1981 XJ750 seca bobber project

Hey there everybody!! This is my first bike! It's an old 81' XJ750 Seca. Shortly after I bought it I decided to go for a bobber style build and turn it into my winter project because I don't have my license yet. Now It went a little bit quicker than I anticipated which I don't mind ;D But a few days ago I had put some straight pipes on my bike and was reving it up in my garage and it attracted some guys from a local riding club. One of the guys seemed super knowledgeable about these beast. He recommended I put 124 main jets in since I want to keep the stock air box and have the straight pipes, or wide open exhaust. It does have a K&N stock style air filter in it so I don't really know if that'll make a difference. He said if I keep it like it is, it'll start melting the internals since its an aluminum head and such. It is running lean, I honestly can't remember if thats the too much air or too much gas. It's not like I don't believe him, I would just like to have some other opinions. Now like I said, this is my first bike and I literally don't know jack about these lil 2 wheel monsters. SO if I could get someone to shed some light on this for me, it'd be much appreciated!!



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Pic in the link, idk how to put pics on this thing yet!!

 

nice looking xj. because there is a direct relationship between the exhaust and the intake, any time you make a change from stock, you will have to make some kind of tuning change.

while your neighbors experience says use a certain jet, that may not be the case for your situation. but since you made some change to the exhaust, there will be some necessary changes to the jetting for "proper operation". as for what those specific changes are, that is left to trial and error.

CN

 

Your bike has CV(constant velocity) style carbs. CV carbs don't like exhaust and air mods and requires much tuning to run right, but can be done. A lean condition(too much air) will eventually burn up a motor and would require re-jetting. You can tell if it's running lean by reading the plugs: White=lean, Black=rich and Tan=just right.
There is a formula for jetting, it's not always right but can get you close. Top right hand corner of the page is a link for XJ4Ever, click the link and browse til you find the jetting for exhaust and air filter mods.
Since this is your first bike and it's an old bike, it's better to get it running right and safe before changing everything. Things to fix and look for: is the compression of the motor good?, are the valves in spec?(you'll never get the carbs tuned right if they're not), brake lines?( they have expiration dates), brake pads and shoes?(rear shoes like to come apart and lock up the wheel), fork seals, bearings, tires, wiring and fuse box?
These are things that some first time buyers don't think of. Get yourself a manual and the people on this site will help you as much as we can. Chacal at XJ4Ever can hook you up with whatever parts you need quickly and at a fair price. Good luck with your build, be safe and have fun. 8)

 

Good to see you on here. the 124 jet was a guess. mine runs just a little rich with a 124 and the open exhaust. looking forward to seeing how u finish it. im building a 1980 xs1100 bobber. let me know if you need help with the bike. I'm in the area as you know these guys are great at figuring out what needs to be done. btw photobucket is the easiest way to put pics on here

 

nice looking bike. Im diggin the all black. any updates

 

Thanks guys for all your input. As for an update...no unfortunately no progress since posting this thread. I bought a speedo today at a local swap meet though my speedo drive is the number one suspect for a non working speedo. I still have yet to rejet and clean my carbs. Life got in the way, we all know how that is. Not to mention this winter has be CrAZy COLD!! Been trying to get the funds to finish the custom seat pan I made and still gotta get the lights mounted properly. It's sad seeing this beast sitting begging to be ridden. But I promise, when I start working on it again, I'll be updating like crazy!!

 

Hey guys. Finally got a little update. Made my seat although it still needs work. And finally got my tailights made up. Still need to wire them and make a mounting bracket for the seat. Rode around the neighborhood to stretch her legs. Can def tell I need to go thru the carbs and get a new throttle and choke cable. The choke isnt a need but hell do it while im doing the work. The throttle cable appears to be stretched and the linkage is sticking I believe becuz the idle isnt right. So basic maintenance needs done and replacing the these parts.

 

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^Forgive the lop sided one, it fits lose in the frame hole, that'll be fixed by bending the tabs out a bit.






^Ik it looks like crap, first seat ive ever done, the corner folds will be hidden under the tank, the rear im thinkin of sandwiching with a piece of fogged acrylic with a pin stripe design

 

Where did u get those straight pipes?

 

they were Harley pipes I bought off craigslist for 15$. just cut em up and clamped em on. used some exhaust goop stuff to make a solid seal.

 

for those xj gurus out there. how low can I drop my bike from factory height before I start running into drive shaft problems? I was just thinking a small drop of like 2". Haven't decided if I still want a sprung set up or solid struts.

 

I think you start hitting the fender before that becomes an issue. That being said, I put new shocks on my XJ, and blew my u-joint a month later. It was probably just the change that did it. 2" should be fine, but mostly I've seen people lower more like 1.5".

I'm not the bobber XJ guy, though. I'm the off-road XJ guy.