, especially with a few well aimed questions on here. So I’m a big believer in teach yourself wiring diagnostics and fault finding. One day, stuck on the side of the road it might well get you home.

 

Just to be sure the "diode" is the diode block located in the headlight bucket?

And the Atari is initializing normally?

 

Thank you for the inspiring words haha. Fiddling with stuff until it works is certainly a rush of dopamine, though there's been a few close calls of things going horribly wrong cause my newbieness. So that's been scary!

Yessir, block diode in the headlight bucket. Atari is fine, runs through its checks. Warning light can be turned off etc.

 

So now you need to start testing for +12V at the light switch harness plug - is it there going in? Is it there coming out?
Something to sit on (with wheels) helps, something to put the wiring diagram on helps too.
My Haynes manual has the switches labelled wrongly, start is kill and vice versa. It’s the colour diagram and otherwise excellent.

 

As you know going through the same thing on my 100$ bike, try this remove the headlight relay this relay should be a yellow relay. Take short piece of wire strip it back on both ends bridge the two slots on the inboard side of the plug, turn ignition to the on position should light up for headlight and the auxiliary light, this works on mine at least . Still TS I think I have a wiring harness issue , I have a spare harness but really don't want to swap it in . The cluster was missing from the bike , I have a couple one I can get neutral light to work and Atari displays but won't cycle, the other Atari lights up up but no neutral light and once in .awhile will cycle, still playing with it

 

Hi all,

Before I go rooting around in my stator, I checked the 3 white and 2 brown/green wires. They weren't perfectly in spec but they aren't reading zero or infinity ohms.

I think .5 for two white wires and 1 ohm for the last one. The Brown/Green read 14.5 and I got around 7V at the headlight harness

I'll check the stator brushes later.

My Atari dash reads everything just fine, my bike runs just fine, so this is where I'm lost:

I read the '82 XJ750 Seca light should turn on when the key is switch on while the 650 has to be turned on for the relay to "latch" onto something. Shouldn't the battery handle that then? Why would the stator be needed to switch on the headlight if the bike isn't running?

 

The headlight does not come on until the bike is started on the 750 Seca. The way it works is when started the AC Generator outputs a voltage on one of the legs that is fed directly to the Atari to initialize it, and that voltage must stay there for it to be active. The Atari that receives that voltage has in internal diode that rectifies it.

For the headlight that same leg of the alternator is used, but this time it routes to the diode block where an internal diode rectifies that voltage and then sends it to the headlight relay. That voltage only needs to appear for a brief instance as it will latch the headlight relay



A couple of tests you can do to isolate the problem. As Jetfixer suggested you can remove the headlight relay and install a jumper from the R/Y to L/B wire. With this done the headlight should come on when the key is turned to on. The aux light should also be working at this point

If this works you can test the headlight relay / diode block / wiring by disconnecting the 3 pin AC Generator connector from the main harness. With that disconnected turn the key to on and take a jumper and touch it to each one of those three pins on the harness side with the other end of the jumper connected to battery positive. When you find the right one it will initialize the Atari and should turn on the headlight. If you then disconnect it the Atari will drop back to standby but the headlight will remain illuminated until the ignition key is cycled to off

If you are checking the voltage at the headlight H4 connector with the headlight disconnected the Atari sense voltage will be present. This is the voltage that is used to set a warning if the headlight filament is open and is usually about 5V

 

Wow!

Heaps of information! Thanks a lot! All of you!

 

What gauge wire should it be? I'm not too familiar with the electronics work

Also I removed the Headlight fuse to see if my Atari would register it as a warning... but nothing happened so I don't know whats up with that

 

Just about any wire even a paper clip ,just bridge the two terminals note there are four terminals , turn on key if done right head light should come on . Your relay could be bad , this relay should have a yellow on it so this is only one like it .

 

At least 18 gauge (or the paperclip is fine too), and be sure you go from R/Y to L/B. There is a hot and a ground on that connector so if you just willy-nilly short out wires you will pop a fuse

That would be normal - the headlight BIT circuit either detects an open filament or if 12V is applied it looks for no current by utilizing a reed switch - if 12 V present and reed switch not closed the HEAD fail is set

 

So I tried the paper clip and some wire but still nothing.

I have a replacement headlight relay to test but it didnt work.

I noticed my headlight relay buzzing though. It's clearly coming from the relay too as when I unplug it, there is no buzzing, it happens every few seconds

I guess the connection isn't fully going through?