New Member - '82 XJ750 Seca

As the title says, just snagged myself an '82 XJ750RJ Seca.

The odometer has 38k on it, but the PO said the speedo never worked for him, so who knows how many miles the motor really has. The carbs had also dumped about half a tank's worth of gas into the crankcase, the forks leaked bad enough to coat the brake rotors, half the turn signals were broken off, and he did a crappy job at painting (and bondo'ing a tank dent). Needless to say I have my work cut out for me, lol.

Once I cut off the oil cover bolt and replaced it (he stripped the head BAD), flushed the oil, and checked the carb floats... I finally got it to run, but it did so VERY poorly. Long story short for some reason two of the carbs had their needles pulled out of their seats a bit, causing the engine to bog on any throttle and barely stay running. It revs pretty nice now with that fixed, but idle still needs to be tuned and sync'd.


My main concern is the fuel in the oil. I have no way to know how long he drove it like that, and there is a concerning knocking/rattling coming from the lower motor region at around 800-2k rpm. Worst case: toasted bearings, best case: slack timing chain or just needing a valve adjustment (praying for best case).

The compression is around 125psi on every cylinder, so the motor isn't in great shape to begin with. I'm brand new to bikes though, so I'm really hoping I can at least ride it for a little while before it decides to give up the ghost. For now I'm repainting, replacing the toast break pads, replacing and rebuilding the badly pitted forks, swapping to LED turn signals, and replacing the dry rotted tires. Hopefully it'll hold together for me!


I'll post some pictures once I get all the aesthetic improvements finished.

This forum has already been a wealth of information, thanks to all!

 

I wouldnt worry about the compression, because there are so many variables that play into it, the best way to do it is with WOT, no airbox, a brand new battery, and maybe some extra assistance from a small charger, THEN you could deal with the accuracy of the gauge, really, the only thing that matters is if all 4 are close, it sounds like they are, so iwouldnt worry, but that bottom end noise, mm, maybe adjust the slack in the chain and run it till it blows,

I consider these engines disposable, because you can find any beater bike with 10-20K miles for like 500 bucks, part it out and maybe you will have spent 100 on another engine, rather than the hassle of buying new pistons, rings, gaskets, blah blah blah

just my two Lincolns

 

Yeah I just need to pull the valve cover and check out the chain and valve clearances in there.

Well, I did the compression check at WOT throttle engine warm with the airbox off, so I don't think it can get much better. AFAIK this guy was riding the bike, so I don't think it's an issue of just running out the gunk. The brief period I had it running I took it on a quick spin, and after cruising at high rpms it would smoke out both tail pipes as I would engine brake and come back to idle.

Unfortunately I'm in a bit of an obscure area so the best I can likely hope for is finding an engine for sale, probably to the note of $200-300. As you said though, run it till it blows is the plan, i just want to delay it as long as possible

 

If the carbs are not synched and tuned properly, the motor can knock a bit because your cylinders are fighting each other insted of working together. Drain the oil, rebuild your carbs, sync, tune the pilot mixtures, then see if it still rattles. These motors are harder to kill than you would think.

 

Yeah, fingers crossed. Good to know, if I heard this kind of noise coming form a car motor, I'd already be shopping for a new engine, haha.

 

Alright, got quite a bit of progress done this weekend. I got lucky and ALL of my parts came in

- Rebuilt my petcock, no more leaks!
- Installed the new turn signals, MUCH better! Still need to wire in an electronic relay so they'll flash
- Had the local bike shop mount and balance the front tire, still need to have them do the back before I ride too much.
- Finished the paint job for now, more on this later
- Swapped the front forks. No rebuild for now, they're not really very leaky.
- Got my new brake pads on and bled the system.
- Installed my new "sport-bike" style handlebars, they're sooo much more comfortable for me.


So about the paint... after two weeks of working on it i've just said "good enough". I'm thinking some jackass at autozone swapped lids or something, b/c the tank and fender are more semi-gloss, while the tail section and side fairings are matte like intended. Oh well, it's worlds better than it was. The forks don't really leak very much (compared to the old ones) so I figured I'll leave them alone for now and get in some ride-time. I'll take it down over the winter and really dig in.


There are still some nit-picky things I'll be doing here and there, but for the time being this will at least let me ride it. Now to get my permit and insurance all setup.

 

hey man, good looking scoot, it cleaned up very nicely. props.

 

Off to a rough start...

Clutch exploded in a turn at about 20mph, locked up the back tire and high sided, toasted my brand new bars and paint job, killed the brake lever and throttle cable, and scuffed the headlight bucket.

 

Wow, well glad your okay anyways. u sure it was the clutch? and not the rear brake from delamination(sp)?

 

My buddy was test riding it for me. Minor rash and bruising but I feel bad. Guess I found out what that rattle was

 

Wow, that really sucks. Dang man. Thats not good. Hows the rest of the bike??

 

Just the aforementioned stuff, plus added rash on the crash bar and exhaust (already had some from a PO). I guess one of the mirrors exploding off counts too, but I wanted to put on bar-end mirrors anyway, just not so soon lol. Oh and a nice dent in the tank... after all the work getting it smooth *sigh*

 

Got a few things done this weekend.

Checked the valves:
E1 .127 E2 .178 E3 .127 E4 .102
I1 .102 I2 .102 I3 .127 I4 .152

In the process I broke off the top two ignition cover bolts... not having much luck drilling them out. Need to get some better bits... probably some helicoils too. E4 is the only one that really concerns me, but I'll probably wait till I get some miles on it and make sure it's not going to blow up again before I drop money on a valve update.

Got the used ebay clutch back in, but I'm wary to ride it after the last incident. I may wait till I get a new lock washer pressure plate bolts and clutch cover, we'll see.

I also finally decided to dig in and adjust some of the idle screws after seeing silver specs on my #3 spark plug (has always been pure white, but I thought it was fuel supply). Turns out it was only 1.5 turns out. Set it to 4 turns and it idles much smoother. Can't wait to get a proper sync and tune on it.

 

glad to see you putting it back together and fixing it, after the freak accident.

 

I'm glad no one was injured badly and you are making lemonade out of lemons... Good on you!

 

Warm weather! Got the battery charged back up from sitting all winter, re-cleaned the enrichment circuit and blew everything out with compressed air, and got it running like it was last season. I've got a friend with tuning/syncing tools, but he's a busy guy so I may try the single vaccum gauge method for a rough sync until I can get some of his time. Fingers crossed I can get it running smoothly and get some miles on her in the next week or so!

 

Well, after 8 months I finally got to truly ride the bike. A local yamaha bike guru offered to help me sync the bike this evening. Threw the sync gauges on and twiddled some knobs, and everything smoothed up nicely. It actually idles and runs pretty decently now. He took it around the block, then I rode it to his house, then back the 25 min back to mine.

I'm going to need to order a colortune plug to dial in the idle mixture just right, and likely pull the carbs off to give them one final thorough cleaning. Around 4-5k rpm it's like they stick/unstick and give me a surge/bog. Other than that it's not smoking much while riding like I was worried it was going to (based off idling in the garage).

Overall, all my money spent is finally coming together, regretting the purchase much less now :lol:

 

Well, I just finished replacing my throttle shaft seals and going through the carbs, AGAIN, and it's still leaking. Propane tracked it down to the intake manifolds... still. Two of them are cracked all the way through, and all the plasti-dip and liquid electrical tape in the world couldn't stop them from re-cracking once I tightened the carbs down. I tried several other methods, and never could get those two to seal. I'm just going to have to bite the bullet and get replacements

 

Haven't tried it myself, but have you tried using a piece of tire innertube and then the liquid electrical tape and/or black rtv? Sounds like a few people have had success with that and saved some $....

Mac

 

I've put some LET on my intakes, not cause they were leaking, just more preventative maintenance

 

Alright, got some replacement intake manifolds on, and no more leaks! Built myself a manometer and got the carbs sync'd pretty decently. It'll actually hold an idle below 2000rpm!



Didn't have any luck colortuning, but I was reading that you need to do it below 1200, and I was around 1500 so that's probably my problem. I need to adjust my valves now, as I know a few are out of spec slightly and probably causing some syncing difficulty.

Still have that surge around 4k rpm, but it's better, and I'm hoping colortuning and hooking the airbox boots back up will eliminate it. If not, probably will need to triple check the float levels and go ahead and do the valves.

I also got a maxim headlight installed, not the best but it still looks way better than the rectangular one.