Exhaust and rebuild ??

Hi, I have a few questions about doing an exhaust kit and motor rebuild on my 82 xj750 maxim. First, I'm wanting to put a Mac 4-1 exhaust, but I have no clue of the jet sizes I'd need. I plan on keeping the stock airbox, mainly because I hear it's a real b**** to tune these style carbs with pods. Now for the fun part: the rebuild. This motor has a little over 35K on the clock and it's showing. Fires right up, but cylinders 1 and 2 are close to dead. 3 and 4 fire right up, but it's not until after 15-20 seconds after, then the first 2 fire up. Not sure if it's the carbs or what. Either way, what would I need to do to rebuild it? I'm wanting new pistons, if not possible, definitely rings. But I'm worried there's a ridge on the cylinders. If there is, then what would I have to do? I'd also like to change rod bearings of there are any? (I only know mainly truck motors) I just need sort of a guide from someone that's done this before, lol
Thanks

 

If the factory exhaust is in good condition, keep it (even if you want to go to a 4-1, keep it in storage for later).

Carbs need refreshed; a full teardown, and cleaning, along with new throttle shaft seals and mixture screw o-rings.
IN THE CHURCH OF CLEAN
Setting the fuel levels


There is no need to even touch the engine internals unless the starter clutch is slipping, or the alternator chain guide has broken apart. These engines are easily capable of 200,000 miles before rebuild (if not more).

An exhaustive intro and how-to guide can be found in my signature.

Shops are not your friend.

 

Take it to a shop, or do it myself?
Zen answer: Become the shop and do it yourself.

 

Actually just took a screenshot, and going to print that for my wall

 

Thanks for the info. Had no idea that these engines were capable of that much, lol. The stock exhaust was chopped and left with straight pipes. Might just order a stock exhaust online and see if backpressure changes anything, which it will. Straight pipes are nice and all, but I'd rather have it done "right" instead of the most common way these bikes are straight piped. I'll post a picture of the exhaust

 

There's very little back pressure, if any. The xj is a very free-blowing engine

 

You're just missing the mufflers. Nothing was cut from your system. It looks like the gaskets are even still in place (though fitting new gaskets is a good idea).

 

Well, now knowing that a rebuild isn't necessary, how about an exhaust? I've looked on eBay, and the only one I can find to fit is the Mac 4-1 that sounds like a Honda Civic with the same can. Any suggestions? Edit: not really looking to spend over a few hundred, that's just ridiculous, lol

 

The chrome shield is cut

 

I ended up putting a small flexible exhaust from the collector to get the correct angle needed and fitted Harley pipes . this was a temporary measure but now i can fit any muffler i want.

 

Yeah, I cut those off because no matter what, they rattled. You could only imagine how irritating that was

 

I was also kinda thinking if getting just the header from Mac, then using an adapter if I needed one to fit a small glasspack. Then I could run a tip if I have room for it, lol. If you can't tell already, I work on mainly vehicles, not bikes

 

The rattle can (well, could. no going back now) be fixed with two quick tack welds.

 

A vehicle is a mobile machine that transports people or cargo. Bikes are vehicles.

 

Ya know...I've never thought of that till now

 

Yeah, I realized what I said after I posted that, lmao. Trucks mainly, bikes being what I'm learning on working on. That's why I was thinking I was close to a motor rebuild, since I've been told that's pretty high miles for a motorcycle, at 35K.

 

35k is only high in that some people don't ride enough due to limited riding season, and so they don't see the odo get that high. These 4 cylinder engines can easily handle triple that amount!

 

I'll leave this here, and point out that the Evolution engine in the FXR is a steaming pile of crap in comparison to the XJ engine (I'm not H-D Bashing. the EVO is a good engine, just not nearly as good as what Yamaha was making at the time).
https://recordsetter.com/world-record/miles-ridden-motorcycle/585

 

Damn. Never realized that bikes were capable of that and more. That's actually really useful information. That bike was in rough shape when I got it, is why I was thinking it needed rebuilt. Long story short, I got it for $250 at a scrapyard in running and rideable condition with a clean title. Since then I've put a choke cable, clutch cable, new clutch (kg powersports), new stator, new regulator, and I'm working on getting a new petcock since mine drips fuel when shut off, and getting a new valve cover gasket. It's one hell of a project, but man I love that bike.

 

Chacal has rebuild kits for the petcock in stock (and everything else that's still available, and that actually fits correctly).
Rebuilding the Yamaha Vacuum Fuel Valve w/pics
The pics are being held hostage by Photobucket (for now), but the descripion is thorough.

 

Might buy the kit and a new petcock. That was I always have a spare just in case.

 

Mac sells a 4 into 2 exhaust which is what I have nice sound and good performance . From reading your post one item you have not mentioned , have you adjusted valve clearance ? This is important for engine longevity and will keep it happy and can also restore performance just make sure you use metric feeler gauges and read on how to change shims . only tool required is a large ziptie and patience and a service manual has the clearance chart .

 

Hey all, new member here. Thot id chime in with what I did. I've had a handful of sportbikes and always liked the danmoto exhausts. U can find them on Amazon or ebay, built quality is superb and they cost around $130 each. Obviously they dont build one specifically for an xj700 so I looked thru all the kits they sold, looking for the right mid pipe size and angle. The dual carbon fibers for the honda cb919 looked like they would work, 260$ for the kit that had 2 mufflers, 2 mid pipes, springs, brackets. So I bought it kinda on a whim, and it could not fit more perfect! Everything is like it was made exactly for this bike, lucked out, no modification at all. The bike screams like an r1, people can't believe how good it sounds. I have stock carbs, not jetted, and just a k&N filter in the stock airbox. No adjustment to carbs needed for these pipes.

 

Your running lean. Probably not dangerously lean, but lean sure enough.

 

Some say that the k&n alone is enough to make rejetting necessary. You might want to perform plug chops.

Also, once you've reached 5 posts, you'll be able to post pictures, and we'd love to see that exhaust.

 

I like it ...!!!!!!! looks good now how about some sound to go with pics ???

 

I like the sticker "paint job". I did that on parts of my car that weren't color matched.

 

Don't slide backward off of the seat.

 

Hell yeah man!! I'm glad I asked, and super stoked you found that! I'll look into buying them. Thanks!

 

As for the valve clearances and everything else, I'm kinda scared to do that because I couldn't even set the valves on a riding mower, lmao. What I was planning on doing, was getting an exhaust, putting that on, new petcock, then taking it to a shop and have the carbs rebuilt if needed, or just a sync and tune with a re getting since I too have the k&n filter. Last thing I want is a lean mixture. Valve cover gasket also needs done, but I can do that myself. I just kinda want the entire bike gone through by someone more qualified than I. Since I did buy the bike from a scrapyard that might've come from a tweaker. More on that if y'all care to hear the story, lol.

 

You can do the valves yourself. It's easy. Basis steps are:
1. Measure current clearance
2. Pull the current shim out, look at the bottom to see its size
3. Look at the chart to see what size needs to be put in
4. Put the new one in
5. Do the same for each
6. Close it up and go ride

The detailed how-to is in the forums.

http://xjbikes.com/forums/threads/bigfitzs-airhead-valve-adjustment-with-pics-parts-i-ii.116006/

Carb rebuild-- bet the shop doesn't do it right. Either learn to do it yourself, or contact me-- I offer total rebuild services.

Dave Fox

 

I've never done more with a lawn mower engine than put gas in it, but I did my XJ's valve shims without a problem. Read the guide, print out the guide, and then re-read the guide. Also, I found the valve shim tool very easy to use.

 

Zip-tie or wire is even easier

 

This is a link to a video of the danmoto exhausts on my xj700. Headphones help to hear it a little better

 

Very cool

 

So I tried to find a petcock (fuel valve) on eBay, and didn't find a one that either didn't need rebuilt, or didn't "match" the one I have. Meaning the vacuum lune, and fuel outlet line were in a different location. Wouldn't matter I guess, but I don't know how much trust I put in a $20 fuel valve...brand new, lol. I did order one that was tested and guranteed to work, but it leaked almost as bad as the one I'm trying to replace!! Getting a refund as soon as I send it back, so nothing more than a bit of time lost. Still frustrating though. Gotta love old bikes.

 

Ran my bike with the rebuilt petcock, and holy hell is it rough. Actually sat on the bike with no seat to feel what the motor was doing, and it's bad. Let me clear that up, motor is excellent, carbs are bad. I hate to spend a few hundred bucks on a bike I've worked on myself, so how do I sync the carbs? When the bike is cold or hot? I think I'm going to go with the danmoto exhaust, since that's the best looking alternative. I've been told about jet sizes and re-jetting for exhaust, but how do I know what size to get and where to get them to fit these carbs? This is the first bike I've ever worked on by myself, so I apologise for sounding like an idiot, lmao!

 

Haven't seen in this thread where the carbs have been to the church of clean and rebuilt. If not I suspect that's your problem.
Had to learn it too after a lot of meddling with petcocks and float needles, etc.

 

They haven't. Best I've done so far was drain them and take the test out, give those a clean, then take carb cleaner to each carb till the fluid came out clear. Other than that, they haven't been touched. The most intimidating thing for me, is getting the carb rack off since I still have the stock airbox

 

The airbox slides backwards once the mounting bolts for it have ben removed or loosened (one on top center gets loosened, one on the botom left (under the side cover) gets removed). Loosen all of the boot clamps until they have a large gap between them and the boot circumferences. Warm the boots with a hair dryer. Free the airbox boots from the carbs. Work along the rear flanges of the airbox boots to push them into the airbox. Unhook the cables and fuel line from the carb rack. Twist the rack down and back to release them from the intake boots.

Until you take the carbs to church, she won't run right.

 

On the list so far: rebuild the carbs, need new boots for the intake and for the air box, and sync the carbs once it's all done. All I can say is thank God Yamaha is cheap to fix. Had a Suzuki, and a carb rebuild kit on eBay was $100 for all 4. Yamaha is somewhere in the realm of $50 or less for all 4. Boots are cheap too. Only reason I haven't bought any of those yet is because it seemed like the only way to get the carb rack off, was to remove the air box. To do that, other forums and YouTube suggested either a heat gun to bend the plastic, or remove a couple engine mount blots so the motor can tilt forward. Negative, Ghost Rider.

 

If you're thinking you're gonna pay only $50 bucks for carb rebuild, I'll tell you right now --it won't run right when you're done.

Plus, I bet the shop doesn't do them right, either

 

Your poll choices should be
1. Do it yourself
2. Send the rack to hogfiddles, 0r K-moe......

Lol

 

Nathan,
The carbs aren't too bad to get off... K-MOE has good advice, and once you take them off a couple times it becomes second nature. I put mine on and off about ten minutes in each direction now.

I notice all your posts are in this thread so far... you probably want to start your own thread for this bike so people who read it will know what you've done so far when diagnosing problems.

I just started one for my bike after having multiple threads before...
http://www.xjbikes.com/forums/threads/1982-xj750-seca-ongoing.118087/#post-591355

I bought a bike that was "running" and I really enjoyed it for a few months, but as soon as it started acting up and I disturbed things the problems started coming out... Carbs are key. Hogfiddles is right about the carbs, they have to be completely disassembled and cleaned back to new, replace jets, needles, seals, etc. I messed with the aftermarket crap until he did it right for me. Bad news is by the time I was done with carbs, boots, petcock, valve shims, I was out $600... worse news was I spent $200 messing around with cheap crap before I decided to do it right. The carbs have a lot of seals in which leaks will mimic boot and hose or valve problems. You may not need any boots front or back... clean and inspect.

With the help of folks here you could do it all... I just didn't have the time.
From my experience here:

1. Valve clearances
2. Carb rebuild
3. plugs
4. No vacuum leaks and original air box
5. She WILL run on all four cylinders and be tons of fun

 

I know she's pulling air other than from the airbox, probably from the boots to the intake since they're cracked. Once it warms up, I'll do the rebuild on the carbs and get those fresh. I have newer plugs in it, but the bike has been ran as it is for a while, so I'll buy new ones when it's all said and done. Got a rebuild kit for my petcock, only to find out that it still drips. Not from the fuel line, but from the screw on the bottom that's all the way tight. The airbox has a K&N filter, but it doesn't stay in place, so I need the stock filter or an alternative (wondering if light foam would work? Only asking because I can get loads of it from work) OEM parts are stupid expensive, so can you make a list of the brands you used, unless it is OEM, lol. That's a route I can take and be fine with it, just wondering if I can save a few bucks. As for valves, I'll get them checked at a shop, and the carbs synced there as well. An older gentleman owns and runs the shop, that has been a mechanic for forever now, and used to be a Yamaha dealer until I guess he got too old for it. He's an honest guy that does good work, I'll just do what I can so I can save that much. Sorry for the long posts, I just have a lot to say and a lot of questions as well

 

Long posts don't bother us at all

 

The bike loves the original style paper filter. Anything else will cause issues.

 

I'll put one on order then. How does it set in there? The one that's in it looks like a "D" shape and has a foam gasket and it kinda just moves on its own free will. Asking about the foam because it's easy to get from work.

 

I believe the air box lid holds the filter tight up against the foam gasket when properly installed. Someone will correct me if I'm wrong