Why the XJ?

So I am at a bit of a cross roads today pondering a question.. A question for all of you fellow XJ owners..

Why the XJ?

I have a 1985 XJ700 Maxim that I've done quite a bit of work on and I think I am reaching my end with this particular bike. I have a stage 3 jet kit with 2" velocity stacks and a 4-2 high flow exhaust and the bike performs like a potato. I have spent countless hours trying to tune this bike, making tiny little turns on multiple screws just to see if I can get the "pop" to go away and bashing my head against the wall every time I turn the idle mixture screw all the way in, only to find it has made NO difference to the colortune.. This bike seems like a tuning monster.

Now, I am no expert on bikes by any stretch of the word, but from the information I gather every time I need to figure out a new problem with this bike (which happens to be about 2-3 times a day now) seems to lead me to believe that these bikes are just too temperamental to work on. They can't be tuned with standard equipment (colortune doesn't work even with YICS eliminator installed), they ALWAYS have issues with ANY type of modifications, and the cost to replace the OEM parts is absolutely astronomical. I'm trying to find a good reason to hang onto this bike (besides all the blood sweat and tears that went into it) and I'm having a hard time reasoning with myself.

So my question to all of you is...

Why the XJ?

 

Them's fighting words!

If you keep the intake and exhaust stock they are a breeze to tune. OEM parts will be expensive if you're looking for NOS, but realistically they're getting close to 40 years old, and parts bikes are plentiful and plenty of parts on ebay if you don't want to store one. Wiring is relatively simple and easy to repair if you take your time.

Colortune is only for idle mixture, you'll melt the glass if you try to tune anywhere else in the rev range. Potato-like performance definitely depends on your expectations, it's a high revving inline four that makes it's power up-top but also doesn't rev THAT high. If you ride it between 5-9k rpm, it's really pretty good.

I'd say the real weaknesses of these bikes comes more from the era, brakes, frame, suspension, and tires (bias-ply vs radial) leave much to be desired once you ride a more modern bike (sportier, aluminium frame with stressed member engine, 4 pot front brakes, and compression/rebound/preload adjustable suspension). But for early 80s tech, you really can't beat it, and it will check all but the most extreme boxes. <--This is coming from someone trying to get out of XJs because I have too many bikes, don't ride enough, and prefer the more modern sports tourers to my turbo. But I'm sure I'll still miss them

 

https://xjbikes.com/forums/threads/good-information-on-pods-vs-airbox-thanks-sybe.113331/

 

If turning the mixture screws all the way in (or out) makes no difference in the combustion "color" (as seen thru the colortune plug window), then your pilot fuel circuit is clogged (most probably, internally to the carb body itself, as those passage are tiny and fuel debris and varnish will accumulate in them), thus disabling (in effect) the pilot fuel circuit, which brings on potato-like performance.

http://www.xj4ever.com/inside your carbs.pdf

 

Did you ever have it running well when stock, or did you just jump right in and start modifying her?

 

she ran great when it was stock. rode it maybe 4 or 5 times before I jumped into the big build. The stage 3 kit was one of those things and it hasn't been right ever since. Quick question about a jet kit, the instructions had me drill out two holes on the slides. Is this a common procedure? Because everything I read about upgrading your jetting when modifying intake, exhaust, etc. all says to upgrade the main jets and maybe the pilot jet, but I never read anything on drilling out the slides.

*sigh*... I've had these damn things off and apart 6 times already and I haven't even been able to hit the freeway with it. Thank you for this write up though, extremely informative. I assume the only way to get these passages truly clean is with an ultrasonic cleaning system?

 

With enough thin wire, B12 Chem tool and compressed air you can clean it. Do not just spray any type of carb cleaning at the carbs and think it will clean the carbs. The rubber in the throttle bodies and other parts that get wet from the carb cleaner will never be the same.

I have found different bred ties seem to work best for the little hole in the fuel bowl, once that opens up you can see fluid drain into the fuel bowl. Keep hitting it with the wire and some B12 after that, those little holes will clean up.

Looks like you and I have something in common, my first XJ took me 6 times of not cleaning the carbs correctly the first times. Take the time to do it right, feel good about them before you put them on the bike. Bench sync and wet set outside the bike will really give you the confidence to get here running right.

As for going stage 3 to 300 with all the after market you want. These carbs still run the best with the OEM airbox on them. Constant velocity is what they were designed from birth and work best that way. If you have to have PODS and stage 3 to 300 kits on them, you will have to put the time, blood, sweat and tears in to make it run the way you want. They could be a day by day thing too. Some have had great luck, but I think most of them started from a great running stock bike.

 

It seems like I learn a little more about these things each time I dig into them. Damn, I felt really good the last time I put these things on. But the cutaway photos of this carb body that chacal provided really shows me exactly where I need to clean. I was talking with a buddy of mine yesterday and decided I'm going to return the carbs to stock internals. I wasn't really thinking about "if I want more speed, just get a bigger bike". I had a honeymoon phase with this bike after I bought it and I just bought as many things as I could for it.

 

If you go back to stock jetting you will also need to get different slides, or plug and redrill the larger holes.

 

yeah, I've ordered those already. Is it common to drill these out with jetting upgrades?

 

the kits sold on line for rejetting come with a drill bit and recomend drilling . once you have drilled you cant make the hole smaller

 

Most of what I've read about "tuning" these carbs is BS. Have you ever wondered what drilling out the slides does for your mixture strength? Nothing - at all. What it does do is change the rate at which the vacuum below the slide is transferred to above it - thereby changing the rate it lifts (which can change the mixture during fast accelleration, but only then). So it can cause a flat spot - or fix one. Reffering to them as constant velocity doesn't help either, but that's an old argument that I gave up with long ago.
Unless you fully understand what your doing leave them alone with the original airbox seems to be the default advice, and I wouldn't disagree with that. And if you really want to start modding them, you shouldn't need to ask here.

 

Everyone overcomplicates carbs... And IMHO they are the most simple thing on the whole bike. All carbs do is meter fuel. Keeping that in mind, a "pop" is a lean condition, with multiple reasons. Anywhere from a lack of restriction to valve timing, lash, to jet sizes. If you have a "stage 3" jet kit generally tells you how to do it (dynojet is the best jet kit for beginners because it tells you exactly what to do for what you have). With experience, you learn that to properly tune a bike (car) you need a dyno. More specifically you need a way to read the AFM electronically for the full diag. Depending on where the "pop" is is your best cause of action. Generally 0-25% throttle, on most carbs, is pure idle jet. After 25%, it the idle jet bleeds through for the complete AFM. If you get a pop under 25% and throughout the band, up the idle jet, if you get a pop off throttle but not during the mid/high band, IMS is where it's at. If you max out IMS, the again, need to up the idle jet size. But I would recommend upping the idle jet 1-2 sizes and lowering main jet .5 size. Again, idle jet is the only one that works 100% of the band, so if you up the idle, you will inadvertently make the mid/high band richer. Also needle position is important. But that part takes... Experience, and lots of it. End of the science lesson, get on a dyno, see what's going on, then make adjustments.

Also, usually hopped up engines end up needing an accelerator pump.

 

Also, this is all assuming everything else is in order. Keep with the basics, compression test, valve lash, balanced carbs. Eliminate the easy ones before getting to the harder part. Sorry for the huge reply btw lol.

 

My KLR650 needed the slide hole larger to get rid of the dead spot it had. I had a stage 3, slip-on and modded the air box. So for bike and that application it worked great.

 

Count the threads that are "this is my first bike". Then, "this is my first build". Then, "this is my 25th XJ, I am pondering throwing out some of my furniture to make it fit".

This is going to cover about 90-95% of the answer to your question.

XJ is a fairly long-lasting bike. Longer that Yamaha expected it, probably. That makes it plentiful and inexpensive. Like any old bike, carbs go to hell from sitting and people buy them cheap thinking it will be an easy fix. Or, they buy them cheap because they plan to take a hacksaw to them and build yet another bobber or cafe racer, as if there aren't enough uncomfortable bikes in the world already.

Some people (you know who you are) learn the little quirks of the design and get used to them. They stick to the design they know well. Those are the "my 25th XJ" guys.

I'm guessing you're "it was a cheap project bike" kinda guy?

This is the case for pretty much any old carbureted bike. Most older Japanese bikes run either Mikuni or Keihin carbs, with a smattering of Hitachi. Which means they are either exactly the same or very close to the carbs on your XJ.

Carburetors are a pain in the ass, no matter what people tell you. Properly tuning them outside factory defaults involves either expensive equipment, or a lot of guesswork and cussing. Doubly so if they are of the vacuum-operated variety. The guys at Yamaha had flow benches, dynos, gas analyzers. And you are trying to re-do this work with only your ear to go by. Also, they were working with shiny new carbs, not ones that have been gummed once or twice, and may have lingering gunk somewhere.

The guys who had success with modification got lucky. Plus, there is a fair amount of selection bias - the people who abandoned projects don't go around talking about them like the guys who succeeded. The guys who failed can generally be found on Craigslist selling "almost finished projects" that they "just lost interest" in.

Modding is easier with very popular models, but only because lots more people suffered before you to get it all figured out.

Generally, the "25th XJ" guys don't do that much modification. They replace the bad bits, restore bikes to stock, and ride them. They are a lot happier than modders.

That said, I've been trying to make this one rideable for several years. If I don't make these damn carbs work in another week or two, I will seriously consider a fuel injection build. I may be a bit of a masochist, though.

Compared to what? What's your point of reference?

Again, this is the case for pretty much any 30-40 year old bike. With the possible exception of Harley. But then, the bike itself is expensive - those guys think even a complete boat anchor is made of platinum.

Yamaha parts are at least available. Go look at Kawasaki - their parts catalog starts in the mid-80's. Got an 82, you're SOL.

Why did you get into trying to "tune" this thing? What did stock configuration not do for you that you wanted?

 

Well, at first it was a "cheap project bike" in my eyes. Before this build, I had very little knowledge of carbs or motorcycles in general. Since then, my knowledge has grown exponentially. When I first bought the bike, I had a honey moon phase with it and I started buying everything I could for it. One of those things was a stage 3 jet kit but I had completely neglected to do any type of research on modifying carbs. I now know that it's a pretty common idea to just leave the carbs alone and run them at their peak performance (which is usually stock setup) and if you do want more power, just get a bigger bike.

I got into tuning this bike because I want to learn about old carburetor setups. I've been an automotive technician for the last 9 years and I'm always wanting to expand my knowledge somewhere. My buddy had this bike for sale and I viewed it as a great opportunity to use this bike as my guinea pig. Needless to say, this journey is a lot longer and a hell of a lot more complicated than I thought. I've wanted to light this bike on fire more times than I've wanted to ride it, but it is forcing me to learn things I didn't know before and I'm becoming a better technician because of it.

 

Like you have stated, faster=bigger bike. People with gsxr or r6 or other smaller bikes ask me what can they do, big bore, head work, exhaust, ECT. I always retort "Why?". Why put so much money in a small bike, you will never get the money back out of it, you will not get the fun factor out of it, and with everything you buy to hop it up could have been a down payment on a faster bike. Small bikes, 400-750cc is a great learning bike. But faster means bigger, plain and simple.

 

consider with the xj that top speed(faster) is capped by redline no matter what you do to motor.
as far as quickness(1/4 mile) 550 is about a second slower13.4 seconds than a 650 and 750 at 12 seconds aproximitly.
so you can make them a little quicker you will never make them faster.

 

To be fair(ish): The most fun I've ever had on a smaller bike was throwing a big bore kit onto a Zuma 125. I went a bit to conservative with a 165cc kit, but power wheelies became an instant gigglefest..for less than $200. Sometimes I wonder if I should have kept it (and gone with a 205cc kit). The wife won though. Only one motorcycle in the garage at a time....for now...

 

Truthfully all motorcocyles are speed capped by aerodynamics. The world record for a 50cc scooter is just a tad over 122 MPH, with about 22 HP turning the rear wheel.
Put an XJ 750 engine in the right body and frame combo and it should easily exceeded 200 in stock trim.

 

Time to expand the garage, or have another one she doesn't know about... Lol

 

Did I nail it, or did I nail it?

That is not necessarily true.

You can get more power out of a bike. The thing is, you won't get it with carbs alone.

My other bike is an FJ1200, and my other hangout is the FJ owners board. People over there soup up the already pretty beefy FJ into all manner of wild things. There were several drag bikes, and at least one guy is building a land speed bike to run on Bonneville salt flats.

They do things like bore out the 1200 to 1400, lighten and balance crank and pistons, do weird magic with camshafts. And then they tune carbs to match. One guy added a turbo, but he went fuel injection. Sure did get more power out of the bike, let me tell ya...

You are an auto tech, but you were probably born after carburetors in automobiles already died. I am betting pretty much all cars you work on are fuel injected.

It's pretty common to tune EFI, and I'm sure that's where you got the idea. But do you know what they are doing when they do that? One of two things - they are either adjusting for changes made in the mechanicals of the engine or removing restrictions set for emissions reasons. Factory doesn't get the tune wrong, but they will tune to emissions before performance. Emissions regs are law. Performance in a stock model is optional.

There are two things that motorcycle carburetors of the type found on XJ series had for emissions - idle circuit jetted lean, and, on some later California models, vent tubes connected to a charcoal canister to collect vapor emissions. So, outside of those two things there aren't really any emissions restrictions to remove, and the charcoal canister doesn't matter, anyway. Therefore, you enter into the realm of altering the engine and matching carbs to the alteration.

Cheap engine alterations pretty much end at exhaust. People really like to muck with intakes, but that gains you no performance. Cone filters add bling and noise, and some dirt sucked into the engine, because they filter worse than either foam or paper. Performance improvement is comparable to painting your bike red, or putting stickers on it. All the tuning people do for them is just compensating for the problem they created. An air filter of any type is only a restriction at wide open throttle.

If you want to make your bike faster, you can either add a jug of displacement, or turbo that sucker. That'll make it go. Probably would make you wish for bigger brakes.

By the way, neither mod is impossible. 700cc bikes appeared in response to the Harley-protecting tariff, and mostly were just 750s with reduced stroke. There is a good chance that if you do your research, you'll find some other Yamaha engine that will donate conrods and pistons to make your 700 a 750. Turbo parts can likely be adapted from the Turbo Seca.

While possible, neither mod is easy or cheap.


Or, you could become a hero of legend and work up an EFI setup for that bike. Should you succeed, you will get better fuel mileage, better throttle response, probably a little quicker acceleration. And you will never have to muck with those carbs again. Now, that would be a hella impressive piece of tuning. Also, I bet other people who hate carbs would put up a statue in your honor, if they manage to follow your steps.

About a half dozen people have tried that, but no one seems to have actually completed this monumental task.

You could mess with the redline some. Or, you could re-gear the final drive. See above - neither easy, nor cheap.

No replacement for displacement.

 

Red ones do go faster (guarenteed )
The 700's made more power than the 750's, in part due to a higher compression ratio.

There are at least two sucessful EFI conversion threads on this forum. Lots of trouble, but worth it IMO.

 

My wife is VERY observant. I value my life.

 

Mekboyz know.

Maybe they can be bored out, too. No idea how much meat there is in the block.

Either way. That would be an alteration needing tuning.

Really? I have only seen a couple of incomplete ones.